file.c

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/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2008  Miklos Szeredi <[email protected]>

  This program can be distributed under the terms of the GNU GPL.
  See the file COPYING.
*/

#include "fuse_i.h"

#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/compat.h>
#include <linux/swap.h>

static const struct file_operations fuse_direct_io_file_operations;

static int fuse_send_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
              int opcode, struct fuse_open_out *outargp)
{
    struct fuse_open_in inarg;
    struct fuse_req *req;
    int err;

    req = fuse_get_req(fc);
    if (IS_ERR(req))
        return PTR_ERR(req);

    memset(&inarg, 0, sizeof(inarg));
    inarg.flags = file->f_flags & ~(O_CREAT | O_EXCL | O_NOCTTY);
    if (!fc->atomic_o_trunc)
        inarg.flags &= ~O_TRUNC;
    req->in.h.opcode = opcode;
    req->in.h.nodeid = nodeid;
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(inarg);
    req->in.args[0].value = &inarg;
    req->out.numargs = 1;
    req->out.args[0].size = sizeof(*outargp);
    req->out.args[0].value = outargp;
    fuse_request_send(fc, req);
    err = req->out.h.error;
    fuse_put_request(fc, req);

    return err;
}

struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
{
    struct fuse_file *ff;

    ff = kmalloc(sizeof(struct fuse_file), GFP_KERNEL);
    if (unlikely(!ff))
        return NULL;

    ff->fc = fc;
    ff->reserved_req = fuse_request_alloc();
    if (unlikely(!ff->reserved_req)) {
        kfree(ff);
        return NULL;
    }

    INIT_LIST_HEAD(&ff->write_entry);
    atomic_set(&ff->count, 0);
    RB_CLEAR_NODE(&ff->polled_node);
    init_waitqueue_head(&ff->poll_wait);

    spin_lock(&fc->lock);
    ff->kh = ++fc->khctr;
    spin_unlock(&fc->lock);

    return ff;
}

void fuse_file_free(struct fuse_file *ff)
{
    fuse_request_free(ff->reserved_req);
    kfree(ff);
}

struct fuse_file *fuse_file_get(struct fuse_file *ff)
{
    atomic_inc(&ff->count);
    return ff;
}

static void fuse_release_async(struct work_struct *work)
{
    struct fuse_req *req;
    struct fuse_conn *fc;
    struct path path;

    req = container_of(work, struct fuse_req, misc.release.work);
    path = req->misc.release.path;
    fc = get_fuse_conn(path.dentry->d_inode);

    fuse_put_request(fc, req);
    path_put(&path);
}

static void fuse_release_end(struct fuse_conn *fc, struct fuse_req *req)
{
    if (fc->destroy_req) {
        /*
         * If this is a fuseblk mount, then it's possible that
         * releasing the path will result in releasing the
         * super block and sending the DESTROY request.  If
         * the server is single threaded, this would hang.
         * For this reason do the path_put() in a separate
         * thread.
         */
        atomic_inc(&req->count);
        INIT_WORK(&req->misc.release.work, fuse_release_async);
        schedule_work(&req->misc.release.work);
    } else {
        path_put(&req->misc.release.path);
    }
}

static void fuse_file_put(struct fuse_file *ff, bool sync)
{
    if (atomic_dec_and_test(&ff->count)) {
        struct fuse_req *req = ff->reserved_req;

        if (sync) {
            fuse_request_send(ff->fc, req);
            path_put(&req->misc.release.path);
            fuse_put_request(ff->fc, req);
        } else {
            req->end = fuse_release_end;
            fuse_request_send_background(ff->fc, req);
        }
        kfree(ff);
    }
}

int fuse_do_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
         bool isdir)
{
    struct fuse_open_out outarg;
    struct fuse_file *ff;
    int err;
    int opcode = isdir ? FUSE_OPENDIR : FUSE_OPEN;

    ff = fuse_file_alloc(fc);
    if (!ff)
        return -ENOMEM;

    err = fuse_send_open(fc, nodeid, file, opcode, &outarg);
    if (err) {
        fuse_file_free(ff);
        return err;
    }

    if (isdir)
        outarg.open_flags &= ~FOPEN_DIRECT_IO;

    ff->fh = outarg.fh;
    ff->nodeid = nodeid;
    ff->open_flags = outarg.open_flags;
    file->private_data = fuse_file_get(ff);

    return 0;
}
EXPORT_SYMBOL_GPL(fuse_do_open);

void fuse_finish_open(struct inode *inode, struct file *file)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = get_fuse_conn(inode);

    if (ff->open_flags & FOPEN_DIRECT_IO)
        file->f_op = &fuse_direct_io_file_operations;
    if (!(ff->open_flags & FOPEN_KEEP_CACHE))
        invalidate_inode_pages2(inode->i_mapping);
    if (ff->open_flags & FOPEN_NONSEEKABLE)
        nonseekable_open(inode, file);
    if (fc->atomic_o_trunc && (file->f_flags & O_TRUNC)) {
        struct fuse_inode *fi = get_fuse_inode(inode);

        spin_lock(&fc->lock);
        fi->attr_version = ++fc->attr_version;
        i_size_write(inode, 0);
        spin_unlock(&fc->lock);
        fuse_invalidate_attr(inode);
    }
}

int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
{
    struct fuse_conn *fc = get_fuse_conn(inode);
    int err;

    err = generic_file_open(inode, file);
    if (err)
        return err;

    err = fuse_do_open(fc, get_node_id(inode), file, isdir);
    if (err)
        return err;

    fuse_finish_open(inode, file);

    return 0;
}

static void fuse_prepare_release(struct fuse_file *ff, int flags, int opcode)
{
    struct fuse_conn *fc = ff->fc;
    struct fuse_req *req = ff->reserved_req;
    struct fuse_release_in *inarg = &req->misc.release.in;

    spin_lock(&fc->lock);
    list_del(&ff->write_entry);
    if (!RB_EMPTY_NODE(&ff->polled_node))
        rb_erase(&ff->polled_node, &fc->polled_files);
    spin_unlock(&fc->lock);

    wake_up_interruptible_all(&ff->poll_wait);

    inarg->fh = ff->fh;
    inarg->flags = flags;
    req->in.h.opcode = opcode;
    req->in.h.nodeid = ff->nodeid;
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(struct fuse_release_in);
    req->in.args[0].value = inarg;
}

void fuse_release_common(struct file *file, int opcode)
{
    struct fuse_file *ff;
    struct fuse_req *req;

    ff = file->private_data;
    if (unlikely(!ff))
        return;

    req = ff->reserved_req;
    fuse_prepare_release(ff, file->f_flags, opcode);

    if (ff->flock) {
        struct fuse_release_in *inarg = &req->misc.release.in;
        inarg->release_flags |= FUSE_RELEASE_FLOCK_UNLOCK;
        inarg->lock_owner = fuse_lock_owner_id(ff->fc,
                               (fl_owner_t) file);
    }
    /* Hold vfsmount and dentry until release is finished */
    path_get(&file->f_path);
    req->misc.release.path = file->f_path;

    /*
     * Normally this will send the RELEASE request, however if
     * some asynchronous READ or WRITE requests are outstanding,
     * the sending will be delayed.
     *
     * Make the release synchronous if this is a fuseblk mount,
     * synchronous RELEASE is allowed (and desirable) in this case
     * because the server can be trusted not to screw up.
     */
    fuse_file_put(ff, ff->fc->destroy_req != NULL);
}

static int fuse_open(struct inode *inode, struct file *file)
{
    return fuse_open_common(inode, file, false);
}

static int fuse_release(struct inode *inode, struct file *file)
{
    fuse_release_common(file, FUSE_RELEASE);

    /* return value is ignored by VFS */
    return 0;
}

void fuse_sync_release(struct fuse_file *ff, int flags)
{
    WARN_ON(atomic_read(&ff->count) > 1);
    fuse_prepare_release(ff, flags, FUSE_RELEASE);
    ff->reserved_req->force = 1;
    fuse_request_send(ff->fc, ff->reserved_req);
    fuse_put_request(ff->fc, ff->reserved_req);
    kfree(ff);
}
EXPORT_SYMBOL_GPL(fuse_sync_release);

