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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 /*
   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/sched/signal.h>
 #include <linux/module.h>
 #include <linux/swap.h>
 #include <linux/falloc.h>
 #include <linux/uio.h>
 #include <linux/fs.h>
 
 static int fuse_send_open(struct fuse_mount *fm, u64 nodeid,
               unsigned int open_flags, int opcode,
               struct fuse_open_out *outargp)
 {
     struct fuse_open_in inarg;
     FUSE_ARGS(args);
 
     memset(&inarg, 0, sizeof(inarg));
     inarg.flags = open_flags & ~(O_CREAT | O_EXCL | O_NOCTTY);
     if (!fm->fc->atomic_o_trunc)
         inarg.flags &= ~O_TRUNC;
 
     if (fm->fc->handle_killpriv_v2 &&
         (inarg.flags & O_TRUNC) && !capable(CAP_FSETID)) {
         inarg.open_flags |= FUSE_OPEN_KILL_SUIDGID;
     }
 
     args.opcode = opcode;
     args.nodeid = nodeid;
     args.in_numargs = 1;
     args.in_args[0].size = sizeof(inarg);
     args.in_args[0].value = &inarg;
     args.out_numargs = 1;
     args.out_args[0].size = sizeof(*outargp);
     args.out_args[0].value = outargp;
 
     return fuse_simple_request(fm, &args);
 }
 
 struct fuse_release_args {
     struct fuse_args args;
     struct fuse_release_in inarg;
     struct inode *inode;
 };
 
 struct fuse_file *fuse_file_alloc(struct fuse_mount *fm)
 {
     struct fuse_file *ff;
 
     ff = kzalloc(sizeof(struct fuse_file), GFP_KERNEL_ACCOUNT);
     if (unlikely(!ff))
         return NULL;
 
     ff->fm = fm;
     ff->release_args = kzalloc(sizeof(*ff->release_args),
                    GFP_KERNEL_ACCOUNT);
     if (!ff->release_args) {
         kfree(ff);
         return NULL;
     }
 
     INIT_LIST_HEAD(&ff->write_entry);
     mutex_init(&ff->readdir.lock);
     refcount_set(&ff->count, 1);
     RB_CLEAR_NODE(&ff->polled_node);
     init_waitqueue_head(&ff->poll_wait);
 
     ff->kh = atomic64_inc_return(&fm->fc->khctr);
 
     return ff;
 }
 
 void fuse_file_free(struct fuse_file *ff)
 {
     kfree(ff->release_args);
     mutex_destroy(&ff->readdir.lock);
     kfree(ff);
 }
 
 static struct fuse_file *fuse_file_get(struct fuse_file *ff)
 {
     refcount_inc(&ff->count);
     return ff;
 }
 
 static void fuse_release_end(struct fuse_mount *fm, struct fuse_args *args,
                  int error)
 {
     struct fuse_release_args *ra = container_of(args, typeof(*ra), args);
 
     iput(ra->inode);
     kfree(ra);
 }
 
 static void fuse_file_put(struct fuse_file *ff, bool sync, bool isdir)
 {
     if (refcount_dec_and_test(&ff->count)) {
         struct fuse_args *args = &ff->release_args->args;
 
         if (isdir ? ff->fm->fc->no_opendir : ff->fm->fc->no_open) {
             /* Do nothing when client does not implement 'open' */
             fuse_release_end(ff->fm, args, 0);
         } else if (sync) {
             fuse_simple_request(ff->fm, args);
             fuse_release_end(ff->fm, args, 0);
         } else {
             args->end = fuse_release_end;
             if (fuse_simple_background(ff->fm, args,
                            GFP_KERNEL | __GFP_NOFAIL))
                 fuse_release_end(ff->fm, args, -ENOTCONN);
         }
         kfree(ff);
     }
 }
 
 struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
                  unsigned int open_flags, bool isdir)
 {
     struct fuse_conn *fc = fm->fc;
     struct fuse_file *ff;
     int opcode = isdir ? FUSE_OPENDIR : FUSE_OPEN;
 
     ff = fuse_file_alloc(fm);
     if (!ff)
         return ERR_PTR(-ENOMEM);
 
     ff->fh = 0;
     /* Default for no-open */
     ff->open_flags = FOPEN_KEEP_CACHE | (isdir ? FOPEN_CACHE_DIR : 0);
     if (isdir ? !fc->no_opendir : !fc->no_open) {
         struct fuse_open_out outarg;
         int err;
 
         err = fuse_send_open(fm, nodeid, open_flags, opcode, &outarg);
         if (!err) {
             ff->fh = outarg.fh;
             ff->open_flags = outarg.open_flags;
 
         } else if (err != -ENOSYS) {
             fuse_file_free(ff);
             return ERR_PTR(err);
         } else {
             if (isdir)
                 fc->no_opendir = 1;
             else
                 fc->no_open = 1;
         }
     }
 
     if (isdir)
         ff->open_flags &= ~FOPEN_DIRECT_IO;
 
     ff->nodeid = nodeid;
 
     return ff;
 }
 
 int fuse_do_open(struct fuse_mount *fm, u64 nodeid, struct file *file,
          bool isdir)
 {
     struct fuse_file *ff = fuse_file_open(fm, nodeid, file->f_flags, isdir);
 
     if (!IS_ERR(ff))
         file->private_data = ff;
 
     return PTR_ERR_OR_ZERO(ff);
 }
 EXPORT_SYMBOL_GPL(fuse_do_open);
 
 static void fuse_link_write_file(struct file *file)
 {
     struct inode *inode = file_inode(file);
     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(&fi->lock);
     if (list_empty(&ff->write_entry))
         list_add(&ff->write_entry, &fi->write_files);
     spin_unlock(&fi->lock);
 }
 
 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_STREAM)
         stream_open(inode, file);
     else 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(&fi->lock);
         fi->attr_version = atomic64_inc_return(&fc->attr_version);
         i_size_write(inode, 0);
         spin_unlock(&fi->lock);
         file_update_time(file);
         fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
     }
     if ((file->f_mode & FMODE_WRITE) && fc->writeback_cache)
         fuse_link_write_file(file);
 }
 
 int fuse_open_common(struct inode *inode, struct file *file, bool isdir)
 {
     struct fuse_mount *fm = get_fuse_mount(inode);
     struct fuse_conn *fc = fm->fc;
     int err;
     bool is_wb_truncate = (file->f_flags & O_TRUNC) &&
               fc->atomic_o_trunc &&
               fc->writeback_cache;
     bool dax_truncate = (file->f_flags & O_TRUNC) &&
               fc->atomic_o_trunc && FUSE_IS_DAX(inode);
 
     if (fuse_is_bad(inode))
         return -EIO;
 
     err = generic_file_open(inode, file);
     if (err)
         return err;
 
     if (is_wb_truncate || dax_truncate)
         inode_lock(inode);
 
     if (dax_truncate) {
         filemap_invalidate_lock(inode->i_mapping);
         err = fuse_dax_break_layouts(inode, 0, 0);
         if (err)
             goto out_inode_unlock;
     }
 
     if (is_wb_truncate || dax_truncate)
         fuse_set_nowrite(inode);
 
     err = fuse_do_open(fm, get_node_id(inode), file, isdir);
     if (!err)
         fuse_finish_open(inode, file);
 
     if (is_wb_truncate || dax_truncate)
         fuse_release_nowrite(inode);
     if (!err) {
         struct fuse_file *ff = file->private_data;
 
         if (fc->atomic_o_trunc && (file->f_flags & O_TRUNC))
             truncate_pagecache(inode, 0);
         else if (!(ff->open_flags & FOPEN_KEEP_CACHE))
             invalidate_inode_pages2(inode->i_mapping);
     }
     if (dax_truncate)
         filemap_invalidate_unlock(inode->i_mapping);
 out_inode_unlock:
     if (is_wb_truncate || dax_truncate)
         inode_unlock(inode);
 
     return err;
 }
 
 static void fuse_prepare_release(struct fuse_inode *fi, struct fuse_file *ff,
                  unsigned int flags, int opcode)
 {
     struct fuse_conn *fc = ff->fm->fc;
     struct fuse_release_args *ra = ff->release_args;
 
     /* Inode is NULL on error path of fuse_create_open() */
     if (likely(fi)) {
         spin_lock(&fi->lock);
         list_del(&ff->write_entry);
         spin_unlock(&fi->lock);
     }
     spin_lock(&fc->lock);
     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);
 
     ra->inarg.fh = ff->fh;
     ra->inarg.flags = flags;
     ra->args.in_numargs = 1;
     ra->args.in_args[0].size = sizeof(struct fuse_release_in);
     ra->args.in_args[0].value = &ra->inarg;
     ra->args.opcode = opcode;
     ra->args.nodeid = ff->nodeid;
     ra->args.force = true;
     ra->args.nocreds = true;
 }
 
 void fuse_file_release(struct inode *inode, struct fuse_file *ff,
                unsigned int open_flags, fl_owner_t id, bool isdir)
 {
     struct fuse_inode *fi = get_fuse_inode(inode);
     struct fuse_release_args *ra = ff->release_args;
     int opcode = isdir ? FUSE_RELEASEDIR : FUSE_RELEASE;
 
     fuse_prepare_release(fi, ff, open_flags, opcode);
 
     if (ff->flock) {
         ra->inarg.release_flags |= FUSE_RELEASE_FLOCK_UNLOCK;
         ra->inarg.lock_owner = fuse_lock_owner_id(ff->fm->fc, id);
     }
     /* Hold inode until release is finished */
     ra->inode = igrab(inode);
 
     /*
      * 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->fm->fc->destroy, isdir);
 }
 
 void fuse_release_common(struct file *file, bool isdir)
 {
     fuse_file_release(file_inode(file), file->private_data, file->f_flags,
               (fl_owner_t) file, isdir);
 }
 
 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)
 {
     struct fuse_conn *fc = get_fuse_conn(inode);
 
     /*
      * Dirty pages might remain despite write_inode_now() call from
      * fuse_flush() due to writes racing with the close.
      */
     if (fc->writeback_cache)
         write_inode_now(inode, 1);
 
     fuse_release_common(file, false);
 
     /* return value is ignored by VFS */
     return 0;
 }
 
 void fuse_sync_release(struct fuse_inode *fi, struct fuse_file *ff,
                unsigned int flags)
 {
     WARN_ON(refcount_read(&ff->count) > 1);
     fuse_prepare_release(fi, ff, flags, FUSE_RELEASE);
     /*
      * iput(NULL) is a no-op and since the refcount is 1 and everything's
      * synchronous, we are fine with not doing igrab() here"
      */
     fuse_file_put(ff, true, false);
 }
 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);
 }
 
 struct fuse_writepage_args {
     struct fuse_io_args ia;
     struct rb_node writepages_entry;
     struct list_head queue_entry;
     struct fuse_writepage_args *next;
     struct inode *inode;
     struct fuse_sync_bucket *bucket;
 };
 
 static struct fuse_writepage_args *fuse_find_writeback(struct fuse_inode *fi,
                         pgoff_t idx_from, pgoff_t idx_to)
 {
     struct rb_node *n;
 
     n = fi->writepages.rb_node;
 
     while (n) {
         struct fuse_writepage_args *wpa;
         pgoff_t curr_index;
 
         wpa = rb_entry(n, struct fuse_writepage_args, writepages_entry);
         WARN_ON(get_fuse_inode(wpa->inode) != fi);
         curr_index = wpa->ia.write.in.offset >> PAGE_SHIFT;
         if (idx_from >= curr_index + wpa->ia.ap.num_pages)
             n = n->rb_right;
         else if (idx_to < curr_index)
             n = n->rb_left;
         else
             return wpa;
     }
     return NULL;
 }
 
