text: /*
    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/compat.h>
  #include <linux/swap.h>
  #include <linux/falloc.h>
  #include <linux/uio.h>
  
  static int fuse_send_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
  			  int opcode, struct fuse_open_out *outargp)
  {
  	struct fuse_open_in inarg;
  	FUSE_ARGS(args);
  
  	memset(&inarg, 0, sizeof(inarg));
  	inarg.flags = file->f_flags & ~(O_CREAT | O_EXCL | O_NOCTTY);
  	if (!fc->atomic_o_trunc)
  		inarg.flags &= ~O_TRUNC;
  	args.in.h.opcode = opcode;
  	args.in.h.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(fc, &args);
  }
  
  struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
  {
  	struct fuse_file *ff;
  
  	ff = kzalloc(sizeof(struct fuse_file), GFP_KERNEL);
  	if (unlikely(!ff))
  		return NULL;
  
  	ff->fc = fc;
  	ff->reserved_req = fuse_request_alloc(0);
  	if (unlikely(!ff->reserved_req)) {
  		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(&fc->khctr);
  
  	return ff;
  }
  
  void fuse_file_free(struct fuse_file *ff)
  {
  	fuse_request_free(ff->reserved_req);
  	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_conn *fc, struct fuse_req *req)
  {
  	iput(req->misc.release.inode);
  }
  
  static void fuse_file_put(struct fuse_file *ff, bool sync, bool isdir)
  {
  	if (refcount_dec_and_test(&ff->count)) {
  		struct fuse_req *req = ff->reserved_req;
  
  		if (isdir ? ff->fc->no_opendir : ff->fc->no_open) {
  			/*
  			 * Drop the release request when client does not
  			 * implement 'open'
  			 */
  			__clear_bit(FR_BACKGROUND, &req->flags);
  			iput(req->misc.release.inode);
  			fuse_put_request(ff->fc, req);
  		} else if (sync) {
  			__set_bit(FR_FORCE, &req->flags);
  			__clear_bit(FR_BACKGROUND, &req->flags);
  			fuse_request_send(ff->fc, req);
  			iput(req->misc.release.inode);
  			fuse_put_request(ff->fc, req);
  		} else {
  			req->end = fuse_release_end;
  			__set_bit(FR_BACKGROUND, &req->flags);
  			fuse_request_send_background(ff->fc, req);
  		}
  		kfree(ff);
  	}
  }
  
  int fuse_do_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
  		 bool isdir)
  {
  	struct fuse_file *ff;
  	int opcode = isdir ? FUSE_OPENDIR : FUSE_OPEN;
  
  	ff = fuse_file_alloc(fc);
  	if (!ff)
  		return -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(fc, nodeid, file, opcode, &outarg);
  		if (!err) {
  			ff->fh = outarg.fh;
  			ff->open_flags = outarg.open_flags;
  
  		} else if (err != -ENOSYS) {
  			fuse_file_free(ff);
  			return err;
  		} else {
  			if (isdir)
  				fc->no_opendir = 1;
  			else
  				fc->no_open = 1;
  		}
  	}
  
  	if (isdir)
  		ff->open_flags &= ~FOPEN_DIRECT_IO;
  
  	ff->nodeid = nodeid;
  	file->private_data = ff;
  
  	return 0;
  }
  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_KEEP_CACHE))
  		invalidate_inode_pages2(inode->i_mapping);
  	if (ff->open_flags & FOPEN_NONSEEKABLE)
  		nonseekable_open(inode, file);
  	if (fc->atomic_o_trunc && (file->f_flags & O_TRUNC)) {
  		struct fuse_inode *fi = get_fuse_inode(inode);
  
  		spin_lock(&fi->lock);
  		fi->attr_version = atomic64_inc_return(&fc->attr_version);
  		i_size_write(inode, 0);
  		spin_unlock(&fi->lock);
  		fuse_invalidate_attr(inode);
  		if (fc->writeback_cache)
  			file_update_time(file);
  	}
  	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_conn *fc = get_fuse_conn(inode);
  	int err;
  	bool lock_inode = (file->f_flags & O_TRUNC) &&
  			  fc->atomic_o_trunc &&
  			  fc->writeback_cache;
  
  	err = generic_file_open(inode, file);
  	if (err)
  		return err;
  
  	if (lock_inode)
  		inode_lock(inode);
  
  	err = fuse_do_open(fc, get_node_id(inode), file, isdir);
  
  	if (!err)
  		fuse_finish_open(inode, file);
  
  	if (lock_inode)
  		inode_unlock(inode);
  
  	return err;
  }
  
  static void fuse_prepare_release(struct fuse_inode *fi, struct fuse_file *ff,
  				 int flags, int opcode)
  {
  	struct fuse_conn *fc = ff->fc;
  	struct fuse_req *req = ff->reserved_req;
  	struct fuse_release_in *inarg = &req->misc.release.in;
  
