super.c

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/*
 * Copyright (C) 2007 Oracle.  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/blkdev.h>
#include <linux/module.h>
#include <linux/buffer_head.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/seq_file.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/mount.h>
#include <linux/mpage.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/statfs.h>
#include <linux/compat.h>
#include <linux/parser.h>
#include <linux/ctype.h>
#include <linux/namei.h>
#include <linux/miscdevice.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/cleancache.h>
#include <linux/ratelimit.h>
#include "compat.h"
#include "delayed-inode.h"
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "ioctl.h"
#include "print-tree.h"
#include "xattr.h"
#include "volumes.h"
#include "version.h"
#include "export.h"
#include "compression.h"
#include "rcu-string.h"

#define CREATE_TRACE_POINTS
#include <trace/events/btrfs.h>

static const struct super_operations btrfs_super_ops;
static struct file_system_type btrfs_fs_type;

static const char *btrfs_decode_error(struct btrfs_fs_info *fs_info, int errno,
                      char nbuf[16])
{
    char *errstr = NULL;

    switch (errno) {
    case -EIO:
        errstr = "IO failure";
        break;
    case -ENOMEM:
        errstr = "Out of memory";
        break;
    case -EROFS:
        errstr = "Readonly filesystem";
        break;
    case -EEXIST:
        errstr = "Object already exists";
        break;
    default:
        if (nbuf) {
            if (snprintf(nbuf, 16, "error %d", -errno) >= 0)
                errstr = nbuf;
        }
        break;
    }

    return errstr;
}

static void __save_error_info(struct btrfs_fs_info *fs_info)
{
    /*
     * today we only save the error info into ram.  Long term we'll
     * also send it down to the disk
     */
    fs_info->fs_state = BTRFS_SUPER_FLAG_ERROR;
}

static void save_error_info(struct btrfs_fs_info *fs_info)
{
    __save_error_info(fs_info);
}

/* btrfs handle error by forcing the filesystem readonly */
static void btrfs_handle_error(struct btrfs_fs_info *fs_info)
{
    struct super_block *sb = fs_info->sb;

    if (sb->s_flags & MS_RDONLY)
        return;

    if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
        sb->s_flags |= MS_RDONLY;
        printk(KERN_INFO "btrfs is forced readonly\n");
        __btrfs_scrub_cancel(fs_info);
//      WARN_ON(1);
    }
}

#ifdef CONFIG_PRINTK
/*
 * __btrfs_std_error decodes expected errors from the caller and
 * invokes the approciate error response.
 */
void __btrfs_std_error(struct btrfs_fs_info *fs_info, const char *function,
               unsigned int line, int errno, const char *fmt, ...)
{
    struct super_block *sb = fs_info->sb;
    char nbuf[16];
    const char *errstr;
    va_list args;
    va_start(args, fmt);

    /*
     * Special case: if the error is EROFS, and we're already
     * under MS_RDONLY, then it is safe here.
     */
    if (errno == -EROFS && (sb->s_flags & MS_RDONLY))
        return;

    errstr = btrfs_decode_error(fs_info, errno, nbuf);
    if (fmt) {
        struct va_format vaf = {
            .fmt = fmt,
            .va = &args,
        };

        printk(KERN_CRIT "BTRFS error (device %s) in %s:%d: %s (%pV)\n",
            sb->s_id, function, line, errstr, &vaf);
    } else {
        printk(KERN_CRIT "BTRFS error (device %s) in %s:%d: %s\n",
            sb->s_id, function, line, errstr);
    }

    /* Don't go through full error handling during mount */
    if (sb->s_flags & MS_BORN) {
        save_error_info(fs_info);
        btrfs_handle_error(fs_info);
    }
    va_end(args);
}

static const char * const logtypes[] = {
    "emergency",
    "alert",
    "critical",
    "error",
    "warning",
    "notice",
    "info",
    "debug",
};

void btrfs_printk(struct btrfs_fs_info *fs_info, const char *fmt, ...)
{
    struct super_block *sb = fs_info->sb;
    char lvl[4];
    struct va_format vaf;
    va_list args;
    const char *type = logtypes[4];
    int kern_level;

    va_start(args, fmt);

    kern_level = printk_get_level(fmt);
    if (kern_level) {
        size_t size = printk_skip_level(fmt) - fmt;
        memcpy(lvl, fmt,  size);
        lvl[size] = '\0';
        fmt += size;
        type = logtypes[kern_level - '0'];
    } else
        *lvl = '\0';

    vaf.fmt = fmt;
    vaf.va = &args;

    printk("%sBTRFS %s (device %s): %pV", lvl, type, sb->s_id, &vaf);

    va_end(args);
}

#else

void __btrfs_std_error(struct btrfs_fs_info *fs_info, const char *function,
               unsigned int line, int errno, const char *fmt, ...)
{
    struct super_block *sb = fs_info->sb;

    /*
     * Special case: if the error is EROFS, and we're already
     * under MS_RDONLY, then it is safe here.
     */
    if (errno == -EROFS && (sb->s_flags & MS_RDONLY))
        return;

    /* Don't go through full error handling during mount */
    if (sb->s_flags & MS_BORN) {
        save_error_info(fs_info);
        btrfs_handle_error(fs_info);
    }
}
#endif

/*
 * We only mark the transaction aborted and then set the file system read-only.
 * This will prevent new transactions from starting or trying to join this
 * one.
 *
 * This means that error recovery at the call site is limited to freeing
 * any local memory allocations and passing the error code up without
 * further cleanup. The transaction should complete as it normally would
 * in the call path but will return -EIO.
 *
 * We'll complete the cleanup in btrfs_end_transaction and
 * btrfs_commit_transaction.
 */
void __btrfs_abort_transaction(struct btrfs_trans_handle *trans,
                   struct btrfs_root *root, const char *function,
                   unsigned int line, int errno)
{
    WARN_ONCE(1, KERN_DEBUG "btrfs: Transaction aborted\n");
    trans->aborted = errno;
    /* Nothing used. The other threads that have joined this
     * transaction may be able to continue. */
    if (!trans->blocks_used) {
        char nbuf[16];
        const char *errstr;

        errstr = btrfs_decode_error(root->fs_info, errno, nbuf);
        btrfs_printk(root->fs_info,
                 "%s:%d: Aborting unused transaction(%s).\n",
                 function, line, errstr);
        return;
    }
    trans->transaction->aborted = errno;
    __btrfs_std_error(root->fs_info, function, line, errno, NULL);
}
/*
 * __btrfs_panic decodes unexpected, fatal errors from the caller,
 * issues an alert, and either panics or BUGs, depending on mount options.
 */
void __btrfs_panic(struct btrfs_fs_info *fs_info, const char *function,
           unsigned int line, int errno, const char *fmt, ...)
{
    char nbuf[16];
    char *s_id = "<unknown>";
    const char *errstr;
    struct va_format vaf = { .fmt = fmt };
    va_list args;