 /*
  * Check if any page in a range 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_range_is_writeback(struct inode *inode, pgoff_t idx_from,
                    pgoff_t idx_to)
 {
     struct fuse_inode *fi = get_fuse_inode(inode);
     bool found;
 
     spin_lock(&fi->lock);
     found = fuse_find_writeback(fi, idx_from, idx_to);
     spin_unlock(&fi->lock);
 
     return found;
 }
 
 static inline bool fuse_page_is_writeback(struct inode *inode, pgoff_t index)
 {
     return fuse_range_is_writeback(inode, index, index);
 }
 
 /*
  * 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 void 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));
 }
 
 /*
  * 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);
 }
 
 static int fuse_flush(struct file *file, fl_owner_t id)
 {
     struct inode *inode = file_inode(file);
     struct fuse_mount *fm = get_fuse_mount(inode);
     struct fuse_file *ff = file->private_data;
     struct fuse_flush_in inarg;
     FUSE_ARGS(args);
     int err;
 
     if (fuse_is_bad(inode))
         return -EIO;
 
     if (ff->open_flags & FOPEN_NOFLUSH && !fm->fc->writeback_cache)
         return 0;
 
     err = write_inode_now(inode, 1);
     if (err)
         return err;
 
     inode_lock(inode);
     fuse_sync_writes(inode);
     inode_unlock(inode);
 
     err = filemap_check_errors(file->f_mapping);
     if (err)
         return err;
 
     err = 0;
     if (fm->fc->no_flush)
         goto inval_attr_out;
 
     memset(&inarg, 0, sizeof(inarg));
     inarg.fh = ff->fh;
     inarg.lock_owner = fuse_lock_owner_id(fm->fc, id);
     args.opcode = FUSE_FLUSH;
     args.nodeid = get_node_id(inode);
     args.in_numargs = 1;
     args.in_args[0].size = sizeof(inarg);
     args.in_args[0].value = &inarg;
     args.force = true;
 
     err = fuse_simple_request(fm, &args);
     if (err == -ENOSYS) {
         fm->fc->no_flush = 1;
         err = 0;
     }
 
 inval_attr_out:
     /*
      * In memory i_blocks is not maintained by fuse, if writeback cache is
      * enabled, i_blocks from cached attr may not be accurate.
      */
     if (!err && fm->fc->writeback_cache)
         fuse_invalidate_attr_mask(inode, STATX_BLOCKS);
     return err;
 }
 
 int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
               int datasync, int opcode)
 {
     struct inode *inode = file->f_mapping->host;
     struct fuse_mount *fm = get_fuse_mount(inode);
     struct fuse_file *ff = file->private_data;
     FUSE_ARGS(args);
     struct fuse_fsync_in inarg;
 
     memset(&inarg, 0, sizeof(inarg));
     inarg.fh = ff->fh;
     inarg.fsync_flags = datasync ? FUSE_FSYNC_FDATASYNC : 0;
     args.opcode = opcode;
     args.nodeid = get_node_id(inode);
     args.in_numargs = 1;
     args.in_args[0].size = sizeof(inarg);
     args.in_args[0].value = &inarg;
     return fuse_simple_request(fm, &args);
 }
 
 static int fuse_fsync(struct file *file, loff_t start, loff_t end,
               int datasync)
 {
     struct inode *inode = file->f_mapping->host;
     struct fuse_conn *fc = get_fuse_conn(inode);
     int err;
 
     if (fuse_is_bad(inode))
         return -EIO;
 
     inode_lock(inode);
 
     /*
      * Start writeback against all dirty pages of the inode, then
      * wait for all outstanding writes, before sending the FSYNC
      * request.
      */
     err = file_write_and_wait_range(file, start, end);
     if (err)
         goto out;
 
     fuse_sync_writes(inode);
 
     /*
      * Due to implementation of fuse writeback
      * file_write_and_wait_range() does not catch errors.
      * We have to do this directly after fuse_sync_writes()
      */
     err = file_check_and_advance_wb_err(file);
     if (err)
         goto out;
 
     err = sync_inode_metadata(inode, 1);
     if (err)
         goto out;
 
     if (fc->no_fsync)
         goto out;
 
     err = fuse_fsync_common(file, start, end, datasync, FUSE_FSYNC);
     if (err == -ENOSYS) {
         fc->no_fsync = 1;
         err = 0;
     }
 out:
     inode_unlock(inode);
 
     return err;
 }
 
 void fuse_read_args_fill(struct fuse_io_args *ia, struct file *file, loff_t pos,
              size_t count, int opcode)
 {
     struct fuse_file *ff = file->private_data;
     struct fuse_args *args = &ia->ap.args;
 
     ia->read.in.fh = ff->fh;
     ia->read.in.offset = pos;
     ia->read.in.size = count;
     ia->read.in.flags = file->f_flags;
     args->opcode = opcode;
     args->nodeid = ff->nodeid;
     args->in_numargs = 1;
     args->in_args[0].size = sizeof(ia->read.in);
     args->in_args[0].value = &ia->read.in;
     args->out_argvar = true;
     args->out_numargs = 1;
     args->out_args[0].size = count;
 }
 
 static void fuse_release_user_pages(struct fuse_args_pages *ap,
                     bool should_dirty)
 {
     unsigned int i;
 
     for (i = 0; i < ap->num_pages; i++) {
         if (should_dirty)
             set_page_dirty_lock(ap->pages[i]);
         put_page(ap->pages[i]);
     }
 }
 
 static void fuse_io_release(struct kref *kref)
 {
     kfree(container_of(kref, struct fuse_io_priv, refcnt));
 }
 
 static ssize_t fuse_get_res_by_io(struct fuse_io_priv *io)
 {
     if (io->err)
         return io->err;
 
     if (io->bytes >= 0 && io->write)
         return -EIO;
 
     return io->bytes < 0 ? io->size : io->bytes;
 }
 
 /**
  * In case of short read, the caller sets 'pos' to the position of
  * actual end of fuse request in IO request. Otherwise, if bytes_requested
  * == bytes_transferred or rw == WRITE, the caller sets 'pos' to -1.
  *
  * An example:
  * User requested DIO read of 64K. It was split into two 32K fuse requests,
  * both submitted asynchronously. The first of them was ACKed by userspace as
  * fully completed (req->out.args[0].size == 32K) resulting in pos == -1. The
  * second request was ACKed as short, e.g. only 1K was read, resulting in
  * pos == 33K.
  *
  * Thus, when all fuse requests are completed, the minimal non-negative 'pos'
  * will be equal to the length of the longest contiguous fragment of
  * transferred data starting from the beginning of IO request.
  */
 static void fuse_aio_complete(struct fuse_io_priv *io, int err, ssize_t pos)
 {
     int left;
 
     spin_lock(&io->lock);
     if (err)
         io->err = io->err ? : err;
     else if (pos >= 0 && (io->bytes < 0 || pos < io->bytes))
         io->bytes = pos;
 
     left = --io->reqs;
     if (!left && io->blocking)
         complete(io->done);
     spin_unlock(&io->lock);
 
     if (!left && !io->blocking) {
         ssize_t res = fuse_get_res_by_io(io);
 
         if (res >= 0) {
             struct inode *inode = file_inode(io->iocb->ki_filp);
             struct fuse_conn *fc = get_fuse_conn(inode);
             struct fuse_inode *fi = get_fuse_inode(inode);
 
             spin_lock(&fi->lock);
             fi->attr_version = atomic64_inc_return(&fc->attr_version);
             spin_unlock(&fi->lock);
         }
 
         io->iocb->ki_complete(io->iocb, res);
     }
 
     kref_put(&io->refcnt, fuse_io_release);
 }
 
 static struct fuse_io_args *fuse_io_alloc(struct fuse_io_priv *io,
                       unsigned int npages)
 {
     struct fuse_io_args *ia;
 
     ia = kzalloc(sizeof(*ia), GFP_KERNEL);
     if (ia) {
         ia->io = io;
         ia->ap.pages = fuse_pages_alloc(npages, GFP_KERNEL,
                         &ia->ap.descs);
         if (!ia->ap.pages) {
             kfree(ia);
             ia = NULL;
         }
     }
     return ia;
 }
 
 static void fuse_io_free(struct fuse_io_args *ia)
 {
     kfree(ia->ap.pages);
     kfree(ia);
 }
 
 static void fuse_aio_complete_req(struct fuse_mount *fm, struct fuse_args *args,
                   int err)
 {
     struct fuse_io_args *ia = container_of(args, typeof(*ia), ap.args);
     struct fuse_io_priv *io = ia->io;
     ssize_t pos = -1;
 
     fuse_release_user_pages(&ia->ap, io->should_dirty);
 
     if (err) {
         /* Nothing */
     } else if (io->write) {
         if (ia->write.out.size > ia->write.in.size) {
             err = -EIO;
         } else if (ia->write.in.size != ia->write.out.size) {
             pos = ia->write.in.offset - io->offset +
                 ia->write.out.size;
         }
     } else {
         u32 outsize = args->out_args[0].size;
 
         if (ia->read.in.size != outsize)
             pos = ia->read.in.offset - io->offset + outsize;
     }
 
     fuse_aio_complete(io, err, pos);
     fuse_io_free(ia);
 }
 
 static ssize_t fuse_async_req_send(struct fuse_mount *fm,
                    struct fuse_io_args *ia, size_t num_bytes)
 {
     ssize_t err;
     struct fuse_io_priv *io = ia->io;
 
     spin_lock(&io->lock);
     kref_get(&io->refcnt);
     io->size += num_bytes;
     io->reqs++;
     spin_unlock(&io->lock);
 
     ia->ap.args.end = fuse_aio_complete_req;
     ia->ap.args.may_block = io->should_dirty;
     err = fuse_simple_background(fm, &ia->ap.args, GFP_KERNEL);
     if (err)
         fuse_aio_complete_req(fm, &ia->ap.args, err);
 
     return num_bytes;
 }
 
 static ssize_t fuse_send_read(struct fuse_io_args *ia, loff_t pos, size_t count,
                   fl_owner_t owner)
 {
     struct file *file = ia->io->iocb->ki_filp;
     struct fuse_file *ff = file->private_data;
     struct fuse_mount *fm = ff->fm;
 
     fuse_read_args_fill(ia, file, pos, count, FUSE_READ);
     if (owner != NULL) {
         ia->read.in.read_flags |= FUSE_READ_LOCKOWNER;
         ia->read.in.lock_owner = fuse_lock_owner_id(fm->fc, owner);
     }
 
     if (ia->io->async)
         return fuse_async_req_send(fm, ia, count);
 
     return fuse_simple_request(fm, &ia->ap.args);
 }
 
 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(&fi->lock);
     if (attr_ver >= fi->attr_version && size < inode->i_size &&
         !test_bit(FUSE_I_SIZE_UNSTABLE, &fi->state)) {
         fi->attr_version = atomic64_inc_return(&fc->attr_version);
         i_size_write(inode, size);
     }
     spin_unlock(&fi->lock);
 }
 
 static void fuse_short_read(struct inode *inode, u64 attr_ver, size_t num_read,
                 struct fuse_args_pages *ap)
 {
     struct fuse_conn *fc = get_fuse_conn(inode);
 