  	/* 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);
  
  	inarg->fh = ff->fh;
  	inarg->flags = flags;
  	req->in.h.opcode = opcode;
  	req->in.h.nodeid = ff->nodeid;
  	req->in.numargs = 1;
  	req->in.args[0].size = sizeof(struct fuse_release_in);
  	req->in.args[0].value = inarg;
  }
  
  void fuse_release_common(struct file *file, bool isdir)
  {
  	struct fuse_inode *fi = get_fuse_inode(file_inode(file));
  	struct fuse_file *ff = file->private_data;
  	struct fuse_req *req = ff->reserved_req;
  	int opcode = isdir ? FUSE_RELEASEDIR : FUSE_RELEASE;
  
  	fuse_prepare_release(fi, ff, file->f_flags, opcode);
  
  	if (ff->flock) {
  		struct fuse_release_in *inarg = &req->misc.release.in;
  		inarg->release_flags |= FUSE_RELEASE_FLOCK_UNLOCK;
  		inarg->lock_owner = fuse_lock_owner_id(ff->fc,
  						       (fl_owner_t) file);
  	}
  	/* Hold inode until release is finished */
  	req->misc.release.inode = igrab(file_inode(file));
  
  	/*
  	 * Normally this will send the RELEASE request, however if
  	 * some asynchronous READ or WRITE requests are outstanding,
  	 * the sending will be delayed.
  	 *
  	 * Make the release synchronous if this is a fuseblk mount,
  	 * synchronous RELEASE is allowed (and desirable) in this case
  	 * because the server can be trusted not to screw up.
  	 */
  	fuse_file_put(ff, ff->fc->destroy_req != NULL, 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);
  
  	/* see fuse_vma_close() for !writeback_cache case */
  	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, 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);
  }
  
  static struct fuse_req *fuse_find_writeback(struct fuse_inode *fi,
  					    pgoff_t idx_from, pgoff_t idx_to)
  {
  	struct fuse_req *req;
  
  	list_for_each_entry(req, &fi->writepages, writepages_entry) {
  		pgoff_t curr_index;
  
  		WARN_ON(get_fuse_inode(req->inode) != fi);
  		curr_index = req->misc.write.in.offset >> PAGE_SHIFT;
  		if (idx_from < curr_index + req->num_pages &&
  		    curr_index <= idx_to) {
  			return req;
  		}
  	}
  	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 int fuse_wait_on_page_writeback(struct inode *inode, pgoff_t index)
  {
  	struct fuse_inode *fi = get_fuse_inode(inode);
  
  	wait_event(fi->page_waitq, !fuse_page_is_writeback(inode, index));
  	return 0;
  }
  
  /*
   * 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_conn *fc = get_fuse_conn(inode);
  	struct fuse_file *ff = file->private_data;
  	struct fuse_req *req;
  	struct fuse_flush_in inarg;
  	int err;
  
  	if (is_bad_inode(inode))
  		return -EIO;
  
  	if (fc->no_flush)
  		return 0;
  
  	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;
  
  	req = fuse_get_req_nofail_nopages(fc, file);
  	memset(&inarg, 0, sizeof(inarg));
  	inarg.fh = ff->fh;
  	inarg.lock_owner = fuse_lock_owner_id(fc, id);
  	req->in.h.opcode = FUSE_FLUSH;
  	req->in.h.nodeid = get_node_id(inode);
  	req->in.numargs = 1;
  	req->in.args[0].size = sizeof(inarg);
  	req->in.args[0].value = &inarg;
  	__set_bit(FR_FORCE, &req->flags);
  	fuse_request_send(fc, req);
  	err = req->out.h.error;
  	fuse_put_request(fc, req);
  	if (err == -ENOSYS) {
  		fc->no_flush = 1;
  		err = 0;
  	}
  	return err;
  }
  