    if (fs_info)
        s_id = fs_info->sb->s_id;

    va_start(args, fmt);
    vaf.va = &args;

    errstr = btrfs_decode_error(fs_info, errno, nbuf);
    if (fs_info->mount_opt & BTRFS_MOUNT_PANIC_ON_FATAL_ERROR)
        panic(KERN_CRIT "BTRFS panic (device %s) in %s:%d: %pV (%s)\n",
            s_id, function, line, &vaf, errstr);

    printk(KERN_CRIT "BTRFS panic (device %s) in %s:%d: %pV (%s)\n",
           s_id, function, line, &vaf, errstr);
    va_end(args);
    /* Caller calls BUG() */
}

static void btrfs_put_super(struct super_block *sb)
{
    (void)close_ctree(btrfs_sb(sb)->tree_root);
    /* FIXME: need to fix VFS to return error? */
    /* AV: return it _where_?  ->put_super() can be triggered by any number
     * of async events, up to and including delivery of SIGKILL to the
     * last process that kept it busy.  Or segfault in the aforementioned
     * process...  Whom would you report that to?
     */
}

enum {
    Opt_degraded, Opt_subvol, Opt_subvolid, Opt_device, Opt_nodatasum,
    Opt_nodatacow, Opt_max_inline, Opt_alloc_start, Opt_nobarrier, Opt_ssd,
    Opt_nossd, Opt_ssd_spread, Opt_thread_pool, Opt_noacl, Opt_compress,
    Opt_compress_type, Opt_compress_force, Opt_compress_force_type,
    Opt_notreelog, Opt_ratio, Opt_flushoncommit, Opt_discard,
    Opt_space_cache, Opt_clear_cache, Opt_user_subvol_rm_allowed,
    Opt_enospc_debug, Opt_subvolrootid, Opt_defrag, Opt_inode_cache,
    Opt_no_space_cache, Opt_recovery, Opt_skip_balance,
    Opt_check_integrity, Opt_check_integrity_including_extent_data,
    Opt_check_integrity_print_mask, Opt_fatal_errors,
    Opt_err,
};

static match_table_t tokens = {
    {Opt_degraded, "degraded"},
    {Opt_subvol, "subvol=%s"},
    {Opt_subvolid, "subvolid=%d"},
    {Opt_device, "device=%s"},
    {Opt_nodatasum, "nodatasum"},
    {Opt_nodatacow, "nodatacow"},
    {Opt_nobarrier, "nobarrier"},
    {Opt_max_inline, "max_inline=%s"},
    {Opt_alloc_start, "alloc_start=%s"},
    {Opt_thread_pool, "thread_pool=%d"},
    {Opt_compress, "compress"},
    {Opt_compress_type, "compress=%s"},
    {Opt_compress_force, "compress-force"},
    {Opt_compress_force_type, "compress-force=%s"},
    {Opt_ssd, "ssd"},
    {Opt_ssd_spread, "ssd_spread"},
    {Opt_nossd, "nossd"},
    {Opt_noacl, "noacl"},
    {Opt_notreelog, "notreelog"},
    {Opt_flushoncommit, "flushoncommit"},
    {Opt_ratio, "metadata_ratio=%d"},
    {Opt_discard, "discard"},
    {Opt_space_cache, "space_cache"},
    {Opt_clear_cache, "clear_cache"},
    {Opt_user_subvol_rm_allowed, "user_subvol_rm_allowed"},
    {Opt_enospc_debug, "enospc_debug"},
    {Opt_subvolrootid, "subvolrootid=%d"},
    {Opt_defrag, "autodefrag"},
    {Opt_inode_cache, "inode_cache"},
    {Opt_no_space_cache, "nospace_cache"},
    {Opt_recovery, "recovery"},
    {Opt_skip_balance, "skip_balance"},
    {Opt_check_integrity, "check_int"},
    {Opt_check_integrity_including_extent_data, "check_int_data"},
    {Opt_check_integrity_print_mask, "check_int_print_mask=%d"},
    {Opt_fatal_errors, "fatal_errors=%s"},
    {Opt_err, NULL},
};

/*
 * Regular mount options parser.  Everything that is needed only when
 * reading in a new superblock is parsed here.
 * XXX JDM: This needs to be cleaned up for remount.
 */
int btrfs_parse_options(struct btrfs_root *root, char *options)
{
    struct btrfs_fs_info *info = root->fs_info;
    substring_t args[MAX_OPT_ARGS];
    char *p, *num, *orig = NULL;
    u64 cache_gen;
    int intarg;
    int ret = 0;
    char *compress_type;
    bool compress_force = false;

    cache_gen = btrfs_super_cache_generation(root->fs_info->super_copy);
    if (cache_gen)
        btrfs_set_opt(info->mount_opt, SPACE_CACHE);

    if (!options)
        goto out;

    /*
     * strsep changes the string, duplicate it because parse_options
     * gets called twice
     */
    options = kstrdup(options, GFP_NOFS);
    if (!options)
        return -ENOMEM;

    orig = options;

    while ((p = strsep(&options, ",")) != NULL) {
        int token;
        if (!*p)
            continue;

        token = match_token(p, tokens, args);
        switch (token) {
        case Opt_degraded:
            printk(KERN_INFO "btrfs: allowing degraded mounts\n");
            btrfs_set_opt(info->mount_opt, DEGRADED);
            break;
        case Opt_subvol:
        case Opt_subvolid:
        case Opt_subvolrootid:
        case Opt_device:
            /*
             * These are parsed by btrfs_parse_early_options
             * and can be happily ignored here.
             */
            break;
        case Opt_nodatasum:
            printk(KERN_INFO "btrfs: setting nodatasum\n");
            btrfs_set_opt(info->mount_opt, NODATASUM);
            break;
        case Opt_nodatacow:
            if (!btrfs_test_opt(root, COMPRESS) ||
                !btrfs_test_opt(root, FORCE_COMPRESS)) {
                    printk(KERN_INFO "btrfs: setting nodatacow, compression disabled\n");
            } else {
                printk(KERN_INFO "btrfs: setting nodatacow\n");
            }
            info->compress_type = BTRFS_COMPRESS_NONE;
            btrfs_clear_opt(info->mount_opt, COMPRESS);
            btrfs_clear_opt(info->mount_opt, FORCE_COMPRESS);
            btrfs_set_opt(info->mount_opt, NODATACOW);
            btrfs_set_opt(info->mount_opt, NODATASUM);
            break;
        case Opt_compress_force:
        case Opt_compress_force_type:
            compress_force = true;
        case Opt_compress:
        case Opt_compress_type:
            if (token == Opt_compress ||
                token == Opt_compress_force ||
                strcmp(args[0].from, "zlib") == 0) {
                compress_type = "zlib";
                info->compress_type = BTRFS_COMPRESS_ZLIB;
                btrfs_set_opt(info->mount_opt, COMPRESS);
                btrfs_clear_opt(info->mount_opt, NODATACOW);
                btrfs_clear_opt(info->mount_opt, NODATASUM);
            } else if (strcmp(args[0].from, "lzo") == 0) {
                compress_type = "lzo";
                info->compress_type = BTRFS_COMPRESS_LZO;
                btrfs_set_opt(info->mount_opt, COMPRESS);
                btrfs_clear_opt(info->mount_opt, NODATACOW);
                btrfs_clear_opt(info->mount_opt, NODATASUM);
                btrfs_set_fs_incompat(info, COMPRESS_LZO);
            } else if (strncmp(args[0].from, "no", 2) == 0) {
                compress_type = "no";
                info->compress_type = BTRFS_COMPRESS_NONE;
                btrfs_clear_opt(info->mount_opt, COMPRESS);
                btrfs_clear_opt(info->mount_opt, FORCE_COMPRESS);
                compress_force = false;
            } else {
                ret = -EINVAL;
                goto out;
            }