/*
 * Scramble the ID space with XTEA, so that the value of the files_struct
 * pointer is not exposed to userspace.
 */
u64 fuse_lock_owner_id(struct fuse_conn *fc, fl_owner_t id)
{
    u32 *k = fc->scramble_key;
    u64 v = (unsigned long) id;
    u32 v0 = v;
    u32 v1 = v >> 32;
    u32 sum = 0;
    int i;

    for (i = 0; i < 32; i++) {
        v0 += ((v1 << 4 ^ v1 >> 5) + v1) ^ (sum + k[sum & 3]);
        sum += 0x9E3779B9;
        v1 += ((v0 << 4 ^ v0 >> 5) + v0) ^ (sum + k[sum>>11 & 3]);
    }

    return (u64) v0 + ((u64) v1 << 32);
}

/*
 * Check if page is under writeback
 *
 * This is currently done by walking the list of writepage requests
 * for the inode, which can be pretty inefficient.
 */
static bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)
{
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_inode *fi = get_fuse_inode(inode);
    struct fuse_req *req;
    bool found = false;

    spin_lock(&fc->lock);
    list_for_each_entry(req, &fi->writepages, writepages_entry) {
        pgoff_t curr_index;

        BUG_ON(req->inode != inode);
        curr_index = req->misc.write.in.offset >> PAGE_CACHE_SHIFT;
        if (curr_index == index) {
            found = true;
            break;
        }
    }
    spin_unlock(&fc->lock);

    return found;
}

/*
 * Wait for page writeback to be completed.
 *
 * Since fuse doesn't rely on the VM writeback tracking, this has to
 * use some other means.
 */
static int fuse_wait_on_page_writeback(struct inode *inode, pgoff_t index)
{
    struct fuse_inode *fi = get_fuse_inode(inode);

    wait_event(fi->page_waitq, !fuse_page_is_writeback(inode, index));
    return 0;
}

static int fuse_flush(struct file *file, fl_owner_t id)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_file *ff = file->private_data;
    struct fuse_req *req;
    struct fuse_flush_in inarg;
    int err;

    if (is_bad_inode(inode))
        return -EIO;

    if (fc->no_flush)
        return 0;

    req = fuse_get_req_nofail(fc, file);
    memset(&inarg, 0, sizeof(inarg));
    inarg.fh = ff->fh;
    inarg.lock_owner = fuse_lock_owner_id(fc, id);
    req->in.h.opcode = FUSE_FLUSH;
    req->in.h.nodeid = get_node_id(inode);
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(inarg);
    req->in.args[0].value = &inarg;
    req->force = 1;
    fuse_request_send(fc, req);
    err = req->out.h.error;
    fuse_put_request(fc, req);
    if (err == -ENOSYS) {
        fc->no_flush = 1;
        err = 0;
    }
    return err;
}

/*
 * Wait for all pending writepages on the inode to finish.
 *
 * This is currently done by blocking further writes with FUSE_NOWRITE
 * and waiting for all sent writes to complete.
 *
 * This must be called under i_mutex, otherwise the FUSE_NOWRITE usage
 * could conflict with truncation.
 */
static void fuse_sync_writes(struct inode *inode)
{
    fuse_set_nowrite(inode);
    fuse_release_nowrite(inode);
}

int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
              int datasync, int isdir)
{
    struct inode *inode = file->f_mapping->host;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_file *ff = file->private_data;
    struct fuse_req *req;
    struct fuse_fsync_in inarg;
    int err;

    if (is_bad_inode(inode))
        return -EIO;

    err = filemap_write_and_wait_range(inode->i_mapping, start, end);
    if (err)
        return err;

    if ((!isdir && fc->no_fsync) || (isdir && fc->no_fsyncdir))
        return 0;

    mutex_lock(&inode->i_mutex);

    /*
     * Start writeback against all dirty pages of the inode, then
     * wait for all outstanding writes, before sending the FSYNC
     * request.
     */
    err = write_inode_now(inode, 0);
    if (err)
        goto out;

    fuse_sync_writes(inode);

    req = fuse_get_req(fc);
    if (IS_ERR(req)) {
        err = PTR_ERR(req);
        goto out;
    }

    memset(&inarg, 0, sizeof(inarg));
    inarg.fh = ff->fh;
    inarg.fsync_flags = datasync ? 1 : 0;
    req->in.h.opcode = isdir ? FUSE_FSYNCDIR : FUSE_FSYNC;
    req->in.h.nodeid = get_node_id(inode);
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(inarg);
    req->in.args[0].value = &inarg;
    fuse_request_send(fc, req);
    err = req->out.h.error;
    fuse_put_request(fc, req);
    if (err == -ENOSYS) {
        if (isdir)
            fc->no_fsyncdir = 1;
        else
            fc->no_fsync = 1;
        err = 0;
    }
out:
    mutex_unlock(&inode->i_mutex);
    return err;
}

static int fuse_fsync(struct file *file, loff_t start, loff_t end,
              int datasync)
{
    return fuse_fsync_common(file, start, end, datasync, 0);
}

void fuse_read_fill(struct fuse_req *req, struct file *file, loff_t pos,
            size_t count, int opcode)
{
    struct fuse_read_in *inarg = &req->misc.read.in;
    struct fuse_file *ff = file->private_data;

    inarg->fh = ff->fh;
    inarg->offset = pos;
    inarg->size = count;
    inarg->flags = file->f_flags;
    req->in.h.opcode = opcode;
    req->in.h.nodeid = ff->nodeid;
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(struct fuse_read_in);
    req->in.args[0].value = inarg;
    req->out.argvar = 1;
    req->out.numargs = 1;
    req->out.args[0].size = count;
}

static size_t fuse_send_read(struct fuse_req *req, struct file *file,
                 loff_t pos, size_t count, fl_owner_t owner)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = ff->fc;

    fuse_read_fill(req, file, pos, count, FUSE_READ);
    if (owner != NULL) {
        struct fuse_read_in *inarg = &req->misc.read.in;

        inarg->read_flags |= FUSE_READ_LOCKOWNER;
        inarg->lock_owner = fuse_lock_owner_id(fc, owner);
    }
    fuse_request_send(fc, req);
    return req->out.args[0].size;
}

static void fuse_read_update_size(struct inode *inode, loff_t size,
                  u64 attr_ver)
{
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_inode *fi = get_fuse_inode(inode);

    spin_lock(&fc->lock);
    if (attr_ver == fi->attr_version && size < inode->i_size) {
        fi->attr_version = ++fc->attr_version;
        i_size_write(inode, size);
    }
    spin_unlock(&fc->lock);
}

static int fuse_readpage(struct file *file, struct page *page)
{
    struct inode *inode = page->mapping->host;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_req *req;
    size_t num_read;
    loff_t pos = page_offset(page);
    size_t count = PAGE_CACHE_SIZE;
    u64 attr_ver;
    int err;

    err = -EIO;
    if (is_bad_inode(inode))
        goto out;

    /*
     * Page writeback can extend beyond the lifetime of the
     * page-cache page, so make sure we read a properly synced
     * page.
     */
    fuse_wait_on_page_writeback(inode, page->index);

    req = fuse_get_req(fc);
    err = PTR_ERR(req);
    if (IS_ERR(req))
        goto out;

    attr_ver = fuse_get_attr_version(fc);

    req->out.page_zeroing = 1;
    req->out.argpages = 1;
    req->num_pages = 1;
    req->pages[0] = page;
    num_read = fuse_send_read(req, file, pos, count, NULL);
    err = req->out.h.error;
    fuse_put_request(fc, req);

    if (!err) {
        /*
         * Short read means EOF.  If file size is larger, truncate it
         */
        if (num_read < count)
            fuse_read_update_size(inode, pos + num_read, attr_ver);

        SetPageUptodate(page);
    }

    fuse_invalidate_attr(inode); /* atime changed */
 out:
    unlock_page(page);
    return err;
}

static void fuse_readpages_end(struct fuse_conn *fc, struct fuse_req *req)
{
    int i;
    size_t count = req->misc.read.in.size;
    size_t num_read = req->out.args[0].size;
    struct address_space *mapping = NULL;

    for (i = 0; mapping == NULL && i < req->num_pages; i++)
        mapping = req->pages[i]->mapping;

    if (mapping) {
        struct inode *inode = mapping->host;