  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_conn *fc = get_fuse_conn(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 ? 1 : 0;
  	args.in.h.opcode = opcode;
  	args.in.h.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(fc, &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 (is_bad_inode(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_fill(struct fuse_req *req, struct file *file, loff_t pos,
  		    size_t count, int opcode)
  {
  	struct fuse_read_in *inarg = &req->misc.read.in;
  	struct fuse_file *ff = file->private_data;
  
  	inarg->fh = ff->fh;
  	inarg->offset = pos;
  	inarg->size = count;
  	inarg->flags = file->f_flags;
  	req->in.h.opcode = opcode;
  	req->in.h.nodeid = ff->nodeid;
  	req->in.numargs = 1;
  	req->in.args[0].size = sizeof(struct fuse_read_in);
  	req->in.args[0].value = inarg;
  	req->out.argvar = 1;
  	req->out.numargs = 1;
  	req->out.args[0].size = count;
  }
  
  static void fuse_release_user_pages(struct fuse_req *req, bool should_dirty)
  {
  	unsigned i;
  
  	for (i = 0; i < req->num_pages; i++) {
  		struct page *page = req->pages[i];
  		if (should_dirty)
  			set_page_dirty_lock(page);
  		put_page(page);
  	}
  }
  
  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 splitted 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, 0);
  	}
  
  	kref_put(&io->refcnt, fuse_io_release);
  }
  
  static void fuse_aio_complete_req(struct fuse_conn *fc, struct fuse_req *req)
  {
  	struct fuse_io_priv *io = req->io;
  	ssize_t pos = -1;
  
  	fuse_release_user_pages(req, io->should_dirty);
  
  	if (io->write) {
  		if (req->misc.write.in.size != req->misc.write.out.size)
  			pos = req->misc.write.in.offset - io->offset +
  				req->misc.write.out.size;
  	} else {
  		if (req->misc.read.in.size != req->out.args[0].size)
  			pos = req->misc.read.in.offset - io->offset +
  				req->out.args[0].size;
  	}
  
  	fuse_aio_complete(io, req->out.h.error, pos);
  }
  
  static size_t fuse_async_req_send(struct fuse_conn *fc, struct fuse_req *req,
  		size_t num_bytes, struct fuse_io_priv *io)
  {
  	spin_lock(&io->lock);
  	kref_get(&io->refcnt);
  	io->size += num_bytes;
  	io->reqs++;
  	spin_unlock(&io->lock);
  
  	req->io = io;
  	req->end = fuse_aio_complete_req;
  
  	__fuse_get_request(req);
  	fuse_request_send_background(fc, req);
  
  	return num_bytes;
  }
  
  static size_t fuse_send_read(struct fuse_req *req, struct fuse_io_priv *io,
  			     loff_t pos, size_t count, fl_owner_t owner)
  {
  	struct file *file = io->iocb->ki_filp;
  	struct fuse_file *ff = file->private_data;
  	struct fuse_conn *fc = ff->fc;
  
  	fuse_read_fill(req, file, pos, count, FUSE_READ);
  	if (owner != NULL) {
  		struct fuse_read_in *inarg = &req->misc.read.in;
  
  		inarg->read_flags |= FUSE_READ_LOCKOWNER;
  		inarg->lock_owner = fuse_lock_owner_id(fc, owner);
  	}
  
  	if (io->async)
  		return fuse_async_req_send(fc, req, count, io);
  
  	fuse_request_send(fc, req);
  	return req->out.args[0].size;
  }
  
  static void fuse_read_update_size(struct inode *inode, loff_t size,
  				  u64 attr_ver)
  {
  	struct fuse_conn *fc = get_fuse_conn(inode);
  	struct fuse_inode *fi = get_fuse_inode(inode);
  
  	spin_lock(&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 fuse_req *req, struct inode *inode,
  			    u64 attr_ver)
  {
  	size_t num_read = req->out.args[0].size;
  	struct fuse_conn *fc = get_fuse_conn(inode);
  
  	if (fc->writeback_cache) {
  		/*
  		 * A hole in a file. Some data after the hole are in page cache,
  		 * but have not reached the client fs yet. So, the hole is not
  		 * present there.
  		 */
  		int i;
  		int start_idx = num_read >> PAGE_SHIFT;
  		size_t off = num_read & (PAGE_SIZE - 1);
  