            if (compress_force) {
                btrfs_set_opt(info->mount_opt, FORCE_COMPRESS);
                pr_info("btrfs: force %s compression\n",
                    compress_type);
            } else
                pr_info("btrfs: use %s compression\n",
                    compress_type);
            break;
        case Opt_ssd:
            printk(KERN_INFO "btrfs: use ssd allocation scheme\n");
            btrfs_set_opt(info->mount_opt, SSD);
            break;
        case Opt_ssd_spread:
            printk(KERN_INFO "btrfs: use spread ssd "
                   "allocation scheme\n");
            btrfs_set_opt(info->mount_opt, SSD);
            btrfs_set_opt(info->mount_opt, SSD_SPREAD);
            break;
        case Opt_nossd:
            printk(KERN_INFO "btrfs: not using ssd allocation "
                   "scheme\n");
            btrfs_set_opt(info->mount_opt, NOSSD);
            btrfs_clear_opt(info->mount_opt, SSD);
            btrfs_clear_opt(info->mount_opt, SSD_SPREAD);
            break;
        case Opt_nobarrier:
            printk(KERN_INFO "btrfs: turning off barriers\n");
            btrfs_set_opt(info->mount_opt, NOBARRIER);
            break;
        case Opt_thread_pool:
            intarg = 0;
            match_int(&args[0], &intarg);
            if (intarg)
                info->thread_pool_size = intarg;
            break;
        case Opt_max_inline:
            num = match_strdup(&args[0]);
            if (num) {
                info->max_inline = memparse(num, NULL);
                kfree(num);

                if (info->max_inline) {
                    info->max_inline = max_t(u64,
                        info->max_inline,
                        root->sectorsize);
                }
                printk(KERN_INFO "btrfs: max_inline at %llu\n",
                    (unsigned long long)info->max_inline);
            }
            break;
        case Opt_alloc_start:
            num = match_strdup(&args[0]);
            if (num) {
                info->alloc_start = memparse(num, NULL);
                kfree(num);
                printk(KERN_INFO
                    "btrfs: allocations start at %llu\n",
                    (unsigned long long)info->alloc_start);
            }
            break;
        case Opt_noacl:
            root->fs_info->sb->s_flags &= ~MS_POSIXACL;
            break;
        case Opt_notreelog:
            printk(KERN_INFO "btrfs: disabling tree log\n");
            btrfs_set_opt(info->mount_opt, NOTREELOG);
            break;
        case Opt_flushoncommit:
            printk(KERN_INFO "btrfs: turning on flush-on-commit\n");
            btrfs_set_opt(info->mount_opt, FLUSHONCOMMIT);
            break;
        case Opt_ratio:
            intarg = 0;
            match_int(&args[0], &intarg);
            if (intarg) {
                info->metadata_ratio = intarg;
                printk(KERN_INFO "btrfs: metadata ratio %d\n",
                       info->metadata_ratio);
            }
            break;
        case Opt_discard:
            btrfs_set_opt(info->mount_opt, DISCARD);
            break;
        case Opt_space_cache:
            btrfs_set_opt(info->mount_opt, SPACE_CACHE);
            break;
        case Opt_no_space_cache:
            printk(KERN_INFO "btrfs: disabling disk space caching\n");
            btrfs_clear_opt(info->mount_opt, SPACE_CACHE);
            break;
        case Opt_inode_cache:
            printk(KERN_INFO "btrfs: enabling inode map caching\n");
            btrfs_set_opt(info->mount_opt, INODE_MAP_CACHE);
            break;
        case Opt_clear_cache:
            printk(KERN_INFO "btrfs: force clearing of disk cache\n");
            btrfs_set_opt(info->mount_opt, CLEAR_CACHE);
            break;
        case Opt_user_subvol_rm_allowed:
            btrfs_set_opt(info->mount_opt, USER_SUBVOL_RM_ALLOWED);
            break;
        case Opt_enospc_debug:
            btrfs_set_opt(info->mount_opt, ENOSPC_DEBUG);
            break;
        case Opt_defrag:
            printk(KERN_INFO "btrfs: enabling auto defrag\n");
            btrfs_set_opt(info->mount_opt, AUTO_DEFRAG);
            break;
        case Opt_recovery:
            printk(KERN_INFO "btrfs: enabling auto recovery\n");
            btrfs_set_opt(info->mount_opt, RECOVERY);
            break;
        case Opt_skip_balance:
            btrfs_set_opt(info->mount_opt, SKIP_BALANCE);
            break;
#ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
        case Opt_check_integrity_including_extent_data:
            printk(KERN_INFO "btrfs: enabling check integrity"
                   " including extent data\n");
            btrfs_set_opt(info->mount_opt,
                      CHECK_INTEGRITY_INCLUDING_EXTENT_DATA);
            btrfs_set_opt(info->mount_opt, CHECK_INTEGRITY);
            break;
        case Opt_check_integrity:
            printk(KERN_INFO "btrfs: enabling check integrity\n");
            btrfs_set_opt(info->mount_opt, CHECK_INTEGRITY);
            break;
        case Opt_check_integrity_print_mask:
            intarg = 0;
            match_int(&args[0], &intarg);
            if (intarg) {
                info->check_integrity_print_mask = intarg;
                printk(KERN_INFO "btrfs:"
                       " check_integrity_print_mask 0x%x\n",
                       info->check_integrity_print_mask);
            }
            break;
#else
        case Opt_check_integrity_including_extent_data:
        case Opt_check_integrity:
        case Opt_check_integrity_print_mask:
            printk(KERN_ERR "btrfs: support for check_integrity*"
                   " not compiled in!\n");
            ret = -EINVAL;
            goto out;
#endif
        case Opt_fatal_errors:
            if (strcmp(args[0].from, "panic") == 0)
                btrfs_set_opt(info->mount_opt,
                          PANIC_ON_FATAL_ERROR);
            else if (strcmp(args[0].from, "bug") == 0)
                btrfs_clear_opt(info->mount_opt,
                          PANIC_ON_FATAL_ERROR);
            else {
                ret = -EINVAL;
                goto out;
            }
            break;
        case Opt_err:
            printk(KERN_INFO "btrfs: unrecognized mount option "
                   "'%s'\n", p);
            ret = -EINVAL;
            goto out;
        default:
            break;
        }
    }
out:
    if (!ret && btrfs_test_opt(root, SPACE_CACHE))
        printk(KERN_INFO "btrfs: disk space caching is enabled\n");
    kfree(orig);
    return ret;
}

