send.c

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/*
 * Copyright (C) 2012 Alexander Block.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/bsearch.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/sort.h>
#include <linux/mount.h>
#include <linux/xattr.h>
#include <linux/posix_acl_xattr.h>
#include <linux/radix-tree.h>
#include <linux/crc32c.h>
#include <linux/vmalloc.h>

#include "send.h"
#include "backref.h"
#include "locking.h"
#include "disk-io.h"
#include "btrfs_inode.h"
#include "transaction.h"

static int g_verbose = 0;

#define verbose_printk(...) if (g_verbose) printk(__VA_ARGS__)

/*
 * A fs_path is a helper to dynamically build path names with unknown size.
 * It reallocates the internal buffer on demand.
 * It allows fast adding of path elements on the right side (normal path) and
 * fast adding to the left side (reversed path). A reversed path can also be
 * unreversed if needed.
 */
struct fs_path {
    union {
        struct {
            char *start;
            char *end;
            char *prepared;

            char *buf;
            int buf_len;
            int reversed:1;
            int virtual_mem:1;
            char inline_buf[];
        };
        char pad[PAGE_SIZE];
    };
};
#define FS_PATH_INLINE_SIZE \
    (sizeof(struct fs_path) - offsetof(struct fs_path, inline_buf))


/* reused for each extent */
struct clone_root {
    struct btrfs_root *root;
    u64 ino;
    u64 offset;

    u64 found_refs;
};

#define SEND_CTX_MAX_NAME_CACHE_SIZE 128
#define SEND_CTX_NAME_CACHE_CLEAN_SIZE (SEND_CTX_MAX_NAME_CACHE_SIZE * 2)

struct send_ctx {
    struct file *send_filp;
    loff_t send_off;
    char *send_buf;
    u32 send_size;
    u32 send_max_size;
    u64 total_send_size;
    u64 cmd_send_size[BTRFS_SEND_C_MAX + 1];

    struct vfsmount *mnt;

    struct btrfs_root *send_root;
    struct btrfs_root *parent_root;
    struct clone_root *clone_roots;
    int clone_roots_cnt;

    /* current state of the compare_tree call */
    struct btrfs_path *left_path;
    struct btrfs_path *right_path;
    struct btrfs_key *cmp_key;

    /*
     * infos of the currently processed inode. In case of deleted inodes,
     * these are the values from the deleted inode.
     */
    u64 cur_ino;
    u64 cur_inode_gen;
    int cur_inode_new;
    int cur_inode_new_gen;
    int cur_inode_deleted;
    u64 cur_inode_size;
    u64 cur_inode_mode;

    u64 send_progress;

    struct list_head new_refs;
    struct list_head deleted_refs;

    struct radix_tree_root name_cache;
    struct list_head name_cache_list;
    int name_cache_size;

    struct file *cur_inode_filp;
    char *read_buf;
};

struct name_cache_entry {
    struct list_head list;
    /*
     * radix_tree has only 32bit entries but we need to handle 64bit inums.
     * We use the lower 32bit of the 64bit inum to store it in the tree. If
     * more then one inum would fall into the same entry, we use radix_list
     * to store the additional entries. radix_list is also used to store
     * entries where two entries have the same inum but different
     * generations.
     */
    struct list_head radix_list;
    u64 ino;
    u64 gen;
    u64 parent_ino;
    u64 parent_gen;
    int ret;
    int need_later_update;
    int name_len;
    char name[];
};

static void fs_path_reset(struct fs_path *p)
{
    if (p->reversed) {
        p->start = p->buf + p->buf_len - 1;
        p->end = p->start;
        *p->start = 0;
    } else {
        p->start = p->buf;
        p->end = p->start;
        *p->start = 0;
    }
}

static struct fs_path *fs_path_alloc(struct send_ctx *sctx)
{
    struct fs_path *p;

    p = kmalloc(sizeof(*p), GFP_NOFS);
    if (!p)
        return NULL;
    p->reversed = 0;
    p->virtual_mem = 0;
    p->buf = p->inline_buf;
    p->buf_len = FS_PATH_INLINE_SIZE;
    fs_path_reset(p);
    return p;
}

static struct fs_path *fs_path_alloc_reversed(struct send_ctx *sctx)
{
    struct fs_path *p;

    p = fs_path_alloc(sctx);
    if (!p)
        return NULL;
    p->reversed = 1;
    fs_path_reset(p);
    return p;
}

static void fs_path_free(struct send_ctx *sctx, struct fs_path *p)
{
    if (!p)
        return;
    if (p->buf != p->inline_buf) {
        if (p->virtual_mem)
            vfree(p->buf);
        else
            kfree(p->buf);
    }
    kfree(p);
}

static int fs_path_len(struct fs_path *p)
{
    return p->end - p->start;
}

static int fs_path_ensure_buf(struct fs_path *p, int len)
{
    char *tmp_buf;
    int path_len;
    int old_buf_len;

    len++;

    if (p->buf_len >= len)
        return 0;

    path_len = p->end - p->start;
    old_buf_len = p->buf_len;
    len = PAGE_ALIGN(len);

    if (p->buf == p->inline_buf) {
        tmp_buf = kmalloc(len, GFP_NOFS);
        if (!tmp_buf) {
            tmp_buf = vmalloc(len);
            if (!tmp_buf)
                return -ENOMEM;
            p->virtual_mem = 1;
        }
        memcpy(tmp_buf, p->buf, p->buf_len);
        p->buf = tmp_buf;
        p->buf_len = len;
    } else {
        if (p->virtual_mem) {
            tmp_buf = vmalloc(len);
            if (!tmp_buf)
                return -ENOMEM;
            memcpy(tmp_buf, p->buf, p->buf_len);
            vfree(p->buf);
        } else {
            tmp_buf = krealloc(p->buf, len, GFP_NOFS);
            if (!tmp_buf) {
                tmp_buf = vmalloc(len);
                if (!tmp_buf)
                    return -ENOMEM;
                memcpy(tmp_buf, p->buf, p->buf_len);
                kfree(p->buf);
                p->virtual_mem = 1;
            }
        }
        p->buf = tmp_buf;
        p->buf_len = len;
    }
    if (p->reversed) {
        tmp_buf = p->buf + old_buf_len - path_len - 1;
        p->end = p->buf + p->buf_len - 1;
        p->start = p->end - path_len;
        memmove(p->start, tmp_buf, path_len + 1);
    } else {
        p->start = p->buf;
        p->end = p->start + path_len;
    }
    return 0;
}

static int fs_path_prepare_for_add(struct fs_path *p, int name_len)
{
    int ret;
    int new_len;

    new_len = p->end - p->start + name_len;
    if (p->start != p->end)
        new_len++;
    ret = fs_path_ensure_buf(p, new_len);
    if (ret < 0)
        goto out;

    if (p->reversed) {
        if (p->start != p->end)
            *--p->start = '/';
        p->start -= name_len;
        p->prepared = p->start;
    } else {
        if (p->start != p->end)
            *p->end++ = '/';
        p->prepared = p->end;
        p->end += name_len;
        *p->end = 0;
    }

out:
    return ret;
}

static int fs_path_add(struct fs_path *p, const char *name, int name_len)
{
    int ret;

    ret = fs_path_prepare_for_add(p, name_len);
    if (ret < 0)
        goto out;
    memcpy(p->prepared, name, name_len);
    p->prepared = NULL;

out:
    return ret;
}

static int fs_path_add_path(struct fs_path *p, struct fs_path *p2)
{
    int ret;

    ret = fs_path_prepare_for_add(p, p2->end - p2->start);
    if (ret < 0)
        goto out;
    memcpy(p->prepared, p2->start, p2->end - p2->start);
    p->prepared = NULL;

out:
    return ret;
}

static int fs_path_add_from_extent_buffer(struct fs_path *p,
                      struct extent_buffer *eb,
                      unsigned long off, int len)
{
    int ret;

    ret = fs_path_prepare_for_add(p, len);
    if (ret < 0)
        goto out;

    read_extent_buffer(eb, p->prepared, off, len);
    p->prepared = NULL;

out:
    return ret;
}

#if 0
static void fs_path_remove(struct fs_path *p)
{
    BUG_ON(p->reversed);
    while (p->start != p->end && *p->end != '/')
        p->end--;
    *p->end = 0;
}
#endif

static int fs_path_copy(struct fs_path *p, struct fs_path *from)
{
    int ret;

    p->reversed = from->reversed;
    fs_path_reset(p);

    ret = fs_path_add_path(p, from);

    return ret;
}


static void fs_path_unreverse(struct fs_path *p)
{
    char *tmp;
    int len;

    if (!p->reversed)
        return;

    tmp = p->start;
    len = p->end - p->start;
    p->start = p->buf;
    p->end = p->start + len;
    memmove(p->start, tmp, len + 1);
    p->reversed = 0;
}

static struct btrfs_path *alloc_path_for_send(void)
{
    struct btrfs_path *path;

    path = btrfs_alloc_path();
    if (!path)
        return NULL;
    path->search_commit_root = 1;
    path->skip_locking = 1;
    return path;
}

int write_buf(struct file *filp, const void *buf, u32 len, loff_t *off)
{
    int ret;
    mm_segment_t old_fs;
    u32 pos = 0;

    old_fs = get_fs();
    set_fs(KERNEL_DS);

    while (pos < len) {
        ret = vfs_write(filp, (char *)buf + pos, len - pos, off);
        /* TODO handle that correctly */
        /*if (ret == -ERESTARTSYS) {
            continue;
        }*/
        if (ret < 0)
            goto out;
        if (ret == 0) {
            ret = -EIO;
            goto out;
        }
        pos += ret;
    }

    ret = 0;

out:
    set_fs(old_fs);
    return ret;
}

static int tlv_put(struct send_ctx *sctx, u16 attr, const void *data, int len)
{
    struct btrfs_tlv_header *hdr;
    int total_len = sizeof(*hdr) + len;
    int left = sctx->send_max_size - sctx->send_size;

    if (unlikely(left < total_len))
        return -EOVERFLOW;

    hdr = (struct btrfs_tlv_header *) (sctx->send_buf + sctx->send_size);
    hdr->tlv_type = cpu_to_le16(attr);
    hdr->tlv_len = cpu_to_le16(len);
    memcpy(hdr + 1, data, len);
    sctx->send_size += total_len;

    return 0;
}

#if 0
static int tlv_put_u8(struct send_ctx *sctx, u16 attr, u8 value)
{
    return tlv_put(sctx, attr, &value, sizeof(value));
}

static int tlv_put_u16(struct send_ctx *sctx, u16 attr, u16 value)
{
    __le16 tmp = cpu_to_le16(value);
    return tlv_put(sctx, attr, &tmp, sizeof(tmp));
}

static int tlv_put_u32(struct send_ctx *sctx, u16 attr, u32 value)
{
    __le32 tmp = cpu_to_le32(value);
    return tlv_put(sctx, attr, &tmp, sizeof(tmp));
}
#endif

static int tlv_put_u64(struct send_ctx *sctx, u16 attr, u64 value)
{
    __le64 tmp = cpu_to_le64(value);
    return tlv_put(sctx, attr, &tmp, sizeof(tmp));
}

static int tlv_put_string(struct send_ctx *sctx, u16 attr,
              const char *str, int len)
{
    if (len == -1)
        len = strlen(str);
    return tlv_put(sctx, attr, str, len);
}

static int tlv_put_uuid(struct send_ctx *sctx, u16 attr,
            const u8 *uuid)
{
    return tlv_put(sctx, attr, uuid, BTRFS_UUID_SIZE);
}

#if 0
static int tlv_put_timespec(struct send_ctx *sctx, u16 attr,
                struct timespec *ts)
{
    struct btrfs_timespec bts;
    bts.sec = cpu_to_le64(ts->tv_sec);
    bts.nsec = cpu_to_le32(ts->tv_nsec);
    return tlv_put(sctx, attr, &bts, sizeof(bts));
}
#endif

static int tlv_put_btrfs_timespec(struct send_ctx *sctx, u16 attr,
                  struct extent_buffer *eb,
                  struct btrfs_timespec *ts)
{
    struct btrfs_timespec bts;
    read_extent_buffer(eb, &bts, (unsigned long)ts, sizeof(bts));
    return tlv_put(sctx, attr, &bts, sizeof(bts));
}


#define TLV_PUT(sctx, attrtype, attrlen, data) \
    do { \
        ret = tlv_put(sctx, attrtype, attrlen, data); \
        if (ret < 0) \
            goto tlv_put_failure; \
    } while (0)

#define TLV_PUT_INT(sctx, attrtype, bits, value) \
    do { \
        ret = tlv_put_u##bits(sctx, attrtype, value); \
        if (ret < 0) \
            goto tlv_put_failure; \
    } while (0)

#define TLV_PUT_U8(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 8, data)
#define TLV_PUT_U16(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 16, data)
#define TLV_PUT_U32(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 32, data)
#define TLV_PUT_U64(sctx, attrtype, data) TLV_PUT_INT(sctx, attrtype, 64, data)
#define TLV_PUT_STRING(sctx, attrtype, str, len) \
    do { \
        ret = tlv_put_string(sctx, attrtype, str, len); \
        if (ret < 0) \
            goto tlv_put_failure; \
    } while (0)
#define TLV_PUT_PATH(sctx, attrtype, p) \
    do { \
        ret = tlv_put_string(sctx, attrtype, p->start, \
            p->end - p->start); \
        if (ret < 0) \
            goto tlv_put_failure; \
    } while(0)
#define TLV_PUT_UUID(sctx, attrtype, uuid) \
    do { \
        ret = tlv_put_uuid(sctx, attrtype, uuid); \
        if (ret < 0) \
            goto tlv_put_failure; \
    } while (0)
#define TLV_PUT_TIMESPEC(sctx, attrtype, ts) \
    do { \
        ret = tlv_put_timespec(sctx, attrtype, ts); \
        if (ret < 0) \
            goto tlv_put_failure; \
    } while (0)
#define TLV_PUT_BTRFS_TIMESPEC(sctx, attrtype, eb, ts) \
    do { \
        ret = tlv_put_btrfs_timespec(sctx, attrtype, eb, ts); \
        if (ret < 0) \
            goto tlv_put_failure; \
    } while (0)

static int send_header(struct send_ctx *sctx)
{
    struct btrfs_stream_header hdr;

    strcpy(hdr.magic, BTRFS_SEND_STREAM_MAGIC);
    hdr.version = cpu_to_le32(BTRFS_SEND_STREAM_VERSION);

    return write_buf(sctx->send_filp, &hdr, sizeof(hdr),
                    &sctx->send_off);
}

/*
 * For each command/item we want to send to userspace, we call this function.
 */
static int begin_cmd(struct send_ctx *sctx, int cmd)
{
    struct btrfs_cmd_header *hdr;

    if (!sctx->send_buf) {
        WARN_ON(1);
        return -EINVAL;
    }

    BUG_ON(sctx->send_size);

    sctx->send_size += sizeof(*hdr);
    hdr = (struct btrfs_cmd_header *)sctx->send_buf;
    hdr->cmd = cpu_to_le16(cmd);

    return 0;
}

static int send_cmd(struct send_ctx *sctx)
{
    int ret;
    struct btrfs_cmd_header *hdr;
    u32 crc;

    hdr = (struct btrfs_cmd_header *)sctx->send_buf;
    hdr->len = cpu_to_le32(sctx->send_size - sizeof(*hdr));
    hdr->crc = 0;

    crc = crc32c(0, (unsigned char *)sctx->send_buf, sctx->send_size);
    hdr->crc = cpu_to_le32(crc);

    ret = write_buf(sctx->send_filp, sctx->send_buf, sctx->send_size,
                    &sctx->send_off);

    sctx->total_send_size += sctx->send_size;
    sctx->cmd_send_size[le16_to_cpu(hdr->cmd)] += sctx->send_size;
    sctx->send_size = 0;

    return ret;
}

/*
 * Sends a move instruction to user space
 */
static int send_rename(struct send_ctx *sctx,
             struct fs_path *from, struct fs_path *to)
{
    int ret;

verbose_printk("btrfs: send_rename %s -> %s\n", from->start, to->start);

    ret = begin_cmd(sctx, BTRFS_SEND_C_RENAME);
    if (ret < 0)
        goto out;