  		for (i = start_idx; i < req->num_pages; i++) {
  			zero_user_segment(req->pages[i], off, PAGE_SIZE);
  			off = 0;
  		}
  	} else {
  		loff_t pos = page_offset(req->pages[0]) + num_read;
  		fuse_read_update_size(inode, pos, attr_ver);
  	}
  }
  
  static int fuse_do_readpage(struct file *file, struct page *page)
  {
  	struct kiocb iocb;
  	struct fuse_io_priv io;
  	struct inode *inode = page->mapping->host;
  	struct fuse_conn *fc = get_fuse_conn(inode);
  	struct fuse_req *req;
  	size_t num_read;
  	loff_t pos = page_offset(page);
  	size_t count = PAGE_SIZE;
  	u64 attr_ver;
  	int err;
  
  	/*
  	 * Page writeback can extend beyond the lifetime of the
  	 * page-cache page, so make sure we read a properly synced
  	 * page.
  	 */
  	fuse_wait_on_page_writeback(inode, page->index);
  
  	req = fuse_get_req(fc, 1);
  	if (IS_ERR(req))
  		return PTR_ERR(req);
  
  	attr_ver = fuse_get_attr_version(fc);
  
  	req->out.page_zeroing = 1;
  	req->out.argpages = 1;
  	req->num_pages = 1;
  	req->pages[0] = page;
  	req->page_descs[0].length = count;
  	init_sync_kiocb(&iocb, file);
  	io = (struct fuse_io_priv) FUSE_IO_PRIV_SYNC(&iocb);
  	num_read = fuse_send_read(req, &io, pos, count, NULL);
  	err = req->out.h.error;
  
  	if (!err) {
  		/*
  		 * Short read means EOF.  If file size is larger, truncate it
  		 */
  		if (num_read < count)
  			fuse_short_read(req, inode, attr_ver);
  
  		SetPageUptodate(page);
  	}
  
  	fuse_put_request(fc, req);
  
  	return err;
  }
  
  static int fuse_readpage(struct file *file, struct page *page)
  {
  	struct inode *inode = page->mapping->host;
  	int err;
  
  	err = -EIO;
  	if (is_bad_inode(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_conn *fc, struct fuse_req *req)
  {
  	int i;
  	size_t count = req->misc.read.in.size;
  	size_t num_read = req->out.args[0].size;
  	struct address_space *mapping = NULL;
  
  	for (i = 0; mapping == NULL && i < req->num_pages; i++)
  		mapping = req->pages[i]->mapping;
  
  	if (mapping) {
  		struct inode *inode = mapping->host;
  
  		/*
  		 * Short read means EOF. If file size is larger, truncate it
  		 */
  		if (!req->out.h.error && num_read < count)
  			fuse_short_read(req, inode, req->misc.read.attr_ver);
  
  		fuse_invalidate_atime(inode);
  	}
  
  	for (i = 0; i < req->num_pages; i++) {
  		struct page *page = req->pages[i];
  		if (!req->out.h.error)
  			SetPageUptodate(page);
  		else
  			SetPageError(page);
  		unlock_page(page);
  		put_page(page);
  	}
  	if (req->ff)
  		fuse_file_put(req->ff, false, false);
  }
  
  static void fuse_send_readpages(struct fuse_req *req, struct file *file)
  {
  	struct fuse_file *ff = file->private_data;
  	struct fuse_conn *fc = ff->fc;
  	loff_t pos = page_offset(req->pages[0]);
  	size_t count = req->num_pages << PAGE_SHIFT;
  
  	req->out.argpages = 1;
  	req->out.page_zeroing = 1;
  	req->out.page_replace = 1;
  	fuse_read_fill(req, file, pos, count, FUSE_READ);
  	req->misc.read.attr_ver = fuse_get_attr_version(fc);
  	if (fc->async_read) {
  		req->ff = fuse_file_get(ff);
  		req->end = fuse_readpages_end;
  		fuse_request_send_background(fc, req);
  	} else {
  		fuse_request_send(fc, req);
  		fuse_readpages_end(fc, req);
  		fuse_put_request(fc, req);
  	}
  }
  
  struct fuse_fill_data {
  	struct fuse_req *req;
  	struct file *file;
  	struct inode *inode;
  	unsigned nr_pages;
  };
  