        /*
         * Short read means EOF. If file size is larger, truncate it
         */
        if (!req->out.h.error && num_read < count) {
            loff_t pos;

            pos = page_offset(req->pages[0]) + num_read;
            fuse_read_update_size(inode, pos,
                          req->misc.read.attr_ver);
        }
        fuse_invalidate_attr(inode); /* atime changed */
    }

    for (i = 0; i < req->num_pages; i++) {
        struct page *page = req->pages[i];
        if (!req->out.h.error)
            SetPageUptodate(page);
        else
            SetPageError(page);
        unlock_page(page);
        page_cache_release(page);
    }
    if (req->ff)
        fuse_file_put(req->ff, false);
}

static void fuse_send_readpages(struct fuse_req *req, struct file *file)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = ff->fc;
    loff_t pos = page_offset(req->pages[0]);
    size_t count = req->num_pages << PAGE_CACHE_SHIFT;

    req->out.argpages = 1;
    req->out.page_zeroing = 1;
    req->out.page_replace = 1;
    fuse_read_fill(req, file, pos, count, FUSE_READ);
    req->misc.read.attr_ver = fuse_get_attr_version(fc);
    if (fc->async_read) {
        req->ff = fuse_file_get(ff);
        req->end = fuse_readpages_end;
        fuse_request_send_background(fc, req);
    } else {
        fuse_request_send(fc, req);
        fuse_readpages_end(fc, req);
        fuse_put_request(fc, req);
    }
}

struct fuse_fill_data {
    struct fuse_req *req;
    struct file *file;
    struct inode *inode;
};

static int fuse_readpages_fill(void *_data, struct page *page)
{
    struct fuse_fill_data *data = _data;
    struct fuse_req *req = data->req;
    struct inode *inode = data->inode;
    struct fuse_conn *fc = get_fuse_conn(inode);

    fuse_wait_on_page_writeback(inode, page->index);

    if (req->num_pages &&
        (req->num_pages == FUSE_MAX_PAGES_PER_REQ ||
         (req->num_pages + 1) * PAGE_CACHE_SIZE > fc->max_read ||
         req->pages[req->num_pages - 1]->index + 1 != page->index)) {
        fuse_send_readpages(req, data->file);
        data->req = req = fuse_get_req(fc);
        if (IS_ERR(req)) {
            unlock_page(page);
            return PTR_ERR(req);
        }
    }
    page_cache_get(page);
    req->pages[req->num_pages] = page;
    req->num_pages++;
    return 0;
}

static int fuse_readpages(struct file *file, struct address_space *mapping,
              struct list_head *pages, unsigned nr_pages)
{
    struct inode *inode = mapping->host;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_fill_data data;
    int err;

    err = -EIO;
    if (is_bad_inode(inode))
        goto out;

    data.file = file;
    data.inode = inode;
    data.req = fuse_get_req(fc);
    err = PTR_ERR(data.req);
    if (IS_ERR(data.req))
        goto out;

    err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data);
    if (!err) {
        if (data.req->num_pages)
            fuse_send_readpages(data.req, file);
        else
            fuse_put_request(fc, data.req);
    }
out:
    return err;
}

static ssize_t fuse_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
                  unsigned long nr_segs, loff_t pos)
{
    struct inode *inode = iocb->ki_filp->f_mapping->host;
    struct fuse_conn *fc = get_fuse_conn(inode);

    /*
     * In auto invalidate mode, always update attributes on read.
     * Otherwise, only update if we attempt to read past EOF (to ensure
     * i_size is up to date).
     */
    if (fc->auto_inval_data ||
        (pos + iov_length(iov, nr_segs) > i_size_read(inode))) {
        int err;
        err = fuse_update_attributes(inode, NULL, iocb->ki_filp, NULL);
        if (err)
            return err;
    }

    return generic_file_aio_read(iocb, iov, nr_segs, pos);
}

static void fuse_write_fill(struct fuse_req *req, struct fuse_file *ff,
                loff_t pos, size_t count)
{
    struct fuse_write_in *inarg = &req->misc.write.in;
    struct fuse_write_out *outarg = &req->misc.write.out;

    inarg->fh = ff->fh;
    inarg->offset = pos;
    inarg->size = count;
    req->in.h.opcode = FUSE_WRITE;
    req->in.h.nodeid = ff->nodeid;
    req->in.numargs = 2;
    if (ff->fc->minor < 9)
        req->in.args[0].size = FUSE_COMPAT_WRITE_IN_SIZE;
    else
        req->in.args[0].size = sizeof(struct fuse_write_in);
    req->in.args[0].value = inarg;
    req->in.args[1].size = count;
    req->out.numargs = 1;
    req->out.args[0].size = sizeof(struct fuse_write_out);
    req->out.args[0].value = outarg;
}

static size_t fuse_send_write(struct fuse_req *req, struct file *file,
                  loff_t pos, size_t count, fl_owner_t owner)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = ff->fc;
    struct fuse_write_in *inarg = &req->misc.write.in;

    fuse_write_fill(req, ff, pos, count);
    inarg->flags = file->f_flags;
    if (owner != NULL) {
        inarg->write_flags |= FUSE_WRITE_LOCKOWNER;
        inarg->lock_owner = fuse_lock_owner_id(fc, owner);
    }
    fuse_request_send(fc, req);
    return req->misc.write.out.size;
}

void fuse_write_update_size(struct inode *inode, loff_t pos)
{
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_inode *fi = get_fuse_inode(inode);

    spin_lock(&fc->lock);
    fi->attr_version = ++fc->attr_version;
    if (pos > inode->i_size)
        i_size_write(inode, pos);
    spin_unlock(&fc->lock);
}

static size_t fuse_send_write_pages(struct fuse_req *req, struct file *file,
                    struct inode *inode, loff_t pos,
                    size_t count)
{
    size_t res;
    unsigned offset;
    unsigned i;

    for (i = 0; i < req->num_pages; i++)
        fuse_wait_on_page_writeback(inode, req->pages[i]->index);

    res = fuse_send_write(req, file, pos, count, NULL);

    offset = req->page_offset;
    count = res;
    for (i = 0; i < req->num_pages; i++) {
        struct page *page = req->pages[i];

        if (!req->out.h.error && !offset && count >= PAGE_CACHE_SIZE)
            SetPageUptodate(page);

        if (count > PAGE_CACHE_SIZE - offset)
            count -= PAGE_CACHE_SIZE - offset;
        else
            count = 0;
        offset = 0;

        unlock_page(page);
        page_cache_release(page);
    }

    return res;
}

static ssize_t fuse_fill_write_pages(struct fuse_req *req,
                   struct address_space *mapping,
                   struct iov_iter *ii, loff_t pos)
{
    struct fuse_conn *fc = get_fuse_conn(mapping->host);
    unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
    size_t count = 0;
    int err;

    req->in.argpages = 1;
    req->page_offset = offset;

    do {
        size_t tmp;
        struct page *page;
        pgoff_t index = pos >> PAGE_CACHE_SHIFT;
        size_t bytes = min_t(size_t, PAGE_CACHE_SIZE - offset,
                     iov_iter_count(ii));

        bytes = min_t(size_t, bytes, fc->max_write - count);

 again:
        err = -EFAULT;
        if (iov_iter_fault_in_readable(ii, bytes))
            break;

        err = -ENOMEM;
        page = grab_cache_page_write_begin(mapping, index, 0);
        if (!page)
            break;

        if (mapping_writably_mapped(mapping))
            flush_dcache_page(page);

        pagefault_disable();
        tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
        pagefault_enable();
        flush_dcache_page(page);

        mark_page_accessed(page);

        if (!tmp) {
            unlock_page(page);
            page_cache_release(page);
            bytes = min(bytes, iov_iter_single_seg_count(ii));
            goto again;
        }

        err = 0;
        req->pages[req->num_pages] = page;
        req->num_pages++;

        iov_iter_advance(ii, tmp);
        count += tmp;
        pos += tmp;
        offset += tmp;
        if (offset == PAGE_CACHE_SIZE)
            offset = 0;

        if (!fc->big_writes)
            break;
    } while (iov_iter_count(ii) && count < fc->max_write &&
         req->num_pages < FUSE_MAX_PAGES_PER_REQ && offset == 0);

    return count > 0 ? count : err;
}

static ssize_t fuse_perform_write(struct file *file,
                  struct address_space *mapping,
                  struct iov_iter *ii, loff_t pos)
{
    struct inode *inode = mapping->host;
    struct fuse_conn *fc = get_fuse_conn(inode);
    int err = 0;
    ssize_t res = 0;

    if (is_bad_inode(inode))
        return -EIO;

    do {
        struct fuse_req *req;
        ssize_t count;

        req = fuse_get_req(fc);
        if (IS_ERR(req)) {
            err = PTR_ERR(req);
            break;
        }

        count = fuse_fill_write_pages(req, mapping, ii, pos);
        if (count <= 0) {
            err = count;
        } else {
            size_t num_written;

            num_written = fuse_send_write_pages(req, file, inode,
                                pos, count);
            err = req->out.h.error;
            if (!err) {
                res += num_written;
                pos += num_written;