    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, from);
    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_TO, to);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    return ret;
}

/*
 * Sends a link instruction to user space
 */
static int send_link(struct send_ctx *sctx,
             struct fs_path *path, struct fs_path *lnk)
{
    int ret;

verbose_printk("btrfs: send_link %s -> %s\n", path->start, lnk->start);

    ret = begin_cmd(sctx, BTRFS_SEND_C_LINK);
    if (ret < 0)
        goto out;

    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_LINK, lnk);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    return ret;
}

/*
 * Sends an unlink instruction to user space
 */
static int send_unlink(struct send_ctx *sctx, struct fs_path *path)
{
    int ret;

verbose_printk("btrfs: send_unlink %s\n", path->start);

    ret = begin_cmd(sctx, BTRFS_SEND_C_UNLINK);
    if (ret < 0)
        goto out;

    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    return ret;
}

/*
 * Sends a rmdir instruction to user space
 */
static int send_rmdir(struct send_ctx *sctx, struct fs_path *path)
{
    int ret;

verbose_printk("btrfs: send_rmdir %s\n", path->start);

    ret = begin_cmd(sctx, BTRFS_SEND_C_RMDIR);
    if (ret < 0)
        goto out;

    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    return ret;
}

/*
 * Helper function to retrieve some fields from an inode item.
 */
static int get_inode_info(struct btrfs_root *root,
              u64 ino, u64 *size, u64 *gen,
              u64 *mode, u64 *uid, u64 *gid,
              u64 *rdev)
{
    int ret;
    struct btrfs_inode_item *ii;
    struct btrfs_key key;
    struct btrfs_path *path;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    key.objectid = ino;
    key.type = BTRFS_INODE_ITEM_KEY;
    key.offset = 0;
    ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
    if (ret < 0)
        goto out;
    if (ret) {
        ret = -ENOENT;
        goto out;
    }

    ii = btrfs_item_ptr(path->nodes[0], path->slots[0],
            struct btrfs_inode_item);
    if (size)
        *size = btrfs_inode_size(path->nodes[0], ii);
    if (gen)
        *gen = btrfs_inode_generation(path->nodes[0], ii);
    if (mode)
        *mode = btrfs_inode_mode(path->nodes[0], ii);
    if (uid)
        *uid = btrfs_inode_uid(path->nodes[0], ii);
    if (gid)
        *gid = btrfs_inode_gid(path->nodes[0], ii);
    if (rdev)
        *rdev = btrfs_inode_rdev(path->nodes[0], ii);

out:
    btrfs_free_path(path);
    return ret;
}

typedef int (*iterate_inode_ref_t)(int num, u64 dir, int index,
                   struct fs_path *p,
                   void *ctx);

/*
 * Helper function to iterate the entries in ONE btrfs_inode_ref or
 * btrfs_inode_extref.
 * The iterate callback may return a non zero value to stop iteration. This can
 * be a negative value for error codes or 1 to simply stop it.
 *
 * path must point to the INODE_REF or INODE_EXTREF when called.
 */
static int iterate_inode_ref(struct send_ctx *sctx,
                 struct btrfs_root *root, struct btrfs_path *path,
                 struct btrfs_key *found_key, int resolve,
                 iterate_inode_ref_t iterate, void *ctx)
{
    struct extent_buffer *eb = path->nodes[0];
    struct btrfs_item *item;
    struct btrfs_inode_ref *iref;
    struct btrfs_inode_extref *extref;
    struct btrfs_path *tmp_path;
    struct fs_path *p;
    u32 cur = 0;
    u32 total;
    int slot = path->slots[0];
    u32 name_len;
    char *start;
    int ret = 0;
    int num = 0;
    int index;
    u64 dir;
    unsigned long name_off;
    unsigned long elem_size;
    unsigned long ptr;

    p = fs_path_alloc_reversed(sctx);
    if (!p)
        return -ENOMEM;

    tmp_path = alloc_path_for_send();
    if (!tmp_path) {
        fs_path_free(sctx, p);
        return -ENOMEM;
    }


    if (found_key->type == BTRFS_INODE_REF_KEY) {
        ptr = (unsigned long)btrfs_item_ptr(eb, slot,
                            struct btrfs_inode_ref);
        item = btrfs_item_nr(eb, slot);
        total = btrfs_item_size(eb, item);
        elem_size = sizeof(*iref);
    } else {
        ptr = btrfs_item_ptr_offset(eb, slot);
        total = btrfs_item_size_nr(eb, slot);
        elem_size = sizeof(*extref);
    }

    while (cur < total) {
        fs_path_reset(p);

        if (found_key->type == BTRFS_INODE_REF_KEY) {
            iref = (struct btrfs_inode_ref *)(ptr + cur);
            name_len = btrfs_inode_ref_name_len(eb, iref);
            name_off = (unsigned long)(iref + 1);
            index = btrfs_inode_ref_index(eb, iref);
            dir = found_key->offset;
        } else {
            extref = (struct btrfs_inode_extref *)(ptr + cur);
            name_len = btrfs_inode_extref_name_len(eb, extref);
            name_off = (unsigned long)&extref->name;
            index = btrfs_inode_extref_index(eb, extref);
            dir = btrfs_inode_extref_parent(eb, extref);
        }

        if (resolve) {
            start = btrfs_ref_to_path(root, tmp_path, name_len,
                          name_off, eb, dir,
                          p->buf, p->buf_len);
            if (IS_ERR(start)) {
                ret = PTR_ERR(start);
                goto out;
            }
            if (start < p->buf) {
                /* overflow , try again with larger buffer */
                ret = fs_path_ensure_buf(p,
                        p->buf_len + p->buf - start);
                if (ret < 0)
                    goto out;
                start = btrfs_ref_to_path(root, tmp_path,
                              name_len, name_off,
                              eb, dir,
                              p->buf, p->buf_len);
                if (IS_ERR(start)) {
                    ret = PTR_ERR(start);
                    goto out;
                }
                BUG_ON(start < p->buf);
            }
            p->start = start;
        } else {
            ret = fs_path_add_from_extent_buffer(p, eb, name_off,
                                 name_len);
            if (ret < 0)
                goto out;
        }

        cur += elem_size + name_len;
        ret = iterate(num, dir, index, p, ctx);
        if (ret)
            goto out;
        num++;
    }

out:
    btrfs_free_path(tmp_path);
    fs_path_free(sctx, p);
    return ret;
}

typedef int (*iterate_dir_item_t)(int num, struct btrfs_key *di_key,
                  const char *name, int name_len,
                  const char *data, int data_len,
                  u8 type, void *ctx);

/*
 * Helper function to iterate the entries in ONE btrfs_dir_item.
 * The iterate callback may return a non zero value to stop iteration. This can
 * be a negative value for error codes or 1 to simply stop it.
 *
 * path must point to the dir item when called.
 */
static int iterate_dir_item(struct send_ctx *sctx,
                struct btrfs_root *root, struct btrfs_path *path,
                struct btrfs_key *found_key,
                iterate_dir_item_t iterate, void *ctx)
{
    int ret = 0;
    struct extent_buffer *eb;
    struct btrfs_item *item;
    struct btrfs_dir_item *di;
    struct btrfs_key di_key;
    char *buf = NULL;
    char *buf2 = NULL;
    int buf_len;
    int buf_virtual = 0;
    u32 name_len;
    u32 data_len;
    u32 cur;
    u32 len;
    u32 total;
    int slot;
    int num;
    u8 type;

    buf_len = PAGE_SIZE;
    buf = kmalloc(buf_len, GFP_NOFS);
    if (!buf) {
        ret = -ENOMEM;
        goto out;
    }

    eb = path->nodes[0];
    slot = path->slots[0];
    item = btrfs_item_nr(eb, slot);
    di = btrfs_item_ptr(eb, slot, struct btrfs_dir_item);
    cur = 0;
    len = 0;
    total = btrfs_item_size(eb, item);

    num = 0;
    while (cur < total) {
        name_len = btrfs_dir_name_len(eb, di);
        data_len = btrfs_dir_data_len(eb, di);
        type = btrfs_dir_type(eb, di);
        btrfs_dir_item_key_to_cpu(eb, di, &di_key);

        if (name_len + data_len > buf_len) {
            buf_len = PAGE_ALIGN(name_len + data_len);
            if (buf_virtual) {
                buf2 = vmalloc(buf_len);
                if (!buf2) {
                    ret = -ENOMEM;
                    goto out;
                }
                vfree(buf);
            } else {
                buf2 = krealloc(buf, buf_len, GFP_NOFS);
                if (!buf2) {
                    buf2 = vmalloc(buf_len);
                    if (!buf2) {
                        ret = -ENOMEM;
                        goto out;
                    }
                    kfree(buf);
                    buf_virtual = 1;
                }
            }

            buf = buf2;
            buf2 = NULL;
        }

        read_extent_buffer(eb, buf, (unsigned long)(di + 1),
                name_len + data_len);

        len = sizeof(*di) + name_len + data_len;
        di = (struct btrfs_dir_item *)((char *)di + len);
        cur += len;

        ret = iterate(num, &di_key, buf, name_len, buf + name_len,
                data_len, type, ctx);
        if (ret < 0)
            goto out;
        if (ret) {
            ret = 0;
            goto out;
        }

        num++;
    }

out:
    if (buf_virtual)
        vfree(buf);
    else
        kfree(buf);
    return ret;
}

static int __copy_first_ref(int num, u64 dir, int index,
                struct fs_path *p, void *ctx)
{
    int ret;
    struct fs_path *pt = ctx;

    ret = fs_path_copy(pt, p);
    if (ret < 0)
        return ret;

    /* we want the first only */
    return 1;
}

/*
 * Retrieve the first path of an inode. If an inode has more then one
 * ref/hardlink, this is ignored.
 */
static int get_inode_path(struct send_ctx *sctx, struct btrfs_root *root,
              u64 ino, struct fs_path *path)
{
    int ret;
    struct btrfs_key key, found_key;
    struct btrfs_path *p;

    p = alloc_path_for_send();
    if (!p)
        return -ENOMEM;

    fs_path_reset(path);

    key.objectid = ino;
    key.type = BTRFS_INODE_REF_KEY;
    key.offset = 0;

    ret = btrfs_search_slot_for_read(root, &key, p, 1, 0);
    if (ret < 0)
        goto out;
    if (ret) {
        ret = 1;
        goto out;
    }
    btrfs_item_key_to_cpu(p->nodes[0], &found_key, p->slots[0]);
    if (found_key.objectid != ino ||
        (found_key.type != BTRFS_INODE_REF_KEY &&
         found_key.type != BTRFS_INODE_EXTREF_KEY)) {
        ret = -ENOENT;
        goto out;
    }

    ret = iterate_inode_ref(sctx, root, p, &found_key, 1,
            __copy_first_ref, path);
    if (ret < 0)
        goto out;
    ret = 0;

out:
    btrfs_free_path(p);
    return ret;
}

struct backref_ctx {
    struct send_ctx *sctx;

    /* number of total found references */
    u64 found;

    /*
     * used for clones found in send_root. clones found behind cur_objectid
     * and cur_offset are not considered as allowed clones.
     */
    u64 cur_objectid;
    u64 cur_offset;

    /* may be truncated in case it's the last extent in a file */
    u64 extent_len;

    /* Just to check for bugs in backref resolving */
    int found_itself;
};

static int __clone_root_cmp_bsearch(const void *key, const void *elt)
{
    u64 root = (u64)(uintptr_t)key;
    struct clone_root *cr = (struct clone_root *)elt;

    if (root < cr->root->objectid)
        return -1;
    if (root > cr->root->objectid)
        return 1;
    return 0;
}

static int __clone_root_cmp_sort(const void *e1, const void *e2)
{
    struct clone_root *cr1 = (struct clone_root *)e1;
    struct clone_root *cr2 = (struct clone_root *)e2;

    if (cr1->root->objectid < cr2->root->objectid)
        return -1;
    if (cr1->root->objectid > cr2->root->objectid)
        return 1;
    return 0;
}

/*
 * Called for every backref that is found for the current extent.
 * Results are collected in sctx->clone_roots->ino/offset/found_refs
 */
static int __iterate_backrefs(u64 ino, u64 offset, u64 root, void *ctx_)
{
    struct backref_ctx *bctx = ctx_;
    struct clone_root *found;
    int ret;
    u64 i_size;

    /* First check if the root is in the list of accepted clone sources */
    found = bsearch((void *)(uintptr_t)root, bctx->sctx->clone_roots,
            bctx->sctx->clone_roots_cnt,
            sizeof(struct clone_root),
            __clone_root_cmp_bsearch);
    if (!found)
        return 0;

    if (found->root == bctx->sctx->send_root &&
        ino == bctx->cur_objectid &&
        offset == bctx->cur_offset) {
        bctx->found_itself = 1;
    }

    /*
     * There are inodes that have extents that lie behind its i_size. Don't
     * accept clones from these extents.
     */
    ret = get_inode_info(found->root, ino, &i_size, NULL, NULL, NULL, NULL,
            NULL);
    if (ret < 0)
        return ret;

    if (offset + bctx->extent_len > i_size)
        return 0;

    /*
     * Make sure we don't consider clones from send_root that are
     * behind the current inode/offset.
     */
    if (found->root == bctx->sctx->send_root) {
        /*
         * TODO for the moment we don't accept clones from the inode
         * that is currently send. We may change this when
         * BTRFS_IOC_CLONE_RANGE supports cloning from and to the same
         * file.
         */
        if (ino >= bctx->cur_objectid)
            return 0;
#if 0
        if (ino > bctx->cur_objectid)
            return 0;
        if (offset + bctx->extent_len > bctx->cur_offset)
            return 0;
#endif
    }

    bctx->found++;
    found->found_refs++;
    if (ino < found->ino) {
        found->ino = ino;
        found->offset = offset;
    } else if (found->ino == ino) {
        /*
         * same extent found more then once in the same file.
         */
        if (found->offset > offset + bctx->extent_len)
            found->offset = offset;
    }

    return 0;
}

/*
 * Given an inode, offset and extent item, it finds a good clone for a clone
 * instruction. Returns -ENOENT when none could be found. The function makes
 * sure that the returned clone is usable at the point where sending is at the
 * moment. This means, that no clones are accepted which lie behind the current
 * inode+offset.
 *
 * path must point to the extent item when called.
 */
static int find_extent_clone(struct send_ctx *sctx,
                 struct btrfs_path *path,
                 u64 ino, u64 data_offset,
                 u64 ino_size,
                 struct clone_root **found)
{
    int ret;
    int extent_type;
    u64 logical;
    u64 disk_byte;
    u64 num_bytes;
    u64 extent_item_pos;
    u64 flags = 0;
    struct btrfs_file_extent_item *fi;
    struct extent_buffer *eb = path->nodes[0];
    struct backref_ctx *backref_ctx = NULL;
    struct clone_root *cur_clone_root;
    struct btrfs_key found_key;
    struct btrfs_path *tmp_path;
    int compressed;
    u32 i;

    tmp_path = alloc_path_for_send();
    if (!tmp_path)
        return -ENOMEM;

    backref_ctx = kmalloc(sizeof(*backref_ctx), GFP_NOFS);
    if (!backref_ctx) {
        ret = -ENOMEM;
        goto out;
    }

    if (data_offset >= ino_size) {
        /*
         * There may be extents that lie behind the file's size.
         * I at least had this in combination with snapshotting while
         * writing large files.
         */
        ret = 0;
        goto out;
    }

    fi = btrfs_item_ptr(eb, path->slots[0],
            struct btrfs_file_extent_item);
    extent_type = btrfs_file_extent_type(eb, fi);
    if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
        ret = -ENOENT;
        goto out;
    }
    compressed = btrfs_file_extent_compression(eb, fi);

    num_bytes = btrfs_file_extent_num_bytes(eb, fi);
    disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
    if (disk_byte == 0) {
        ret = -ENOENT;
        goto out;
    }
    logical = disk_byte + btrfs_file_extent_offset(eb, fi);

    ret = extent_from_logical(sctx->send_root->fs_info, disk_byte, tmp_path,
                  &found_key, &flags);
    btrfs_release_path(tmp_path);

    if (ret < 0)
        goto out;
    if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
        ret = -EIO;
        goto out;
    }