  static int fuse_readpages_fill(void *_data, struct page *page)
  {
  	struct fuse_fill_data *data = _data;
  	struct fuse_req *req = data->req;
  	struct inode *inode = data->inode;
  	struct fuse_conn *fc = get_fuse_conn(inode);
  
  	fuse_wait_on_page_writeback(inode, page->index);
  
  	if (req->num_pages &&
  	    (req->num_pages == fc->max_pages ||
  	     (req->num_pages + 1) * PAGE_SIZE > fc->max_read ||
  	     req->pages[req->num_pages - 1]->index + 1 != page->index)) {
  		unsigned int nr_alloc = min_t(unsigned int, data->nr_pages,
  					      fc->max_pages);
  		fuse_send_readpages(req, data->file);
  		if (fc->async_read)
  			req = fuse_get_req_for_background(fc, nr_alloc);
  		else
  			req = fuse_get_req(fc, nr_alloc);
  
  		data->req = req;
  		if (IS_ERR(req)) {
  			unlock_page(page);
  			return PTR_ERR(req);
  		}
  	}
  
  	if (WARN_ON(req->num_pages >= req->max_pages)) {
  		unlock_page(page);
  		fuse_put_request(fc, req);
  		return -EIO;
  	}
  
  	get_page(page);
  	req->pages[req->num_pages] = page;
  	req->page_descs[req->num_pages].length = PAGE_SIZE;
  	req->num_pages++;
  	data->nr_pages--;
  	return 0;
  }
  
  static int fuse_readpages(struct file *file, struct address_space *mapping,
  			  struct list_head *pages, unsigned nr_pages)
  {
  	struct inode *inode = mapping->host;
  	struct fuse_conn *fc = get_fuse_conn(inode);
  	struct fuse_fill_data data;
  	int err;
  	unsigned int nr_alloc = min_t(unsigned int, nr_pages, fc->max_pages);
  
  	err = -EIO;
  	if (is_bad_inode(inode))
  		goto out;
  
  	data.file = file;
  	data.inode = inode;
  	if (fc->async_read)
  		data.req = fuse_get_req_for_background(fc, nr_alloc);
  	else
  		data.req = fuse_get_req(fc, nr_alloc);
  	data.nr_pages = nr_pages;
  	err = PTR_ERR(data.req);
  	if (IS_ERR(data.req))
  		goto out;
  
  	err = read_cache_pages(mapping, pages, fuse_readpages_fill, &data);
  	if (!err) {
  		if (data.req->num_pages)
  			fuse_send_readpages(data.req, file);
  		else
  			fuse_put_request(fc, data.req);
  	}
  out:
  	return err;
  }
  
  static ssize_t fuse_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);
  		if (err)
  			return err;
  	}
  
  	return generic_file_read_iter(iocb, to);
  }
  
  static void fuse_write_fill(struct fuse_req *req, struct fuse_file *ff,
  			    loff_t pos, size_t count)
  {
  	struct fuse_write_in *inarg = &req->misc.write.in;
  	struct fuse_write_out *outarg = &req->misc.write.out;
  
  	inarg->fh = ff->fh;
  	inarg->offset = pos;
  	inarg->size = count;
  	req->in.h.opcode = FUSE_WRITE;
  	req->in.h.nodeid = ff->nodeid;
  	req->in.numargs = 2;
  	if (ff->fc->minor < 9)
  		req->in.args[0].size = FUSE_COMPAT_WRITE_IN_SIZE;
  	else
  		req->in.args[0].size = sizeof(struct fuse_write_in);
  	req->in.args[0].value = inarg;
  	req->in.args[1].size = count;
  	req->out.numargs = 1;
  	req->out.args[0].size = sizeof(struct fuse_write_out);
  	req->out.args[0].value = outarg;
  }
  
  static size_t fuse_send_write(struct fuse_req *req, struct fuse_io_priv *io,
  			      loff_t pos, size_t count, fl_owner_t owner)
  {
  	struct kiocb *iocb = io->iocb;
  	struct file *file = iocb->ki_filp;
  	struct fuse_file *ff = file->private_data;
  	struct fuse_conn *fc = ff->fc;
  	struct fuse_write_in *inarg = &req->misc.write.in;
  
  	fuse_write_fill(req, ff, pos, count);
  	inarg->flags = file->f_flags;
  	if (iocb->ki_flags & IOCB_DSYNC)
  		inarg->flags |= O_DSYNC;
  	if (iocb->ki_flags & IOCB_SYNC)
  		inarg->flags |= O_SYNC;
  	if (owner != NULL) {
  		inarg->write_flags |= FUSE_WRITE_LOCKOWNER;
  		inarg->lock_owner = fuse_lock_owner_id(fc, owner);
  	}
  