                /* break out of the loop on short write */
                if (num_written != count)
                    err = -EIO;
            }
        }
        fuse_put_request(fc, req);
    } while (!err && iov_iter_count(ii));

    if (res > 0)
        fuse_write_update_size(inode, pos);

    fuse_invalidate_attr(inode);

    return res > 0 ? res : err;
}

static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
                   unsigned long nr_segs, loff_t pos)
{
    struct file *file = iocb->ki_filp;
    struct address_space *mapping = file->f_mapping;
    size_t count = 0;
    size_t ocount = 0;
    ssize_t written = 0;
    ssize_t written_buffered = 0;
    struct inode *inode = mapping->host;
    ssize_t err;
    struct iov_iter i;
    loff_t endbyte = 0;

    WARN_ON(iocb->ki_pos != pos);

    ocount = 0;
    err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
    if (err)
        return err;

    count = ocount;
    sb_start_write(inode->i_sb);
    mutex_lock(&inode->i_mutex);

    /* We can write back this queue in page reclaim */
    current->backing_dev_info = mapping->backing_dev_info;

    err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
    if (err)
        goto out;

    if (count == 0)
        goto out;

    err = file_remove_suid(file);
    if (err)
        goto out;

    err = file_update_time(file);
    if (err)
        goto out;

    if (file->f_flags & O_DIRECT) {
        written = generic_file_direct_write(iocb, iov, &nr_segs,
                            pos, &iocb->ki_pos,
                            count, ocount);
        if (written < 0 || written == count)
            goto out;

        pos += written;
        count -= written;

        iov_iter_init(&i, iov, nr_segs, count, written);
        written_buffered = fuse_perform_write(file, mapping, &i, pos);
        if (written_buffered < 0) {
            err = written_buffered;
            goto out;
        }
        endbyte = pos + written_buffered - 1;

        err = filemap_write_and_wait_range(file->f_mapping, pos,
                           endbyte);
        if (err)
            goto out;

        invalidate_mapping_pages(file->f_mapping,
                     pos >> PAGE_CACHE_SHIFT,
                     endbyte >> PAGE_CACHE_SHIFT);

        written += written_buffered;
        iocb->ki_pos = pos + written_buffered;
    } else {
        iov_iter_init(&i, iov, nr_segs, count, 0);
        written = fuse_perform_write(file, mapping, &i, pos);
        if (written >= 0)
            iocb->ki_pos = pos + written;
    }
out:
    current->backing_dev_info = NULL;
    mutex_unlock(&inode->i_mutex);
    sb_end_write(inode->i_sb);

    return written ? written : err;
}

static void fuse_release_user_pages(struct fuse_req *req, int write)
{
    unsigned i;

    for (i = 0; i < req->num_pages; i++) {
        struct page *page = req->pages[i];
        if (write)
            set_page_dirty_lock(page);
        put_page(page);
    }
}

static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
                   size_t *nbytesp, int write)
{
    size_t nbytes = *nbytesp;
    unsigned long user_addr = (unsigned long) buf;
    unsigned offset = user_addr & ~PAGE_MASK;
    int npages;

    /* Special case for kernel I/O: can copy directly into the buffer */
    if (segment_eq(get_fs(), KERNEL_DS)) {
        if (write)
            req->in.args[1].value = (void *) user_addr;
        else
            req->out.args[0].value = (void *) user_addr;

        return 0;
    }

    nbytes = min_t(size_t, nbytes, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
    npages = (nbytes + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
    npages = clamp(npages, 1, FUSE_MAX_PAGES_PER_REQ);
    npages = get_user_pages_fast(user_addr, npages, !write, req->pages);
    if (npages < 0)
        return npages;

    req->num_pages = npages;
    req->page_offset = offset;

    if (write)
        req->in.argpages = 1;
    else
        req->out.argpages = 1;

    nbytes = (req->num_pages << PAGE_SHIFT) - req->page_offset;
    *nbytesp = min(*nbytesp, nbytes);

    return 0;
}

ssize_t fuse_direct_io(struct file *file, const char __user *buf,
               size_t count, loff_t *ppos, int write)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = ff->fc;
    size_t nmax = write ? fc->max_write : fc->max_read;
    loff_t pos = *ppos;
    ssize_t res = 0;
    struct fuse_req *req;

    req = fuse_get_req(fc);
    if (IS_ERR(req))
        return PTR_ERR(req);

    while (count) {
        size_t nres;
        fl_owner_t owner = current->files;
        size_t nbytes = min(count, nmax);
        int err = fuse_get_user_pages(req, buf, &nbytes, write);
        if (err) {
            res = err;
            break;
        }

        if (write)
            nres = fuse_send_write(req, file, pos, nbytes, owner);
        else
            nres = fuse_send_read(req, file, pos, nbytes, owner);

        fuse_release_user_pages(req, !write);
        if (req->out.h.error) {
            if (!res)
                res = req->out.h.error;
            break;
        } else if (nres > nbytes) {
            res = -EIO;
            break;
        }
        count -= nres;
        res += nres;
        pos += nres;
        buf += nres;
        if (nres != nbytes)
            break;
        if (count) {
            fuse_put_request(fc, req);
            req = fuse_get_req(fc);
            if (IS_ERR(req))
                break;
        }
    }
    if (!IS_ERR(req))
        fuse_put_request(fc, req);
    if (res > 0)
        *ppos = pos;

    return res;
}
EXPORT_SYMBOL_GPL(fuse_direct_io);

static ssize_t fuse_direct_read(struct file *file, char __user *buf,
                     size_t count, loff_t *ppos)
{
    ssize_t res;
    struct inode *inode = file->f_path.dentry->d_inode;

    if (is_bad_inode(inode))
        return -EIO;

    res = fuse_direct_io(file, buf, count, ppos, 0);

    fuse_invalidate_attr(inode);

    return res;
}

static ssize_t __fuse_direct_write(struct file *file, const char __user *buf,
                   size_t count, loff_t *ppos)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    ssize_t res;

    res = generic_write_checks(file, ppos, &count, 0);
    if (!res) {
        res = fuse_direct_io(file, buf, count, ppos, 1);
        if (res > 0)
            fuse_write_update_size(inode, *ppos);
    }

    fuse_invalidate_attr(inode);

    return res;
}

static ssize_t fuse_direct_write(struct file *file, const char __user *buf,
                 size_t count, loff_t *ppos)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    ssize_t res;

    if (is_bad_inode(inode))
        return -EIO;

    /* Don't allow parallel writes to the same file */
    mutex_lock(&inode->i_mutex);
    res = __fuse_direct_write(file, buf, count, ppos);
    mutex_unlock(&inode->i_mutex);

    return res;
}

static void fuse_writepage_free(struct fuse_conn *fc, struct fuse_req *req)
{
    __free_page(req->pages[0]);
    fuse_file_put(req->ff, false);
}

static void fuse_writepage_finish(struct fuse_conn *fc, struct fuse_req *req)
{
    struct inode *inode = req->inode;
    struct fuse_inode *fi = get_fuse_inode(inode);
    struct backing_dev_info *bdi = inode->i_mapping->backing_dev_info;

    list_del(&req->writepages_entry);
    dec_bdi_stat(bdi, BDI_WRITEBACK);
    dec_zone_page_state(req->pages[0], NR_WRITEBACK_TEMP);
    bdi_writeout_inc(bdi);
    wake_up(&fi->page_waitq);
}