    /*
     * Setup the clone roots.
     */
    for (i = 0; i < sctx->clone_roots_cnt; i++) {
        cur_clone_root = sctx->clone_roots + i;
        cur_clone_root->ino = (u64)-1;
        cur_clone_root->offset = 0;
        cur_clone_root->found_refs = 0;
    }

    backref_ctx->sctx = sctx;
    backref_ctx->found = 0;
    backref_ctx->cur_objectid = ino;
    backref_ctx->cur_offset = data_offset;
    backref_ctx->found_itself = 0;
    backref_ctx->extent_len = num_bytes;

    /*
     * The last extent of a file may be too large due to page alignment.
     * We need to adjust extent_len in this case so that the checks in
     * __iterate_backrefs work.
     */
    if (data_offset + num_bytes >= ino_size)
        backref_ctx->extent_len = ino_size - data_offset;

    /*
     * Now collect all backrefs.
     */
    if (compressed == BTRFS_COMPRESS_NONE)
        extent_item_pos = logical - found_key.objectid;
    else
        extent_item_pos = 0;

    extent_item_pos = logical - found_key.objectid;
    ret = iterate_extent_inodes(sctx->send_root->fs_info,
                    found_key.objectid, extent_item_pos, 1,
                    __iterate_backrefs, backref_ctx);

    if (ret < 0)
        goto out;

    if (!backref_ctx->found_itself) {
        /* found a bug in backref code? */
        ret = -EIO;
        printk(KERN_ERR "btrfs: ERROR did not find backref in "
                "send_root. inode=%llu, offset=%llu, "
                "disk_byte=%llu found extent=%llu\n",
                ino, data_offset, disk_byte, found_key.objectid);
        goto out;
    }

verbose_printk(KERN_DEBUG "btrfs: find_extent_clone: data_offset=%llu, "
        "ino=%llu, "
        "num_bytes=%llu, logical=%llu\n",
        data_offset, ino, num_bytes, logical);

    if (!backref_ctx->found)
        verbose_printk("btrfs:    no clones found\n");

    cur_clone_root = NULL;
    for (i = 0; i < sctx->clone_roots_cnt; i++) {
        if (sctx->clone_roots[i].found_refs) {
            if (!cur_clone_root)
                cur_clone_root = sctx->clone_roots + i;
            else if (sctx->clone_roots[i].root == sctx->send_root)
                /* prefer clones from send_root over others */
                cur_clone_root = sctx->clone_roots + i;
        }

    }

    if (cur_clone_root) {
        *found = cur_clone_root;
        ret = 0;
    } else {
        ret = -ENOENT;
    }

out:
    btrfs_free_path(tmp_path);
    kfree(backref_ctx);
    return ret;
}

static int read_symlink(struct send_ctx *sctx,
            struct btrfs_root *root,
            u64 ino,
            struct fs_path *dest)
{
    int ret;
    struct btrfs_path *path;
    struct btrfs_key key;
    struct btrfs_file_extent_item *ei;
    u8 type;
    u8 compression;
    unsigned long off;
    int len;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    key.objectid = ino;
    key.type = BTRFS_EXTENT_DATA_KEY;
    key.offset = 0;
    ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
    if (ret < 0)
        goto out;
    BUG_ON(ret);

    ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
            struct btrfs_file_extent_item);
    type = btrfs_file_extent_type(path->nodes[0], ei);
    compression = btrfs_file_extent_compression(path->nodes[0], ei);
    BUG_ON(type != BTRFS_FILE_EXTENT_INLINE);
    BUG_ON(compression);

    off = btrfs_file_extent_inline_start(ei);
    len = btrfs_file_extent_inline_len(path->nodes[0], ei);

    ret = fs_path_add_from_extent_buffer(dest, path->nodes[0], off, len);

out:
    btrfs_free_path(path);
    return ret;
}

/*
 * Helper function to generate a file name that is unique in the root of
 * send_root and parent_root. This is used to generate names for orphan inodes.
 */
static int gen_unique_name(struct send_ctx *sctx,
               u64 ino, u64 gen,
               struct fs_path *dest)
{
    int ret = 0;
    struct btrfs_path *path;
    struct btrfs_dir_item *di;
    char tmp[64];
    int len;
    u64 idx = 0;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    while (1) {
        len = snprintf(tmp, sizeof(tmp) - 1, "o%llu-%llu-%llu",
                ino, gen, idx);
        if (len >= sizeof(tmp)) {
            /* should really not happen */
            ret = -EOVERFLOW;
            goto out;
        }

        di = btrfs_lookup_dir_item(NULL, sctx->send_root,
                path, BTRFS_FIRST_FREE_OBJECTID,
                tmp, strlen(tmp), 0);
        btrfs_release_path(path);
        if (IS_ERR(di)) {
            ret = PTR_ERR(di);
            goto out;
        }
        if (di) {
            /* not unique, try again */
            idx++;
            continue;
        }

        if (!sctx->parent_root) {
            /* unique */
            ret = 0;
            break;
        }

        di = btrfs_lookup_dir_item(NULL, sctx->parent_root,
                path, BTRFS_FIRST_FREE_OBJECTID,
                tmp, strlen(tmp), 0);
        btrfs_release_path(path);
        if (IS_ERR(di)) {
            ret = PTR_ERR(di);
            goto out;
        }
        if (di) {
            /* not unique, try again */
            idx++;
            continue;
        }
        /* unique */
        break;
    }

    ret = fs_path_add(dest, tmp, strlen(tmp));

out:
    btrfs_free_path(path);
    return ret;
}

enum inode_state {
    inode_state_no_change,
    inode_state_will_create,
    inode_state_did_create,
    inode_state_will_delete,
    inode_state_did_delete,
};

static int get_cur_inode_state(struct send_ctx *sctx, u64 ino, u64 gen)
{
    int ret;
    int left_ret;
    int right_ret;
    u64 left_gen;
    u64 right_gen;

    ret = get_inode_info(sctx->send_root, ino, NULL, &left_gen, NULL, NULL,
            NULL, NULL);
    if (ret < 0 && ret != -ENOENT)
        goto out;
    left_ret = ret;

    if (!sctx->parent_root) {
        right_ret = -ENOENT;
    } else {
        ret = get_inode_info(sctx->parent_root, ino, NULL, &right_gen,
                NULL, NULL, NULL, NULL);
        if (ret < 0 && ret != -ENOENT)
            goto out;
        right_ret = ret;
    }

    if (!left_ret && !right_ret) {
        if (left_gen == gen && right_gen == gen) {
            ret = inode_state_no_change;
        } else if (left_gen == gen) {
            if (ino < sctx->send_progress)
                ret = inode_state_did_create;
            else
                ret = inode_state_will_create;
        } else if (right_gen == gen) {
            if (ino < sctx->send_progress)
                ret = inode_state_did_delete;
            else
                ret = inode_state_will_delete;
        } else  {
            ret = -ENOENT;
        }
    } else if (!left_ret) {
        if (left_gen == gen) {
            if (ino < sctx->send_progress)
                ret = inode_state_did_create;
            else
                ret = inode_state_will_create;
        } else {
            ret = -ENOENT;
        }
    } else if (!right_ret) {
        if (right_gen == gen) {
            if (ino < sctx->send_progress)
                ret = inode_state_did_delete;
            else
                ret = inode_state_will_delete;
        } else {
            ret = -ENOENT;
        }
    } else {
        ret = -ENOENT;
    }

out:
    return ret;
}

static int is_inode_existent(struct send_ctx *sctx, u64 ino, u64 gen)
{
    int ret;

    ret = get_cur_inode_state(sctx, ino, gen);
    if (ret < 0)
        goto out;

    if (ret == inode_state_no_change ||
        ret == inode_state_did_create ||
        ret == inode_state_will_delete)
        ret = 1;
    else
        ret = 0;

out:
    return ret;
}

/*
 * Helper function to lookup a dir item in a dir.
 */
static int lookup_dir_item_inode(struct btrfs_root *root,
                 u64 dir, const char *name, int name_len,
                 u64 *found_inode,
                 u8 *found_type)
{
    int ret = 0;
    struct btrfs_dir_item *di;
    struct btrfs_key key;
    struct btrfs_path *path;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    di = btrfs_lookup_dir_item(NULL, root, path,
            dir, name, name_len, 0);
    if (!di) {
        ret = -ENOENT;
        goto out;
    }
    if (IS_ERR(di)) {
        ret = PTR_ERR(di);
        goto out;
    }
    btrfs_dir_item_key_to_cpu(path->nodes[0], di, &key);
    *found_inode = key.objectid;
    *found_type = btrfs_dir_type(path->nodes[0], di);

out:
    btrfs_free_path(path);
    return ret;
}

/*
 * Looks up the first btrfs_inode_ref of a given ino. It returns the parent dir,
 * generation of the parent dir and the name of the dir entry.
 */
static int get_first_ref(struct send_ctx *sctx,
             struct btrfs_root *root, u64 ino,
             u64 *dir, u64 *dir_gen, struct fs_path *name)
{
    int ret;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct btrfs_path *path;
    int len;
    u64 parent_dir;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    key.objectid = ino;
    key.type = BTRFS_INODE_REF_KEY;
    key.offset = 0;

    ret = btrfs_search_slot_for_read(root, &key, path, 1, 0);
    if (ret < 0)
        goto out;
    if (!ret)
        btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                path->slots[0]);
    if (ret || found_key.objectid != ino ||
        (found_key.type != BTRFS_INODE_REF_KEY &&
         found_key.type != BTRFS_INODE_EXTREF_KEY)) {
        ret = -ENOENT;
        goto out;
    }

    if (key.type == BTRFS_INODE_REF_KEY) {
        struct btrfs_inode_ref *iref;
        iref = btrfs_item_ptr(path->nodes[0], path->slots[0],
                      struct btrfs_inode_ref);
        len = btrfs_inode_ref_name_len(path->nodes[0], iref);
        ret = fs_path_add_from_extent_buffer(name, path->nodes[0],
                             (unsigned long)(iref + 1),
                             len);
        parent_dir = found_key.offset;
    } else {
        struct btrfs_inode_extref *extref;
        extref = btrfs_item_ptr(path->nodes[0], path->slots[0],
                    struct btrfs_inode_extref);
        len = btrfs_inode_extref_name_len(path->nodes[0], extref);
        ret = fs_path_add_from_extent_buffer(name, path->nodes[0],
                    (unsigned long)&extref->name, len);
        parent_dir = btrfs_inode_extref_parent(path->nodes[0], extref);
    }
    if (ret < 0)
        goto out;
    btrfs_release_path(path);

    ret = get_inode_info(root, parent_dir, NULL, dir_gen, NULL, NULL,
            NULL, NULL);
    if (ret < 0)
        goto out;

    *dir = parent_dir;

out:
    btrfs_free_path(path);
    return ret;
}

static int is_first_ref(struct send_ctx *sctx,
            struct btrfs_root *root,
            u64 ino, u64 dir,
            const char *name, int name_len)
{
    int ret;
    struct fs_path *tmp_name;
    u64 tmp_dir;
    u64 tmp_dir_gen;

    tmp_name = fs_path_alloc(sctx);
    if (!tmp_name)
        return -ENOMEM;

    ret = get_first_ref(sctx, root, ino, &tmp_dir, &tmp_dir_gen, tmp_name);
    if (ret < 0)
        goto out;

    if (dir != tmp_dir || name_len != fs_path_len(tmp_name)) {
        ret = 0;
        goto out;
    }

    ret = !memcmp(tmp_name->start, name, name_len);

out:
    fs_path_free(sctx, tmp_name);
    return ret;
}

/*
 * Used by process_recorded_refs to determine if a new ref would overwrite an
 * already existing ref. In case it detects an overwrite, it returns the
 * inode/gen in who_ino/who_gen.
 * When an overwrite is detected, process_recorded_refs does proper orphanizing
 * to make sure later references to the overwritten inode are possible.
 * Orphanizing is however only required for the first ref of an inode.
 * process_recorded_refs does an additional is_first_ref check to see if
 * orphanizing is really required.
 */
static int will_overwrite_ref(struct send_ctx *sctx, u64 dir, u64 dir_gen,
                  const char *name, int name_len,
                  u64 *who_ino, u64 *who_gen)
{
    int ret = 0;
    u64 other_inode = 0;
    u8 other_type = 0;

    if (!sctx->parent_root)
        goto out;

    ret = is_inode_existent(sctx, dir, dir_gen);
    if (ret <= 0)
        goto out;

    ret = lookup_dir_item_inode(sctx->parent_root, dir, name, name_len,
            &other_inode, &other_type);
    if (ret < 0 && ret != -ENOENT)
        goto out;
    if (ret) {
        ret = 0;
        goto out;
    }

    /*
     * Check if the overwritten ref was already processed. If yes, the ref
     * was already unlinked/moved, so we can safely assume that we will not
     * overwrite anything at this point in time.
     */
    if (other_inode > sctx->send_progress) {
        ret = get_inode_info(sctx->parent_root, other_inode, NULL,
                who_gen, NULL, NULL, NULL, NULL);
        if (ret < 0)
            goto out;

        ret = 1;
        *who_ino = other_inode;
    } else {
        ret = 0;
    }

out:
    return ret;
}

/*
 * Checks if the ref was overwritten by an already processed inode. This is
 * used by __get_cur_name_and_parent to find out if the ref was orphanized and
 * thus the orphan name needs be used.
 * process_recorded_refs also uses it to avoid unlinking of refs that were
 * overwritten.
 */
static int did_overwrite_ref(struct send_ctx *sctx,
                u64 dir, u64 dir_gen,
                u64 ino, u64 ino_gen,
                const char *name, int name_len)
{
    int ret = 0;
    u64 gen;
    u64 ow_inode;
    u8 other_type;

    if (!sctx->parent_root)
        goto out;

    ret = is_inode_existent(sctx, dir, dir_gen);
    if (ret <= 0)
        goto out;

    /* check if the ref was overwritten by another ref */
    ret = lookup_dir_item_inode(sctx->send_root, dir, name, name_len,
            &ow_inode, &other_type);
    if (ret < 0 && ret != -ENOENT)
        goto out;
    if (ret) {
        /* was never and will never be overwritten */
        ret = 0;
        goto out;
    }

    ret = get_inode_info(sctx->send_root, ow_inode, NULL, &gen, NULL, NULL,
            NULL, NULL);
    if (ret < 0)
        goto out;

    if (ow_inode == ino && gen == ino_gen) {
        ret = 0;
        goto out;
    }