/*
 * Parse mount options that are required early in the mount process.
 *
 * All other options will be parsed on much later in the mount process and
 * only when we need to allocate a new super block.
 */
static int btrfs_parse_early_options(const char *options, fmode_t flags,
        void *holder, char **subvol_name, u64 *subvol_objectid,
        u64 *subvol_rootid, struct btrfs_fs_devices **fs_devices)
{
    substring_t args[MAX_OPT_ARGS];
    char *device_name, *opts, *orig, *p;
    int error = 0;
    int intarg;

    if (!options)
        return 0;

    /*
     * strsep changes the string, duplicate it because parse_options
     * gets called twice
     */
    opts = kstrdup(options, GFP_KERNEL);
    if (!opts)
        return -ENOMEM;
    orig = opts;

    while ((p = strsep(&opts, ",")) != NULL) {
        int token;
        if (!*p)
            continue;

        token = match_token(p, tokens, args);
        switch (token) {
        case Opt_subvol:
            kfree(*subvol_name);
            *subvol_name = match_strdup(&args[0]);
            break;
        case Opt_subvolid:
            intarg = 0;
            error = match_int(&args[0], &intarg);
            if (!error) {
                /* we want the original fs_tree */
                if (!intarg)
                    *subvol_objectid =
                        BTRFS_FS_TREE_OBJECTID;
                else
                    *subvol_objectid = intarg;
            }
            break;
        case Opt_subvolrootid:
            intarg = 0;
            error = match_int(&args[0], &intarg);
            if (!error) {
                /* we want the original fs_tree */
                if (!intarg)
                    *subvol_rootid =
                        BTRFS_FS_TREE_OBJECTID;
                else
                    *subvol_rootid = intarg;
            }
            break;
        case Opt_device:
            device_name = match_strdup(&args[0]);
            if (!device_name) {
                error = -ENOMEM;
                goto out;
            }
            error = btrfs_scan_one_device(device_name,
                    flags, holder, fs_devices);
            kfree(device_name);
            if (error)
                goto out;
            break;
        default:
            break;
        }
    }

out:
    kfree(orig);
    return error;
}

static struct dentry *get_default_root(struct super_block *sb,
                       u64 subvol_objectid)
{
    struct btrfs_fs_info *fs_info = btrfs_sb(sb);
    struct btrfs_root *root = fs_info->tree_root;
    struct btrfs_root *new_root;
    struct btrfs_dir_item *di;
    struct btrfs_path *path;
    struct btrfs_key location;
    struct inode *inode;
    u64 dir_id;
    int new = 0;

    /*
     * We have a specific subvol we want to mount, just setup location and
     * go look up the root.
     */
    if (subvol_objectid) {
        location.objectid = subvol_objectid;
        location.type = BTRFS_ROOT_ITEM_KEY;
        location.offset = (u64)-1;
        goto find_root;
    }

    path = btrfs_alloc_path();
    if (!path)
        return ERR_PTR(-ENOMEM);
    path->leave_spinning = 1;

    /*
     * Find the "default" dir item which points to the root item that we
     * will mount by default if we haven't been given a specific subvolume
     * to mount.
     */
    dir_id = btrfs_super_root_dir(fs_info->super_copy);
    di = btrfs_lookup_dir_item(NULL, root, path, dir_id, "default", 7, 0);
    if (IS_ERR(di)) {
        btrfs_free_path(path);
        return ERR_CAST(di);
    }
    if (!di) {
        /*
         * Ok the default dir item isn't there.  This is weird since
         * it's always been there, but don't freak out, just try and
         * mount to root most subvolume.
         */
        btrfs_free_path(path);
        dir_id = BTRFS_FIRST_FREE_OBJECTID;
        new_root = fs_info->fs_root;
        goto setup_root;
    }

    btrfs_dir_item_key_to_cpu(path->nodes[0], di, &location);
    btrfs_free_path(path);

find_root:
    new_root = btrfs_read_fs_root_no_name(fs_info, &location);
    if (IS_ERR(new_root))
        return ERR_CAST(new_root);

    if (btrfs_root_refs(&new_root->root_item) == 0)
        return ERR_PTR(-ENOENT);

    dir_id = btrfs_root_dirid(&new_root->root_item);
setup_root:
    location.objectid = dir_id;
    location.type = BTRFS_INODE_ITEM_KEY;
    location.offset = 0;

    inode = btrfs_iget(sb, &location, new_root, &new);
    if (IS_ERR(inode))
        return ERR_CAST(inode);

    /*
     * If we're just mounting the root most subvol put the inode and return
     * a reference to the dentry.  We will have already gotten a reference
     * to the inode in btrfs_fill_super so we're good to go.
     */
    if (!new && sb->s_root->d_inode == inode) {
        iput(inode);
        return dget(sb->s_root);
    }

    return d_obtain_alias(inode);
}

static int btrfs_fill_super(struct super_block *sb,
                struct btrfs_fs_devices *fs_devices,
                void *data, int silent)
{
    struct inode *inode;
    struct btrfs_fs_info *fs_info = btrfs_sb(sb);
    struct btrfs_key key;
    int err;

    sb->s_maxbytes = MAX_LFS_FILESIZE;
    sb->s_magic = BTRFS_SUPER_MAGIC;
    sb->s_op = &btrfs_super_ops;
    sb->s_d_op = &btrfs_dentry_operations;
    sb->s_export_op = &btrfs_export_ops;
    sb->s_xattr = btrfs_xattr_handlers;
    sb->s_time_gran = 1;
#ifdef CONFIG_BTRFS_FS_POSIX_ACL
    sb->s_flags |= MS_POSIXACL;
#endif
    sb->s_flags |= MS_I_VERSION;
    err = open_ctree(sb, fs_devices, (char *)data);
    if (err) {
        printk("btrfs: open_ctree failed\n");
        return err;
    }

    key.objectid = BTRFS_FIRST_FREE_OBJECTID;
    key.type = BTRFS_INODE_ITEM_KEY;
    key.offset = 0;
    inode = btrfs_iget(sb, &key, fs_info->fs_root, NULL);
    if (IS_ERR(inode)) {
        err = PTR_ERR(inode);
        goto fail_close;
    }