  	if (io->async)
  		return fuse_async_req_send(fc, req, count, io);
  
  	fuse_request_send(fc, req);
  	return req->misc.write.out.size;
  }
  
  bool fuse_write_update_size(struct inode *inode, loff_t pos)
  {
  	struct fuse_conn *fc = get_fuse_conn(inode);
  	struct fuse_inode *fi = get_fuse_inode(inode);
  	bool ret = false;
  
  	spin_lock(&fi->lock);
  	fi->attr_version = atomic64_inc_return(&fc->attr_version);
  	if (pos > inode->i_size) {
  		i_size_write(inode, pos);
  		ret = true;
  	}
  	spin_unlock(&fi->lock);
  
  	return ret;
  }
  
  static size_t fuse_send_write_pages(struct fuse_req *req, struct kiocb *iocb,
  				    struct inode *inode, loff_t pos,
  				    size_t count)
  {
  	size_t res;
  	unsigned offset;
  	unsigned i;
  	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);
  
  	for (i = 0; i < req->num_pages; i++)
  		fuse_wait_on_page_writeback(inode, req->pages[i]->index);
  
  	res = fuse_send_write(req, &io, pos, count, NULL);
  
  	offset = req->page_descs[0].offset;
  	count = res;
  	for (i = 0; i < req->num_pages; i++) {
  		struct page *page = req->pages[i];
  
  		if (!req->out.h.error && !offset && count >= PAGE_SIZE)
  			SetPageUptodate(page);
  
  		if (count > PAGE_SIZE - offset)
  			count -= PAGE_SIZE - offset;
  		else
  			count = 0;
  		offset = 0;
  
  		unlock_page(page);
  		put_page(page);
  	}
  
  	return res;
  }
  
  static ssize_t fuse_fill_write_pages(struct fuse_req *req,
  			       struct address_space *mapping,
  			       struct iov_iter *ii, loff_t pos)
  {
  	struct fuse_conn *fc = get_fuse_conn(mapping->host);
  	unsigned offset = pos & (PAGE_SIZE - 1);
  	size_t count = 0;
  	int err;
  
  	req->in.argpages = 1;
  	req->page_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 (iov_iter_fault_in_readable(ii, bytes))
  			break;
  
  		err = -ENOMEM;
  		page = grab_cache_page_write_begin(mapping, index, 0);
  		if (!page)
  			break;
  
  		if (mapping_writably_mapped(mapping))
  			flush_dcache_page(page);
  
  		tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
  		flush_dcache_page(page);
  
  		iov_iter_advance(ii, tmp);
  		if (!tmp) {
  			unlock_page(page);
  			put_page(page);
  			bytes = min(bytes, iov_iter_single_seg_count(ii));
  			goto again;
  		}
  
  		err = 0;
  		req->pages[req->num_pages] = page;
  		req->page_descs[req->num_pages].length = tmp;
  		req->num_pages++;
  
  		count += tmp;
  		pos += tmp;
  		offset += tmp;
  		if (offset == PAGE_SIZE)
  			offset = 0;
  
  		if (!fc->big_writes)
  			break;
  	} while (iov_iter_count(ii) && count < fc->max_write &&
  		 req->num_pages < req->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 {
  		struct fuse_req *req;
  		ssize_t count;
  		unsigned int nr_pages = fuse_wr_pages(pos, iov_iter_count(ii),
  						      fc->max_pages);
  
  		req = fuse_get_req(fc, nr_pages);
  		if (IS_ERR(req)) {
  			err = PTR_ERR(req);
  			break;
  		}
  
  		count = fuse_fill_write_pages(req, mapping, ii, pos);
  		if (count <= 0) {
  			err = count;
  		} else {
  			size_t num_written;
  
  			num_written = fuse_send_write_pages(req, iocb, inode,
  							    pos, count);
  			err = req->out.h.error;
  			if (!err) {
  				res += num_written;
  				pos += num_written;
  
  				/* break out of the loop on short write */
  				if (num_written != count)
  					err = -EIO;
  			}
  		}
  		fuse_put_request(fc, req);
  	} while (!err && iov_iter_count(ii));
  
  	if (res > 0)
  		fuse_write_update_size(inode, pos);
  
  	clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
  	fuse_invalidate_attr(inode);
  