    /* we know that it is or will be overwritten. check this now */
    if (ow_inode < sctx->send_progress)
        ret = 1;
    else
        ret = 0;

out:
    return ret;
}

/*
 * Same as did_overwrite_ref, but also checks if it is the first ref of an inode
 * that got overwritten. This is used by process_recorded_refs to determine
 * if it has to use the path as returned by get_cur_path or the orphan name.
 */
static int did_overwrite_first_ref(struct send_ctx *sctx, u64 ino, u64 gen)
{
    int ret = 0;
    struct fs_path *name = NULL;
    u64 dir;
    u64 dir_gen;

    if (!sctx->parent_root)
        goto out;

    name = fs_path_alloc(sctx);
    if (!name)
        return -ENOMEM;

    ret = get_first_ref(sctx, sctx->parent_root, ino, &dir, &dir_gen, name);
    if (ret < 0)
        goto out;

    ret = did_overwrite_ref(sctx, dir, dir_gen, ino, gen,
            name->start, fs_path_len(name));

out:
    fs_path_free(sctx, name);
    return ret;
}

/*
 * Insert a name cache entry. On 32bit kernels the radix tree index is 32bit,
 * so we need to do some special handling in case we have clashes. This function
 * takes care of this with the help of name_cache_entry::radix_list.
 * In case of error, nce is kfreed.
 */
static int name_cache_insert(struct send_ctx *sctx,
                 struct name_cache_entry *nce)
{
    int ret = 0;
    struct list_head *nce_head;

    nce_head = radix_tree_lookup(&sctx->name_cache,
            (unsigned long)nce->ino);
    if (!nce_head) {
        nce_head = kmalloc(sizeof(*nce_head), GFP_NOFS);
        if (!nce_head)
            return -ENOMEM;
        INIT_LIST_HEAD(nce_head);

        ret = radix_tree_insert(&sctx->name_cache, nce->ino, nce_head);
        if (ret < 0) {
            kfree(nce_head);
            kfree(nce);
            return ret;
        }
    }
    list_add_tail(&nce->radix_list, nce_head);
    list_add_tail(&nce->list, &sctx->name_cache_list);
    sctx->name_cache_size++;

    return ret;
}

static void name_cache_delete(struct send_ctx *sctx,
                  struct name_cache_entry *nce)
{
    struct list_head *nce_head;

    nce_head = radix_tree_lookup(&sctx->name_cache,
            (unsigned long)nce->ino);
    BUG_ON(!nce_head);

    list_del(&nce->radix_list);
    list_del(&nce->list);
    sctx->name_cache_size--;

    if (list_empty(nce_head)) {
        radix_tree_delete(&sctx->name_cache, (unsigned long)nce->ino);
        kfree(nce_head);
    }
}

static struct name_cache_entry *name_cache_search(struct send_ctx *sctx,
                            u64 ino, u64 gen)
{
    struct list_head *nce_head;
    struct name_cache_entry *cur;

    nce_head = radix_tree_lookup(&sctx->name_cache, (unsigned long)ino);
    if (!nce_head)
        return NULL;

    list_for_each_entry(cur, nce_head, radix_list) {
        if (cur->ino == ino && cur->gen == gen)
            return cur;
    }
    return NULL;
}

/*
 * Removes the entry from the list and adds it back to the end. This marks the
 * entry as recently used so that name_cache_clean_unused does not remove it.
 */
static void name_cache_used(struct send_ctx *sctx, struct name_cache_entry *nce)
{
    list_del(&nce->list);
    list_add_tail(&nce->list, &sctx->name_cache_list);
}

/*
 * Remove some entries from the beginning of name_cache_list.
 */
static void name_cache_clean_unused(struct send_ctx *sctx)
{
    struct name_cache_entry *nce;

    if (sctx->name_cache_size < SEND_CTX_NAME_CACHE_CLEAN_SIZE)
        return;

    while (sctx->name_cache_size > SEND_CTX_MAX_NAME_CACHE_SIZE) {
        nce = list_entry(sctx->name_cache_list.next,
                struct name_cache_entry, list);
        name_cache_delete(sctx, nce);
        kfree(nce);
    }
}

static void name_cache_free(struct send_ctx *sctx)
{
    struct name_cache_entry *nce;

    while (!list_empty(&sctx->name_cache_list)) {
        nce = list_entry(sctx->name_cache_list.next,
                struct name_cache_entry, list);
        name_cache_delete(sctx, nce);
        kfree(nce);
    }
}

/*
 * Used by get_cur_path for each ref up to the root.
 * Returns 0 if it succeeded.
 * Returns 1 if the inode is not existent or got overwritten. In that case, the
 * name is an orphan name. This instructs get_cur_path to stop iterating. If 1
 * is returned, parent_ino/parent_gen are not guaranteed to be valid.
 * Returns <0 in case of error.
 */
static int __get_cur_name_and_parent(struct send_ctx *sctx,
                     u64 ino, u64 gen,
                     u64 *parent_ino,
                     u64 *parent_gen,
                     struct fs_path *dest)
{
    int ret;
    int nce_ret;
    struct btrfs_path *path = NULL;
    struct name_cache_entry *nce = NULL;

    /*
     * First check if we already did a call to this function with the same
     * ino/gen. If yes, check if the cache entry is still up-to-date. If yes
     * return the cached result.
     */
    nce = name_cache_search(sctx, ino, gen);
    if (nce) {
        if (ino < sctx->send_progress && nce->need_later_update) {
            name_cache_delete(sctx, nce);
            kfree(nce);
            nce = NULL;
        } else {
            name_cache_used(sctx, nce);
            *parent_ino = nce->parent_ino;
            *parent_gen = nce->parent_gen;
            ret = fs_path_add(dest, nce->name, nce->name_len);
            if (ret < 0)
                goto out;
            ret = nce->ret;
            goto out;
        }
    }

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    /*
     * If the inode is not existent yet, add the orphan name and return 1.
     * This should only happen for the parent dir that we determine in
     * __record_new_ref
     */
    ret = is_inode_existent(sctx, ino, gen);
    if (ret < 0)
        goto out;

    if (!ret) {
        ret = gen_unique_name(sctx, ino, gen, dest);
        if (ret < 0)
            goto out;
        ret = 1;
        goto out_cache;
    }

    /*
     * Depending on whether the inode was already processed or not, use
     * send_root or parent_root for ref lookup.
     */
    if (ino < sctx->send_progress)
        ret = get_first_ref(sctx, sctx->send_root, ino,
                parent_ino, parent_gen, dest);
    else
        ret = get_first_ref(sctx, sctx->parent_root, ino,
                parent_ino, parent_gen, dest);
    if (ret < 0)
        goto out;

    /*
     * Check if the ref was overwritten by an inode's ref that was processed
     * earlier. If yes, treat as orphan and return 1.
     */
    ret = did_overwrite_ref(sctx, *parent_ino, *parent_gen, ino, gen,
            dest->start, dest->end - dest->start);
    if (ret < 0)
        goto out;
    if (ret) {
        fs_path_reset(dest);
        ret = gen_unique_name(sctx, ino, gen, dest);
        if (ret < 0)
            goto out;
        ret = 1;
    }

out_cache:
    /*
     * Store the result of the lookup in the name cache.
     */
    nce = kmalloc(sizeof(*nce) + fs_path_len(dest) + 1, GFP_NOFS);
    if (!nce) {
        ret = -ENOMEM;
        goto out;
    }

    nce->ino = ino;
    nce->gen = gen;
    nce->parent_ino = *parent_ino;
    nce->parent_gen = *parent_gen;
    nce->name_len = fs_path_len(dest);
    nce->ret = ret;
    strcpy(nce->name, dest->start);

    if (ino < sctx->send_progress)
        nce->need_later_update = 0;
    else
        nce->need_later_update = 1;

    nce_ret = name_cache_insert(sctx, nce);
    if (nce_ret < 0)
        ret = nce_ret;
    name_cache_clean_unused(sctx);

out:
    btrfs_free_path(path);
    return ret;
}

/*
 * Magic happens here. This function returns the first ref to an inode as it
 * would look like while receiving the stream at this point in time.
 * We walk the path up to the root. For every inode in between, we check if it
 * was already processed/sent. If yes, we continue with the parent as found
 * in send_root. If not, we continue with the parent as found in parent_root.
 * If we encounter an inode that was deleted at this point in time, we use the
 * inodes "orphan" name instead of the real name and stop. Same with new inodes
 * that were not created yet and overwritten inodes/refs.
 *
 * When do we have have orphan inodes:
 * 1. When an inode is freshly created and thus no valid refs are available yet
 * 2. When a directory lost all it's refs (deleted) but still has dir items
 *    inside which were not processed yet (pending for move/delete). If anyone
 *    tried to get the path to the dir items, it would get a path inside that
 *    orphan directory.
 * 3. When an inode is moved around or gets new links, it may overwrite the ref
 *    of an unprocessed inode. If in that case the first ref would be
 *    overwritten, the overwritten inode gets "orphanized". Later when we
 *    process this overwritten inode, it is restored at a new place by moving
 *    the orphan inode.
 *
 * sctx->send_progress tells this function at which point in time receiving
 * would be.
 */
static int get_cur_path(struct send_ctx *sctx, u64 ino, u64 gen,
            struct fs_path *dest)
{
    int ret = 0;
    struct fs_path *name = NULL;
    u64 parent_inode = 0;
    u64 parent_gen = 0;
    int stop = 0;

    name = fs_path_alloc(sctx);
    if (!name) {
        ret = -ENOMEM;
        goto out;
    }

    dest->reversed = 1;
    fs_path_reset(dest);

    while (!stop && ino != BTRFS_FIRST_FREE_OBJECTID) {
        fs_path_reset(name);

        ret = __get_cur_name_and_parent(sctx, ino, gen,
                &parent_inode, &parent_gen, name);
        if (ret < 0)
            goto out;
        if (ret)
            stop = 1;

        ret = fs_path_add_path(dest, name);
        if (ret < 0)
            goto out;

        ino = parent_inode;
        gen = parent_gen;
    }

out:
    fs_path_free(sctx, name);
    if (!ret)
        fs_path_unreverse(dest);
    return ret;
}

/*
 * Called for regular files when sending extents data. Opens a struct file
 * to read from the file.
 */
static int open_cur_inode_file(struct send_ctx *sctx)
{
    int ret = 0;
    struct btrfs_key key;
    struct path path;
    struct inode *inode;
    struct dentry *dentry;
    struct file *filp;
    int new = 0;

    if (sctx->cur_inode_filp)
        goto out;

    key.objectid = sctx->cur_ino;
    key.type = BTRFS_INODE_ITEM_KEY;
    key.offset = 0;

    inode = btrfs_iget(sctx->send_root->fs_info->sb, &key, sctx->send_root,
            &new);
    if (IS_ERR(inode)) {
        ret = PTR_ERR(inode);
        goto out;
    }

    dentry = d_obtain_alias(inode);
    inode = NULL;
    if (IS_ERR(dentry)) {
        ret = PTR_ERR(dentry);
        goto out;
    }

    path.mnt = sctx->mnt;
    path.dentry = dentry;
    filp = dentry_open(&path, O_RDONLY | O_LARGEFILE, current_cred());
    dput(dentry);
    dentry = NULL;
    if (IS_ERR(filp)) {
        ret = PTR_ERR(filp);
        goto out;
    }
    sctx->cur_inode_filp = filp;

out:
    /*
     * no xxxput required here as every vfs op
     * does it by itself on failure
     */
    return ret;
}

/*
 * Closes the struct file that was created in open_cur_inode_file
 */
static int close_cur_inode_file(struct send_ctx *sctx)
{
    int ret = 0;

    if (!sctx->cur_inode_filp)
        goto out;

    ret = filp_close(sctx->cur_inode_filp, NULL);
    sctx->cur_inode_filp = NULL;

out:
    return ret;
}

/*
 * Sends a BTRFS_SEND_C_SUBVOL command/item to userspace
 */
static int send_subvol_begin(struct send_ctx *sctx)
{
    int ret;
    struct btrfs_root *send_root = sctx->send_root;
    struct btrfs_root *parent_root = sctx->parent_root;
    struct btrfs_path *path;
    struct btrfs_key key;
    struct btrfs_root_ref *ref;
    struct extent_buffer *leaf;
    char *name = NULL;
    int namelen;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    name = kmalloc(BTRFS_PATH_NAME_MAX, GFP_NOFS);
    if (!name) {
        btrfs_free_path(path);
        return -ENOMEM;
    }

    key.objectid = send_root->objectid;
    key.type = BTRFS_ROOT_BACKREF_KEY;
    key.offset = 0;

    ret = btrfs_search_slot_for_read(send_root->fs_info->tree_root,
                &key, path, 1, 0);
    if (ret < 0)
        goto out;
    if (ret) {
        ret = -ENOENT;
        goto out;
    }

    leaf = path->nodes[0];
    btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
    if (key.type != BTRFS_ROOT_BACKREF_KEY ||
        key.objectid != send_root->objectid) {
        ret = -ENOENT;
        goto out;
    }
    ref = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_root_ref);
    namelen = btrfs_root_ref_name_len(leaf, ref);
    read_extent_buffer(leaf, name, (unsigned long)(ref + 1), namelen);
    btrfs_release_path(path);

    if (parent_root) {
        ret = begin_cmd(sctx, BTRFS_SEND_C_SNAPSHOT);
        if (ret < 0)
            goto out;
    } else {
        ret = begin_cmd(sctx, BTRFS_SEND_C_SUBVOL);
        if (ret < 0)
            goto out;
    }

    TLV_PUT_STRING(sctx, BTRFS_SEND_A_PATH, name, namelen);
    TLV_PUT_UUID(sctx, BTRFS_SEND_A_UUID,
            sctx->send_root->root_item.uuid);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_CTRANSID,
            sctx->send_root->root_item.ctransid);
    if (parent_root) {
        TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
                sctx->parent_root->root_item.uuid);
        TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_CTRANSID,
                sctx->parent_root->root_item.ctransid);
    }

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    btrfs_free_path(path);
    kfree(name);
    return ret;
}

static int send_truncate(struct send_ctx *sctx, u64 ino, u64 gen, u64 size)
{
    int ret = 0;
    struct fs_path *p;

verbose_printk("btrfs: send_truncate %llu size=%llu\n", ino, size);

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    ret = begin_cmd(sctx, BTRFS_SEND_C_TRUNCATE);
    if (ret < 0)
        goto out;

    ret = get_cur_path(sctx, ino, gen, p);
    if (ret < 0)
        goto out;
    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_SIZE, size);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    fs_path_free(sctx, p);
    return ret;
}

static int send_chmod(struct send_ctx *sctx, u64 ino, u64 gen, u64 mode)
{
    int ret = 0;
    struct fs_path *p;

verbose_printk("btrfs: send_chmod %llu mode=%llu\n", ino, mode);

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    ret = begin_cmd(sctx, BTRFS_SEND_C_CHMOD);
    if (ret < 0)
        goto out;

    ret = get_cur_path(sctx, ino, gen, p);
    if (ret < 0)
        goto out;
    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_MODE, mode & 07777);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    fs_path_free(sctx, p);
    return ret;
}

static int send_chown(struct send_ctx *sctx, u64 ino, u64 gen, u64 uid, u64 gid)
{
    int ret = 0;
    struct fs_path *p;

verbose_printk("btrfs: send_chown %llu uid=%llu, gid=%llu\n", ino, uid, gid);

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    ret = begin_cmd(sctx, BTRFS_SEND_C_CHOWN);
    if (ret < 0)
        goto out;

    ret = get_cur_path(sctx, ino, gen, p);
    if (ret < 0)
        goto out;
    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_UID, uid);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_GID, gid);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    fs_path_free(sctx, p);
    return ret;
}

static int send_utimes(struct send_ctx *sctx, u64 ino, u64 gen)
{
    int ret = 0;
    struct fs_path *p = NULL;
    struct btrfs_inode_item *ii;
    struct btrfs_path *path = NULL;
    struct extent_buffer *eb;
    struct btrfs_key key;
    int slot;

verbose_printk("btrfs: send_utimes %llu\n", ino);

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    path = alloc_path_for_send();
    if (!path) {
        ret = -ENOMEM;
        goto out;
    }

    key.objectid = ino;
    key.type = BTRFS_INODE_ITEM_KEY;
    key.offset = 0;
    ret = btrfs_search_slot(NULL, sctx->send_root, &key, path, 0, 0);
    if (ret < 0)
        goto out;

    eb = path->nodes[0];
    slot = path->slots[0];
    ii = btrfs_item_ptr(eb, slot, struct btrfs_inode_item);

    ret = begin_cmd(sctx, BTRFS_SEND_C_UTIMES);
    if (ret < 0)
        goto out;

    ret = get_cur_path(sctx, ino, gen, p);
    if (ret < 0)
        goto out;
    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
    TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_ATIME, eb,
            btrfs_inode_atime(ii));
    TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_MTIME, eb,
            btrfs_inode_mtime(ii));
    TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_CTIME, eb,
            btrfs_inode_ctime(ii));
    /* TODO Add otime support when the otime patches get into upstream */

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    fs_path_free(sctx, p);
    btrfs_free_path(path);
    return ret;
}