     /*
      * If writeback_cache is enabled, a short read means there's a hole in
      * the file.  Some data after the hole is in page cache, but has not
      * reached the client fs yet.  So the hole is not present there.
      */
     if (!fc->writeback_cache) {
         loff_t pos = page_offset(ap->pages[0]) + num_read;
         fuse_read_update_size(inode, pos, attr_ver);
     }
 }
 
 static int fuse_do_readpage(struct file *file, struct page *page)
 {
     struct inode *inode = page->mapping->host;
     struct fuse_mount *fm = get_fuse_mount(inode);
     loff_t pos = page_offset(page);
     struct fuse_page_desc desc = { .length = PAGE_SIZE };
     struct fuse_io_args ia = {
         .ap.args.page_zeroing = true,
         .ap.args.out_pages = true,
         .ap.num_pages = 1,
         .ap.pages = &page,
         .ap.descs = &desc,
     };
     ssize_t res;
     u64 attr_ver;
 
     /*
      * 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);
 
     attr_ver = fuse_get_attr_version(fm->fc);
 
     /* Don't overflow end offset */
     if (pos + (desc.length - 1) == LLONG_MAX)
         desc.length--;
 
     fuse_read_args_fill(&ia, file, pos, desc.length, FUSE_READ);
     res = fuse_simple_request(fm, &ia.ap.args);
     if (res < 0)
         return res;
     /*
      * Short read means EOF.  If file size is larger, truncate it
      */
     if (res < desc.length)
         fuse_short_read(inode, attr_ver, res, &ia.ap);
 
     SetPageUptodate(page);
 
     return 0;
 }
 
 static int fuse_read_folio(struct file *file, struct folio *folio)
 {
     struct page *page = &folio->page;
     struct inode *inode = page->mapping->host;
     int err;
 
     err = -EIO;
     if (fuse_is_bad(inode))
         goto out;
 
     err = fuse_do_readpage(file, page);
     fuse_invalidate_atime(inode);
  out:
     unlock_page(page);
     return err;
 }
 
 static void fuse_readpages_end(struct fuse_mount *fm, struct fuse_args *args,
                    int err)
 {
     int i;
     struct fuse_io_args *ia = container_of(args, typeof(*ia), ap.args);
     struct fuse_args_pages *ap = &ia->ap;
     size_t count = ia->read.in.size;
     size_t num_read = args->out_args[0].size;
     struct address_space *mapping = NULL;
 
     for (i = 0; mapping == NULL && i < ap->num_pages; i++)
         mapping = ap->pages[i]->mapping;
 
     if (mapping) {
         struct inode *inode = mapping->host;
 
         /*
          * Short read means EOF. If file size is larger, truncate it
          */
         if (!err && num_read < count)
             fuse_short_read(inode, ia->read.attr_ver, num_read, ap);
 
         fuse_invalidate_atime(inode);
     }
 
     for (i = 0; i < ap->num_pages; i++) {
         struct page *page = ap->pages[i];
 
         if (!err)
             SetPageUptodate(page);
         else
             SetPageError(page);
         unlock_page(page);
         put_page(page);
     }
     if (ia->ff)
         fuse_file_put(ia->ff, false, false);
 
     fuse_io_free(ia);
 }
 
 static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file)
 {
     struct fuse_file *ff = file->private_data;
     struct fuse_mount *fm = ff->fm;
     struct fuse_args_pages *ap = &ia->ap;
     loff_t pos = page_offset(ap->pages[0]);
     size_t count = ap->num_pages << PAGE_SHIFT;
     ssize_t res;
     int err;
 
     ap->args.out_pages = true;
     ap->args.page_zeroing = true;
     ap->args.page_replace = true;
 
     /* Don't overflow end offset */
     if (pos + (count - 1) == LLONG_MAX) {
         count--;
         ap->descs[ap->num_pages - 1].length--;
     }
     WARN_ON((loff_t) (pos + count) < 0);
 
     fuse_read_args_fill(ia, file, pos, count, FUSE_READ);
     ia->read.attr_ver = fuse_get_attr_version(fm->fc);
     if (fm->fc->async_read) {
         ia->ff = fuse_file_get(ff);
         ap->args.end = fuse_readpages_end;
         err = fuse_simple_background(fm, &ap->args, GFP_KERNEL);
         if (!err)
             return;
     } else {
         res = fuse_simple_request(fm, &ap->args);
         err = res < 0 ? res : 0;
     }
     fuse_readpages_end(fm, &ap->args, err);
 }
 
 static void fuse_readahead(struct readahead_control *rac)
 {
     struct inode *inode = rac->mapping->host;
     struct fuse_conn *fc = get_fuse_conn(inode);
     unsigned int i, max_pages, nr_pages = 0;
 
     if (fuse_is_bad(inode))
         return;
 
     max_pages = min_t(unsigned int, fc->max_pages,
             fc->max_read / PAGE_SIZE);
 
     for (;;) {
         struct fuse_io_args *ia;
         struct fuse_args_pages *ap;
 
         if (fc->num_background >= fc->congestion_threshold &&
             rac->ra->async_size >= readahead_count(rac))
             /*
              * Congested and only async pages left, so skip the
              * rest.
              */
             break;
 
         nr_pages = readahead_count(rac) - nr_pages;
         if (nr_pages > max_pages)
             nr_pages = max_pages;
         if (nr_pages == 0)
             break;
         ia = fuse_io_alloc(NULL, nr_pages);
         if (!ia)
             return;
         ap = &ia->ap;
         nr_pages = __readahead_batch(rac, ap->pages, nr_pages);
         for (i = 0; i < nr_pages; i++) {
             fuse_wait_on_page_writeback(inode,
                             readahead_index(rac) + i);
             ap->descs[i].length = PAGE_SIZE;
         }
         ap->num_pages = nr_pages;
         fuse_send_readpages(ia, rac->file);
     }
 }
 
 static ssize_t fuse_cache_read_iter(struct kiocb *iocb, struct iov_iter *to)
 {
     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 ||
         (iocb->ki_pos + iov_iter_count(to) > i_size_read(inode))) {
         int err;
         err = fuse_update_attributes(inode, iocb->ki_filp, STATX_SIZE);
         if (err)
             return err;
     }
 
     return generic_file_read_iter(iocb, to);
 }
 
 static void fuse_write_args_fill(struct fuse_io_args *ia, struct fuse_file *ff,
                  loff_t pos, size_t count)
 {
     struct fuse_args *args = &ia->ap.args;
 
     ia->write.in.fh = ff->fh;
     ia->write.in.offset = pos;
     ia->write.in.size = count;
     args->opcode = FUSE_WRITE;
     args->nodeid = ff->nodeid;
     args->in_numargs = 2;
     if (ff->fm->fc->minor < 9)
         args->in_args[0].size = FUSE_COMPAT_WRITE_IN_SIZE;
     else
         args->in_args[0].size = sizeof(ia->write.in);
     args->in_args[0].value = &ia->write.in;
     args->in_args[1].size = count;
     args->out_numargs = 1;
     args->out_args[0].size = sizeof(ia->write.out);
     args->out_args[0].value = &ia->write.out;
 }
 
 static unsigned int fuse_write_flags(struct kiocb *iocb)
 {
     unsigned int flags = iocb->ki_filp->f_flags;
 
     if (iocb_is_dsync(iocb))
         flags |= O_DSYNC;
     if (iocb->ki_flags & IOCB_SYNC)
         flags |= O_SYNC;
 
     return flags;
 }
 
 static ssize_t fuse_send_write(struct fuse_io_args *ia, loff_t pos,
                    size_t count, fl_owner_t owner)
 {
     struct kiocb *iocb = ia->io->iocb;
     struct file *file = iocb->ki_filp;
     struct fuse_file *ff = file->private_data;
     struct fuse_mount *fm = ff->fm;
     struct fuse_write_in *inarg = &ia->write.in;
     ssize_t err;
 
     fuse_write_args_fill(ia, ff, pos, count);
     inarg->flags = fuse_write_flags(iocb);
     if (owner != NULL) {
         inarg->write_flags |= FUSE_WRITE_LOCKOWNER;
         inarg->lock_owner = fuse_lock_owner_id(fm->fc, owner);
     }
 
     if (ia->io->async)
         return fuse_async_req_send(fm, ia, count);
 
     err = fuse_simple_request(fm, &ia->ap.args);
     if (!err && ia->write.out.size > count)
         err = -EIO;
 
     return err ?: ia->write.out.size;
 }
 
 bool fuse_write_update_attr(struct inode *inode, loff_t pos, ssize_t written)
 {
     struct fuse_conn *fc = get_fuse_conn(inode);
     struct fuse_inode *fi = get_fuse_inode(inode);
     bool ret = false;
 
     spin_lock(&fi->lock);
     fi->attr_version = atomic64_inc_return(&fc->attr_version);
     if (written > 0 && pos > inode->i_size) {
         i_size_write(inode, pos);
         ret = true;
     }
     spin_unlock(&fi->lock);
 
     fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
 
     return ret;
 }
 
 static ssize_t fuse_send_write_pages(struct fuse_io_args *ia,
                      struct kiocb *iocb, struct inode *inode,
                      loff_t pos, size_t count)
 {
     struct fuse_args_pages *ap = &ia->ap;
     struct file *file = iocb->ki_filp;
     struct fuse_file *ff = file->private_data;
     struct fuse_mount *fm = ff->fm;
     unsigned int offset, i;
     bool short_write;
     int err;
 
     for (i = 0; i < ap->num_pages; i++)
         fuse_wait_on_page_writeback(inode, ap->pages[i]->index);
 
     fuse_write_args_fill(ia, ff, pos, count);
     ia->write.in.flags = fuse_write_flags(iocb);
     if (fm->fc->handle_killpriv_v2 && !capable(CAP_FSETID))
         ia->write.in.write_flags |= FUSE_WRITE_KILL_SUIDGID;
 
     err = fuse_simple_request(fm, &ap->args);
     if (!err && ia->write.out.size > count)
         err = -EIO;
 
     short_write = ia->write.out.size < count;
     offset = ap->descs[0].offset;
     count = ia->write.out.size;
     for (i = 0; i < ap->num_pages; i++) {
         struct page *page = ap->pages[i];
 
         if (err) {
             ClearPageUptodate(page);
         } else {
             if (count >= PAGE_SIZE - offset)
                 count -= PAGE_SIZE - offset;
             else {
                 if (short_write)
                     ClearPageUptodate(page);
                 count = 0;
             }
             offset = 0;
         }
         if (ia->write.page_locked && (i == ap->num_pages - 1))
             unlock_page(page);
         put_page(page);
     }
 
     return err;
 }
 
 static ssize_t fuse_fill_write_pages(struct fuse_io_args *ia,
                      struct address_space *mapping,
                      struct iov_iter *ii, loff_t pos,
                      unsigned int max_pages)
 {
     struct fuse_args_pages *ap = &ia->ap;
     struct fuse_conn *fc = get_fuse_conn(mapping->host);
     unsigned offset = pos & (PAGE_SIZE - 1);
     size_t count = 0;
     int err;
 
     ap->args.in_pages = true;
     ap->descs[0].offset = offset;
 
     do {
         size_t tmp;
         struct page *page;
         pgoff_t index = pos >> PAGE_SHIFT;
         size_t bytes = min_t(size_t, PAGE_SIZE - offset,
                      iov_iter_count(ii));
 
         bytes = min_t(size_t, bytes, fc->max_write - count);
 
  again:
         err = -EFAULT;
         if (fault_in_iov_iter_readable(ii, bytes))
             break;
 
         err = -ENOMEM;
         page = grab_cache_page_write_begin(mapping, index);
         if (!page)
             break;
 
         if (mapping_writably_mapped(mapping))
             flush_dcache_page(page);
 
         tmp = copy_page_from_iter_atomic(page, offset, bytes, ii);
         flush_dcache_page(page);
 
         if (!tmp) {
             unlock_page(page);
             put_page(page);
             goto again;
         }
 
         err = 0;
         ap->pages[ap->num_pages] = page;
         ap->descs[ap->num_pages].length = tmp;
         ap->num_pages++;
 
         count += tmp;
         pos += tmp;
         offset += tmp;
         if (offset == PAGE_SIZE)
             offset = 0;
 