  	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;
  	loff_t endbyte = 0;
  
  	if (get_fuse_conn(inode)->writeback_cache) {
  		/* Update size (EOF optimization) and mode (SUID clearing) */
  		err = fuse_update_attributes(mapping->host, file);
  		if (err)
  			return err;
  
  		return generic_file_write_iter(iocb, from);
  	}
  
  	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 void fuse_page_descs_length_init(struct fuse_req *req,
  		unsigned index, unsigned nr_pages)
  {
  	int i;
  
  	for (i = index; i < index + nr_pages; i++)
  		req->page_descs[i].length = PAGE_SIZE -
  			req->page_descs[i].offset;
  }
  
  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_req *req, struct iov_iter *ii,
  			       size_t *nbytesp, int write)
  {
  	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)
  			req->in.args[1].value = (void *) user_addr;
  		else
  			req->out.args[0].value = (void *) user_addr;
  
  		iov_iter_advance(ii, frag_size);
  		*nbytesp = frag_size;
  		return 0;
  	}
  
  	while (nbytes < *nbytesp && req->num_pages < req->max_pages) {
  		unsigned npages;
  		size_t start;
  		ret = iov_iter_get_pages(ii, &req->pages[req->num_pages],
  					*nbytesp - nbytes,
  					req->max_pages - req->num_pages,
  					&start);
  		if (ret < 0)
  			break;
  
  		iov_iter_advance(ii, ret);
  		nbytes += ret;
  
  		ret += start;
  		npages = (ret + PAGE_SIZE - 1) / PAGE_SIZE;
  
  		req->page_descs[req->num_pages].offset = start;
  		fuse_page_descs_length_init(req, req->num_pages, npages);
  
  		req->num_pages += npages;
  		req->page_descs[req->num_pages - 1].length -=
  			(PAGE_SIZE - ret) & (PAGE_SIZE - 1);
  	}
  
  	if (write)
  		req->in.argpages = 1;
  	else
  		req->out.argpages = 1;
  
  	*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->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;
  	struct fuse_req *req;
  	int err = 0;
  
  	if (io->async)
  		req = fuse_get_req_for_background(fc, iov_iter_npages(iter,
  								fc->max_pages));
  	else
  		req = fuse_get_req(fc, iov_iter_npages(iter, fc->max_pages));
  	if (IS_ERR(req))
  		return PTR_ERR(req);
  
  	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 && iter_is_iovec(iter);
  	while (count) {
  		size_t nres;
  		fl_owner_t owner = current->files;
  		size_t nbytes = min(count, nmax);
  		err = fuse_get_user_pages(req, iter, &nbytes, write);
  		if (err && !nbytes)
  			break;
  
  		if (write)
  			nres = fuse_send_write(req, io, pos, nbytes, owner);
  		else
  			nres = fuse_send_read(req, io, pos, nbytes, owner);
  
  		if (!io->async)
  			fuse_release_user_pages(req, io->should_dirty);
  		if (req->out.h.error) {
  			err = req->out.h.error;
  			break;
  		} else if (nres > nbytes) {
  			res = 0;
  			err = -EIO;
  			break;
  		}
  		count -= nres;
  		res += nres;
  		pos += nres;
  		if (nres != nbytes)
  			break;
  		if (count) {
  			fuse_put_request(fc, req);
  			if (io->async)
  				req = fuse_get_req_for_background(fc,
  					iov_iter_npages(iter, fc->max_pages));
  			else
  				req = fuse_get_req(fc, iov_iter_npages(iter,
  								fc->max_pages));
  			if (IS_ERR(req))
  				break;
  		}
  	}
  	if (!IS_ERR(req))
  		fuse_put_request(fc, req);
  	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_invalidate_attr(inode);
  	if (res > 0)
  		fuse_write_update_size(inode, iocb->ki_pos);
  	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;
  
  	if (is_bad_inode(file_inode(file)))
  		return -EIO;
  
  	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;
  
  	if (is_bad_inode(file_inode(file)))
  		return -EIO;
  