/*
 * Sends a BTRFS_SEND_C_MKXXX or SYMLINK command to user space. We don't have
 * a valid path yet because we did not process the refs yet. So, the inode
 * is created as orphan.
 */
static int send_create_inode(struct send_ctx *sctx, u64 ino)
{
    int ret = 0;
    struct fs_path *p;
    int cmd;
    u64 gen;
    u64 mode;
    u64 rdev;

verbose_printk("btrfs: send_create_inode %llu\n", ino);

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    ret = get_inode_info(sctx->send_root, ino, NULL, &gen, &mode, NULL,
            NULL, &rdev);
    if (ret < 0)
        goto out;

    if (S_ISREG(mode)) {
        cmd = BTRFS_SEND_C_MKFILE;
    } else if (S_ISDIR(mode)) {
        cmd = BTRFS_SEND_C_MKDIR;
    } else if (S_ISLNK(mode)) {
        cmd = BTRFS_SEND_C_SYMLINK;
    } else if (S_ISCHR(mode) || S_ISBLK(mode)) {
        cmd = BTRFS_SEND_C_MKNOD;
    } else if (S_ISFIFO(mode)) {
        cmd = BTRFS_SEND_C_MKFIFO;
    } else if (S_ISSOCK(mode)) {
        cmd = BTRFS_SEND_C_MKSOCK;
    } else {
        printk(KERN_WARNING "btrfs: unexpected inode type %o",
                (int)(mode & S_IFMT));
        ret = -ENOTSUPP;
        goto out;
    }

    ret = begin_cmd(sctx, cmd);
    if (ret < 0)
        goto out;

    ret = gen_unique_name(sctx, ino, gen, p);
    if (ret < 0)
        goto out;

    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_INO, ino);

    if (S_ISLNK(mode)) {
        fs_path_reset(p);
        ret = read_symlink(sctx, sctx->send_root, ino, p);
        if (ret < 0)
            goto out;
        TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH_LINK, p);
    } else if (S_ISCHR(mode) || S_ISBLK(mode) ||
           S_ISFIFO(mode) || S_ISSOCK(mode)) {
        TLV_PUT_U64(sctx, BTRFS_SEND_A_RDEV, new_encode_dev(rdev));
        TLV_PUT_U64(sctx, BTRFS_SEND_A_MODE, mode);
    }

    ret = send_cmd(sctx);
    if (ret < 0)
        goto out;


tlv_put_failure:
out:
    fs_path_free(sctx, p);
    return ret;
}

/*
 * We need some special handling for inodes that get processed before the parent
 * directory got created. See process_recorded_refs for details.
 * This function does the check if we already created the dir out of order.
 */
static int did_create_dir(struct send_ctx *sctx, u64 dir)
{
    int ret = 0;
    struct btrfs_path *path = NULL;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct btrfs_key di_key;
    struct extent_buffer *eb;
    struct btrfs_dir_item *di;
    int slot;

    path = alloc_path_for_send();
    if (!path) {
        ret = -ENOMEM;
        goto out;
    }

    key.objectid = dir;
    key.type = BTRFS_DIR_INDEX_KEY;
    key.offset = 0;
    while (1) {
        ret = btrfs_search_slot_for_read(sctx->send_root, &key, path,
                1, 0);
        if (ret < 0)
            goto out;
        if (!ret) {
            eb = path->nodes[0];
            slot = path->slots[0];
            btrfs_item_key_to_cpu(eb, &found_key, slot);
        }
        if (ret || found_key.objectid != key.objectid ||
            found_key.type != key.type) {
            ret = 0;
            goto out;
        }

        di = btrfs_item_ptr(eb, slot, struct btrfs_dir_item);
        btrfs_dir_item_key_to_cpu(eb, di, &di_key);

        if (di_key.objectid < sctx->send_progress) {
            ret = 1;
            goto out;
        }

        key.offset = found_key.offset + 1;
        btrfs_release_path(path);
    }

out:
    btrfs_free_path(path);
    return ret;
}

/*
 * Only creates the inode if it is:
 * 1. Not a directory
 * 2. Or a directory which was not created already due to out of order
 *    directories. See did_create_dir and process_recorded_refs for details.
 */
static int send_create_inode_if_needed(struct send_ctx *sctx)
{
    int ret;

    if (S_ISDIR(sctx->cur_inode_mode)) {
        ret = did_create_dir(sctx, sctx->cur_ino);
        if (ret < 0)
            goto out;
        if (ret) {
            ret = 0;
            goto out;
        }
    }

    ret = send_create_inode(sctx, sctx->cur_ino);
    if (ret < 0)
        goto out;

out:
    return ret;
}

struct recorded_ref {
    struct list_head list;
    char *dir_path;
    char *name;
    struct fs_path *full_path;
    u64 dir;
    u64 dir_gen;
    int dir_path_len;
    int name_len;
};

/*
 * We need to process new refs before deleted refs, but compare_tree gives us
 * everything mixed. So we first record all refs and later process them.
 * This function is a helper to record one ref.
 */
static int record_ref(struct list_head *head, u64 dir,
              u64 dir_gen, struct fs_path *path)
{
    struct recorded_ref *ref;
    char *tmp;

    ref = kmalloc(sizeof(*ref), GFP_NOFS);
    if (!ref)
        return -ENOMEM;

    ref->dir = dir;
    ref->dir_gen = dir_gen;
    ref->full_path = path;

    tmp = strrchr(ref->full_path->start, '/');
    if (!tmp) {
        ref->name_len = ref->full_path->end - ref->full_path->start;
        ref->name = ref->full_path->start;
        ref->dir_path_len = 0;
        ref->dir_path = ref->full_path->start;
    } else {
        tmp++;
        ref->name_len = ref->full_path->end - tmp;
        ref->name = tmp;
        ref->dir_path = ref->full_path->start;
        ref->dir_path_len = ref->full_path->end -
                ref->full_path->start - 1 - ref->name_len;
    }

    list_add_tail(&ref->list, head);
    return 0;
}

static void __free_recorded_refs(struct send_ctx *sctx, struct list_head *head)
{
    struct recorded_ref *cur;

    while (!list_empty(head)) {
        cur = list_entry(head->next, struct recorded_ref, list);
        fs_path_free(sctx, cur->full_path);
        list_del(&cur->list);
        kfree(cur);
    }
}

static void free_recorded_refs(struct send_ctx *sctx)
{
    __free_recorded_refs(sctx, &sctx->new_refs);
    __free_recorded_refs(sctx, &sctx->deleted_refs);
}

/*
 * Renames/moves a file/dir to its orphan name. Used when the first
 * ref of an unprocessed inode gets overwritten and for all non empty
 * directories.
 */
static int orphanize_inode(struct send_ctx *sctx, u64 ino, u64 gen,
              struct fs_path *path)
{
    int ret;
    struct fs_path *orphan;

    orphan = fs_path_alloc(sctx);
    if (!orphan)
        return -ENOMEM;

    ret = gen_unique_name(sctx, ino, gen, orphan);
    if (ret < 0)
        goto out;

    ret = send_rename(sctx, path, orphan);

out:
    fs_path_free(sctx, orphan);
    return ret;
}

/*
 * Returns 1 if a directory can be removed at this point in time.
 * We check this by iterating all dir items and checking if the inode behind
 * the dir item was already processed.
 */
static int can_rmdir(struct send_ctx *sctx, u64 dir, u64 send_progress)
{
    int ret = 0;
    struct btrfs_root *root = sctx->parent_root;
    struct btrfs_path *path;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct btrfs_key loc;
    struct btrfs_dir_item *di;

    /*
     * Don't try to rmdir the top/root subvolume dir.
     */
    if (dir == BTRFS_FIRST_FREE_OBJECTID)
        return 0;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    key.objectid = dir;
    key.type = BTRFS_DIR_INDEX_KEY;
    key.offset = 0;

    while (1) {
        ret = btrfs_search_slot_for_read(root, &key, path, 1, 0);
        if (ret < 0)
            goto out;
        if (!ret) {
            btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                    path->slots[0]);
        }
        if (ret || found_key.objectid != key.objectid ||
            found_key.type != key.type) {
            break;
        }

        di = btrfs_item_ptr(path->nodes[0], path->slots[0],
                struct btrfs_dir_item);
        btrfs_dir_item_key_to_cpu(path->nodes[0], di, &loc);

        if (loc.objectid > send_progress) {
            ret = 0;
            goto out;
        }

        btrfs_release_path(path);
        key.offset = found_key.offset + 1;
    }

    ret = 1;

out:
    btrfs_free_path(path);
    return ret;
}

/*
 * This does all the move/link/unlink/rmdir magic.
 */
static int process_recorded_refs(struct send_ctx *sctx)
{
    int ret = 0;
    struct recorded_ref *cur;
    struct recorded_ref *cur2;
    struct ulist *check_dirs = NULL;
    struct ulist_iterator uit;
    struct ulist_node *un;
    struct fs_path *valid_path = NULL;
    u64 ow_inode = 0;
    u64 ow_gen;
    int did_overwrite = 0;
    int is_orphan = 0;

verbose_printk("btrfs: process_recorded_refs %llu\n", sctx->cur_ino);

    /*
     * This should never happen as the root dir always has the same ref
     * which is always '..'
     */
    BUG_ON(sctx->cur_ino <= BTRFS_FIRST_FREE_OBJECTID);

    valid_path = fs_path_alloc(sctx);
    if (!valid_path) {
        ret = -ENOMEM;
        goto out;
    }

    check_dirs = ulist_alloc(GFP_NOFS);
    if (!check_dirs) {
        ret = -ENOMEM;
        goto out;
    }

    /*
     * First, check if the first ref of the current inode was overwritten
     * before. If yes, we know that the current inode was already orphanized
     * and thus use the orphan name. If not, we can use get_cur_path to
     * get the path of the first ref as it would like while receiving at
     * this point in time.
     * New inodes are always orphan at the beginning, so force to use the
     * orphan name in this case.
     * The first ref is stored in valid_path and will be updated if it
     * gets moved around.
     */
    if (!sctx->cur_inode_new) {
        ret = did_overwrite_first_ref(sctx, sctx->cur_ino,
                sctx->cur_inode_gen);
        if (ret < 0)
            goto out;
        if (ret)
            did_overwrite = 1;
    }
    if (sctx->cur_inode_new || did_overwrite) {
        ret = gen_unique_name(sctx, sctx->cur_ino,
                sctx->cur_inode_gen, valid_path);
        if (ret < 0)
            goto out;
        is_orphan = 1;
    } else {
        ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                valid_path);
        if (ret < 0)
            goto out;
    }

    list_for_each_entry(cur, &sctx->new_refs, list) {
        /*
         * We may have refs where the parent directory does not exist
         * yet. This happens if the parent directories inum is higher
         * the the current inum. To handle this case, we create the
         * parent directory out of order. But we need to check if this
         * did already happen before due to other refs in the same dir.
         */
        ret = get_cur_inode_state(sctx, cur->dir, cur->dir_gen);
        if (ret < 0)
            goto out;
        if (ret == inode_state_will_create) {
            ret = 0;
            /*
             * First check if any of the current inodes refs did
             * already create the dir.
             */
            list_for_each_entry(cur2, &sctx->new_refs, list) {
                if (cur == cur2)
                    break;
                if (cur2->dir == cur->dir) {
                    ret = 1;
                    break;
                }
            }

            /*
             * If that did not happen, check if a previous inode
             * did already create the dir.
             */
            if (!ret)
                ret = did_create_dir(sctx, cur->dir);
            if (ret < 0)
                goto out;
            if (!ret) {
                ret = send_create_inode(sctx, cur->dir);
                if (ret < 0)
                    goto out;
            }
        }

        /*
         * Check if this new ref would overwrite the first ref of
         * another unprocessed inode. If yes, orphanize the
         * overwritten inode. If we find an overwritten ref that is
         * not the first ref, simply unlink it.
         */
        ret = will_overwrite_ref(sctx, cur->dir, cur->dir_gen,
                cur->name, cur->name_len,
                &ow_inode, &ow_gen);
        if (ret < 0)
            goto out;
        if (ret) {
            ret = is_first_ref(sctx, sctx->parent_root,
                    ow_inode, cur->dir, cur->name,
                    cur->name_len);
            if (ret < 0)
                goto out;
            if (ret) {
                ret = orphanize_inode(sctx, ow_inode, ow_gen,
                        cur->full_path);
                if (ret < 0)
                    goto out;
            } else {
                ret = send_unlink(sctx, cur->full_path);
                if (ret < 0)
                    goto out;
            }
        }

        /*
         * link/move the ref to the new place. If we have an orphan
         * inode, move it and update valid_path. If not, link or move
         * it depending on the inode mode.
         */
        if (is_orphan) {
            ret = send_rename(sctx, valid_path, cur->full_path);
            if (ret < 0)
                goto out;
            is_orphan = 0;
            ret = fs_path_copy(valid_path, cur->full_path);
            if (ret < 0)
                goto out;
        } else {
            if (S_ISDIR(sctx->cur_inode_mode)) {
                /*
                 * Dirs can't be linked, so move it. For moved
                 * dirs, we always have one new and one deleted
                 * ref. The deleted ref is ignored later.
                 */
                ret = send_rename(sctx, valid_path,
                        cur->full_path);
                if (ret < 0)
                    goto out;
                ret = fs_path_copy(valid_path, cur->full_path);
                if (ret < 0)
                    goto out;
            } else {
                ret = send_link(sctx, cur->full_path,
                        valid_path);
                if (ret < 0)
                    goto out;
            }
        }
        ret = ulist_add(check_dirs, cur->dir, cur->dir_gen,
                GFP_NOFS);
        if (ret < 0)
            goto out;
    }

    if (S_ISDIR(sctx->cur_inode_mode) && sctx->cur_inode_deleted) {
        /*
         * Check if we can already rmdir the directory. If not,
         * orphanize it. For every dir item inside that gets deleted
         * later, we do this check again and rmdir it then if possible.
         * See the use of check_dirs for more details.
         */
        ret = can_rmdir(sctx, sctx->cur_ino, sctx->cur_ino);
        if (ret < 0)
            goto out;
        if (ret) {
            ret = send_rmdir(sctx, valid_path);
            if (ret < 0)
                goto out;
        } else if (!is_orphan) {
            ret = orphanize_inode(sctx, sctx->cur_ino,
                    sctx->cur_inode_gen, valid_path);
            if (ret < 0)
                goto out;
            is_orphan = 1;
        }

        list_for_each_entry(cur, &sctx->deleted_refs, list) {
            ret = ulist_add(check_dirs, cur->dir, cur->dir_gen,
                    GFP_NOFS);
            if (ret < 0)
                goto out;
        }
    } else if (S_ISDIR(sctx->cur_inode_mode) &&
           !list_empty(&sctx->deleted_refs)) {
        /*
         * We have a moved dir. Add the old parent to check_dirs
         */
        cur = list_entry(sctx->deleted_refs.next, struct recorded_ref,
                list);
        ret = ulist_add(check_dirs, cur->dir, cur->dir_gen,
                GFP_NOFS);
        if (ret < 0)
            goto out;
    } else if (!S_ISDIR(sctx->cur_inode_mode)) {
        /*
         * We have a non dir inode. Go through all deleted refs and
         * unlink them if they were not already overwritten by other
         * inodes.
         */
        list_for_each_entry(cur, &sctx->deleted_refs, list) {
            ret = did_overwrite_ref(sctx, cur->dir, cur->dir_gen,
                    sctx->cur_ino, sctx->cur_inode_gen,
                    cur->name, cur->name_len);
            if (ret < 0)
                goto out;
            if (!ret) {
                ret = send_unlink(sctx, cur->full_path);
                if (ret < 0)
                    goto out;
            }
            ret = ulist_add(check_dirs, cur->dir, cur->dir_gen,
                    GFP_NOFS);
            if (ret < 0)
                goto out;
        }

        /*
         * If the inode is still orphan, unlink the orphan. This may
         * happen when a previous inode did overwrite the first ref
         * of this inode and no new refs were added for the current
         * inode. Unlinking does not mean that the inode is deleted in
         * all cases. There may still be links to this inode in other
         * places.
         */
        if (is_orphan) {
            ret = send_unlink(sctx, valid_path);
            if (ret < 0)
                goto out;
        }
    }