/* Called under fc->lock, may release and reacquire it */
static void fuse_send_writepage(struct fuse_conn *fc, struct fuse_req *req)
__releases(fc->lock)
__acquires(fc->lock)
{
    struct fuse_inode *fi = get_fuse_inode(req->inode);
    loff_t size = i_size_read(req->inode);
    struct fuse_write_in *inarg = &req->misc.write.in;

    if (!fc->connected)
        goto out_free;

    if (inarg->offset + PAGE_CACHE_SIZE <= size) {
        inarg->size = PAGE_CACHE_SIZE;
    } else if (inarg->offset < size) {
        inarg->size = size & (PAGE_CACHE_SIZE - 1);
    } else {
        /* Got truncated off completely */
        goto out_free;
    }

    req->in.args[1].size = inarg->size;
    fi->writectr++;
    fuse_request_send_background_locked(fc, req);
    return;

 out_free:
    fuse_writepage_finish(fc, req);
    spin_unlock(&fc->lock);
    fuse_writepage_free(fc, req);
    fuse_put_request(fc, req);
    spin_lock(&fc->lock);
}

/*
 * If fi->writectr is positive (no truncate or fsync going on) send
 * all queued writepage requests.
 *
 * Called with fc->lock
 */
void fuse_flush_writepages(struct inode *inode)
__releases(fc->lock)
__acquires(fc->lock)
{
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_inode *fi = get_fuse_inode(inode);
    struct fuse_req *req;

    while (fi->writectr >= 0 && !list_empty(&fi->queued_writes)) {
        req = list_entry(fi->queued_writes.next, struct fuse_req, list);
        list_del_init(&req->list);
        fuse_send_writepage(fc, req);
    }
}

static void fuse_writepage_end(struct fuse_conn *fc, struct fuse_req *req)
{
    struct inode *inode = req->inode;
    struct fuse_inode *fi = get_fuse_inode(inode);

    mapping_set_error(inode->i_mapping, req->out.h.error);
    spin_lock(&fc->lock);
    fi->writectr--;
    fuse_writepage_finish(fc, req);
    spin_unlock(&fc->lock);
    fuse_writepage_free(fc, req);
}

static int fuse_writepage_locked(struct page *page)
{
    struct address_space *mapping = page->mapping;
    struct inode *inode = mapping->host;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_inode *fi = get_fuse_inode(inode);
    struct fuse_req *req;
    struct fuse_file *ff;
    struct page *tmp_page;

    set_page_writeback(page);

    req = fuse_request_alloc_nofs();
    if (!req)
        goto err;

    tmp_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
    if (!tmp_page)
        goto err_free;

    spin_lock(&fc->lock);
    BUG_ON(list_empty(&fi->write_files));
    ff = list_entry(fi->write_files.next, struct fuse_file, write_entry);
    req->ff = fuse_file_get(ff);
    spin_unlock(&fc->lock);

    fuse_write_fill(req, ff, page_offset(page), 0);

    copy_highpage(tmp_page, page);
    req->misc.write.in.write_flags |= FUSE_WRITE_CACHE;
    req->in.argpages = 1;
    req->num_pages = 1;
    req->pages[0] = tmp_page;
    req->page_offset = 0;
    req->end = fuse_writepage_end;
    req->inode = inode;

    inc_bdi_stat(mapping->backing_dev_info, BDI_WRITEBACK);
    inc_zone_page_state(tmp_page, NR_WRITEBACK_TEMP);
    end_page_writeback(page);

    spin_lock(&fc->lock);
    list_add(&req->writepages_entry, &fi->writepages);
    list_add_tail(&req->list, &fi->queued_writes);
    fuse_flush_writepages(inode);
    spin_unlock(&fc->lock);

    return 0;

err_free:
    fuse_request_free(req);
err:
    end_page_writeback(page);
    return -ENOMEM;
}

static int fuse_writepage(struct page *page, struct writeback_control *wbc)
{
    int err;

    err = fuse_writepage_locked(page);
    unlock_page(page);

    return err;
}

static int fuse_launder_page(struct page *page)
{
    int err = 0;
    if (clear_page_dirty_for_io(page)) {
        struct inode *inode = page->mapping->host;
        err = fuse_writepage_locked(page);
        if (!err)
            fuse_wait_on_page_writeback(inode, page->index);
    }
    return err;
}

/*
 * Write back dirty pages now, because there may not be any suitable
 * open files later
 */
static void fuse_vma_close(struct vm_area_struct *vma)
{
    filemap_write_and_wait(vma->vm_file->f_mapping);
}

/*
 * Wait for writeback against this page to complete before allowing it
 * to be marked dirty again, and hence written back again, possibly
 * before the previous writepage completed.
 *
 * Block here, instead of in ->writepage(), so that the userspace fs
 * can only block processes actually operating on the filesystem.
 *
 * Otherwise unprivileged userspace fs would be able to block
 * unrelated:
 *
 * - page migration
 * - sync(2)
 * - try_to_free_pages() with order > PAGE_ALLOC_COSTLY_ORDER
 */
static int fuse_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
    struct page *page = vmf->page;
    /*
     * Don't use page->mapping as it may become NULL from a
     * concurrent truncate.
     */
    struct inode *inode = vma->vm_file->f_mapping->host;

    fuse_wait_on_page_writeback(inode, page->index);
    return 0;
}

static const struct vm_operations_struct fuse_file_vm_ops = {
    .close      = fuse_vma_close,
    .fault      = filemap_fault,
    .page_mkwrite   = fuse_page_mkwrite,
    .remap_pages    = generic_file_remap_pages,
};

static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
{
    if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) {
        struct inode *inode = file->f_dentry->d_inode;
        struct fuse_conn *fc = get_fuse_conn(inode);
        struct fuse_inode *fi = get_fuse_inode(inode);
        struct fuse_file *ff = file->private_data;
        /*
         * file may be written through mmap, so chain it onto the
         * inodes's write_file list
         */
        spin_lock(&fc->lock);
        if (list_empty(&ff->write_entry))
            list_add(&ff->write_entry, &fi->write_files);
        spin_unlock(&fc->lock);
    }
    file_accessed(file);
    vma->vm_ops = &fuse_file_vm_ops;
    return 0;
}

static int fuse_direct_mmap(struct file *file, struct vm_area_struct *vma)
{
    /* Can't provide the coherency needed for MAP_SHARED */
    if (vma->vm_flags & VM_MAYSHARE)
        return -ENODEV;

    invalidate_inode_pages2(file->f_mapping);

    return generic_file_mmap(file, vma);
}

static int convert_fuse_file_lock(const struct fuse_file_lock *ffl,
                  struct file_lock *fl)
{
    switch (ffl->type) {
    case F_UNLCK:
        break;

    case F_RDLCK:
    case F_WRLCK:
        if (ffl->start > OFFSET_MAX || ffl->end > OFFSET_MAX ||
            ffl->end < ffl->start)
            return -EIO;

        fl->fl_start = ffl->start;
        fl->fl_end = ffl->end;
        fl->fl_pid = ffl->pid;
        break;

    default:
        return -EIO;
    }
    fl->fl_type = ffl->type;
    return 0;
}

static void fuse_lk_fill(struct fuse_req *req, struct file *file,
             const struct file_lock *fl, int opcode, pid_t pid,
             int flock)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_file *ff = file->private_data;
    struct fuse_lk_in *arg = &req->misc.lk_in;

    arg->fh = ff->fh;
    arg->owner = fuse_lock_owner_id(fc, fl->fl_owner);
    arg->lk.start = fl->fl_start;
    arg->lk.end = fl->fl_end;
    arg->lk.type = fl->fl_type;
    arg->lk.pid = pid;
    if (flock)
        arg->lk_flags |= FUSE_LK_FLOCK;
    req->in.h.opcode = opcode;
    req->in.h.nodeid = get_node_id(inode);
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(*arg);
    req->in.args[0].value = arg;
}

static int fuse_getlk(struct file *file, struct file_lock *fl)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_req *req;
    struct fuse_lk_out outarg;
    int err;

    req = fuse_get_req(fc);
    if (IS_ERR(req))
        return PTR_ERR(req);

    fuse_lk_fill(req, file, fl, FUSE_GETLK, 0, 0);
    req->out.numargs = 1;
    req->out.args[0].size = sizeof(outarg);
    req->out.args[0].value = &outarg;
    fuse_request_send(fc, req);
    err = req->out.h.error;
    fuse_put_request(fc, req);
    if (!err)
        err = convert_fuse_file_lock(&outarg.lk, fl);

    return err;
}

static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_req *req;
    int opcode = (fl->fl_flags & FL_SLEEP) ? FUSE_SETLKW : FUSE_SETLK;
    pid_t pid = fl->fl_type != F_UNLCK ? current->tgid : 0;
    int err;

    if (fl->fl_lmops && fl->fl_lmops->lm_grant) {
        /* NLM needs asynchronous locks, which we don't support yet */
        return -ENOLCK;
    }