    sb->s_root = d_make_root(inode);
    if (!sb->s_root) {
        err = -ENOMEM;
        goto fail_close;
    }

    save_mount_options(sb, data);
    cleancache_init_fs(sb);
    sb->s_flags |= MS_ACTIVE;
    return 0;

fail_close:
    close_ctree(fs_info->tree_root);
    return err;
}

int btrfs_sync_fs(struct super_block *sb, int wait)
{
    struct btrfs_trans_handle *trans;
    struct btrfs_fs_info *fs_info = btrfs_sb(sb);
    struct btrfs_root *root = fs_info->tree_root;

    trace_btrfs_sync_fs(wait);

    if (!wait) {
        filemap_flush(fs_info->btree_inode->i_mapping);
        return 0;
    }

    btrfs_wait_ordered_extents(root, 0);

    trans = btrfs_attach_transaction(root);
    if (IS_ERR(trans)) {
        /* no transaction, don't bother */
        if (PTR_ERR(trans) == -ENOENT)
            return 0;
        return PTR_ERR(trans);
    }
    return btrfs_commit_transaction(trans, root);
}

static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
{
    struct btrfs_fs_info *info = btrfs_sb(dentry->d_sb);
    struct btrfs_root *root = info->tree_root;
    char *compress_type;

    if (btrfs_test_opt(root, DEGRADED))
        seq_puts(seq, ",degraded");
    if (btrfs_test_opt(root, NODATASUM))
        seq_puts(seq, ",nodatasum");
    if (btrfs_test_opt(root, NODATACOW))
        seq_puts(seq, ",nodatacow");
    if (btrfs_test_opt(root, NOBARRIER))
        seq_puts(seq, ",nobarrier");
    if (info->max_inline != 8192 * 1024)
        seq_printf(seq, ",max_inline=%llu",
               (unsigned long long)info->max_inline);
    if (info->alloc_start != 0)
        seq_printf(seq, ",alloc_start=%llu",
               (unsigned long long)info->alloc_start);
    if (info->thread_pool_size !=  min_t(unsigned long,
                         num_online_cpus() + 2, 8))
        seq_printf(seq, ",thread_pool=%d", info->thread_pool_size);
    if (btrfs_test_opt(root, COMPRESS)) {
        if (info->compress_type == BTRFS_COMPRESS_ZLIB)
            compress_type = "zlib";
        else
            compress_type = "lzo";
        if (btrfs_test_opt(root, FORCE_COMPRESS))
            seq_printf(seq, ",compress-force=%s", compress_type);
        else
            seq_printf(seq, ",compress=%s", compress_type);
    }
    if (btrfs_test_opt(root, NOSSD))
        seq_puts(seq, ",nossd");
    if (btrfs_test_opt(root, SSD_SPREAD))
        seq_puts(seq, ",ssd_spread");
    else if (btrfs_test_opt(root, SSD))
        seq_puts(seq, ",ssd");
    if (btrfs_test_opt(root, NOTREELOG))
        seq_puts(seq, ",notreelog");
    if (btrfs_test_opt(root, FLUSHONCOMMIT))
        seq_puts(seq, ",flushoncommit");
    if (btrfs_test_opt(root, DISCARD))
        seq_puts(seq, ",discard");
    if (!(root->fs_info->sb->s_flags & MS_POSIXACL))
        seq_puts(seq, ",noacl");
    if (btrfs_test_opt(root, SPACE_CACHE))
        seq_puts(seq, ",space_cache");
    else
        seq_puts(seq, ",nospace_cache");
    if (btrfs_test_opt(root, CLEAR_CACHE))
        seq_puts(seq, ",clear_cache");
    if (btrfs_test_opt(root, USER_SUBVOL_RM_ALLOWED))
        seq_puts(seq, ",user_subvol_rm_allowed");
    if (btrfs_test_opt(root, ENOSPC_DEBUG))
        seq_puts(seq, ",enospc_debug");
    if (btrfs_test_opt(root, AUTO_DEFRAG))
        seq_puts(seq, ",autodefrag");
    if (btrfs_test_opt(root, INODE_MAP_CACHE))
        seq_puts(seq, ",inode_cache");
    if (btrfs_test_opt(root, SKIP_BALANCE))
        seq_puts(seq, ",skip_balance");
    if (btrfs_test_opt(root, PANIC_ON_FATAL_ERROR))
        seq_puts(seq, ",fatal_errors=panic");
    return 0;
}

static int btrfs_test_super(struct super_block *s, void *data)
{
    struct btrfs_fs_info *p = data;
    struct btrfs_fs_info *fs_info = btrfs_sb(s);

    return fs_info->fs_devices == p->fs_devices;
}

static int btrfs_set_super(struct super_block *s, void *data)
{
    int err = set_anon_super(s, data);
    if (!err)
        s->s_fs_info = data;
    return err;
}

/*
 * subvolumes are identified by ino 256
 */
static inline int is_subvolume_inode(struct inode *inode)
{
    if (inode && inode->i_ino == BTRFS_FIRST_FREE_OBJECTID)
        return 1;
    return 0;
}

/*
 * This will strip out the subvol=%s argument for an argument string and add
 * subvolid=0 to make sure we get the actual tree root for path walking to the
 * subvol we want.
 */
static char *setup_root_args(char *args)
{
    unsigned len = strlen(args) + 2 + 1;
    char *src, *dst, *buf;

    /*
     * We need the same args as before, but with this substitution:
     * s!subvol=[^,]+!subvolid=0!
     *
     * Since the replacement string is up to 2 bytes longer than the
     * original, allocate strlen(args) + 2 + 1 bytes.
     */

    src = strstr(args, "subvol=");
    /* This shouldn't happen, but just in case.. */
    if (!src)
        return NULL;

    buf = dst = kmalloc(len, GFP_NOFS);
    if (!buf)
        return NULL;

    /*
     * If the subvol= arg is not at the start of the string,
     * copy whatever precedes it into buf.
     */
    if (src != args) {
        *src++ = '\0';
        strcpy(buf, args);
        dst += strlen(args);
    }

    strcpy(dst, "subvolid=0");
    dst += strlen("subvolid=0");