    /*
     * We did collect all parent dirs where cur_inode was once located. We
     * now go through all these dirs and check if they are pending for
     * deletion and if it's finally possible to perform the rmdir now.
     * We also update the inode stats of the parent dirs here.
     */
    ULIST_ITER_INIT(&uit);
    while ((un = ulist_next(check_dirs, &uit))) {
        /*
         * In case we had refs into dirs that were not processed yet,
         * we don't need to do the utime and rmdir logic for these dirs.
         * The dir will be processed later.
         */
        if (un->val > sctx->cur_ino)
            continue;

        ret = get_cur_inode_state(sctx, un->val, un->aux);
        if (ret < 0)
            goto out;

        if (ret == inode_state_did_create ||
            ret == inode_state_no_change) {
            /* TODO delayed utimes */
            ret = send_utimes(sctx, un->val, un->aux);
            if (ret < 0)
                goto out;
        } else if (ret == inode_state_did_delete) {
            ret = can_rmdir(sctx, un->val, sctx->cur_ino);
            if (ret < 0)
                goto out;
            if (ret) {
                ret = get_cur_path(sctx, un->val, un->aux,
                        valid_path);
                if (ret < 0)
                    goto out;
                ret = send_rmdir(sctx, valid_path);
                if (ret < 0)
                    goto out;
            }
        }
    }

    ret = 0;

out:
    free_recorded_refs(sctx);
    ulist_free(check_dirs);
    fs_path_free(sctx, valid_path);
    return ret;
}

static int __record_new_ref(int num, u64 dir, int index,
                struct fs_path *name,
                void *ctx)
{
    int ret = 0;
    struct send_ctx *sctx = ctx;
    struct fs_path *p;
    u64 gen;

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    ret = get_inode_info(sctx->send_root, dir, NULL, &gen, NULL, NULL,
            NULL, NULL);
    if (ret < 0)
        goto out;

    ret = get_cur_path(sctx, dir, gen, p);
    if (ret < 0)
        goto out;
    ret = fs_path_add_path(p, name);
    if (ret < 0)
        goto out;

    ret = record_ref(&sctx->new_refs, dir, gen, p);

out:
    if (ret)
        fs_path_free(sctx, p);
    return ret;
}

static int __record_deleted_ref(int num, u64 dir, int index,
                struct fs_path *name,
                void *ctx)
{
    int ret = 0;
    struct send_ctx *sctx = ctx;
    struct fs_path *p;
    u64 gen;

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    ret = get_inode_info(sctx->parent_root, dir, NULL, &gen, NULL, NULL,
            NULL, NULL);
    if (ret < 0)
        goto out;

    ret = get_cur_path(sctx, dir, gen, p);
    if (ret < 0)
        goto out;
    ret = fs_path_add_path(p, name);
    if (ret < 0)
        goto out;

    ret = record_ref(&sctx->deleted_refs, dir, gen, p);

out:
    if (ret)
        fs_path_free(sctx, p);
    return ret;
}

static int record_new_ref(struct send_ctx *sctx)
{
    int ret;

    ret = iterate_inode_ref(sctx, sctx->send_root, sctx->left_path,
            sctx->cmp_key, 0, __record_new_ref, sctx);
    if (ret < 0)
        goto out;
    ret = 0;

out:
    return ret;
}

static int record_deleted_ref(struct send_ctx *sctx)
{
    int ret;

    ret = iterate_inode_ref(sctx, sctx->parent_root, sctx->right_path,
            sctx->cmp_key, 0, __record_deleted_ref, sctx);
    if (ret < 0)
        goto out;
    ret = 0;

out:
    return ret;
}

struct find_ref_ctx {
    u64 dir;
    struct fs_path *name;
    int found_idx;
};

static int __find_iref(int num, u64 dir, int index,
               struct fs_path *name,
               void *ctx_)
{
    struct find_ref_ctx *ctx = ctx_;

    if (dir == ctx->dir && fs_path_len(name) == fs_path_len(ctx->name) &&
        strncmp(name->start, ctx->name->start, fs_path_len(name)) == 0) {
        ctx->found_idx = num;
        return 1;
    }
    return 0;
}

static int find_iref(struct send_ctx *sctx,
             struct btrfs_root *root,
             struct btrfs_path *path,
             struct btrfs_key *key,
             u64 dir, struct fs_path *name)
{
    int ret;
    struct find_ref_ctx ctx;

    ctx.dir = dir;
    ctx.name = name;
    ctx.found_idx = -1;

    ret = iterate_inode_ref(sctx, root, path, key, 0, __find_iref, &ctx);
    if (ret < 0)
        return ret;

    if (ctx.found_idx == -1)
        return -ENOENT;

    return ctx.found_idx;
}

static int __record_changed_new_ref(int num, u64 dir, int index,
                    struct fs_path *name,
                    void *ctx)
{
    int ret;
    struct send_ctx *sctx = ctx;

    ret = find_iref(sctx, sctx->parent_root, sctx->right_path,
            sctx->cmp_key, dir, name);
    if (ret == -ENOENT)
        ret = __record_new_ref(num, dir, index, name, sctx);
    else if (ret > 0)
        ret = 0;

    return ret;
}

static int __record_changed_deleted_ref(int num, u64 dir, int index,
                    struct fs_path *name,
                    void *ctx)
{
    int ret;
    struct send_ctx *sctx = ctx;

    ret = find_iref(sctx, sctx->send_root, sctx->left_path, sctx->cmp_key,
            dir, name);
    if (ret == -ENOENT)
        ret = __record_deleted_ref(num, dir, index, name, sctx);
    else if (ret > 0)
        ret = 0;

    return ret;
}

static int record_changed_ref(struct send_ctx *sctx)
{
    int ret = 0;

    ret = iterate_inode_ref(sctx, sctx->send_root, sctx->left_path,
            sctx->cmp_key, 0, __record_changed_new_ref, sctx);
    if (ret < 0)
        goto out;
    ret = iterate_inode_ref(sctx, sctx->parent_root, sctx->right_path,
            sctx->cmp_key, 0, __record_changed_deleted_ref, sctx);
    if (ret < 0)
        goto out;
    ret = 0;

out:
    return ret;
}

/*
 * Record and process all refs at once. Needed when an inode changes the
 * generation number, which means that it was deleted and recreated.
 */
static int process_all_refs(struct send_ctx *sctx,
                enum btrfs_compare_tree_result cmd)
{
    int ret;
    struct btrfs_root *root;
    struct btrfs_path *path;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct extent_buffer *eb;
    int slot;
    iterate_inode_ref_t cb;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    if (cmd == BTRFS_COMPARE_TREE_NEW) {
        root = sctx->send_root;
        cb = __record_new_ref;
    } else if (cmd == BTRFS_COMPARE_TREE_DELETED) {
        root = sctx->parent_root;
        cb = __record_deleted_ref;
    } else {
        BUG();
    }

    key.objectid = sctx->cmp_key->objectid;
    key.type = BTRFS_INODE_REF_KEY;
    key.offset = 0;
    while (1) {
        ret = btrfs_search_slot_for_read(root, &key, path, 1, 0);
        if (ret < 0)
            goto out;
        if (ret)
            break;

        eb = path->nodes[0];
        slot = path->slots[0];
        btrfs_item_key_to_cpu(eb, &found_key, slot);

        if (found_key.objectid != key.objectid ||
            (found_key.type != BTRFS_INODE_REF_KEY &&
             found_key.type != BTRFS_INODE_EXTREF_KEY))
            break;

        ret = iterate_inode_ref(sctx, root, path, &found_key, 0, cb,
                sctx);
        btrfs_release_path(path);
        if (ret < 0)
            goto out;

        key.offset = found_key.offset + 1;
    }
    btrfs_release_path(path);

    ret = process_recorded_refs(sctx);

out:
    btrfs_free_path(path);
    return ret;
}

static int send_set_xattr(struct send_ctx *sctx,
              struct fs_path *path,
              const char *name, int name_len,
              const char *data, int data_len)
{
    int ret = 0;

    ret = begin_cmd(sctx, BTRFS_SEND_C_SET_XATTR);
    if (ret < 0)
        goto out;

    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
    TLV_PUT_STRING(sctx, BTRFS_SEND_A_XATTR_NAME, name, name_len);
    TLV_PUT(sctx, BTRFS_SEND_A_XATTR_DATA, data, data_len);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    return ret;
}

static int send_remove_xattr(struct send_ctx *sctx,
              struct fs_path *path,
              const char *name, int name_len)
{
    int ret = 0;

    ret = begin_cmd(sctx, BTRFS_SEND_C_REMOVE_XATTR);
    if (ret < 0)
        goto out;

    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, path);
    TLV_PUT_STRING(sctx, BTRFS_SEND_A_XATTR_NAME, name, name_len);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    return ret;
}

static int __process_new_xattr(int num, struct btrfs_key *di_key,
                   const char *name, int name_len,
                   const char *data, int data_len,
                   u8 type, void *ctx)
{
    int ret;
    struct send_ctx *sctx = ctx;
    struct fs_path *p;
    posix_acl_xattr_header dummy_acl;

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    /*
     * This hack is needed because empty acl's are stored as zero byte
     * data in xattrs. Problem with that is, that receiving these zero byte
     * acl's will fail later. To fix this, we send a dummy acl list that
     * only contains the version number and no entries.
     */
    if (!strncmp(name, XATTR_NAME_POSIX_ACL_ACCESS, name_len) ||
        !strncmp(name, XATTR_NAME_POSIX_ACL_DEFAULT, name_len)) {
        if (data_len == 0) {
            dummy_acl.a_version =
                    cpu_to_le32(POSIX_ACL_XATTR_VERSION);
            data = (char *)&dummy_acl;
            data_len = sizeof(dummy_acl);
        }
    }

    ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
    if (ret < 0)
        goto out;

    ret = send_set_xattr(sctx, p, name, name_len, data, data_len);

out:
    fs_path_free(sctx, p);
    return ret;
}

static int __process_deleted_xattr(int num, struct btrfs_key *di_key,
                   const char *name, int name_len,
                   const char *data, int data_len,
                   u8 type, void *ctx)
{
    int ret;
    struct send_ctx *sctx = ctx;
    struct fs_path *p;

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
    if (ret < 0)
        goto out;

    ret = send_remove_xattr(sctx, p, name, name_len);

out:
    fs_path_free(sctx, p);
    return ret;
}

static int process_new_xattr(struct send_ctx *sctx)
{
    int ret = 0;

    ret = iterate_dir_item(sctx, sctx->send_root, sctx->left_path,
            sctx->cmp_key, __process_new_xattr, sctx);

    return ret;
}

static int process_deleted_xattr(struct send_ctx *sctx)
{
    int ret;

    ret = iterate_dir_item(sctx, sctx->parent_root, sctx->right_path,
            sctx->cmp_key, __process_deleted_xattr, sctx);

    return ret;
}

struct find_xattr_ctx {
    const char *name;
    int name_len;
    int found_idx;
    char *found_data;
    int found_data_len;
};

static int __find_xattr(int num, struct btrfs_key *di_key,
            const char *name, int name_len,
            const char *data, int data_len,
            u8 type, void *vctx)
{
    struct find_xattr_ctx *ctx = vctx;

    if (name_len == ctx->name_len &&
        strncmp(name, ctx->name, name_len) == 0) {
        ctx->found_idx = num;
        ctx->found_data_len = data_len;
        ctx->found_data = kmalloc(data_len, GFP_NOFS);
        if (!ctx->found_data)
            return -ENOMEM;
        memcpy(ctx->found_data, data, data_len);
        return 1;
    }
    return 0;
}

static int find_xattr(struct send_ctx *sctx,
              struct btrfs_root *root,
              struct btrfs_path *path,
              struct btrfs_key *key,
              const char *name, int name_len,
              char **data, int *data_len)
{
    int ret;
    struct find_xattr_ctx ctx;

    ctx.name = name;
    ctx.name_len = name_len;
    ctx.found_idx = -1;
    ctx.found_data = NULL;
    ctx.found_data_len = 0;

    ret = iterate_dir_item(sctx, root, path, key, __find_xattr, &ctx);
    if (ret < 0)
        return ret;

    if (ctx.found_idx == -1)
        return -ENOENT;
    if (data) {
        *data = ctx.found_data;
        *data_len = ctx.found_data_len;
    } else {
        kfree(ctx.found_data);
    }
    return ctx.found_idx;
}


static int __process_changed_new_xattr(int num, struct btrfs_key *di_key,
                       const char *name, int name_len,
                       const char *data, int data_len,
                       u8 type, void *ctx)
{
    int ret;
    struct send_ctx *sctx = ctx;
    char *found_data = NULL;
    int found_data_len  = 0;
    struct fs_path *p = NULL;

    ret = find_xattr(sctx, sctx->parent_root, sctx->right_path,
            sctx->cmp_key, name, name_len, &found_data,
            &found_data_len);
    if (ret == -ENOENT) {
        ret = __process_new_xattr(num, di_key, name, name_len, data,
                data_len, type, ctx);
    } else if (ret >= 0) {
        if (data_len != found_data_len ||
            memcmp(data, found_data, data_len)) {
            ret = __process_new_xattr(num, di_key, name, name_len,
                    data, data_len, type, ctx);
        } else {
            ret = 0;
        }
    }

    kfree(found_data);
    fs_path_free(sctx, p);
    return ret;
}

static int __process_changed_deleted_xattr(int num, struct btrfs_key *di_key,
                       const char *name, int name_len,
                       const char *data, int data_len,
                       u8 type, void *ctx)
{
    int ret;
    struct send_ctx *sctx = ctx;

    ret = find_xattr(sctx, sctx->send_root, sctx->left_path, sctx->cmp_key,
            name, name_len, NULL, NULL);
    if (ret == -ENOENT)
        ret = __process_deleted_xattr(num, di_key, name, name_len, data,
                data_len, type, ctx);
    else if (ret >= 0)
        ret = 0;

    return ret;
}

static int process_changed_xattr(struct send_ctx *sctx)
{
    int ret = 0;

    ret = iterate_dir_item(sctx, sctx->send_root, sctx->left_path,
            sctx->cmp_key, __process_changed_new_xattr, sctx);
    if (ret < 0)
        goto out;
    ret = iterate_dir_item(sctx, sctx->parent_root, sctx->right_path,
            sctx->cmp_key, __process_changed_deleted_xattr, sctx);

out:
    return ret;
}

static int process_all_new_xattrs(struct send_ctx *sctx)
{
    int ret;
    struct btrfs_root *root;
    struct btrfs_path *path;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct extent_buffer *eb;
    int slot;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    root = sctx->send_root;

    key.objectid = sctx->cmp_key->objectid;
    key.type = BTRFS_XATTR_ITEM_KEY;
    key.offset = 0;
    while (1) {
        ret = btrfs_search_slot_for_read(root, &key, path, 1, 0);
        if (ret < 0)
            goto out;
        if (ret) {
            ret = 0;
            goto out;
        }

        eb = path->nodes[0];
        slot = path->slots[0];
        btrfs_item_key_to_cpu(eb, &found_key, slot);

        if (found_key.objectid != key.objectid ||
            found_key.type != key.type) {
            ret = 0;
            goto out;
        }

        ret = iterate_dir_item(sctx, root, path, &found_key,
                __process_new_xattr, sctx);
        if (ret < 0)
            goto out;

        btrfs_release_path(path);
        key.offset = found_key.offset + 1;
    }

out:
    btrfs_free_path(path);
    return ret;
}

/*
 * Read some bytes from the current inode/file and send a write command to
 * user space.
 */
static int send_write(struct send_ctx *sctx, u64 offset, u32 len)
{
    int ret = 0;
    struct fs_path *p;
    loff_t pos = offset;
    int num_read = 0;
    mm_segment_t old_fs;