         /* If we copied full page, mark it uptodate */
         if (tmp == PAGE_SIZE)
             SetPageUptodate(page);
 
         if (PageUptodate(page)) {
             unlock_page(page);
         } else {
             ia->write.page_locked = true;
             break;
         }
         if (!fc->big_writes)
             break;
     } while (iov_iter_count(ii) && count < fc->max_write &&
          ap->num_pages < max_pages && offset == 0);
 
     return count > 0 ? count : err;
 }
 
 static inline unsigned int fuse_wr_pages(loff_t pos, size_t len,
                      unsigned int max_pages)
 {
     return min_t(unsigned int,
              ((pos + len - 1) >> PAGE_SHIFT) -
              (pos >> PAGE_SHIFT) + 1,
              max_pages);
 }
 
 static ssize_t fuse_perform_write(struct kiocb *iocb,
                   struct address_space *mapping,
                   struct iov_iter *ii, loff_t pos)
 {
     struct inode *inode = mapping->host;
     struct fuse_conn *fc = get_fuse_conn(inode);
     struct fuse_inode *fi = get_fuse_inode(inode);
     int err = 0;
     ssize_t res = 0;
 
     if (inode->i_size < pos + iov_iter_count(ii))
         set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
 
     do {
         ssize_t count;
         struct fuse_io_args ia = {};
         struct fuse_args_pages *ap = &ia.ap;
         unsigned int nr_pages = fuse_wr_pages(pos, iov_iter_count(ii),
                               fc->max_pages);
 
         ap->pages = fuse_pages_alloc(nr_pages, GFP_KERNEL, &ap->descs);
         if (!ap->pages) {
             err = -ENOMEM;
             break;
         }
 
         count = fuse_fill_write_pages(&ia, mapping, ii, pos, nr_pages);
         if (count <= 0) {
             err = count;
         } else {
             err = fuse_send_write_pages(&ia, iocb, inode,
                             pos, count);
             if (!err) {
                 size_t num_written = ia.write.out.size;
 
                 res += num_written;
                 pos += num_written;
 
                 /* break out of the loop on short write */
                 if (num_written != count)
                     err = -EIO;
             }
         }
         kfree(ap->pages);
     } while (!err && iov_iter_count(ii));
 
     fuse_write_update_attr(inode, pos, res);
     clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
 
     return res > 0 ? res : err;
 }
 
 static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
     struct file *file = iocb->ki_filp;
     struct address_space *mapping = file->f_mapping;
     ssize_t written = 0;
     ssize_t written_buffered = 0;
     struct inode *inode = mapping->host;
     ssize_t err;
     struct fuse_conn *fc = get_fuse_conn(inode);
     loff_t endbyte = 0;
 
     if (fc->writeback_cache) {
         /* Update size (EOF optimization) and mode (SUID clearing) */
         err = fuse_update_attributes(mapping->host, file,
                          STATX_SIZE | STATX_MODE);
         if (err)
             return err;
 
         if (fc->handle_killpriv_v2 &&
             should_remove_suid(file_dentry(file))) {
             goto writethrough;
         }
 
         return generic_file_write_iter(iocb, from);
     }
 
 writethrough:
     inode_lock(inode);
 
     /* We can write back this queue in page reclaim */
     current->backing_dev_info = inode_to_bdi(inode);
 
     err = generic_write_checks(iocb, from);
     if (err <= 0)
         goto out;
 
     err = file_remove_privs(file);
     if (err)
         goto out;
 
     err = file_update_time(file);
     if (err)
         goto out;
 
     if (iocb->ki_flags & IOCB_DIRECT) {
         loff_t pos = iocb->ki_pos;
         written = generic_file_direct_write(iocb, from);
         if (written < 0 || !iov_iter_count(from))
             goto out;
 
         pos += written;
 
         written_buffered = fuse_perform_write(iocb, mapping, from, 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_SHIFT,
                      endbyte >> PAGE_SHIFT);
 
         written += written_buffered;
         iocb->ki_pos = pos + written_buffered;
     } else {
         written = fuse_perform_write(iocb, mapping, from, iocb->ki_pos);
         if (written >= 0)
             iocb->ki_pos += written;
     }
 out:
     current->backing_dev_info = NULL;
     inode_unlock(inode);
     if (written > 0)
         written = generic_write_sync(iocb, written);
 
     return written ? written : err;
 }
 
 static inline unsigned long fuse_get_user_addr(const struct iov_iter *ii)
 {
     return (unsigned long)ii->iov->iov_base + ii->iov_offset;
 }
 
 static inline size_t fuse_get_frag_size(const struct iov_iter *ii,
                     size_t max_size)
 {
     return min(iov_iter_single_seg_count(ii), max_size);
 }
 
 static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
                    size_t *nbytesp, int write,
                    unsigned int max_pages)
 {
     size_t nbytes = 0;  /* # bytes already packed in req */
     ssize_t ret = 0;
 
     /* Special case for kernel I/O: can copy directly into the buffer */
     if (iov_iter_is_kvec(ii)) {
         unsigned long user_addr = fuse_get_user_addr(ii);
         size_t frag_size = fuse_get_frag_size(ii, *nbytesp);
 
         if (write)
             ap->args.in_args[1].value = (void *) user_addr;
         else
             ap->args.out_args[0].value = (void *) user_addr;
 
         iov_iter_advance(ii, frag_size);
         *nbytesp = frag_size;
         return 0;
     }
 
     while (nbytes < *nbytesp && ap->num_pages < max_pages) {
         unsigned npages;
         size_t start;
         ret = iov_iter_get_pages2(ii, &ap->pages[ap->num_pages],
                     *nbytesp - nbytes,
                     max_pages - ap->num_pages,
                     &start);
         if (ret < 0)
             break;
 
         nbytes += ret;
 
         ret += start;
         npages = DIV_ROUND_UP(ret, PAGE_SIZE);
 
         ap->descs[ap->num_pages].offset = start;
         fuse_page_descs_length_init(ap->descs, ap->num_pages, npages);
 
         ap->num_pages += npages;
         ap->descs[ap->num_pages - 1].length -=
             (PAGE_SIZE - ret) & (PAGE_SIZE - 1);
     }
 
     ap->args.user_pages = true;
     if (write)
         ap->args.in_pages = true;
     else
         ap->args.out_pages = true;
 
     *nbytesp = nbytes;
 
     return ret < 0 ? ret : 0;
 }
 
 ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
                loff_t *ppos, int flags)
 {
     int write = flags & FUSE_DIO_WRITE;
     int cuse = flags & FUSE_DIO_CUSE;
     struct file *file = io->iocb->ki_filp;
     struct inode *inode = file->f_mapping->host;
     struct fuse_file *ff = file->private_data;
     struct fuse_conn *fc = ff->fm->fc;
     size_t nmax = write ? fc->max_write : fc->max_read;
     loff_t pos = *ppos;
     size_t count = iov_iter_count(iter);
     pgoff_t idx_from = pos >> PAGE_SHIFT;
     pgoff_t idx_to = (pos + count - 1) >> PAGE_SHIFT;
     ssize_t res = 0;
     int err = 0;
     struct fuse_io_args *ia;
     unsigned int max_pages;
 
     max_pages = iov_iter_npages(iter, fc->max_pages);
     ia = fuse_io_alloc(io, max_pages);
     if (!ia)
         return -ENOMEM;
 
     if (!cuse && fuse_range_is_writeback(inode, idx_from, idx_to)) {
         if (!write)
             inode_lock(inode);
         fuse_sync_writes(inode);
         if (!write)
             inode_unlock(inode);
     }
 
     io->should_dirty = !write && user_backed_iter(iter);
     while (count) {
         ssize_t nres;
         fl_owner_t owner = current->files;
         size_t nbytes = min(count, nmax);
 
         err = fuse_get_user_pages(&ia->ap, iter, &nbytes, write,
                       max_pages);
         if (err && !nbytes)
             break;
 
         if (write) {
             if (!capable(CAP_FSETID))
                 ia->write.in.write_flags |= FUSE_WRITE_KILL_SUIDGID;
 
             nres = fuse_send_write(ia, pos, nbytes, owner);
         } else {
             nres = fuse_send_read(ia, pos, nbytes, owner);
         }
 
         if (!io->async || nres < 0) {
             fuse_release_user_pages(&ia->ap, io->should_dirty);
             fuse_io_free(ia);
         }
         ia = NULL;
         if (nres < 0) {
             iov_iter_revert(iter, nbytes);
             err = nres;
             break;
         }
         WARN_ON(nres > nbytes);
 
         count -= nres;
         res += nres;
         pos += nres;
         if (nres != nbytes) {
             iov_iter_revert(iter, nbytes - nres);
             break;
         }
         if (count) {
             max_pages = iov_iter_npages(iter, fc->max_pages);
             ia = fuse_io_alloc(io, max_pages);
             if (!ia)
                 break;
         }
     }
     if (ia)
         fuse_io_free(ia);
     if (res > 0)
         *ppos = pos;
 
     return res > 0 ? res : err;
 }
 EXPORT_SYMBOL_GPL(fuse_direct_io);
 
 static ssize_t __fuse_direct_read(struct fuse_io_priv *io,
                   struct iov_iter *iter,
                   loff_t *ppos)
 {
     ssize_t res;
     struct inode *inode = file_inode(io->iocb->ki_filp);
 
     res = fuse_direct_io(io, iter, ppos, 0);
 
     fuse_invalidate_atime(inode);
 
     return res;
 }
 
 static ssize_t fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter);
 
 static ssize_t fuse_direct_read_iter(struct kiocb *iocb, struct iov_iter *to)
 {
     ssize_t res;
 
     if (!is_sync_kiocb(iocb) && iocb->ki_flags & IOCB_DIRECT) {
         res = fuse_direct_IO(iocb, to);
     } else {
         struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);
 
         res = __fuse_direct_read(&io, to, &iocb->ki_pos);
     }
 
     return res;
 }
 
 static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
     struct inode *inode = file_inode(iocb->ki_filp);
     struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);
     ssize_t res;
 
     /* Don't allow parallel writes to the same file */
     inode_lock(inode);
     res = generic_write_checks(iocb, from);
     if (res > 0) {
         if (!is_sync_kiocb(iocb) && iocb->ki_flags & IOCB_DIRECT) {
             res = fuse_direct_IO(iocb, from);
         } else {
             res = fuse_direct_io(&io, from, &iocb->ki_pos,
                          FUSE_DIO_WRITE);
             fuse_write_update_attr(inode, iocb->ki_pos, res);
         }
     }
     inode_unlock(inode);
 
     return res;
 }
 
 static ssize_t fuse_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 {
     struct file *file = iocb->ki_filp;
     struct fuse_file *ff = file->private_data;
     struct inode *inode = file_inode(file);
 
     if (fuse_is_bad(inode))
         return -EIO;
 
     if (FUSE_IS_DAX(inode))
         return fuse_dax_read_iter(iocb, to);
 
     if (!(ff->open_flags & FOPEN_DIRECT_IO))
         return fuse_cache_read_iter(iocb, to);
     else
         return fuse_direct_read_iter(iocb, to);
 }
 
 static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
     struct file *file = iocb->ki_filp;
     struct fuse_file *ff = file->private_data;
     struct inode *inode = file_inode(file);
 
     if (fuse_is_bad(inode))
         return -EIO;
 
     if (FUSE_IS_DAX(inode))
         return fuse_dax_write_iter(iocb, from);
 
     if (!(ff->open_flags & FOPEN_DIRECT_IO))
         return fuse_cache_write_iter(iocb, from);
     else
         return fuse_direct_write_iter(iocb, from);
 }
 
 static void fuse_writepage_free(struct fuse_writepage_args *wpa)
 {
     struct fuse_args_pages *ap = &wpa->ia.ap;
     int i;
 
     if (wpa->bucket)
         fuse_sync_bucket_dec(wpa->bucket);
 
     for (i = 0; i < ap->num_pages; i++)
         __free_page(ap->pages[i]);
 
     if (wpa->ia.ff)
         fuse_file_put(wpa->ia.ff, false, false);
 
     kfree(ap->pages);
     kfree(wpa);
 }
 
 static void fuse_writepage_finish(struct fuse_mount *fm,
                   struct fuse_writepage_args *wpa)
 {
     struct fuse_args_pages *ap = &wpa->ia.ap;
     struct inode *inode = wpa->inode;
     struct fuse_inode *fi = get_fuse_inode(inode);
     struct backing_dev_info *bdi = inode_to_bdi(inode);
     int i;
 
     for (i = 0; i < ap->num_pages; i++) {
         dec_wb_stat(&bdi->wb, WB_WRITEBACK);
         dec_node_page_state(ap->pages[i], NR_WRITEBACK_TEMP);
         wb_writeout_inc(&bdi->wb);
     }
     wake_up(&fi->page_waitq);
 }
 