    /*
     * If there is a "," after the original subvol=... string,
     * copy that suffix into our buffer.  Otherwise, we're done.
     */
    src = strchr(src, ',');
    if (src)
        strcpy(dst, src);

    return buf;
}

static struct dentry *mount_subvol(const char *subvol_name, int flags,
                   const char *device_name, char *data)
{
    struct dentry *root;
    struct vfsmount *mnt;
    char *newargs;

    newargs = setup_root_args(data);
    if (!newargs)
        return ERR_PTR(-ENOMEM);
    mnt = vfs_kern_mount(&btrfs_fs_type, flags, device_name,
                 newargs);
    kfree(newargs);
    if (IS_ERR(mnt))
        return ERR_CAST(mnt);

    root = mount_subtree(mnt, subvol_name);

    if (!IS_ERR(root) && !is_subvolume_inode(root->d_inode)) {
        struct super_block *s = root->d_sb;
        dput(root);
        root = ERR_PTR(-EINVAL);
        deactivate_locked_super(s);
        printk(KERN_ERR "btrfs: '%s' is not a valid subvolume\n",
                subvol_name);
    }

    return root;
}

/*
 * Find a superblock for the given device / mount point.
 *
 * Note:  This is based on get_sb_bdev from fs/super.c with a few additions
 *    for multiple device setup.  Make sure to keep it in sync.
 */
static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
        const char *device_name, void *data)
{
    struct block_device *bdev = NULL;
    struct super_block *s;
    struct dentry *root;
    struct btrfs_fs_devices *fs_devices = NULL;
    struct btrfs_fs_info *fs_info = NULL;
    fmode_t mode = FMODE_READ;
    char *subvol_name = NULL;
    u64 subvol_objectid = 0;
    u64 subvol_rootid = 0;
    int error = 0;

    if (!(flags & MS_RDONLY))
        mode |= FMODE_WRITE;

    error = btrfs_parse_early_options(data, mode, fs_type,
                      &subvol_name, &subvol_objectid,
                      &subvol_rootid, &fs_devices);
    if (error) {
        kfree(subvol_name);
        return ERR_PTR(error);
    }

    if (subvol_name) {
        root = mount_subvol(subvol_name, flags, device_name, data);
        kfree(subvol_name);
        return root;
    }

    error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
    if (error)
        return ERR_PTR(error);

    /*
     * Setup a dummy root and fs_info for test/set super.  This is because
     * we don't actually fill this stuff out until open_ctree, but we need
     * it for searching for existing supers, so this lets us do that and
     * then open_ctree will properly initialize everything later.
     */
    fs_info = kzalloc(sizeof(struct btrfs_fs_info), GFP_NOFS);
    if (!fs_info)
        return ERR_PTR(-ENOMEM);

    fs_info->fs_devices = fs_devices;

    fs_info->super_copy = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
    fs_info->super_for_commit = kzalloc(BTRFS_SUPER_INFO_SIZE, GFP_NOFS);
    if (!fs_info->super_copy || !fs_info->super_for_commit) {
        error = -ENOMEM;
        goto error_fs_info;
    }

    error = btrfs_open_devices(fs_devices, mode, fs_type);
    if (error)
        goto error_fs_info;

    if (!(flags & MS_RDONLY) && fs_devices->rw_devices == 0) {
        error = -EACCES;
        goto error_close_devices;
    }

    bdev = fs_devices->latest_bdev;
    s = sget(fs_type, btrfs_test_super, btrfs_set_super, flags | MS_NOSEC,
         fs_info);
    if (IS_ERR(s)) {
        error = PTR_ERR(s);
        goto error_close_devices;
    }

    if (s->s_root) {
        btrfs_close_devices(fs_devices);
        free_fs_info(fs_info);
        if ((flags ^ s->s_flags) & MS_RDONLY)
            error = -EBUSY;
    } else {
        char b[BDEVNAME_SIZE];

        strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
        btrfs_sb(s)->bdev_holder = fs_type;
        error = btrfs_fill_super(s, fs_devices, data,
                     flags & MS_SILENT ? 1 : 0);
    }

    root = !error ? get_default_root(s, subvol_objectid) : ERR_PTR(error);
    if (IS_ERR(root))
        deactivate_locked_super(s);

    return root;

error_close_devices:
    btrfs_close_devices(fs_devices);
error_fs_info:
    free_fs_info(fs_info);
    return ERR_PTR(error);
}

static void btrfs_set_max_workers(struct btrfs_workers *workers, int new_limit)
{
    spin_lock_irq(&workers->lock);
    workers->max_workers = new_limit;
    spin_unlock_irq(&workers->lock);
}

static void btrfs_resize_thread_pool(struct btrfs_fs_info *fs_info,
                     int new_pool_size, int old_pool_size)
{
    if (new_pool_size == old_pool_size)
        return;

    fs_info->thread_pool_size = new_pool_size;

    printk(KERN_INFO "btrfs: resize thread pool %d -> %d\n",
           old_pool_size, new_pool_size);

    btrfs_set_max_workers(&fs_info->generic_worker, new_pool_size);
    btrfs_set_max_workers(&fs_info->workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->delalloc_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->submit_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->caching_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->fixup_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->endio_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->endio_meta_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->endio_meta_write_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->endio_write_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->endio_freespace_worker, new_pool_size);
    btrfs_set_max_workers(&fs_info->delayed_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->readahead_workers, new_pool_size);
    btrfs_set_max_workers(&fs_info->scrub_workers, new_pool_size);
}

static int btrfs_remount(struct super_block *sb, int *flags, char *data)
{
    struct btrfs_fs_info *fs_info = btrfs_sb(sb);
    struct btrfs_root *root = fs_info->tree_root;
    unsigned old_flags = sb->s_flags;
    unsigned long old_opts = fs_info->mount_opt;
    unsigned long old_compress_type = fs_info->compress_type;
    u64 old_max_inline = fs_info->max_inline;
    u64 old_alloc_start = fs_info->alloc_start;
    int old_thread_pool_size = fs_info->thread_pool_size;
    unsigned int old_metadata_ratio = fs_info->metadata_ratio;
    int ret;

    ret = btrfs_parse_options(root, data);
    if (ret) {
        ret = -EINVAL;
        goto restore;
    }

    btrfs_resize_thread_pool(fs_info,
        fs_info->thread_pool_size, old_thread_pool_size);

    if ((*flags & MS_RDONLY) == (sb->s_flags & MS_RDONLY))
        return 0;

    if (*flags & MS_RDONLY) {
        sb->s_flags |= MS_RDONLY;

        ret = btrfs_commit_super(root);
        if (ret)
            goto restore;
    } else {
        if (fs_info->fs_devices->rw_devices == 0) {
            ret = -EACCES;
            goto restore;
        }

        if (btrfs_super_log_root(fs_info->super_copy) != 0) {
            ret = -EINVAL;
            goto restore;
        }

        ret = btrfs_cleanup_fs_roots(fs_info);
        if (ret)
            goto restore;

        /* recover relocation */
        ret = btrfs_recover_relocation(root);
        if (ret)
            goto restore;

        ret = btrfs_resume_balance_async(fs_info);
        if (ret)
            goto restore;

        sb->s_flags &= ~MS_RDONLY;
    }

    return 0;

restore:
    /* We've hit an error - don't reset MS_RDONLY */
    if (sb->s_flags & MS_RDONLY)
        old_flags |= MS_RDONLY;
    sb->s_flags = old_flags;
    fs_info->mount_opt = old_opts;
    fs_info->compress_type = old_compress_type;
    fs_info->max_inline = old_max_inline;
    fs_info->alloc_start = old_alloc_start;
    btrfs_resize_thread_pool(fs_info,
        old_thread_pool_size, fs_info->thread_pool_size);
    fs_info->metadata_ratio = old_metadata_ratio;
    return ret;
}