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    /*
     * vfs normally only accepts user space buffers for security reasons.
     * we only read from the file and also only provide the read_buf buffer
     * to vfs. As this buffer does not come from a user space call, it's
     * ok to temporary allow kernel space buffers.
     */
    old_fs = get_fs();
    set_fs(KERNEL_DS);

verbose_printk("btrfs: send_write offset=%llu, len=%d\n", offset, len);

    ret = open_cur_inode_file(sctx);
    if (ret < 0)
        goto out;

    ret = vfs_read(sctx->cur_inode_filp, sctx->read_buf, len, &pos);
    if (ret < 0)
        goto out;
    num_read = ret;
    if (!num_read)
        goto out;

    ret = begin_cmd(sctx, BTRFS_SEND_C_WRITE);
    if (ret < 0)
        goto out;

    ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
    if (ret < 0)
        goto out;

    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
    TLV_PUT(sctx, BTRFS_SEND_A_DATA, sctx->read_buf, num_read);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    fs_path_free(sctx, p);
    set_fs(old_fs);
    if (ret < 0)
        return ret;
    return num_read;
}

/*
 * Send a clone command to user space.
 */
static int send_clone(struct send_ctx *sctx,
              u64 offset, u32 len,
              struct clone_root *clone_root)
{
    int ret = 0;
    struct fs_path *p;
    u64 gen;

verbose_printk("btrfs: send_clone offset=%llu, len=%d, clone_root=%llu, "
           "clone_inode=%llu, clone_offset=%llu\n", offset, len,
        clone_root->root->objectid, clone_root->ino,
        clone_root->offset);

    p = fs_path_alloc(sctx);
    if (!p)
        return -ENOMEM;

    ret = begin_cmd(sctx, BTRFS_SEND_C_CLONE);
    if (ret < 0)
        goto out;

    ret = get_cur_path(sctx, sctx->cur_ino, sctx->cur_inode_gen, p);
    if (ret < 0)
        goto out;

    TLV_PUT_U64(sctx, BTRFS_SEND_A_FILE_OFFSET, offset);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_LEN, len);
    TLV_PUT_PATH(sctx, BTRFS_SEND_A_PATH, p);

    if (clone_root->root == sctx->send_root) {
        ret = get_inode_info(sctx->send_root, clone_root->ino, NULL,
                &gen, NULL, NULL, NULL, NULL);
        if (ret < 0)
            goto out;
        ret = get_cur_path(sctx, clone_root->ino, gen, p);
    } else {
        ret = get_inode_path(sctx, clone_root->root,
                clone_root->ino, p);
    }
    if (ret < 0)
        goto out;

    TLV_PUT_UUID(sctx, BTRFS_SEND_A_CLONE_UUID,
            clone_root->root->root_item.uuid);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_CTRANSID,
            clone_root->root->root_item.ctransid);
    TLV_PUT_PATH(sctx, BTRFS_SEND_A_CLONE_PATH, p);
    TLV_PUT_U64(sctx, BTRFS_SEND_A_CLONE_OFFSET,
            clone_root->offset);

    ret = send_cmd(sctx);

tlv_put_failure:
out:
    fs_path_free(sctx, p);
    return ret;
}

static int send_write_or_clone(struct send_ctx *sctx,
                   struct btrfs_path *path,
                   struct btrfs_key *key,
                   struct clone_root *clone_root)
{
    int ret = 0;
    struct btrfs_file_extent_item *ei;
    u64 offset = key->offset;
    u64 pos = 0;
    u64 len;
    u32 l;
    u8 type;

    ei = btrfs_item_ptr(path->nodes[0], path->slots[0],
            struct btrfs_file_extent_item);
    type = btrfs_file_extent_type(path->nodes[0], ei);
    if (type == BTRFS_FILE_EXTENT_INLINE) {
        len = btrfs_file_extent_inline_len(path->nodes[0], ei);
        /*
         * it is possible the inline item won't cover the whole page,
         * but there may be items after this page.  Make
         * sure to send the whole thing
         */
        len = PAGE_CACHE_ALIGN(len);
    } else {
        len = btrfs_file_extent_num_bytes(path->nodes[0], ei);
    }

    if (offset + len > sctx->cur_inode_size)
        len = sctx->cur_inode_size - offset;
    if (len == 0) {
        ret = 0;
        goto out;
    }

    if (!clone_root) {
        while (pos < len) {
            l = len - pos;
            if (l > BTRFS_SEND_READ_SIZE)
                l = BTRFS_SEND_READ_SIZE;
            ret = send_write(sctx, pos + offset, l);
            if (ret < 0)
                goto out;
            if (!ret)
                break;
            pos += ret;
        }
        ret = 0;
    } else {
        ret = send_clone(sctx, offset, len, clone_root);
    }

out:
    return ret;
}

static int is_extent_unchanged(struct send_ctx *sctx,
                   struct btrfs_path *left_path,
                   struct btrfs_key *ekey)
{
    int ret = 0;
    struct btrfs_key key;
    struct btrfs_path *path = NULL;
    struct extent_buffer *eb;
    int slot;
    struct btrfs_key found_key;
    struct btrfs_file_extent_item *ei;
    u64 left_disknr;
    u64 right_disknr;
    u64 left_offset;
    u64 right_offset;
    u64 left_offset_fixed;
    u64 left_len;
    u64 right_len;
    u64 left_gen;
    u64 right_gen;
    u8 left_type;
    u8 right_type;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    eb = left_path->nodes[0];
    slot = left_path->slots[0];
    ei = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
    left_type = btrfs_file_extent_type(eb, ei);

    if (left_type != BTRFS_FILE_EXTENT_REG) {
        ret = 0;
        goto out;
    }
    left_disknr = btrfs_file_extent_disk_bytenr(eb, ei);
    left_len = btrfs_file_extent_num_bytes(eb, ei);
    left_offset = btrfs_file_extent_offset(eb, ei);
    left_gen = btrfs_file_extent_generation(eb, ei);

    /*
     * Following comments will refer to these graphics. L is the left
     * extents which we are checking at the moment. 1-8 are the right
     * extents that we iterate.
     *
     *       |-----L-----|
     * |-1-|-2a-|-3-|-4-|-5-|-6-|
     *
     *       |-----L-----|
     * |--1--|-2b-|...(same as above)
     *
     * Alternative situation. Happens on files where extents got split.
     *       |-----L-----|
     * |-----------7-----------|-6-|
     *
     * Alternative situation. Happens on files which got larger.
     *       |-----L-----|
     * |-8-|
     * Nothing follows after 8.
     */

    key.objectid = ekey->objectid;
    key.type = BTRFS_EXTENT_DATA_KEY;
    key.offset = ekey->offset;
    ret = btrfs_search_slot_for_read(sctx->parent_root, &key, path, 0, 0);
    if (ret < 0)
        goto out;
    if (ret) {
        ret = 0;
        goto out;
    }

    /*
     * Handle special case where the right side has no extents at all.
     */
    eb = path->nodes[0];
    slot = path->slots[0];
    btrfs_item_key_to_cpu(eb, &found_key, slot);
    if (found_key.objectid != key.objectid ||
        found_key.type != key.type) {
        ret = 0;
        goto out;
    }

    /*
     * We're now on 2a, 2b or 7.
     */
    key = found_key;
    while (key.offset < ekey->offset + left_len) {
        ei = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
        right_type = btrfs_file_extent_type(eb, ei);
        right_disknr = btrfs_file_extent_disk_bytenr(eb, ei);
        right_len = btrfs_file_extent_num_bytes(eb, ei);
        right_offset = btrfs_file_extent_offset(eb, ei);
        right_gen = btrfs_file_extent_generation(eb, ei);

        if (right_type != BTRFS_FILE_EXTENT_REG) {
            ret = 0;
            goto out;
        }

        /*
         * Are we at extent 8? If yes, we know the extent is changed.
         * This may only happen on the first iteration.
         */
        if (found_key.offset + right_len <= ekey->offset) {
            ret = 0;
            goto out;
        }

        left_offset_fixed = left_offset;
        if (key.offset < ekey->offset) {
            /* Fix the right offset for 2a and 7. */
            right_offset += ekey->offset - key.offset;
        } else {
            /* Fix the left offset for all behind 2a and 2b */
            left_offset_fixed += key.offset - ekey->offset;
        }

        /*
         * Check if we have the same extent.
         */
        if (left_disknr != right_disknr ||
            left_offset_fixed != right_offset ||
            left_gen != right_gen) {
            ret = 0;
            goto out;
        }

        /*
         * Go to the next extent.
         */
        ret = btrfs_next_item(sctx->parent_root, path);
        if (ret < 0)
            goto out;
        if (!ret) {
            eb = path->nodes[0];
            slot = path->slots[0];
            btrfs_item_key_to_cpu(eb, &found_key, slot);
        }
        if (ret || found_key.objectid != key.objectid ||
            found_key.type != key.type) {
            key.offset += right_len;
            break;
        } else {
            if (found_key.offset != key.offset + right_len) {
                /* Should really not happen */
                ret = -EIO;
                goto out;
            }
        }
        key = found_key;
    }

    /*
     * We're now behind the left extent (treat as unchanged) or at the end
     * of the right side (treat as changed).
     */
    if (key.offset >= ekey->offset + left_len)
        ret = 1;
    else
        ret = 0;


out:
    btrfs_free_path(path);
    return ret;
}

static int process_extent(struct send_ctx *sctx,
              struct btrfs_path *path,
              struct btrfs_key *key)
{
    int ret = 0;
    struct clone_root *found_clone = NULL;

    if (S_ISLNK(sctx->cur_inode_mode))
        return 0;

    if (sctx->parent_root && !sctx->cur_inode_new) {
        ret = is_extent_unchanged(sctx, path, key);
        if (ret < 0)
            goto out;
        if (ret) {
            ret = 0;
            goto out;
        }
    }

    ret = find_extent_clone(sctx, path, key->objectid, key->offset,
            sctx->cur_inode_size, &found_clone);
    if (ret != -ENOENT && ret < 0)
        goto out;

    ret = send_write_or_clone(sctx, path, key, found_clone);

out:
    return ret;
}

static int process_all_extents(struct send_ctx *sctx)
{
    int ret;
    struct btrfs_root *root;
    struct btrfs_path *path;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct extent_buffer *eb;
    int slot;

    root = sctx->send_root;
    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    key.objectid = sctx->cmp_key->objectid;
    key.type = BTRFS_EXTENT_DATA_KEY;
    key.offset = 0;
    while (1) {
        ret = btrfs_search_slot_for_read(root, &key, path, 1, 0);
        if (ret < 0)
            goto out;
        if (ret) {
            ret = 0;
            goto out;
        }

        eb = path->nodes[0];
        slot = path->slots[0];
        btrfs_item_key_to_cpu(eb, &found_key, slot);

        if (found_key.objectid != key.objectid ||
            found_key.type != key.type) {
            ret = 0;
            goto out;
        }

        ret = process_extent(sctx, path, &found_key);
        if (ret < 0)
            goto out;

        btrfs_release_path(path);
        key.offset = found_key.offset + 1;
    }

out:
    btrfs_free_path(path);
    return ret;
}

static int process_recorded_refs_if_needed(struct send_ctx *sctx, int at_end)
{
    int ret = 0;

    if (sctx->cur_ino == 0)
        goto out;
    if (!at_end && sctx->cur_ino == sctx->cmp_key->objectid &&
        sctx->cmp_key->type <= BTRFS_INODE_EXTREF_KEY)
        goto out;
    if (list_empty(&sctx->new_refs) && list_empty(&sctx->deleted_refs))
        goto out;

    ret = process_recorded_refs(sctx);
    if (ret < 0)
        goto out;

    /*
     * We have processed the refs and thus need to advance send_progress.
     * Now, calls to get_cur_xxx will take the updated refs of the current
     * inode into account.
     */
    sctx->send_progress = sctx->cur_ino + 1;

out:
    return ret;
}

static int finish_inode_if_needed(struct send_ctx *sctx, int at_end)
{
    int ret = 0;
    u64 left_mode;
    u64 left_uid;
    u64 left_gid;
    u64 right_mode;
    u64 right_uid;
    u64 right_gid;
    int need_chmod = 0;
    int need_chown = 0;

    ret = process_recorded_refs_if_needed(sctx, at_end);
    if (ret < 0)
        goto out;

    if (sctx->cur_ino == 0 || sctx->cur_inode_deleted)
        goto out;
    if (!at_end && sctx->cmp_key->objectid == sctx->cur_ino)
        goto out;

    ret = get_inode_info(sctx->send_root, sctx->cur_ino, NULL, NULL,
            &left_mode, &left_uid, &left_gid, NULL);
    if (ret < 0)
        goto out;

    if (!sctx->parent_root || sctx->cur_inode_new) {
        need_chown = 1;
        if (!S_ISLNK(sctx->cur_inode_mode))
            need_chmod = 1;
    } else {
        ret = get_inode_info(sctx->parent_root, sctx->cur_ino,
                NULL, NULL, &right_mode, &right_uid,
                &right_gid, NULL);
        if (ret < 0)
            goto out;

        if (left_uid != right_uid || left_gid != right_gid)
            need_chown = 1;
        if (!S_ISLNK(sctx->cur_inode_mode) && left_mode != right_mode)
            need_chmod = 1;
    }

    if (S_ISREG(sctx->cur_inode_mode)) {
        ret = send_truncate(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                sctx->cur_inode_size);
        if (ret < 0)
            goto out;
    }

    if (need_chown) {
        ret = send_chown(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                left_uid, left_gid);
        if (ret < 0)
            goto out;
    }
    if (need_chmod) {
        ret = send_chmod(sctx, sctx->cur_ino, sctx->cur_inode_gen,
                left_mode);
        if (ret < 0)
            goto out;
    }

    /*
     * Need to send that every time, no matter if it actually changed
     * between the two trees as we have done changes to the inode before.
     */
    ret = send_utimes(sctx, sctx->cur_ino, sctx->cur_inode_gen);
    if (ret < 0)
        goto out;

out:
    return ret;
}

static int changed_inode(struct send_ctx *sctx,
             enum btrfs_compare_tree_result result)
{
    int ret = 0;
    struct btrfs_key *key = sctx->cmp_key;
    struct btrfs_inode_item *left_ii = NULL;
    struct btrfs_inode_item *right_ii = NULL;
    u64 left_gen = 0;
    u64 right_gen = 0;

    ret = close_cur_inode_file(sctx);
    if (ret < 0)
        goto out;

    sctx->cur_ino = key->objectid;
    sctx->cur_inode_new_gen = 0;

    /*
     * Set send_progress to current inode. This will tell all get_cur_xxx
     * functions that the current inode's refs are not updated yet. Later,
     * when process_recorded_refs is finished, it is set to cur_ino + 1.
     */
    sctx->send_progress = sctx->cur_ino;

    if (result == BTRFS_COMPARE_TREE_NEW ||
        result == BTRFS_COMPARE_TREE_CHANGED) {
        left_ii = btrfs_item_ptr(sctx->left_path->nodes[0],
                sctx->left_path->slots[0],
                struct btrfs_inode_item);
        left_gen = btrfs_inode_generation(sctx->left_path->nodes[0],
                left_ii);
    } else {
        right_ii = btrfs_item_ptr(sctx->right_path->nodes[0],
                sctx->right_path->slots[0],
                struct btrfs_inode_item);
        right_gen = btrfs_inode_generation(sctx->right_path->nodes[0],
                right_ii);
    }
    if (result == BTRFS_COMPARE_TREE_CHANGED) {
        right_ii = btrfs_item_ptr(sctx->right_path->nodes[0],
                sctx->right_path->slots[0],
                struct btrfs_inode_item);

        right_gen = btrfs_inode_generation(sctx->right_path->nodes[0],
                right_ii);

