Linux 2.6.31.6

[linux/fpc-iii.git] / fs / fuse / file.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2008  Miklos Szeredi <miklos@szeredi.hu>

  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>

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_end(struct fuse_conn *fc, struct fuse_req *req)
{
        path_put(&req->misc.release.path);
}

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

                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;

        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);
}

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

        /* VFS checks this, but only _after_ ->open() */
        if (file->f_flags & O_DIRECT)
                return -EINVAL;

        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_sync(&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);

        /* 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.
         */
        fuse_file_put(ff);
}

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, struct dentry *de, int datasync,
                      int isdir)
{
        struct inode *inode = de->d_inode;
        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;

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

        /*
         * 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)
                return err;

        fuse_sync_writes(inode);

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

        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;
        }
        return err;
}

static int fuse_fsync(struct file *file, struct dentry *de, int datasync)
{
        return fuse_fsync_common(file, de, 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 liftime 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 inode *inode = req->pages[0]->mapping->host;

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

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;
        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);
                }
        }
        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;

        if (pos + iov_length(iov, nr_segs) > i_size_read(inode)) {
                int err;
                /*
                 * If trying to read past EOF, make sure the i_size
                 * attribute is up-to-date.
                 */
                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;
}

static int fuse_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
{
        pgoff_t index = pos >> PAGE_CACHE_SHIFT;

        *pagep = grab_cache_page_write_begin(mapping, index, flags);
        if (!*pagep)
                return -ENOMEM;
        return 0;
}

static 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 int fuse_buffered_write(struct file *file, struct inode *inode,
                               loff_t pos, unsigned count, struct page *page)
{
        int err;
        size_t nres;
        struct fuse_conn *fc = get_fuse_conn(inode);
        unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
        struct fuse_req *req;

        if (is_bad_inode(inode))
                return -EIO;

        /*
         * Make sure writepages on the same page are not mixed up with
         * plain writes.
         */
        fuse_wait_on_page_writeback(inode, page->index);

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

        req->in.argpages = 1;
        req->num_pages = 1;
        req->pages[0] = page;
        req->page_offset = offset;
        nres = fuse_send_write(req, file, pos, count, NULL);
        err = req->out.h.error;
        fuse_put_request(fc, req);
        if (!err && !nres)
                err = -EIO;
        if (!err) {
                pos += nres;
                fuse_write_update_size(inode, pos);
                if (count == PAGE_CACHE_SIZE)
                        SetPageUptodate(page);
        }
        fuse_invalidate_attr(inode);
        return err ? err : nres;
}

static int fuse_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *page, void *fsdata)
{
        struct inode *inode = mapping->host;
        int res = 0;

        if (copied)
                res = fuse_buffered_write(file, inode, pos, copied, page);

        unlock_page(page);
        page_cache_release(page);
        return res;
}

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;

                pagefault_disable();
                tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
                pagefault_enable();
                flush_dcache_page(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;
        ssize_t written = 0;
        struct inode *inode = mapping->host;
        ssize_t err;
        struct iov_iter i;

        WARN_ON(iocb->ki_pos != pos);

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

        mutex_lock(&inode->i_mutex);
        vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);

        /* 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;

        file_update_time(file);

        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);

        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);
        down_read(&current->mm->mmap_sem);
        npages = get_user_pages(current, current->mm, user_addr, npages, !write,
                                0, req->pages, NULL);
        up_read(&current->mm->mmap_sem);
        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;

        if (is_bad_inode(inode))
                return -EIO;

        /* Don't allow parallel writes to the same file */
        mutex_lock(&inode->i_mutex);
        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);
        }
        mutex_unlock(&inode->i_mutex);

        fuse_invalidate_attr(inode);

        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);
}

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 struct vm_operations_struct fuse_file_vm_ops = {
        .close          = fuse_vma_close,
        .fault          = filemap_fault,
        .page_mkwrite   = fuse_page_mkwrite,
};

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->fl_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_lock) {
                err = flock_lock_file_wait(file, fl);
        } else {
                /* emulate flock with POSIX locks */
                fl->fl_owner = (fl_owner_t) file;
                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;

        mutex_lock(&inode->i_mutex);
        switch (origin) {
        case SEEK_END:
                retval = fuse_update_attributes(inode, NULL, file, NULL);
                if (retval)
                        goto exit;
                offset += i_size_read(inode);
                break;
        case SEEK_CUR:
                offset += file->f_pos;
        }
        retval = -EINVAL;
        if (offset >= 0 && offset <= inode->i_sb->s_maxbytes) {
                if (offset != file->f_pos) {
                        file->f_pos = offset;
                        file->f_version = 0;
                }
                retval = offset;
        }
exit:
        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, *map;

                kaddr = map = 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;
}

/*
 * 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 page *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;

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

        err = -ENOMEM;
        pages = kzalloc(sizeof(pages[0]) * FUSE_MAX_PAGES_PER_REQ, GFP_KERNEL);
        iov_page = alloc_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 = page_address(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) {
                char *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;

                err = -EIO;
                if ((in_iovs + out_iovs) * sizeof(struct iovec) != transferred)
                        goto out;

                /* okay, copy in iovs and retry */
                vaddr = kmap_atomic(pages[0], KM_USER0);
                memcpy(page_address(iov_page), vaddr, transferred);
                kunmap_atomic(vaddr, KM_USER0);

                in_iov = page_address(iov_page);
                out_iov = in_iov + in_iovs;

                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);
        if (iov_page)
                __free_page(iov_page);
        while (num_pages)
                __free_page(pages[--num_pages]);
        kfree(pages);

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

static long fuse_file_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_file_ioctl_common(file, cmd, arg, 0);
}

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

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,
        /* no splice_read */
};

static const struct address_space_operations fuse_file_aops  = {
        .readpage       = fuse_readpage,
        .writepage      = fuse_writepage,
        .launder_page   = fuse_launder_page,
        .write_begin    = fuse_write_begin,
        .write_end      = fuse_write_end,
        .readpages      = fuse_readpages,
        .set_page_dirty = __set_page_dirty_nobuffers,
        .bmap           = fuse_bmap,
};

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