/* Used to sort the devices by max_avail(descending sort) */
static int btrfs_cmp_device_free_bytes(const void *dev_info1,
                       const void *dev_info2)
{
    if (((struct btrfs_device_info *)dev_info1)->max_avail >
        ((struct btrfs_device_info *)dev_info2)->max_avail)
        return -1;
    else if (((struct btrfs_device_info *)dev_info1)->max_avail <
         ((struct btrfs_device_info *)dev_info2)->max_avail)
        return 1;
    else
    return 0;
}

/*
 * sort the devices by max_avail, in which max free extent size of each device
 * is stored.(Descending Sort)
 */
static inline void btrfs_descending_sort_devices(
                    struct btrfs_device_info *devices,
                    size_t nr_devices)
{
    sort(devices, nr_devices, sizeof(struct btrfs_device_info),
         btrfs_cmp_device_free_bytes, NULL);
}

/*
 * The helper to calc the free space on the devices that can be used to store
 * file data.
 */
static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes)
{
    struct btrfs_fs_info *fs_info = root->fs_info;
    struct btrfs_device_info *devices_info;
    struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
    struct btrfs_device *device;
    u64 skip_space;
    u64 type;
    u64 avail_space;
    u64 used_space;
    u64 min_stripe_size;
    int min_stripes = 1, num_stripes = 1;
    int i = 0, nr_devices;
    int ret;

    nr_devices = fs_info->fs_devices->open_devices;
    BUG_ON(!nr_devices);

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

    /* calc min stripe number for data space alloction */
    type = btrfs_get_alloc_profile(root, 1);
    if (type & BTRFS_BLOCK_GROUP_RAID0) {
        min_stripes = 2;
        num_stripes = nr_devices;
    } else if (type & BTRFS_BLOCK_GROUP_RAID1) {
        min_stripes = 2;
        num_stripes = 2;
    } else if (type & BTRFS_BLOCK_GROUP_RAID10) {
        min_stripes = 4;
        num_stripes = 4;
    }

    if (type & BTRFS_BLOCK_GROUP_DUP)
        min_stripe_size = 2 * BTRFS_STRIPE_LEN;
    else
        min_stripe_size = BTRFS_STRIPE_LEN;

    list_for_each_entry(device, &fs_devices->devices, dev_list) {
        if (!device->in_fs_metadata || !device->bdev)
            continue;

        avail_space = device->total_bytes - device->bytes_used;

        /* align with stripe_len */
        do_div(avail_space, BTRFS_STRIPE_LEN);
        avail_space *= BTRFS_STRIPE_LEN;

        /*
         * In order to avoid overwritting the superblock on the drive,
         * btrfs starts at an offset of at least 1MB when doing chunk
         * allocation.
         */
        skip_space = 1024 * 1024;

        /* user can set the offset in fs_info->alloc_start. */
        if (fs_info->alloc_start + BTRFS_STRIPE_LEN <=
            device->total_bytes)
            skip_space = max(fs_info->alloc_start, skip_space);

        /*
         * btrfs can not use the free space in [0, skip_space - 1],
         * we must subtract it from the total. In order to implement
         * it, we account the used space in this range first.
         */
        ret = btrfs_account_dev_extents_size(device, 0, skip_space - 1,
                             &used_space);
        if (ret) {
            kfree(devices_info);
            return ret;
        }

        /* calc the free space in [0, skip_space - 1] */
        skip_space -= used_space;

        /*
         * we can use the free space in [0, skip_space - 1], subtract
         * it from the total.
         */
        if (avail_space && avail_space >= skip_space)
            avail_space -= skip_space;
        else
            avail_space = 0;

        if (avail_space < min_stripe_size)
            continue;

        devices_info[i].dev = device;
        devices_info[i].max_avail = avail_space;

        i++;
    }

    nr_devices = i;

    btrfs_descending_sort_devices(devices_info, nr_devices);

    i = nr_devices - 1;
    avail_space = 0;
    while (nr_devices >= min_stripes) {
        if (num_stripes > nr_devices)
            num_stripes = nr_devices;

        if (devices_info[i].max_avail >= min_stripe_size) {
            int j;
            u64 alloc_size;

            avail_space += devices_info[i].max_avail * num_stripes;
            alloc_size = devices_info[i].max_avail;
            for (j = i + 1 - num_stripes; j <= i; j++)
                devices_info[j].max_avail -= alloc_size;
        }
        i--;
        nr_devices--;
    }

    kfree(devices_info);
    *free_bytes = avail_space;
    return 0;
}

static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
    struct btrfs_fs_info *fs_info = btrfs_sb(dentry->d_sb);
    struct btrfs_super_block *disk_super = fs_info->super_copy;
    struct list_head *head = &fs_info->space_info;
    struct btrfs_space_info *found;
    u64 total_used = 0;
    u64 total_free_data = 0;
    int bits = dentry->d_sb->s_blocksize_bits;
    __be32 *fsid = (__be32 *)fs_info->fsid;
    int ret;

    /* holding chunk_muext to avoid allocating new chunks */
    mutex_lock(&fs_info->chunk_mutex);
    rcu_read_lock();
    list_for_each_entry_rcu(found, head, list) {
        if (found->flags & BTRFS_BLOCK_GROUP_DATA) {
            total_free_data += found->disk_total - found->disk_used;
            total_free_data -=
                btrfs_account_ro_block_groups_free_space(found);
        }

        total_used += found->disk_used;
    }
    rcu_read_unlock();

    buf->f_namelen = BTRFS_NAME_LEN;
    buf->f_blocks = btrfs_super_total_bytes(disk_super) >> bits;
    buf->f_bfree = buf->f_blocks - (total_used >> bits);
    buf->f_bsize = dentry->d_sb->s_blocksize;
    buf->f_type = BTRFS_SUPER_MAGIC;
    buf->f_bavail = total_free_data;
    ret = btrfs_calc_avail_data_space(fs_info->tree_root, &total_free_data);
    if (ret) {
        mutex_unlock(&fs_info->chunk_mutex);
        return ret;
    }
    buf->f_bavail += total_free_data;
    buf->f_bavail = buf->f_bavail >> bits;
    mutex_unlock(&fs_info->chunk_mutex);