 /* Called under fi->lock, may release and reacquire it */
 static void fuse_send_writepage(struct fuse_mount *fm,
                 struct fuse_writepage_args *wpa, loff_t size)
 __releases(fi->lock)
 __acquires(fi->lock)
 {
     struct fuse_writepage_args *aux, *next;
     struct fuse_inode *fi = get_fuse_inode(wpa->inode);
     struct fuse_write_in *inarg = &wpa->ia.write.in;
     struct fuse_args *args = &wpa->ia.ap.args;
     __u64 data_size = wpa->ia.ap.num_pages * PAGE_SIZE;
     int err;
 
     fi->writectr++;
     if (inarg->offset + data_size <= size) {
         inarg->size = data_size;
     } else if (inarg->offset < size) {
         inarg->size = size - inarg->offset;
     } else {
         /* Got truncated off completely */
         goto out_free;
     }
 
     args->in_args[1].size = inarg->size;
     args->force = true;
     args->nocreds = true;
 
     err = fuse_simple_background(fm, args, GFP_ATOMIC);
     if (err == -ENOMEM) {
         spin_unlock(&fi->lock);
         err = fuse_simple_background(fm, args, GFP_NOFS | __GFP_NOFAIL);
         spin_lock(&fi->lock);
     }
 
     /* Fails on broken connection only */
     if (unlikely(err))
         goto out_free;
 
     return;
 
  out_free:
     fi->writectr--;
     rb_erase(&wpa->writepages_entry, &fi->writepages);
     fuse_writepage_finish(fm, wpa);
     spin_unlock(&fi->lock);
 
     /* After fuse_writepage_finish() aux request list is private */
     for (aux = wpa->next; aux; aux = next) {
         next = aux->next;
         aux->next = NULL;
         fuse_writepage_free(aux);
     }
 
     fuse_writepage_free(wpa);
     spin_lock(&fi->lock);
 }
 
 /*
  * If fi->writectr is positive (no truncate or fsync going on) send
  * all queued writepage requests.
  *
  * Called with fi->lock
  */
 void fuse_flush_writepages(struct inode *inode)
 __releases(fi->lock)
 __acquires(fi->lock)
 {
     struct fuse_mount *fm = get_fuse_mount(inode);
     struct fuse_inode *fi = get_fuse_inode(inode);
     loff_t crop = i_size_read(inode);
     struct fuse_writepage_args *wpa;
 
     while (fi->writectr >= 0 && !list_empty(&fi->queued_writes)) {
         wpa = list_entry(fi->queued_writes.next,
                  struct fuse_writepage_args, queue_entry);
         list_del_init(&wpa->queue_entry);
         fuse_send_writepage(fm, wpa, crop);
     }
 }
 
 static struct fuse_writepage_args *fuse_insert_writeback(struct rb_root *root,
                         struct fuse_writepage_args *wpa)
 {
     pgoff_t idx_from = wpa->ia.write.in.offset >> PAGE_SHIFT;
     pgoff_t idx_to = idx_from + wpa->ia.ap.num_pages - 1;
     struct rb_node **p = &root->rb_node;
     struct rb_node  *parent = NULL;
 
     WARN_ON(!wpa->ia.ap.num_pages);
     while (*p) {
         struct fuse_writepage_args *curr;
         pgoff_t curr_index;
 
         parent = *p;
         curr = rb_entry(parent, struct fuse_writepage_args,
                 writepages_entry);
         WARN_ON(curr->inode != wpa->inode);
         curr_index = curr->ia.write.in.offset >> PAGE_SHIFT;
 
         if (idx_from >= curr_index + curr->ia.ap.num_pages)
             p = &(*p)->rb_right;
         else if (idx_to < curr_index)
             p = &(*p)->rb_left;
         else
             return curr;
     }
 
     rb_link_node(&wpa->writepages_entry, parent, p);
     rb_insert_color(&wpa->writepages_entry, root);
     return NULL;
 }
 
 static void tree_insert(struct rb_root *root, struct fuse_writepage_args *wpa)
 {
     WARN_ON(fuse_insert_writeback(root, wpa));
 }
 
 static void fuse_writepage_end(struct fuse_mount *fm, struct fuse_args *args,
                    int error)
 {
     struct fuse_writepage_args *wpa =
         container_of(args, typeof(*wpa), ia.ap.args);
     struct inode *inode = wpa->inode;
     struct fuse_inode *fi = get_fuse_inode(inode);
     struct fuse_conn *fc = get_fuse_conn(inode);
 
     mapping_set_error(inode->i_mapping, error);
     /*
      * A writeback finished and this might have updated mtime/ctime on
      * server making local mtime/ctime stale.  Hence invalidate attrs.
      * Do this only if writeback_cache is not enabled.  If writeback_cache
      * is enabled, we trust local ctime/mtime.
      */
     if (!fc->writeback_cache)
         fuse_invalidate_attr_mask(inode, FUSE_STATX_MODIFY);
     spin_lock(&fi->lock);
     rb_erase(&wpa->writepages_entry, &fi->writepages);
     while (wpa->next) {
         struct fuse_mount *fm = get_fuse_mount(inode);
         struct fuse_write_in *inarg = &wpa->ia.write.in;
         struct fuse_writepage_args *next = wpa->next;
 
         wpa->next = next->next;
         next->next = NULL;
         next->ia.ff = fuse_file_get(wpa->ia.ff);
         tree_insert(&fi->writepages, next);
 
         /*
          * Skip fuse_flush_writepages() to make it easy to crop requests
          * based on primary request size.
          *
          * 1st case (trivial): there are no concurrent activities using
          * fuse_set/release_nowrite.  Then we're on safe side because
          * fuse_flush_writepages() would call fuse_send_writepage()
          * anyway.
          *
          * 2nd case: someone called fuse_set_nowrite and it is waiting
          * now for completion of all in-flight requests.  This happens
          * rarely and no more than once per page, so this should be
          * okay.
          *
          * 3rd case: someone (e.g. fuse_do_setattr()) is in the middle
          * of fuse_set_nowrite..fuse_release_nowrite section.  The fact
          * that fuse_set_nowrite returned implies that all in-flight
          * requests were completed along with all of their secondary
          * requests.  Further primary requests are blocked by negative
          * writectr.  Hence there cannot be any in-flight requests and
          * no invocations of fuse_writepage_end() while we're in
          * fuse_set_nowrite..fuse_release_nowrite section.
          */
         fuse_send_writepage(fm, next, inarg->offset + inarg->size);
     }
     fi->writectr--;
     fuse_writepage_finish(fm, wpa);
     spin_unlock(&fi->lock);
     fuse_writepage_free(wpa);
 }
 
 static struct fuse_file *__fuse_write_file_get(struct fuse_inode *fi)
 {
     struct fuse_file *ff;
 
     spin_lock(&fi->lock);
     ff = list_first_entry_or_null(&fi->write_files, struct fuse_file,
                       write_entry);
     if (ff)
         fuse_file_get(ff);
     spin_unlock(&fi->lock);
 
     return ff;
 }
 
 static struct fuse_file *fuse_write_file_get(struct fuse_inode *fi)
 {
     struct fuse_file *ff = __fuse_write_file_get(fi);
     WARN_ON(!ff);
     return ff;
 }
 
 int fuse_write_inode(struct inode *inode, struct writeback_control *wbc)
 {
     struct fuse_inode *fi = get_fuse_inode(inode);
     struct fuse_file *ff;
     int err;
 
     /*
      * Inode is always written before the last reference is dropped and
      * hence this should not be reached from reclaim.
      *
      * Writing back the inode from reclaim can deadlock if the request
      * processing itself needs an allocation.  Allocations triggering
      * reclaim while serving a request can't be prevented, because it can
      * involve any number of unrelated userspace processes.
      */
     WARN_ON(wbc->for_reclaim);
 
     ff = __fuse_write_file_get(fi);
     err = fuse_flush_times(inode, ff);
     if (ff)
         fuse_file_put(ff, false, false);
 
     return err;
 }
 
 static struct fuse_writepage_args *fuse_writepage_args_alloc(void)
 {
     struct fuse_writepage_args *wpa;
     struct fuse_args_pages *ap;
 
     wpa = kzalloc(sizeof(*wpa), GFP_NOFS);
     if (wpa) {
         ap = &wpa->ia.ap;
         ap->num_pages = 0;
         ap->pages = fuse_pages_alloc(1, GFP_NOFS, &ap->descs);
         if (!ap->pages) {
             kfree(wpa);
             wpa = NULL;
         }
     }
     return wpa;
 
 }
 
 static void fuse_writepage_add_to_bucket(struct fuse_conn *fc,
                      struct fuse_writepage_args *wpa)
 {
     if (!fc->sync_fs)
         return;
 
     rcu_read_lock();
     /* Prevent resurrection of dead bucket in unlikely race with syncfs */
     do {
         wpa->bucket = rcu_dereference(fc->curr_bucket);
     } while (unlikely(!atomic_inc_not_zero(&wpa->bucket->count)));
     rcu_read_unlock();
 }
 