    /* Unlock on close is handled by the flush method */
    if (fl->fl_flags & FL_CLOSE)
        return 0;

    req = fuse_get_req(fc);
    if (IS_ERR(req))
        return PTR_ERR(req);

    fuse_lk_fill(req, file, fl, opcode, pid, flock);
    fuse_request_send(fc, req);
    err = req->out.h.error;
    /* locking is restartable */
    if (err == -EINTR)
        err = -ERESTARTSYS;
    fuse_put_request(fc, req);
    return err;
}

static int fuse_file_lock(struct file *file, int cmd, struct file_lock *fl)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct fuse_conn *fc = get_fuse_conn(inode);
    int err;

    if (cmd == F_CANCELLK) {
        err = 0;
    } else if (cmd == F_GETLK) {
        if (fc->no_lock) {
            posix_test_lock(file, fl);
            err = 0;
        } else
            err = fuse_getlk(file, fl);
    } else {
        if (fc->no_lock)
            err = posix_lock_file(file, fl, NULL);
        else
            err = fuse_setlk(file, fl, 0);
    }
    return err;
}

static int fuse_file_flock(struct file *file, int cmd, struct file_lock *fl)
{
    struct inode *inode = file->f_path.dentry->d_inode;
    struct fuse_conn *fc = get_fuse_conn(inode);
    int err;

    if (fc->no_flock) {
        err = flock_lock_file_wait(file, fl);
    } else {
        struct fuse_file *ff = file->private_data;

        /* emulate flock with POSIX locks */
        fl->fl_owner = (fl_owner_t) file;
        ff->flock = true;
        err = fuse_setlk(file, fl, 1);
    }

    return err;
}

static sector_t fuse_bmap(struct address_space *mapping, sector_t block)
{
    struct inode *inode = mapping->host;
    struct fuse_conn *fc = get_fuse_conn(inode);
    struct fuse_req *req;
    struct fuse_bmap_in inarg;
    struct fuse_bmap_out outarg;
    int err;

    if (!inode->i_sb->s_bdev || fc->no_bmap)
        return 0;

    req = fuse_get_req(fc);
    if (IS_ERR(req))
        return 0;

    memset(&inarg, 0, sizeof(inarg));
    inarg.block = block;
    inarg.blocksize = inode->i_sb->s_blocksize;
    req->in.h.opcode = FUSE_BMAP;
    req->in.h.nodeid = get_node_id(inode);
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(inarg);
    req->in.args[0].value = &inarg;
    req->out.numargs = 1;
    req->out.args[0].size = sizeof(outarg);
    req->out.args[0].value = &outarg;
    fuse_request_send(fc, req);
    err = req->out.h.error;
    fuse_put_request(fc, req);
    if (err == -ENOSYS)
        fc->no_bmap = 1;

    return err ? 0 : outarg.block;
}

static loff_t fuse_file_llseek(struct file *file, loff_t offset, int origin)
{
    loff_t retval;
    struct inode *inode = file->f_path.dentry->d_inode;

    /* No i_mutex protection necessary for SEEK_CUR and SEEK_SET */
    if (origin == SEEK_CUR || origin == SEEK_SET)
        return generic_file_llseek(file, offset, origin);

    mutex_lock(&inode->i_mutex);
    retval = fuse_update_attributes(inode, NULL, file, NULL);
    if (!retval)
        retval = generic_file_llseek(file, offset, origin);
    mutex_unlock(&inode->i_mutex);

    return retval;
}

static int fuse_ioctl_copy_user(struct page **pages, struct iovec *iov,
            unsigned int nr_segs, size_t bytes, bool to_user)
{
    struct iov_iter ii;
    int page_idx = 0;

    if (!bytes)
        return 0;

    iov_iter_init(&ii, iov, nr_segs, bytes, 0);

    while (iov_iter_count(&ii)) {
        struct page *page = pages[page_idx++];
        size_t todo = min_t(size_t, PAGE_SIZE, iov_iter_count(&ii));
        void *kaddr;

        kaddr = kmap(page);

        while (todo) {
            char __user *uaddr = ii.iov->iov_base + ii.iov_offset;
            size_t iov_len = ii.iov->iov_len - ii.iov_offset;
            size_t copy = min(todo, iov_len);
            size_t left;

            if (!to_user)
                left = copy_from_user(kaddr, uaddr, copy);
            else
                left = copy_to_user(uaddr, kaddr, copy);

            if (unlikely(left))
                return -EFAULT;

            iov_iter_advance(&ii, copy);
            todo -= copy;
            kaddr += copy;
        }

        kunmap(page);
    }

    return 0;
}

/*
 * CUSE servers compiled on 32bit broke on 64bit kernels because the
 * ABI was defined to be 'struct iovec' which is different on 32bit
 * and 64bit.  Fortunately we can determine which structure the server
 * used from the size of the reply.
 */
static int fuse_copy_ioctl_iovec_old(struct iovec *dst, void *src,
                     size_t transferred, unsigned count,
                     bool is_compat)
{
#ifdef CONFIG_COMPAT
    if (count * sizeof(struct compat_iovec) == transferred) {
        struct compat_iovec *ciov = src;
        unsigned i;

        /*
         * With this interface a 32bit server cannot support
         * non-compat (i.e. ones coming from 64bit apps) ioctl
         * requests
         */
        if (!is_compat)
            return -EINVAL;

        for (i = 0; i < count; i++) {
            dst[i].iov_base = compat_ptr(ciov[i].iov_base);
            dst[i].iov_len = ciov[i].iov_len;
        }
        return 0;
    }
#endif

    if (count * sizeof(struct iovec) != transferred)
        return -EIO;

    memcpy(dst, src, transferred);
    return 0;
}

/* Make sure iov_length() won't overflow */
static int fuse_verify_ioctl_iov(struct iovec *iov, size_t count)
{
    size_t n;
    u32 max = FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT;

    for (n = 0; n < count; n++, iov++) {
        if (iov->iov_len > (size_t) max)
            return -ENOMEM;
        max -= iov->iov_len;
    }
    return 0;
}

static int fuse_copy_ioctl_iovec(struct fuse_conn *fc, struct iovec *dst,
                 void *src, size_t transferred, unsigned count,
                 bool is_compat)
{
    unsigned i;
    struct fuse_ioctl_iovec *fiov = src;

    if (fc->minor < 16) {
        return fuse_copy_ioctl_iovec_old(dst, src, transferred,
                         count, is_compat);
    }

    if (count * sizeof(struct fuse_ioctl_iovec) != transferred)
        return -EIO;

    for (i = 0; i < count; i++) {
        /* Did the server supply an inappropriate value? */
        if (fiov[i].base != (unsigned long) fiov[i].base ||
            fiov[i].len != (unsigned long) fiov[i].len)
            return -EIO;

        dst[i].iov_base = (void __user *) (unsigned long) fiov[i].base;
        dst[i].iov_len = (size_t) fiov[i].len;