        /*
         * The cur_ino = root dir case is special here. We can't treat
         * the inode as deleted+reused because it would generate a
         * stream that tries to delete/mkdir the root dir.
         */
        if (left_gen != right_gen &&
            sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID)
            sctx->cur_inode_new_gen = 1;
    }

    if (result == BTRFS_COMPARE_TREE_NEW) {
        sctx->cur_inode_gen = left_gen;
        sctx->cur_inode_new = 1;
        sctx->cur_inode_deleted = 0;
        sctx->cur_inode_size = btrfs_inode_size(
                sctx->left_path->nodes[0], left_ii);
        sctx->cur_inode_mode = btrfs_inode_mode(
                sctx->left_path->nodes[0], left_ii);
        if (sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID)
            ret = send_create_inode_if_needed(sctx);
    } else if (result == BTRFS_COMPARE_TREE_DELETED) {
        sctx->cur_inode_gen = right_gen;
        sctx->cur_inode_new = 0;
        sctx->cur_inode_deleted = 1;
        sctx->cur_inode_size = btrfs_inode_size(
                sctx->right_path->nodes[0], right_ii);
        sctx->cur_inode_mode = btrfs_inode_mode(
                sctx->right_path->nodes[0], right_ii);
    } else if (result == BTRFS_COMPARE_TREE_CHANGED) {
        /*
         * We need to do some special handling in case the inode was
         * reported as changed with a changed generation number. This
         * means that the original inode was deleted and new inode
         * reused the same inum. So we have to treat the old inode as
         * deleted and the new one as new.
         */
        if (sctx->cur_inode_new_gen) {
            /*
             * First, process the inode as if it was deleted.
             */
            sctx->cur_inode_gen = right_gen;
            sctx->cur_inode_new = 0;
            sctx->cur_inode_deleted = 1;
            sctx->cur_inode_size = btrfs_inode_size(
                    sctx->right_path->nodes[0], right_ii);
            sctx->cur_inode_mode = btrfs_inode_mode(
                    sctx->right_path->nodes[0], right_ii);
            ret = process_all_refs(sctx,
                    BTRFS_COMPARE_TREE_DELETED);
            if (ret < 0)
                goto out;

            /*
             * Now process the inode as if it was new.
             */
            sctx->cur_inode_gen = left_gen;
            sctx->cur_inode_new = 1;
            sctx->cur_inode_deleted = 0;
            sctx->cur_inode_size = btrfs_inode_size(
                    sctx->left_path->nodes[0], left_ii);
            sctx->cur_inode_mode = btrfs_inode_mode(
                    sctx->left_path->nodes[0], left_ii);
            ret = send_create_inode_if_needed(sctx);
            if (ret < 0)
                goto out;

            ret = process_all_refs(sctx, BTRFS_COMPARE_TREE_NEW);
            if (ret < 0)
                goto out;
            /*
             * Advance send_progress now as we did not get into
             * process_recorded_refs_if_needed in the new_gen case.
             */
            sctx->send_progress = sctx->cur_ino + 1;

            /*
             * Now process all extents and xattrs of the inode as if
             * they were all new.
             */
            ret = process_all_extents(sctx);
            if (ret < 0)
                goto out;
            ret = process_all_new_xattrs(sctx);
            if (ret < 0)
                goto out;
        } else {
            sctx->cur_inode_gen = left_gen;
            sctx->cur_inode_new = 0;
            sctx->cur_inode_new_gen = 0;
            sctx->cur_inode_deleted = 0;
            sctx->cur_inode_size = btrfs_inode_size(
                    sctx->left_path->nodes[0], left_ii);
            sctx->cur_inode_mode = btrfs_inode_mode(
                    sctx->left_path->nodes[0], left_ii);
        }
    }

out:
    return ret;
}

/*
 * We have to process new refs before deleted refs, but compare_trees gives us
 * the new and deleted refs mixed. To fix this, we record the new/deleted refs
 * first and later process them in process_recorded_refs.
 * For the cur_inode_new_gen case, we skip recording completely because
 * changed_inode did already initiate processing of refs. The reason for this is
 * that in this case, compare_tree actually compares the refs of 2 different
 * inodes. To fix this, process_all_refs is used in changed_inode to handle all
 * refs of the right tree as deleted and all refs of the left tree as new.
 */
static int changed_ref(struct send_ctx *sctx,
               enum btrfs_compare_tree_result result)
{
    int ret = 0;

    BUG_ON(sctx->cur_ino != sctx->cmp_key->objectid);

    if (!sctx->cur_inode_new_gen &&
        sctx->cur_ino != BTRFS_FIRST_FREE_OBJECTID) {
        if (result == BTRFS_COMPARE_TREE_NEW)
            ret = record_new_ref(sctx);
        else if (result == BTRFS_COMPARE_TREE_DELETED)
            ret = record_deleted_ref(sctx);
        else if (result == BTRFS_COMPARE_TREE_CHANGED)
            ret = record_changed_ref(sctx);
    }

    return ret;
}

/*
 * Process new/deleted/changed xattrs. We skip processing in the
 * cur_inode_new_gen case because changed_inode did already initiate processing
 * of xattrs. The reason is the same as in changed_ref
 */
static int changed_xattr(struct send_ctx *sctx,
             enum btrfs_compare_tree_result result)
{
    int ret = 0;

    BUG_ON(sctx->cur_ino != sctx->cmp_key->objectid);

    if (!sctx->cur_inode_new_gen && !sctx->cur_inode_deleted) {
        if (result == BTRFS_COMPARE_TREE_NEW)
            ret = process_new_xattr(sctx);
        else if (result == BTRFS_COMPARE_TREE_DELETED)
            ret = process_deleted_xattr(sctx);
        else if (result == BTRFS_COMPARE_TREE_CHANGED)
            ret = process_changed_xattr(sctx);
    }

    return ret;
}

/*
 * Process new/deleted/changed extents. We skip processing in the
 * cur_inode_new_gen case because changed_inode did already initiate processing
 * of extents. The reason is the same as in changed_ref
 */
static int changed_extent(struct send_ctx *sctx,
              enum btrfs_compare_tree_result result)
{
    int ret = 0;

    BUG_ON(sctx->cur_ino != sctx->cmp_key->objectid);

    if (!sctx->cur_inode_new_gen && !sctx->cur_inode_deleted) {
        if (result != BTRFS_COMPARE_TREE_DELETED)
            ret = process_extent(sctx, sctx->left_path,
                    sctx->cmp_key);
    }

    return ret;
}

/*
 * Updates compare related fields in sctx and simply forwards to the actual
 * changed_xxx functions.
 */
static int changed_cb(struct btrfs_root *left_root,
              struct btrfs_root *right_root,
              struct btrfs_path *left_path,
              struct btrfs_path *right_path,
              struct btrfs_key *key,
              enum btrfs_compare_tree_result result,
              void *ctx)
{
    int ret = 0;
    struct send_ctx *sctx = ctx;

    sctx->left_path = left_path;
    sctx->right_path = right_path;
    sctx->cmp_key = key;

    ret = finish_inode_if_needed(sctx, 0);
    if (ret < 0)
        goto out;

    /* Ignore non-FS objects */
    if (key->objectid == BTRFS_FREE_INO_OBJECTID ||
        key->objectid == BTRFS_FREE_SPACE_OBJECTID)
        goto out;

    if (key->type == BTRFS_INODE_ITEM_KEY)
        ret = changed_inode(sctx, result);
    else if (key->type == BTRFS_INODE_REF_KEY ||
         key->type == BTRFS_INODE_EXTREF_KEY)
        ret = changed_ref(sctx, result);
    else if (key->type == BTRFS_XATTR_ITEM_KEY)
        ret = changed_xattr(sctx, result);
    else if (key->type == BTRFS_EXTENT_DATA_KEY)
        ret = changed_extent(sctx, result);

out:
    return ret;
}

static int full_send_tree(struct send_ctx *sctx)
{
    int ret;
    struct btrfs_trans_handle *trans = NULL;
    struct btrfs_root *send_root = sctx->send_root;
    struct btrfs_key key;
    struct btrfs_key found_key;
    struct btrfs_path *path;
    struct extent_buffer *eb;
    int slot;
    u64 start_ctransid;
    u64 ctransid;

    path = alloc_path_for_send();
    if (!path)
        return -ENOMEM;

    spin_lock(&send_root->root_times_lock);
    start_ctransid = btrfs_root_ctransid(&send_root->root_item);
    spin_unlock(&send_root->root_times_lock);

    key.objectid = BTRFS_FIRST_FREE_OBJECTID;
    key.type = BTRFS_INODE_ITEM_KEY;
    key.offset = 0;

join_trans:
    /*
     * We need to make sure the transaction does not get committed
     * while we do anything on commit roots. Join a transaction to prevent
     * this.
     */
    trans = btrfs_join_transaction(send_root);
    if (IS_ERR(trans)) {
        ret = PTR_ERR(trans);
        trans = NULL;
        goto out;
    }

    /*
     * Make sure the tree has not changed after re-joining. We detect this
     * by comparing start_ctransid and ctransid. They should always match.
     */
    spin_lock(&send_root->root_times_lock);
    ctransid = btrfs_root_ctransid(&send_root->root_item);
    spin_unlock(&send_root->root_times_lock);

    if (ctransid != start_ctransid) {
        WARN(1, KERN_WARNING "btrfs: the root that you're trying to "
                     "send was modified in between. This is "
                     "probably a bug.\n");
        ret = -EIO;
        goto out;
    }

    ret = btrfs_search_slot_for_read(send_root, &key, path, 1, 0);
    if (ret < 0)
        goto out;
    if (ret)
        goto out_finish;

    while (1) {
        /*
         * When someone want to commit while we iterate, end the
         * joined transaction and rejoin.
         */
        if (btrfs_should_end_transaction(trans, send_root)) {
            ret = btrfs_end_transaction(trans, send_root);
            trans = NULL;
            if (ret < 0)
                goto out;
            btrfs_release_path(path);
            goto join_trans;
        }

        eb = path->nodes[0];
        slot = path->slots[0];
        btrfs_item_key_to_cpu(eb, &found_key, slot);

        ret = changed_cb(send_root, NULL, path, NULL,
                &found_key, BTRFS_COMPARE_TREE_NEW, sctx);
        if (ret < 0)
            goto out;

        key.objectid = found_key.objectid;
        key.type = found_key.type;
        key.offset = found_key.offset + 1;

        ret = btrfs_next_item(send_root, path);
        if (ret < 0)
            goto out;
        if (ret) {
            ret  = 0;
            break;
        }
    }

out_finish:
    ret = finish_inode_if_needed(sctx, 1);

out:
    btrfs_free_path(path);
    if (trans) {
        if (!ret)
            ret = btrfs_end_transaction(trans, send_root);
        else
            btrfs_end_transaction(trans, send_root);
    }
    return ret;
}

static int send_subvol(struct send_ctx *sctx)
{
    int ret;

    ret = send_header(sctx);
    if (ret < 0)
        goto out;

    ret = send_subvol_begin(sctx);
    if (ret < 0)
        goto out;

    if (sctx->parent_root) {
        ret = btrfs_compare_trees(sctx->send_root, sctx->parent_root,
                changed_cb, sctx);
        if (ret < 0)
            goto out;
        ret = finish_inode_if_needed(sctx, 1);
        if (ret < 0)
            goto out;
    } else {
        ret = full_send_tree(sctx);
        if (ret < 0)
            goto out;
    }

out:
    if (!ret)
        ret = close_cur_inode_file(sctx);
    else
        close_cur_inode_file(sctx);

    free_recorded_refs(sctx);
    return ret;
}

long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_)
{
    int ret = 0;
    struct btrfs_root *send_root;
    struct btrfs_root *clone_root;
    struct btrfs_fs_info *fs_info;
    struct btrfs_ioctl_send_args *arg = NULL;
    struct btrfs_key key;
    struct file *filp = NULL;
    struct send_ctx *sctx = NULL;
    u32 i;
    u64 *clone_sources_tmp = NULL;

    if (!capable(CAP_SYS_ADMIN))
        return -EPERM;

    send_root = BTRFS_I(fdentry(mnt_file)->d_inode)->root;
    fs_info = send_root->fs_info;

    arg = memdup_user(arg_, sizeof(*arg));
    if (IS_ERR(arg)) {
        ret = PTR_ERR(arg);
        arg = NULL;
        goto out;
    }

    if (!access_ok(VERIFY_READ, arg->clone_sources,
            sizeof(*arg->clone_sources *
            arg->clone_sources_count))) {
        ret = -EFAULT;
        goto out;
    }

    sctx = kzalloc(sizeof(struct send_ctx), GFP_NOFS);
    if (!sctx) {
        ret = -ENOMEM;
        goto out;
    }

    INIT_LIST_HEAD(&sctx->new_refs);
    INIT_LIST_HEAD(&sctx->deleted_refs);
    INIT_RADIX_TREE(&sctx->name_cache, GFP_NOFS);
    INIT_LIST_HEAD(&sctx->name_cache_list);

    sctx->send_filp = fget(arg->send_fd);
    if (IS_ERR(sctx->send_filp)) {
        ret = PTR_ERR(sctx->send_filp);
        goto out;
    }

    sctx->mnt = mnt_file->f_path.mnt;

    sctx->send_root = send_root;
    sctx->clone_roots_cnt = arg->clone_sources_count;

    sctx->send_max_size = BTRFS_SEND_BUF_SIZE;
    sctx->send_buf = vmalloc(sctx->send_max_size);
    if (!sctx->send_buf) {
        ret = -ENOMEM;
        goto out;
    }

    sctx->read_buf = vmalloc(BTRFS_SEND_READ_SIZE);
    if (!sctx->read_buf) {
        ret = -ENOMEM;
        goto out;
    }

    sctx->clone_roots = vzalloc(sizeof(struct clone_root) *
            (arg->clone_sources_count + 1));
    if (!sctx->clone_roots) {
        ret = -ENOMEM;
        goto out;
    }

    if (arg->clone_sources_count) {
        clone_sources_tmp = vmalloc(arg->clone_sources_count *
                sizeof(*arg->clone_sources));
        if (!clone_sources_tmp) {
            ret = -ENOMEM;
            goto out;
        }

        ret = copy_from_user(clone_sources_tmp, arg->clone_sources,
                arg->clone_sources_count *
                sizeof(*arg->clone_sources));
        if (ret) {
            ret = -EFAULT;
            goto out;
        }

        for (i = 0; i < arg->clone_sources_count; i++) {
            key.objectid = clone_sources_tmp[i];
            key.type = BTRFS_ROOT_ITEM_KEY;
            key.offset = (u64)-1;
            clone_root = btrfs_read_fs_root_no_name(fs_info, &key);
            if (!clone_root) {
                ret = -EINVAL;
                goto out;
            }
            if (IS_ERR(clone_root)) {
                ret = PTR_ERR(clone_root);
                goto out;
            }
            sctx->clone_roots[i].root = clone_root;
        }
        vfree(clone_sources_tmp);
        clone_sources_tmp = NULL;
    }

    if (arg->parent_root) {
        key.objectid = arg->parent_root;
        key.type = BTRFS_ROOT_ITEM_KEY;
        key.offset = (u64)-1;
        sctx->parent_root = btrfs_read_fs_root_no_name(fs_info, &key);
        if (!sctx->parent_root) {
            ret = -EINVAL;
            goto out;
        }
    }

    /*
     * Clones from send_root are allowed, but only if the clone source
     * is behind the current send position. This is checked while searching
     * for possible clone sources.
     */
    sctx->clone_roots[sctx->clone_roots_cnt++].root = sctx->send_root;

    /* We do a bsearch later */
    sort(sctx->clone_roots, sctx->clone_roots_cnt,
            sizeof(*sctx->clone_roots), __clone_root_cmp_sort,
            NULL);

    ret = send_subvol(sctx);
    if (ret < 0)
        goto out;

    ret = begin_cmd(sctx, BTRFS_SEND_C_END);
    if (ret < 0)
        goto out;
    ret = send_cmd(sctx);
    if (ret < 0)
        goto out;

out:
    if (filp)
        fput(filp);
    kfree(arg);
    vfree(clone_sources_tmp);

    if (sctx) {
        if (sctx->send_filp)
            fput(sctx->send_filp);

        vfree(sctx->clone_roots);
        vfree(sctx->send_buf);
        vfree(sctx->read_buf);

        name_cache_free(sctx);

        kfree(sctx);
    }

    return ret;
}