 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_writepage_args *wpa;
     struct fuse_args_pages *ap;
     struct page *tmp_page;
     int error = -ENOMEM;
 
     set_page_writeback(page);
 
     wpa = fuse_writepage_args_alloc();
     if (!wpa)
         goto err;
     ap = &wpa->ia.ap;
 
     tmp_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
     if (!tmp_page)
         goto err_free;
 
     error = -EIO;
     wpa->ia.ff = fuse_write_file_get(fi);
     if (!wpa->ia.ff)
         goto err_nofile;
 
     fuse_writepage_add_to_bucket(fc, wpa);
     fuse_write_args_fill(&wpa->ia, wpa->ia.ff, page_offset(page), 0);
 
     copy_highpage(tmp_page, page);
     wpa->ia.write.in.write_flags |= FUSE_WRITE_CACHE;
     wpa->next = NULL;
     ap->args.in_pages = true;
     ap->num_pages = 1;
     ap->pages[0] = tmp_page;
     ap->descs[0].offset = 0;
     ap->descs[0].length = PAGE_SIZE;
     ap->args.end = fuse_writepage_end;
     wpa->inode = inode;
 
     inc_wb_stat(&inode_to_bdi(inode)->wb, WB_WRITEBACK);
     inc_node_page_state(tmp_page, NR_WRITEBACK_TEMP);
 
     spin_lock(&fi->lock);
     tree_insert(&fi->writepages, wpa);
     list_add_tail(&wpa->queue_entry, &fi->queued_writes);
     fuse_flush_writepages(inode);
     spin_unlock(&fi->lock);
 
     end_page_writeback(page);
 
     return 0;
 
 err_nofile:
     __free_page(tmp_page);
 err_free:
     kfree(wpa);
 err:
     mapping_set_error(page->mapping, error);
     end_page_writeback(page);
     return error;
 }
 
 static int fuse_writepage(struct page *page, struct writeback_control *wbc)
 {
     struct fuse_conn *fc = get_fuse_conn(page->mapping->host);
     int err;
 
     if (fuse_page_is_writeback(page->mapping->host, page->index)) {
         /*
          * ->writepages() should be called for sync() and friends.  We
          * should only get here on direct reclaim and then we are
          * allowed to skip a page which is already in flight
          */
         WARN_ON(wbc->sync_mode == WB_SYNC_ALL);
 
         redirty_page_for_writepage(wbc, page);
         unlock_page(page);
         return 0;
     }
 
     if (wbc->sync_mode == WB_SYNC_NONE &&
         fc->num_background >= fc->congestion_threshold)
         return AOP_WRITEPAGE_ACTIVATE;
 
     err = fuse_writepage_locked(page);
     unlock_page(page);
 
     return err;
 }
 
 struct fuse_fill_wb_data {
     struct fuse_writepage_args *wpa;
     struct fuse_file *ff;
     struct inode *inode;
     struct page **orig_pages;
     unsigned int max_pages;
 };
 
 static bool fuse_pages_realloc(struct fuse_fill_wb_data *data)
 {
     struct fuse_args_pages *ap = &data->wpa->ia.ap;
     struct fuse_conn *fc = get_fuse_conn(data->inode);
     struct page **pages;
     struct fuse_page_desc *descs;
     unsigned int npages = min_t(unsigned int,
                     max_t(unsigned int, data->max_pages * 2,
                       FUSE_DEFAULT_MAX_PAGES_PER_REQ),
                     fc->max_pages);
     WARN_ON(npages <= data->max_pages);
 
     pages = fuse_pages_alloc(npages, GFP_NOFS, &descs);
     if (!pages)
         return false;
 
     memcpy(pages, ap->pages, sizeof(struct page *) * ap->num_pages);
     memcpy(descs, ap->descs, sizeof(struct fuse_page_desc) * ap->num_pages);
     kfree(ap->pages);
     ap->pages = pages;
     ap->descs = descs;
     data->max_pages = npages;
 
     return true;
 }
 
 static void fuse_writepages_send(struct fuse_fill_wb_data *data)
 {
     struct fuse_writepage_args *wpa = data->wpa;
     struct inode *inode = data->inode;
     struct fuse_inode *fi = get_fuse_inode(inode);
     int num_pages = wpa->ia.ap.num_pages;
     int i;
 
     wpa->ia.ff = fuse_file_get(data->ff);
     spin_lock(&fi->lock);
     list_add_tail(&wpa->queue_entry, &fi->queued_writes);
     fuse_flush_writepages(inode);
     spin_unlock(&fi->lock);
 
     for (i = 0; i < num_pages; i++)
         end_page_writeback(data->orig_pages[i]);
 }
 
 /*
  * Check under fi->lock if the page is under writeback, and insert it onto the
  * rb_tree if not. Otherwise iterate auxiliary write requests, to see if there's
  * one already added for a page at this offset.  If there's none, then insert
  * this new request onto the auxiliary list, otherwise reuse the existing one by
  * swapping the new temp page with the old one.
  */
 static bool fuse_writepage_add(struct fuse_writepage_args *new_wpa,
                    struct page *page)
 {
     struct fuse_inode *fi = get_fuse_inode(new_wpa->inode);
     struct fuse_writepage_args *tmp;
     struct fuse_writepage_args *old_wpa;
     struct fuse_args_pages *new_ap = &new_wpa->ia.ap;
 
     WARN_ON(new_ap->num_pages != 0);
     new_ap->num_pages = 1;
 
     spin_lock(&fi->lock);
     old_wpa = fuse_insert_writeback(&fi->writepages, new_wpa);
     if (!old_wpa) {
         spin_unlock(&fi->lock);
         return true;
     }
 
     for (tmp = old_wpa->next; tmp; tmp = tmp->next) {
         pgoff_t curr_index;
 
         WARN_ON(tmp->inode != new_wpa->inode);
         curr_index = tmp->ia.write.in.offset >> PAGE_SHIFT;
         if (curr_index == page->index) {
             WARN_ON(tmp->ia.ap.num_pages != 1);
             swap(tmp->ia.ap.pages[0], new_ap->pages[0]);
             break;
         }
     }
 
     if (!tmp) {
         new_wpa->next = old_wpa->next;
         old_wpa->next = new_wpa;
     }
 
     spin_unlock(&fi->lock);
 
     if (tmp) {
         struct backing_dev_info *bdi = inode_to_bdi(new_wpa->inode);
 
         dec_wb_stat(&bdi->wb, WB_WRITEBACK);
         dec_node_page_state(new_ap->pages[0], NR_WRITEBACK_TEMP);
         wb_writeout_inc(&bdi->wb);
         fuse_writepage_free(new_wpa);
     }
 
     return false;
 }
 
 static bool fuse_writepage_need_send(struct fuse_conn *fc, struct page *page,
                      struct fuse_args_pages *ap,
                      struct fuse_fill_wb_data *data)
 {
     WARN_ON(!ap->num_pages);
 
     /*
      * Being under writeback is unlikely but possible.  For example direct
      * read to an mmaped fuse file will set the page dirty twice; once when
      * the pages are faulted with get_user_pages(), and then after the read
      * completed.
      */
     if (fuse_page_is_writeback(data->inode, page->index))
         return true;
 
     /* Reached max pages */
     if (ap->num_pages == fc->max_pages)
         return true;
 
     /* Reached max write bytes */
     if ((ap->num_pages + 1) * PAGE_SIZE > fc->max_write)
         return true;
 
     /* Discontinuity */
     if (data->orig_pages[ap->num_pages - 1]->index + 1 != page->index)
         return true;
 
     /* Need to grow the pages array?  If so, did the expansion fail? */
     if (ap->num_pages == data->max_pages && !fuse_pages_realloc(data))
         return true;
 
     return false;
 }
 
 static int fuse_writepages_fill(struct page *page,
         struct writeback_control *wbc, void *_data)
 {
     struct fuse_fill_wb_data *data = _data;
     struct fuse_writepage_args *wpa = data->wpa;
     struct fuse_args_pages *ap = &wpa->ia.ap;
     struct inode *inode = data->inode;
     struct fuse_inode *fi = get_fuse_inode(inode);
     struct fuse_conn *fc = get_fuse_conn(inode);
     struct page *tmp_page;
     int err;
 
     if (!data->ff) {
         err = -EIO;
         data->ff = fuse_write_file_get(fi);
         if (!data->ff)
             goto out_unlock;
     }
 
     if (wpa && fuse_writepage_need_send(fc, page, ap, data)) {
         fuse_writepages_send(data);
         data->wpa = NULL;
     }
 
     err = -ENOMEM;
     tmp_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
     if (!tmp_page)
         goto out_unlock;
 
     /*
      * The page must not be redirtied until the writeout is completed
      * (i.e. userspace has sent a reply to the write request).  Otherwise
      * there could be more than one temporary page instance for each real
      * page.
      *
      * This is ensured by holding the page lock in page_mkwrite() while
      * checking fuse_page_is_writeback().  We already hold the page lock
      * since clear_page_dirty_for_io() and keep it held until we add the
      * request to the fi->writepages list and increment ap->num_pages.
      * After this fuse_page_is_writeback() will indicate that the page is
      * under writeback, so we can release the page lock.
      */
     if (data->wpa == NULL) {
         err = -ENOMEM;
         wpa = fuse_writepage_args_alloc();
         if (!wpa) {
             __free_page(tmp_page);
             goto out_unlock;
         }
         fuse_writepage_add_to_bucket(fc, wpa);
 
         data->max_pages = 1;
 
         ap = &wpa->ia.ap;
         fuse_write_args_fill(&wpa->ia, data->ff, page_offset(page), 0);
         wpa->ia.write.in.write_flags |= FUSE_WRITE_CACHE;
         wpa->next = NULL;
         ap->args.in_pages = true;
         ap->args.end = fuse_writepage_end;
         ap->num_pages = 0;
         wpa->inode = inode;
     }
     set_page_writeback(page);
 
     copy_highpage(tmp_page, page);
     ap->pages[ap->num_pages] = tmp_page;
     ap->descs[ap->num_pages].offset = 0;
     ap->descs[ap->num_pages].length = PAGE_SIZE;
     data->orig_pages[ap->num_pages] = page;
 
     inc_wb_stat(&inode_to_bdi(inode)->wb, WB_WRITEBACK);
     inc_node_page_state(tmp_page, NR_WRITEBACK_TEMP);
 
     err = 0;
     if (data->wpa) {
         /*
          * Protected by fi->lock against concurrent access by
          * fuse_page_is_writeback().
          */
         spin_lock(&fi->lock);
         ap->num_pages++;
         spin_unlock(&fi->lock);
     } else if (fuse_writepage_add(wpa, page)) {
         data->wpa = wpa;
     } else {
         end_page_writeback(page);
     }
 out_unlock:
     unlock_page(page);
 
     return err;
 }
 
 static int fuse_writepages(struct address_space *mapping,
                struct writeback_control *wbc)
 {
     struct inode *inode = mapping->host;
     struct fuse_conn *fc = get_fuse_conn(inode);
     struct fuse_fill_wb_data data;
     int err;
 
     err = -EIO;
     if (fuse_is_bad(inode))
         goto out;
 
     if (wbc->sync_mode == WB_SYNC_NONE &&
         fc->num_background >= fc->congestion_threshold)
         return 0;
 
     data.inode = inode;
     data.wpa = NULL;
     data.ff = NULL;
 
     err = -ENOMEM;
     data.orig_pages = kcalloc(fc->max_pages,
                   sizeof(struct page *),
                   GFP_NOFS);
     if (!data.orig_pages)
         goto out;
 
     err = write_cache_pages(mapping, wbc, fuse_writepages_fill, &data);
     if (data.wpa) {
         WARN_ON(!data.wpa->ia.ap.num_pages);
         fuse_writepages_send(&data);
     }
     if (data.ff)
         fuse_file_put(data.ff, false, false);
 
     kfree(data.orig_pages);
 out:
     return err;
 }
 
 /*
  * It's worthy to make sure that space is reserved on disk for the write,
  * but how to implement it without killing performance need more thinking.
  */
 static int fuse_write_begin(struct file *file, struct address_space *mapping,
         loff_t pos, unsigned len, struct page **pagep, void **fsdata)
 {
     pgoff_t index = pos >> PAGE_SHIFT;
     struct fuse_conn *fc = get_fuse_conn(file_inode(file));
     struct page *page;
     loff_t fsize;
     int err = -ENOMEM;
 
     WARN_ON(!fc->writeback_cache);
 
     page = grab_cache_page_write_begin(mapping, index);
     if (!page)
         goto error;
 
     fuse_wait_on_page_writeback(mapping->host, page->index);
 
     if (PageUptodate(page) || len == PAGE_SIZE)
         goto success;
     /*
      * Check if the start this page comes after the end of file, in which
      * case the readpage can be optimized away.
      */
     fsize = i_size_read(mapping->host);
     if (fsize <= (pos & PAGE_MASK)) {
         size_t off = pos & ~PAGE_MASK;
         if (off)
             zero_user_segment(page, 0, off);
         goto success;
     }
     err = fuse_do_readpage(file, page);
     if (err)
         goto cleanup;
 success:
     *pagep = page;
     return 0;
 
 cleanup:
     unlock_page(page);
     put_page(page);
 error:
     return err;
 }
 