    /* We treat it as constant endianness (it doesn't matter _which_)
       because we want the fsid to come out the same whether mounted
       on a big-endian or little-endian host */
    buf->f_fsid.val[0] = be32_to_cpu(fsid[0]) ^ be32_to_cpu(fsid[2]);
    buf->f_fsid.val[1] = be32_to_cpu(fsid[1]) ^ be32_to_cpu(fsid[3]);
    /* Mask in the root object ID too, to disambiguate subvols */
    buf->f_fsid.val[0] ^= BTRFS_I(dentry->d_inode)->root->objectid >> 32;
    buf->f_fsid.val[1] ^= BTRFS_I(dentry->d_inode)->root->objectid;

    return 0;
}

static void btrfs_kill_super(struct super_block *sb)
{
    struct btrfs_fs_info *fs_info = btrfs_sb(sb);
    kill_anon_super(sb);
    free_fs_info(fs_info);
}

static struct file_system_type btrfs_fs_type = {
    .owner      = THIS_MODULE,
    .name       = "btrfs",
    .mount      = btrfs_mount,
    .kill_sb    = btrfs_kill_super,
    .fs_flags   = FS_REQUIRES_DEV,
};

/*
 * used by btrfsctl to scan devices when no FS is mounted
 */
static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
                unsigned long arg)
{
    struct btrfs_ioctl_vol_args *vol;
    struct btrfs_fs_devices *fs_devices;
    int ret = -ENOTTY;

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

    vol = memdup_user((void __user *)arg, sizeof(*vol));
    if (IS_ERR(vol))
        return PTR_ERR(vol);

    switch (cmd) {
    case BTRFS_IOC_SCAN_DEV:
        ret = btrfs_scan_one_device(vol->name, FMODE_READ,
                        &btrfs_fs_type, &fs_devices);
        break;
    case BTRFS_IOC_DEVICES_READY:
        ret = btrfs_scan_one_device(vol->name, FMODE_READ,
                        &btrfs_fs_type, &fs_devices);
        if (ret)
            break;
        ret = !(fs_devices->num_devices == fs_devices->total_devices);
        break;
    }

    kfree(vol);
    return ret;
}

static int btrfs_freeze(struct super_block *sb)
{
    struct btrfs_trans_handle *trans;
    struct btrfs_root *root = btrfs_sb(sb)->tree_root;

    trans = btrfs_attach_transaction(root);
    if (IS_ERR(trans)) {
        /* no transaction, don't bother */
        if (PTR_ERR(trans) == -ENOENT)
            return 0;
        return PTR_ERR(trans);
    }
    return btrfs_commit_transaction(trans, root);
}

static int btrfs_unfreeze(struct super_block *sb)
{
    return 0;
}

static int btrfs_show_devname(struct seq_file *m, struct dentry *root)
{
    struct btrfs_fs_info *fs_info = btrfs_sb(root->d_sb);
    struct btrfs_fs_devices *cur_devices;
    struct btrfs_device *dev, *first_dev = NULL;
    struct list_head *head;
    struct rcu_string *name;

    mutex_lock(&fs_info->fs_devices->device_list_mutex);
    cur_devices = fs_info->fs_devices;
    while (cur_devices) {
        head = &cur_devices->devices;
        list_for_each_entry(dev, head, dev_list) {
            if (dev->missing)
                continue;
            if (!first_dev || dev->devid < first_dev->devid)
                first_dev = dev;
        }
        cur_devices = cur_devices->seed;
    }

    if (first_dev) {
        rcu_read_lock();
        name = rcu_dereference(first_dev->name);
        seq_escape(m, name->str, " \t\n\\");
        rcu_read_unlock();
    } else {
        WARN_ON(1);
    }
    mutex_unlock(&fs_info->fs_devices->device_list_mutex);
    return 0;
}

static const struct super_operations btrfs_super_ops = {
    .drop_inode = btrfs_drop_inode,
    .evict_inode    = btrfs_evict_inode,
    .put_super  = btrfs_put_super,
    .sync_fs    = btrfs_sync_fs,
    .show_options   = btrfs_show_options,
    .show_devname   = btrfs_show_devname,
    .write_inode    = btrfs_write_inode,
    .alloc_inode    = btrfs_alloc_inode,
    .destroy_inode  = btrfs_destroy_inode,
    .statfs     = btrfs_statfs,
    .remount_fs = btrfs_remount,
    .freeze_fs  = btrfs_freeze,
    .unfreeze_fs    = btrfs_unfreeze,
};

static const struct file_operations btrfs_ctl_fops = {
    .unlocked_ioctl  = btrfs_control_ioctl,
    .compat_ioctl = btrfs_control_ioctl,
    .owner   = THIS_MODULE,
    .llseek = noop_llseek,
};

static struct miscdevice btrfs_misc = {
    .minor      = BTRFS_MINOR,
    .name       = "btrfs-control",
    .fops       = &btrfs_ctl_fops
};

MODULE_ALIAS_MISCDEV(BTRFS_MINOR);
MODULE_ALIAS("devname:btrfs-control");

static int btrfs_interface_init(void)
{
    return misc_register(&btrfs_misc);
}

static void btrfs_interface_exit(void)
{
    if (misc_deregister(&btrfs_misc) < 0)
        printk(KERN_INFO "btrfs: misc_deregister failed for control device\n");
}

static int __init init_btrfs_fs(void)
{
    int err;

    err = btrfs_init_sysfs();
    if (err)
        return err;

    btrfs_init_compress();

    err = btrfs_init_cachep();
    if (err)
        goto free_compress;

    err = extent_io_init();
    if (err)
        goto free_cachep;

    err = extent_map_init();
    if (err)
        goto free_extent_io;

    err = ordered_data_init();
    if (err)
        goto free_extent_map;

    err = btrfs_delayed_inode_init();
    if (err)
        goto free_ordered_data;

    err = btrfs_interface_init();
    if (err)
        goto free_delayed_inode;

    err = register_filesystem(&btrfs_fs_type);
    if (err)
        goto unregister_ioctl;

    btrfs_init_lockdep();

    printk(KERN_INFO "%s loaded\n", BTRFS_BUILD_VERSION);
    return 0;

unregister_ioctl:
    btrfs_interface_exit();
free_delayed_inode:
    btrfs_delayed_inode_exit();
free_ordered_data:
    ordered_data_exit();
free_extent_map:
    extent_map_exit();
free_extent_io:
    extent_io_exit();
free_cachep:
    btrfs_destroy_cachep();
free_compress:
    btrfs_exit_compress();
    btrfs_exit_sysfs();
    return err;
}

static void __exit exit_btrfs_fs(void)
{
    btrfs_destroy_cachep();
    btrfs_delayed_inode_exit();
    ordered_data_exit();
    extent_map_exit();
    extent_io_exit();
    btrfs_interface_exit();
    unregister_filesystem(&btrfs_fs_type);
    btrfs_exit_sysfs();
    btrfs_cleanup_fs_uuids();
    btrfs_exit_compress();
}

module_init(init_btrfs_fs)
module_exit(exit_btrfs_fs)

MODULE_LICENSE("GPL");