Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3252 insertions, 0 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
new file mode 100644
index 0000000000..a660f1f215
--- /dev/null
+++ b/fs/fuse/file.c
@@ -0,0 +1,3252 @@
+/*
+  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>
+#include <linux/filelock.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 iov_iter *ii)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	struct inode *inode = mapping->host;
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	loff_t pos = iocb->ki_pos;
+	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);
+
+	if (!res)
+		return err;
+	iocb->ki_pos += res;
+	return res;
+}
+
+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;
+	struct inode *inode = mapping->host;
+	ssize_t err;
+	struct fuse_conn *fc = get_fuse_conn(inode);
+
+	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 &&
+		    setattr_should_drop_suidgid(&nop_mnt_idmap,
+						file_inode(file))) {
+			goto writethrough;
+		}
+
+		return generic_file_write_iter(iocb, from);
+	}
+
+writethrough:
+	inode_lock(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) {
+		written = generic_file_direct_write(iocb, from);
+		if (written < 0 || !iov_iter_count(from))
+			goto out;
+		written = direct_write_fallback(iocb, from, written,
+				fuse_perform_write(iocb, from));
+	} else {
+		written = fuse_perform_write(iocb, from);
+	}
+out:
+	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)iter_iov(ii)->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 address_space *mapping = file->f_mapping;
+	struct inode *inode = 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;
+	bool fopen_direct_io = ff->open_flags & FOPEN_DIRECT_IO;
+
+	max_pages = iov_iter_npages(iter, fc->max_pages);
+	ia = fuse_io_alloc(io, max_pages);
+	if (!ia)
+		return -ENOMEM;
+
+	if (fopen_direct_io && fc->direct_io_allow_mmap) {
+		res = filemap_write_and_wait_range(mapping, pos, pos + count - 1);
+		if (res) {
+			fuse_io_free(ia);
+			return res;
+		}
+	}
+	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);
+	}
+
+	if (fopen_direct_io && write) {
+		res = invalidate_inode_pages2_range(mapping, idx_from, idx_to);
+		if (res) {
+			fuse_io_free(ia);
+			return res;
+		}
+	}
+
+	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 bool fuse_direct_write_extending_i_size(struct kiocb *iocb,
+					       struct iov_iter *iter)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+	return iocb->ki_pos + iov_iter_count(iter) > i_size_read(inode);
+}
+
+static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	struct file *file = iocb->ki_filp;
+	struct fuse_file *ff = file->private_data;
+	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);
+	ssize_t res;
+	bool exclusive_lock =
+		!(ff->open_flags & FOPEN_PARALLEL_DIRECT_WRITES) ||
+		get_fuse_conn(inode)->direct_io_allow_mmap ||
+		iocb->ki_flags & IOCB_APPEND ||
+		fuse_direct_write_extending_i_size(iocb, from);
+
+	/*
+	 * Take exclusive lock if
+	 * - Parallel direct writes are disabled - a user space decision
+	 * - Parallel direct writes are enabled and i_size is being extended.
+	 * - Shared mmap on direct_io file is supported (FUSE_DIRECT_IO_ALLOW_MMAP).
+	 *   This might not be needed at all, but needs further investigation.
+	 */
+	if (exclusive_lock)
+		inode_lock(inode);
+	else {
+		inode_lock_shared(inode);
+
+		/* A race with truncate might have come up as the decision for
+		 * the lock type was done without holding the lock, check again.
+		 */
+		if (fuse_direct_write_extending_i_size(iocb, from)) {
+			inode_unlock_shared(inode);
+			inode_lock(inode);
+			exclusive_lock = true;
+		}
+	}
+
+	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);
+		}
+	}
+	if (exclusive_lock)
+		inode_unlock(inode);
+	else
+		inode_unlock_shared(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 folio *folio,
+		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, &folio->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, folio_pos(folio), 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;
+	}
+	folio_start_writeback(folio);
+
+	copy_highpage(tmp_page, &folio->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] = &folio->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, &folio->page)) {
+		data->wpa = wpa;
+	} else {
+		folio_end_writeback(folio);
+	}
+out_unlock:
+	folio_unlock(folio);
+
+	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;
+	struct fuse_conn *fc = ff->fm->fc;
+
+	/* 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 FUSE_DIRECT_IO_ALLOW_MMAP isn't set.
+		 */
+		if ((vma->vm_flags & VM_MAYSHARE) && !fc->direct_io_allow_mmap)
+			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);
+		/* For extending writes we already hold exclusive lock */
+		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 block_faults = FUSE_IS_DAX(inode) &&
+		(!(mode & FALLOC_FL_KEEP_SIZE) ||
+		 (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE)));
+
+	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
+		     FALLOC_FL_ZERO_RANGE))
+		return -EOPNOTSUPP;
+
+	if (fm->fc->no_fallocate)
+		return -EOPNOTSUPP;
+
+	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;
+	}
+
+	err = file_modified(file);
+	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);
+
+	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	= filemap_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);
+}