 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 = page->mapping->host;
 
     /* Haven't copied anything?  Skip zeroing, size extending, dirtying. */
     if (!copied)
         goto unlock;
 
     pos += copied;
     if (!PageUptodate(page)) {
         /* Zero any unwritten bytes at the end of the page */
         size_t endoff = pos & ~PAGE_MASK;
         if (endoff)
             zero_user_segment(page, endoff, PAGE_SIZE);
         SetPageUptodate(page);
     }
 
     if (pos > inode->i_size)
         i_size_write(inode, pos);
 
     set_page_dirty(page);
 
 unlock:
     unlock_page(page);
     put_page(page);
 
     return copied;
 }
 
 static int fuse_launder_folio(struct folio *folio)
 {
     int err = 0;
     if (folio_clear_dirty_for_io(folio)) {
         struct inode *inode = folio->mapping->host;
 
         /* Serialize with pending writeback for the same page */
         fuse_wait_on_page_writeback(inode, folio->index);
         err = fuse_writepage_locked(&folio->page);
         if (!err)
             fuse_wait_on_page_writeback(inode, folio->index);
     }
     return err;
 }
 
 /*
  * Write back dirty data/metadata now (there may not be any suitable
  * open files later for data)
  */
 static void fuse_vma_close(struct vm_area_struct *vma)
 {
     int err;
 
     err = write_inode_now(vma->vm_file->f_mapping->host, 1);
     mapping_set_error(vma->vm_file->f_mapping, err);
 }
 
 /*
  * 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 vm_fault_t fuse_page_mkwrite(struct vm_fault *vmf)
 {
     struct page *page = vmf->page;
     struct inode *inode = file_inode(vmf->vma->vm_file);
 
     file_update_time(vmf->vma->vm_file);
     lock_page(page);
     if (page->mapping != inode->i_mapping) {
         unlock_page(page);
         return VM_FAULT_NOPAGE;
     }
 
     fuse_wait_on_page_writeback(inode, page->index);
     return VM_FAULT_LOCKED;
 }
 
 static const struct vm_operations_struct fuse_file_vm_ops = {
     .close      = fuse_vma_close,
     .fault      = filemap_fault,
     .map_pages  = filemap_map_pages,
     .page_mkwrite   = fuse_page_mkwrite,
 };
 
 static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
 {
     struct fuse_file *ff = file->private_data;
 
     /* DAX mmap is superior to direct_io mmap */
     if (FUSE_IS_DAX(file_inode(file)))
         return fuse_dax_mmap(file, vma);
 
     if (ff->open_flags & FOPEN_DIRECT_IO) {
         /* 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);
     }
 
     if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
         fuse_link_write_file(file);
 
     file_accessed(file);
     vma->vm_ops = &fuse_file_vm_ops;
     return 0;
 }
 
 static int convert_fuse_file_lock(struct fuse_conn *fc,
                   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;
 
         /*
          * Convert pid into init's pid namespace.  The locks API will
          * translate it into the caller's pid namespace.
          */
         rcu_read_lock();
         fl->fl_pid = pid_nr_ns(find_pid_ns(ffl->pid, fc->pid_ns), &init_pid_ns);
         rcu_read_unlock();
         break;
 
     default:
         return -EIO;
     }
     fl->fl_type = ffl->type;
     return 0;
 }
 
 static void fuse_lk_fill(struct fuse_args *args, struct file *file,
              const struct file_lock *fl, int opcode, pid_t pid,
              int flock, struct fuse_lk_in *inarg)
 {
     struct inode *inode = file_inode(file);
     struct fuse_conn *fc = get_fuse_conn(inode);
     struct fuse_file *ff = file->private_data;
 
     memset(inarg, 0, sizeof(*inarg));
     inarg->fh = ff->fh;
     inarg->owner = fuse_lock_owner_id(fc, fl->fl_owner);
     inarg->lk.start = fl->fl_start;
     inarg->lk.end = fl->fl_end;
     inarg->lk.type = fl->fl_type;
     inarg->lk.pid = pid;
     if (flock)
         inarg->lk_flags |= FUSE_LK_FLOCK;
     args->opcode = opcode;
     args->nodeid = get_node_id(inode);
     args->in_numargs = 1;
     args->in_args[0].size = sizeof(*inarg);
     args->in_args[0].value = inarg;
 }
 
 static int fuse_getlk(struct file *file, struct file_lock *fl)
 {
     struct inode *inode = file_inode(file);
     struct fuse_mount *fm = get_fuse_mount(inode);
     FUSE_ARGS(args);
     struct fuse_lk_in inarg;
     struct fuse_lk_out outarg;
     int err;
 
     fuse_lk_fill(&args, file, fl, FUSE_GETLK, 0, 0, &inarg);
     args.out_numargs = 1;
     args.out_args[0].size = sizeof(outarg);
     args.out_args[0].value = &outarg;
     err = fuse_simple_request(fm, &args);
     if (!err)
         err = convert_fuse_file_lock(fm->fc, &outarg.lk, fl);
 
     return err;
 }
 
 static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 {
     struct inode *inode = file_inode(file);
     struct fuse_mount *fm = get_fuse_mount(inode);
     FUSE_ARGS(args);
     struct fuse_lk_in inarg;
     int opcode = (fl->fl_flags & FL_SLEEP) ? FUSE_SETLKW : FUSE_SETLK;
     struct pid *pid = fl->fl_type != F_UNLCK ? task_tgid(current) : NULL;
     pid_t pid_nr = pid_nr_ns(pid, fm->fc->pid_ns);
     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_POSIX) == FL_CLOSE_POSIX)
         return 0;
 
     fuse_lk_fill(&args, file, fl, opcode, pid_nr, flock, &inarg);
     err = fuse_simple_request(fm, &args);
 
     /* locking is restartable */
     if (err == -EINTR)
         err = -ERESTARTSYS;
 
     return err;
 }
 
 static int fuse_file_lock(struct file *file, int cmd, struct file_lock *fl)
 {
     struct inode *inode = file_inode(file);
     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_inode(file);
     struct fuse_conn *fc = get_fuse_conn(inode);
     int err;
 
     if (fc->no_flock) {
         err = locks_lock_file_wait(file, fl);
     } else {
         struct fuse_file *ff = file->private_data;
 
         /* emulate flock with POSIX locks */
         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_mount *fm = get_fuse_mount(inode);
     FUSE_ARGS(args);
     struct fuse_bmap_in inarg;
     struct fuse_bmap_out outarg;
     int err;
 
     if (!inode->i_sb->s_bdev || fm->fc->no_bmap)
         return 0;
 
     memset(&inarg, 0, sizeof(inarg));
     inarg.block = block;
     inarg.blocksize = inode->i_sb->s_blocksize;
     args.opcode = FUSE_BMAP;
     args.nodeid = get_node_id(inode);
     args.in_numargs = 1;
     args.in_args[0].size = sizeof(inarg);
     args.in_args[0].value = &inarg;
     args.out_numargs = 1;
     args.out_args[0].size = sizeof(outarg);
     args.out_args[0].value = &outarg;
     err = fuse_simple_request(fm, &args);
     if (err == -ENOSYS)
         fm->fc->no_bmap = 1;
 
     return err ? 0 : outarg.block;
 }
 
 static loff_t fuse_lseek(struct file *file, loff_t offset, int whence)
 {
     struct inode *inode = file->f_mapping->host;
     struct fuse_mount *fm = get_fuse_mount(inode);
     struct fuse_file *ff = file->private_data;
     FUSE_ARGS(args);
     struct fuse_lseek_in inarg = {
         .fh = ff->fh,
         .offset = offset,
         .whence = whence
     };
     struct fuse_lseek_out outarg;
     int err;
 
     if (fm->fc->no_lseek)
         goto fallback;
 
     args.opcode = FUSE_LSEEK;
     args.nodeid = ff->nodeid;
     args.in_numargs = 1;
     args.in_args[0].size = sizeof(inarg);
     args.in_args[0].value = &inarg;
     args.out_numargs = 1;
     args.out_args[0].size = sizeof(outarg);
     args.out_args[0].value = &outarg;
     err = fuse_simple_request(fm, &args);
     if (err) {
         if (err == -ENOSYS) {
             fm->fc->no_lseek = 1;
             goto fallback;
         }
         return err;
     }
 
     return vfs_setpos(file, outarg.offset, inode->i_sb->s_maxbytes);
 
 fallback:
     err = fuse_update_attributes(inode, file, STATX_SIZE);
     if (!err)
         return generic_file_llseek(file, offset, whence);
     else
         return err;
 }
 
 static loff_t fuse_file_llseek(struct file *file, loff_t offset, int whence)
 {
     loff_t retval;
     struct inode *inode = file_inode(file);
 
     switch (whence) {
     case SEEK_SET:
     case SEEK_CUR:
          /* No i_mutex protection necessary for SEEK_CUR and SEEK_SET */
         retval = generic_file_llseek(file, offset, whence);
         break;
     case SEEK_END:
         inode_lock(inode);
         retval = fuse_update_attributes(inode, file, STATX_SIZE);
         if (!retval)
             retval = generic_file_llseek(file, offset, whence);
         inode_unlock(inode);
         break;
     case SEEK_HOLE:
     case SEEK_DATA:
         inode_lock(inode);
         retval = fuse_lseek(file, offset, whence);
         inode_unlock(inode);
         break;
     default:
         retval = -EINVAL;
     }
 
     return retval;
 }
 
 /*
  * 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);
 }
 
 __poll_t fuse_file_poll(struct file *file, poll_table *wait)
 {
     struct fuse_file *ff = file->private_data;
     struct fuse_mount *fm = ff->fm;
     struct fuse_poll_in inarg = { .fh = ff->fh, .kh = ff->kh };
     struct fuse_poll_out outarg;
     FUSE_ARGS(args);
     int err;
 
     if (fm->fc->no_poll)
         return DEFAULT_POLLMASK;
 
     poll_wait(file, &ff->poll_wait, wait);
     inarg.events = mangle_poll(poll_requested_events(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(fm->fc, ff);
     }
 
     args.opcode = FUSE_POLL;
     args.nodeid = ff->nodeid;
     args.in_numargs = 1;
     args.in_args[0].size = sizeof(inarg);
     args.in_args[0].value = &inarg;
     args.out_numargs = 1;
     args.out_args[0].size = sizeof(outarg);
     args.out_args[0].value = &outarg;
     err = fuse_simple_request(fm, &args);
 
     if (!err)
         return demangle_poll(outarg.revents);
     if (err == -ENOSYS) {
         fm->fc->no_poll = 1;
         return DEFAULT_POLLMASK;
     }
     return EPOLLERR;
 }
 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 void fuse_do_truncate(struct file *file)
 {
     struct inode *inode = file->f_mapping->host;
     struct iattr attr;
 
     attr.ia_valid = ATTR_SIZE;
     attr.ia_size = i_size_read(inode);
 
     attr.ia_file = file;
     attr.ia_valid |= ATTR_FILE;
 
     fuse_do_setattr(file_dentry(file), &attr, file);
 }
 
 static inline loff_t fuse_round_up(struct fuse_conn *fc, loff_t off)
 {
     return round_up(off, fc->max_pages << PAGE_SHIFT);
 }
 
 static ssize_t
 fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 {
     DECLARE_COMPLETION_ONSTACK(wait);
     ssize_t ret = 0;
     struct file *file = iocb->ki_filp;
     struct fuse_file *ff = file->private_data;
     loff_t pos = 0;
     struct inode *inode;
     loff_t i_size;
     size_t count = iov_iter_count(iter), shortened = 0;
     loff_t offset = iocb->ki_pos;
     struct fuse_io_priv *io;
 
     pos = offset;
     inode = file->f_mapping->host;
     i_size = i_size_read(inode);
 
     if ((iov_iter_rw(iter) == READ) && (offset >= i_size))
         return 0;
 
     io = kmalloc(sizeof(struct fuse_io_priv), GFP_KERNEL);
     if (!io)
         return -ENOMEM;
     spin_lock_init(&io->lock);
     kref_init(&io->refcnt);
     io->reqs = 1;
     io->bytes = -1;
     io->size = 0;
     io->offset = offset;
     io->write = (iov_iter_rw(iter) == WRITE);
     io->err = 0;
     /*
      * By default, we want to optimize all I/Os with async request
      * submission to the client filesystem if supported.
      */
     io->async = ff->fm->fc->async_dio;
     io->iocb = iocb;
     io->blocking = is_sync_kiocb(iocb);
 