#ifdef CONFIG_COMPAT
        if (is_compat &&
            (ptr_to_compat(dst[i].iov_base) != fiov[i].base ||
             (compat_size_t) dst[i].iov_len != fiov[i].len))
            return -EIO;
#endif
    }

    return 0;
}


/*
 * For ioctls, there is no generic way to determine how much memory
 * needs to be read and/or written.  Furthermore, ioctls are allowed
 * to dereference the passed pointer, so the parameter requires deep
 * copying but FUSE has no idea whatsoever about what to copy in or
 * out.
 *
 * This is solved by allowing FUSE server to retry ioctl with
 * necessary in/out iovecs.  Let's assume the ioctl implementation
 * needs to read in the following structure.
 *
 * struct a {
 *  char    *buf;
 *  size_t  buflen;
 * }
 *
 * On the first callout to FUSE server, inarg->in_size and
 * inarg->out_size will be NULL; then, the server completes the ioctl
 * with FUSE_IOCTL_RETRY set in out->flags, out->in_iovs set to 1 and
 * the actual iov array to
 *
 * { { .iov_base = inarg.arg,   .iov_len = sizeof(struct a) } }
 *
 * which tells FUSE to copy in the requested area and retry the ioctl.
 * On the second round, the server has access to the structure and
 * from that it can tell what to look for next, so on the invocation,
 * it sets FUSE_IOCTL_RETRY, out->in_iovs to 2 and iov array to
 *
 * { { .iov_base = inarg.arg,   .iov_len = sizeof(struct a) },
 *   { .iov_base = a.buf,   .iov_len = a.buflen     } }
 *
 * FUSE will copy both struct a and the pointed buffer from the
 * process doing the ioctl and retry ioctl with both struct a and the
 * buffer.
 *
 * This time, FUSE server has everything it needs and completes ioctl
 * without FUSE_IOCTL_RETRY which finishes the ioctl call.
 *
 * Copying data out works the same way.
 *
 * Note that if FUSE_IOCTL_UNRESTRICTED is clear, the kernel
 * automatically initializes in and out iovs by decoding @cmd with
 * _IOC_* macros and the server is not allowed to request RETRY.  This
 * limits ioctl data transfers to well-formed ioctls and is the forced
 * behavior for all FUSE servers.
 */
long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
           unsigned int flags)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = ff->fc;
    struct fuse_ioctl_in inarg = {
        .fh = ff->fh,
        .cmd = cmd,
        .arg = arg,
        .flags = flags
    };
    struct fuse_ioctl_out outarg;
    struct fuse_req *req = NULL;
    struct page **pages = NULL;
    struct iovec *iov_page = NULL;
    struct iovec *in_iov = NULL, *out_iov = NULL;
    unsigned int in_iovs = 0, out_iovs = 0, num_pages = 0, max_pages;
    size_t in_size, out_size, transferred;
    int err;

#if BITS_PER_LONG == 32
    inarg.flags |= FUSE_IOCTL_32BIT;
#else
    if (flags & FUSE_IOCTL_COMPAT)
        inarg.flags |= FUSE_IOCTL_32BIT;
#endif

    /* assume all the iovs returned by client always fits in a page */
    BUILD_BUG_ON(sizeof(struct fuse_ioctl_iovec) * FUSE_IOCTL_MAX_IOV > PAGE_SIZE);

    err = -ENOMEM;
    pages = kcalloc(FUSE_MAX_PAGES_PER_REQ, sizeof(pages[0]), GFP_KERNEL);
    iov_page = (struct iovec *) __get_free_page(GFP_KERNEL);
    if (!pages || !iov_page)
        goto out;

    /*
     * If restricted, initialize IO parameters as encoded in @cmd.
     * RETRY from server is not allowed.
     */
    if (!(flags & FUSE_IOCTL_UNRESTRICTED)) {
        struct iovec *iov = iov_page;

        iov->iov_base = (void __user *)arg;
        iov->iov_len = _IOC_SIZE(cmd);

        if (_IOC_DIR(cmd) & _IOC_WRITE) {
            in_iov = iov;
            in_iovs = 1;
        }

        if (_IOC_DIR(cmd) & _IOC_READ) {
            out_iov = iov;
            out_iovs = 1;
        }
    }

 retry:
    inarg.in_size = in_size = iov_length(in_iov, in_iovs);
    inarg.out_size = out_size = iov_length(out_iov, out_iovs);

    /*
     * Out data can be used either for actual out data or iovs,
     * make sure there always is at least one page.
     */
    out_size = max_t(size_t, out_size, PAGE_SIZE);
    max_pages = DIV_ROUND_UP(max(in_size, out_size), PAGE_SIZE);

    /* make sure there are enough buffer pages and init request with them */
    err = -ENOMEM;
    if (max_pages > FUSE_MAX_PAGES_PER_REQ)
        goto out;
    while (num_pages < max_pages) {
        pages[num_pages] = alloc_page(GFP_KERNEL | __GFP_HIGHMEM);
        if (!pages[num_pages])
            goto out;
        num_pages++;
    }

    req = fuse_get_req(fc);
    if (IS_ERR(req)) {
        err = PTR_ERR(req);
        req = NULL;
        goto out;
    }
    memcpy(req->pages, pages, sizeof(req->pages[0]) * num_pages);
    req->num_pages = num_pages;

    /* okay, let's send it to the client */
    req->in.h.opcode = FUSE_IOCTL;
    req->in.h.nodeid = ff->nodeid;
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(inarg);
    req->in.args[0].value = &inarg;
    if (in_size) {
        req->in.numargs++;
        req->in.args[1].size = in_size;
        req->in.argpages = 1;

        err = fuse_ioctl_copy_user(pages, in_iov, in_iovs, in_size,
                       false);
        if (err)
            goto out;
    }

    req->out.numargs = 2;
    req->out.args[0].size = sizeof(outarg);
    req->out.args[0].value = &outarg;
    req->out.args[1].size = out_size;
    req->out.argpages = 1;
    req->out.argvar = 1;

    fuse_request_send(fc, req);
    err = req->out.h.error;
    transferred = req->out.args[1].size;
    fuse_put_request(fc, req);
    req = NULL;
    if (err)
        goto out;

    /* did it ask for retry? */
    if (outarg.flags & FUSE_IOCTL_RETRY) {
        void *vaddr;

        /* no retry if in restricted mode */
        err = -EIO;
        if (!(flags & FUSE_IOCTL_UNRESTRICTED))
            goto out;

        in_iovs = outarg.in_iovs;
        out_iovs = outarg.out_iovs;

        /*
         * Make sure things are in boundary, separate checks
         * are to protect against overflow.
         */
        err = -ENOMEM;
        if (in_iovs > FUSE_IOCTL_MAX_IOV ||
            out_iovs > FUSE_IOCTL_MAX_IOV ||
            in_iovs + out_iovs > FUSE_IOCTL_MAX_IOV)
            goto out;

        vaddr = kmap_atomic(pages[0]);
        err = fuse_copy_ioctl_iovec(fc, iov_page, vaddr,
                        transferred, in_iovs + out_iovs,
                        (flags & FUSE_IOCTL_COMPAT) != 0);
        kunmap_atomic(vaddr);
        if (err)
            goto out;

        in_iov = iov_page;
        out_iov = in_iov + in_iovs;

        err = fuse_verify_ioctl_iov(in_iov, in_iovs);
        if (err)
            goto out;

        err = fuse_verify_ioctl_iov(out_iov, out_iovs);
        if (err)
            goto out;

        goto retry;
    }

    err = -EIO;
    if (transferred > inarg.out_size)
        goto out;

    err = fuse_ioctl_copy_user(pages, out_iov, out_iovs, transferred, true);
 out:
    if (req)
        fuse_put_request(fc, req);
    free_page((unsigned long) iov_page);
    while (num_pages)
        __free_page(pages[--num_pages]);
    kfree(pages);

    return err ? err : outarg.result;
}
EXPORT_SYMBOL_GPL(fuse_do_ioctl);

long fuse_ioctl_common(struct file *file, unsigned int cmd,
               unsigned long arg, unsigned int flags)
{
    struct inode *inode = file->f_dentry->d_inode;
    struct fuse_conn *fc = get_fuse_conn(inode);

    if (!fuse_allow_task(fc, current))
        return -EACCES;

    if (is_bad_inode(inode))
        return -EIO;

    return fuse_do_ioctl(file, cmd, arg, flags);
}

static long fuse_file_ioctl(struct file *file, unsigned int cmd,
                unsigned long arg)
{
    return fuse_ioctl_common(file, cmd, arg, 0);
}

static long fuse_file_compat_ioctl(struct file *file, unsigned int cmd,
                   unsigned long arg)
{
    return fuse_ioctl_common(file, cmd, arg, FUSE_IOCTL_COMPAT);
}