     /* optimization for short read */
     if (io->async && !io->write && offset + count > i_size) {
         iov_iter_truncate(iter, fuse_round_up(ff->fm->fc, i_size - offset));
         shortened = count - iov_iter_count(iter);
         count -= shortened;
     }
 
     /*
      * We cannot asynchronously extend the size of a file.
      * In such case the aio will behave exactly like sync io.
      */
     if ((offset + count > i_size) && io->write)
         io->blocking = true;
 
     if (io->async && io->blocking) {
         /*
          * Additional reference to keep io around after
          * calling fuse_aio_complete()
          */
         kref_get(&io->refcnt);
         io->done = &wait;
     }
 
     if (iov_iter_rw(iter) == WRITE) {
         ret = fuse_direct_io(io, iter, &pos, FUSE_DIO_WRITE);
         fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
     } else {
         ret = __fuse_direct_read(io, iter, &pos);
     }
     iov_iter_reexpand(iter, iov_iter_count(iter) + shortened);
 
     if (io->async) {
         bool blocking = io->blocking;
 
         fuse_aio_complete(io, ret < 0 ? ret : 0, -1);
 
         /* we have a non-extending, async request, so return */
         if (!blocking)
             return -EIOCBQUEUED;
 
         wait_for_completion(&wait);
         ret = fuse_get_res_by_io(io);
     }
 
     kref_put(&io->refcnt, fuse_io_release);
 
     if (iov_iter_rw(iter) == WRITE) {
         fuse_write_update_attr(inode, pos, ret);
         if (ret < 0 && offset + count > i_size)
             fuse_do_truncate(file);
     }
 
     return ret;
 }
 
 static int fuse_writeback_range(struct inode *inode, loff_t start, loff_t end)
 {
     int err = filemap_write_and_wait_range(inode->i_mapping, start, LLONG_MAX);
 
     if (!err)
         fuse_sync_writes(inode);
 
     return err;
 }
 
 static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
                 loff_t length)
 {
     struct fuse_file *ff = file->private_data;
     struct inode *inode = file_inode(file);
     struct fuse_inode *fi = get_fuse_inode(inode);
     struct fuse_mount *fm = ff->fm;
     FUSE_ARGS(args);
     struct fuse_fallocate_in inarg = {
         .fh = ff->fh,
         .offset = offset,
         .length = length,
         .mode = mode
     };
     int err;
     bool lock_inode = !(mode & FALLOC_FL_KEEP_SIZE) ||
                (mode & (FALLOC_FL_PUNCH_HOLE |
                     FALLOC_FL_ZERO_RANGE));
 
     bool block_faults = FUSE_IS_DAX(inode) && lock_inode;
 
     if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
              FALLOC_FL_ZERO_RANGE))
         return -EOPNOTSUPP;
 
     if (fm->fc->no_fallocate)
         return -EOPNOTSUPP;
 
     if (lock_inode) {
         inode_lock(inode);
         if (block_faults) {
             filemap_invalidate_lock(inode->i_mapping);
             err = fuse_dax_break_layouts(inode, 0, 0);
             if (err)
                 goto out;
         }
 
         if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)) {
             loff_t endbyte = offset + length - 1;
 
             err = fuse_writeback_range(inode, offset, endbyte);
             if (err)
                 goto out;
         }
     }
 
     if (!(mode & FALLOC_FL_KEEP_SIZE) &&
         offset + length > i_size_read(inode)) {
         err = inode_newsize_ok(inode, offset + length);
         if (err)
             goto out;
     }
 
     if (!(mode & FALLOC_FL_KEEP_SIZE))
         set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
 
     args.opcode = FUSE_FALLOCATE;
     args.nodeid = ff->nodeid;
     args.in_numargs = 1;
     args.in_args[0].size = sizeof(inarg);
     args.in_args[0].value = &inarg;
     err = fuse_simple_request(fm, &args);
     if (err == -ENOSYS) {
         fm->fc->no_fallocate = 1;
         err = -EOPNOTSUPP;
     }
     if (err)
         goto out;
 
     /* we could have extended the file */
     if (!(mode & FALLOC_FL_KEEP_SIZE)) {
         if (fuse_write_update_attr(inode, offset + length, length))
             file_update_time(file);
     }
 
     if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE))
         truncate_pagecache_range(inode, offset, offset + length - 1);
 
     fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
 
 out:
     if (!(mode & FALLOC_FL_KEEP_SIZE))
         clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
 
     if (block_faults)
         filemap_invalidate_unlock(inode->i_mapping);
 
     if (lock_inode)
         inode_unlock(inode);
 
     fuse_flush_time_update(inode);
 
     return err;
 }
 
 static ssize_t __fuse_copy_file_range(struct file *file_in, loff_t pos_in,
                       struct file *file_out, loff_t pos_out,
                       size_t len, unsigned int flags)
 {
     struct fuse_file *ff_in = file_in->private_data;
     struct fuse_file *ff_out = file_out->private_data;
     struct inode *inode_in = file_inode(file_in);
     struct inode *inode_out = file_inode(file_out);
     struct fuse_inode *fi_out = get_fuse_inode(inode_out);
     struct fuse_mount *fm = ff_in->fm;
     struct fuse_conn *fc = fm->fc;
     FUSE_ARGS(args);
     struct fuse_copy_file_range_in inarg = {
         .fh_in = ff_in->fh,
         .off_in = pos_in,
         .nodeid_out = ff_out->nodeid,
         .fh_out = ff_out->fh,
         .off_out = pos_out,
         .len = len,
         .flags = flags
     };
     struct fuse_write_out outarg;
     ssize_t err;
     /* mark unstable when write-back is not used, and file_out gets
      * extended */
     bool is_unstable = (!fc->writeback_cache) &&
                ((pos_out + len) > inode_out->i_size);
 
     if (fc->no_copy_file_range)
         return -EOPNOTSUPP;
 
     if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
         return -EXDEV;
 
     inode_lock(inode_in);
     err = fuse_writeback_range(inode_in, pos_in, pos_in + len - 1);
     inode_unlock(inode_in);
     if (err)
         return err;
 
     inode_lock(inode_out);
 
     err = file_modified(file_out);
     if (err)
         goto out;
 
     /*
      * Write out dirty pages in the destination file before sending the COPY
      * request to userspace.  After the request is completed, truncate off
      * pages (including partial ones) from the cache that have been copied,
      * since these contain stale data at that point.
      *
      * This should be mostly correct, but if the COPY writes to partial
      * pages (at the start or end) and the parts not covered by the COPY are
      * written through a memory map after calling fuse_writeback_range(),
      * then these partial page modifications will be lost on truncation.
      *
      * It is unlikely that someone would rely on such mixed style
      * modifications.  Yet this does give less guarantees than if the
      * copying was performed with write(2).
      *
      * To fix this a mapping->invalidate_lock could be used to prevent new
      * faults while the copy is ongoing.
      */
     err = fuse_writeback_range(inode_out, pos_out, pos_out + len - 1);
     if (err)
         goto out;
 
     if (is_unstable)
         set_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);
 
     args.opcode = FUSE_COPY_FILE_RANGE;
     args.nodeid = ff_in->nodeid;
     args.in_numargs = 1;
     args.in_args[0].size = sizeof(inarg);
     args.in_args[0].value = &inarg;
     args.out_numargs = 1;
     args.out_args[0].size = sizeof(outarg);
     args.out_args[0].value = &outarg;
     err = fuse_simple_request(fm, &args);
     if (err == -ENOSYS) {
         fc->no_copy_file_range = 1;
         err = -EOPNOTSUPP;
     }
     if (err)
         goto out;
 
     truncate_inode_pages_range(inode_out->i_mapping,
                    ALIGN_DOWN(pos_out, PAGE_SIZE),
                    ALIGN(pos_out + outarg.size, PAGE_SIZE) - 1);
 
     file_update_time(file_out);
     fuse_write_update_attr(inode_out, pos_out + outarg.size, outarg.size);
 
     err = outarg.size;
 out:
     if (is_unstable)
         clear_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);
 
     inode_unlock(inode_out);
     file_accessed(file_in);
 
     fuse_flush_time_update(inode_out);
 
     return err;
 }
 
 static ssize_t fuse_copy_file_range(struct file *src_file, loff_t src_off,
                     struct file *dst_file, loff_t dst_off,
                     size_t len, unsigned int flags)
 {
     ssize_t ret;
 
     ret = __fuse_copy_file_range(src_file, src_off, dst_file, dst_off,
                      len, flags);
 
     if (ret == -EOPNOTSUPP || ret == -EXDEV)
         ret = generic_copy_file_range(src_file, src_off, dst_file,
                           dst_off, len, flags);
     return ret;
 }
 
 static const struct file_operations fuse_file_operations = {
     .llseek     = fuse_file_llseek,
     .read_iter  = fuse_file_read_iter,
     .write_iter = fuse_file_write_iter,
     .mmap       = fuse_file_mmap,
     .open       = fuse_open,
     .flush      = fuse_flush,
     .release    = fuse_release,
     .fsync      = fuse_fsync,
     .lock       = fuse_file_lock,
     .get_unmapped_area = thp_get_unmapped_area,
     .flock      = fuse_file_flock,
     .splice_read    = generic_file_splice_read,
     .splice_write   = iter_file_splice_write,
     .unlocked_ioctl = fuse_file_ioctl,
     .compat_ioctl   = fuse_file_compat_ioctl,
     .poll       = fuse_file_poll,
     .fallocate  = fuse_file_fallocate,
     .copy_file_range = fuse_copy_file_range,
 };
 
 static const struct address_space_operations fuse_file_aops  = {
     .read_folio = fuse_read_folio,
     .readahead  = fuse_readahead,
     .writepage  = fuse_writepage,
     .writepages = fuse_writepages,
     .launder_folio  = fuse_launder_folio,
     .dirty_folio    = filemap_dirty_folio,
     .bmap       = fuse_bmap,
     .direct_IO  = fuse_direct_IO,
     .write_begin    = fuse_write_begin,
     .write_end  = fuse_write_end,
 };
 
 void fuse_init_file_inode(struct inode *inode, unsigned int flags)
 {
     struct fuse_inode *fi = get_fuse_inode(inode);
 
     inode->i_fop = &fuse_file_operations;
     inode->i_data.a_ops = &fuse_file_aops;
 
     INIT_LIST_HEAD(&fi->write_files);
     INIT_LIST_HEAD(&fi->queued_writes);
     fi->writectr = 0;
     init_waitqueue_head(&fi->page_waitq);
     fi->writepages = RB_ROOT;
 
     if (IS_ENABLED(CONFIG_FUSE_DAX))
         fuse_dax_inode_init(inode, flags);
 }