/*
 * All files which have been polled are linked to RB tree
 * fuse_conn->polled_files which is indexed by kh.  Walk the tree and
 * find the matching one.
 */
static struct rb_node **fuse_find_polled_node(struct fuse_conn *fc, u64 kh,
                          struct rb_node **parent_out)
{
    struct rb_node **link = &fc->polled_files.rb_node;
    struct rb_node *last = NULL;

    while (*link) {
        struct fuse_file *ff;

        last = *link;
        ff = rb_entry(last, struct fuse_file, polled_node);

        if (kh < ff->kh)
            link = &last->rb_left;
        else if (kh > ff->kh)
            link = &last->rb_right;
        else
            return link;
    }

    if (parent_out)
        *parent_out = last;
    return link;
}

/*
 * The file is about to be polled.  Make sure it's on the polled_files
 * RB tree.  Note that files once added to the polled_files tree are
 * not removed before the file is released.  This is because a file
 * polled once is likely to be polled again.
 */
static void fuse_register_polled_file(struct fuse_conn *fc,
                      struct fuse_file *ff)
{
    spin_lock(&fc->lock);
    if (RB_EMPTY_NODE(&ff->polled_node)) {
        struct rb_node **link, *parent;

        link = fuse_find_polled_node(fc, ff->kh, &parent);
        BUG_ON(*link);
        rb_link_node(&ff->polled_node, parent, link);
        rb_insert_color(&ff->polled_node, &fc->polled_files);
    }
    spin_unlock(&fc->lock);
}

unsigned fuse_file_poll(struct file *file, poll_table *wait)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = ff->fc;
    struct fuse_poll_in inarg = { .fh = ff->fh, .kh = ff->kh };
    struct fuse_poll_out outarg;
    struct fuse_req *req;
    int err;

    if (fc->no_poll)
        return DEFAULT_POLLMASK;

    poll_wait(file, &ff->poll_wait, wait);

    /*
     * Ask for notification iff there's someone waiting for it.
     * The client may ignore the flag and always notify.
     */
    if (waitqueue_active(&ff->poll_wait)) {
        inarg.flags |= FUSE_POLL_SCHEDULE_NOTIFY;
        fuse_register_polled_file(fc, ff);
    }

    req = fuse_get_req(fc);
    if (IS_ERR(req))
        return POLLERR;

    req->in.h.opcode = FUSE_POLL;
    req->in.h.nodeid = ff->nodeid;
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(inarg);
    req->in.args[0].value = &inarg;
    req->out.numargs = 1;
    req->out.args[0].size = sizeof(outarg);
    req->out.args[0].value = &outarg;
    fuse_request_send(fc, req);
    err = req->out.h.error;
    fuse_put_request(fc, req);

    if (!err)
        return outarg.revents;
    if (err == -ENOSYS) {
        fc->no_poll = 1;
        return DEFAULT_POLLMASK;
    }
    return POLLERR;
}
EXPORT_SYMBOL_GPL(fuse_file_poll);

/*
 * This is called from fuse_handle_notify() on FUSE_NOTIFY_POLL and
 * wakes up the poll waiters.
 */
int fuse_notify_poll_wakeup(struct fuse_conn *fc,
                struct fuse_notify_poll_wakeup_out *outarg)
{
    u64 kh = outarg->kh;
    struct rb_node **link;

    spin_lock(&fc->lock);

    link = fuse_find_polled_node(fc, kh, NULL);
    if (*link) {
        struct fuse_file *ff;

        ff = rb_entry(*link, struct fuse_file, polled_node);
        wake_up_interruptible_sync(&ff->poll_wait);
    }

    spin_unlock(&fc->lock);
    return 0;
}

static ssize_t fuse_loop_dio(struct file *filp, const struct iovec *iov,
                 unsigned long nr_segs, loff_t *ppos, int rw)
{
    const struct iovec *vector = iov;
    ssize_t ret = 0;

    while (nr_segs > 0) {
        void __user *base;
        size_t len;
        ssize_t nr;

        base = vector->iov_base;
        len = vector->iov_len;
        vector++;
        nr_segs--;

        if (rw == WRITE)
            nr = __fuse_direct_write(filp, base, len, ppos);
        else
            nr = fuse_direct_read(filp, base, len, ppos);

        if (nr < 0) {
            if (!ret)
                ret = nr;
            break;
        }
        ret += nr;
        if (nr != len)
            break;
    }

    return ret;
}


static ssize_t
fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
            loff_t offset, unsigned long nr_segs)
{
    ssize_t ret = 0;
    struct file *file = NULL;
    loff_t pos = 0;

    file = iocb->ki_filp;
    pos = offset;

    ret = fuse_loop_dio(file, iov, nr_segs, &pos, rw);

    return ret;
}

long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
                loff_t length)
{
    struct fuse_file *ff = file->private_data;
    struct fuse_conn *fc = ff->fc;
    struct fuse_req *req;
    struct fuse_fallocate_in inarg = {
        .fh = ff->fh,
        .offset = offset,
        .length = length,
        .mode = mode
    };
    int err;

    if (fc->no_fallocate)
        return -EOPNOTSUPP;

    req = fuse_get_req(fc);
    if (IS_ERR(req))
        return PTR_ERR(req);

    req->in.h.opcode = FUSE_FALLOCATE;
    req->in.h.nodeid = ff->nodeid;
    req->in.numargs = 1;
    req->in.args[0].size = sizeof(inarg);
    req->in.args[0].value = &inarg;
    fuse_request_send(fc, req);
    err = req->out.h.error;
    if (err == -ENOSYS) {
        fc->no_fallocate = 1;
        err = -EOPNOTSUPP;
    }
    fuse_put_request(fc, req);

    return err;
}
EXPORT_SYMBOL_GPL(fuse_file_fallocate);

static const struct file_operations fuse_file_operations = {
    .llseek     = fuse_file_llseek,
    .read       = do_sync_read,
    .aio_read   = fuse_file_aio_read,
    .write      = do_sync_write,
    .aio_write  = fuse_file_aio_write,
    .mmap       = fuse_file_mmap,
    .open       = fuse_open,
    .flush      = fuse_flush,
    .release    = fuse_release,
    .fsync      = fuse_fsync,
    .lock       = fuse_file_lock,
    .flock      = fuse_file_flock,
    .splice_read    = generic_file_splice_read,
    .unlocked_ioctl = fuse_file_ioctl,
    .compat_ioctl   = fuse_file_compat_ioctl,
    .poll       = fuse_file_poll,
    .fallocate  = fuse_file_fallocate,
};

static const struct file_operations fuse_direct_io_file_operations = {
    .llseek     = fuse_file_llseek,
    .read       = fuse_direct_read,
    .write      = fuse_direct_write,
    .mmap       = fuse_direct_mmap,
    .open       = fuse_open,
    .flush      = fuse_flush,
    .release    = fuse_release,
    .fsync      = fuse_fsync,
    .lock       = fuse_file_lock,
    .flock      = fuse_file_flock,
    .unlocked_ioctl = fuse_file_ioctl,
    .compat_ioctl   = fuse_file_compat_ioctl,
    .poll       = fuse_file_poll,
    .fallocate  = fuse_file_fallocate,
    /* no splice_read */
};

static const struct address_space_operations fuse_file_aops  = {
    .readpage   = fuse_readpage,
    .writepage  = fuse_writepage,
    .launder_page   = fuse_launder_page,
    .readpages  = fuse_readpages,
    .set_page_dirty = __set_page_dirty_nobuffers,
    .bmap       = fuse_bmap,
    .direct_IO  = fuse_direct_IO,
};

void fuse_init_file_inode(struct inode *inode)
{
    inode->i_fop = &fuse_file_operations;
    inode->i_data.a_ops = &fuse_file_aops;
}