  	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_conn *fc, struct fuse_req *req)
  {
  	int i;
  
  	for (i = 0; i < req->num_pages; i++)
  		__free_page(req->pages[i]);
  
  	if (req->ff)
  		fuse_file_put(req->ff, false, false);
  }
  
  static void fuse_writepage_finish(struct fuse_conn *fc, struct fuse_req *req)
  {
  	struct inode *inode = req->inode;
  	struct fuse_inode *fi = get_fuse_inode(inode);
  	struct backing_dev_info *bdi = inode_to_bdi(inode);
  	int i;
  
  	list_del(&req->writepages_entry);
  	for (i = 0; i < req->num_pages; i++) {
  		dec_wb_stat(&bdi->wb, WB_WRITEBACK);
  		dec_node_page_state(req->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_conn *fc, struct fuse_req *req,
  				loff_t size)
  __releases(fi->lock)
  __acquires(fi->lock)
  {
  	struct fuse_req *aux, *next;
  	struct fuse_inode *fi = get_fuse_inode(req->inode);
  	struct fuse_write_in *inarg = &req->misc.write.in;
  	__u64 data_size = req->num_pages * PAGE_SIZE;
  	bool queued;
  
  	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;
  	}
  
  	req->in.args[1].size = inarg->size;
  	queued = fuse_request_queue_background(fc, req);
  	/* Fails on broken connection only */
  	if (unlikely(!queued))
  		goto out_free;
  
  	fi->writectr++;
  	return;
  
   out_free:
  	fuse_writepage_finish(fc, req);
  	spin_unlock(&fi->lock);
  
  	/* After fuse_writepage_finish() aux request list is private */
  	for (aux = req->misc.write.next; aux; aux = next) {
  		next = aux->misc.write.next;
  		aux->misc.write.next = NULL;
  		fuse_writepage_free(fc, aux);
  		fuse_put_request(fc, aux);
  	}
  
  	fuse_writepage_free(fc, req);
  	fuse_put_request(fc, req);
  	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_conn *fc = get_fuse_conn(inode);
  	struct fuse_inode *fi = get_fuse_inode(inode);
  	size_t crop = i_size_read(inode);
  	struct fuse_req *req;
  
  	while (fi->writectr >= 0 && !list_empty(&fi->queued_writes)) {
  		req = list_entry(fi->queued_writes.next, struct fuse_req, list);
  		list_del_init(&req->list);
  		fuse_send_writepage(fc, req, crop);
  	}
  }
  
  static void fuse_writepage_end(struct fuse_conn *fc, struct fuse_req *req)
  {
  	struct inode *inode = req->inode;
  	struct fuse_inode *fi = get_fuse_inode(inode);
  
  	mapping_set_error(inode->i_mapping, req->out.h.error);
  	spin_lock(&fi->lock);
  	while (req->misc.write.next) {
  		struct fuse_conn *fc = get_fuse_conn(inode);
  		struct fuse_write_in *inarg = &req->misc.write.in;
  		struct fuse_req *next = req->misc.write.next;
  		req->misc.write.next = next->misc.write.next;
  		next->misc.write.next = NULL;
  		next->ff = fuse_file_get(req->ff);
  		list_add(&next->writepages_entry, &fi->writepages);
  
  		/*
  		 * 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(fc, next, inarg->offset + inarg->size);
  	}
  	fi->writectr--;
  	fuse_writepage_finish(fc, req);
  	spin_unlock(&fi->lock);
  	fuse_writepage_free(fc, req);
  }
  
  static struct fuse_file *__fuse_write_file_get(struct fuse_conn *fc,
  					       struct fuse_inode *fi)
  {
  	struct fuse_file *ff = NULL;
  
  	spin_lock(&fi->lock);
  	if (!list_empty(&fi->write_files)) {
  		ff = list_entry(fi->write_files.next, struct fuse_file,
  				write_entry);
  		fuse_file_get(ff);
  	}
  	spin_unlock(&fi->lock);
  
  	return ff;
  }
  
  static struct fuse_file *fuse_write_file_get(struct fuse_conn *fc,
  					     struct fuse_inode *fi)
  {
  	struct fuse_file *ff = __fuse_write_file_get(fc, fi);
  	WARN_ON(!ff);
  	return ff;
  }
  
  int fuse_write_inode(struct inode *inode, struct writeback_control *wbc)
  {
  	struct fuse_conn *fc = get_fuse_conn(inode);
  	struct fuse_inode *fi = get_fuse_inode(inode);
  	struct fuse_file *ff;
  	int err;
  
  	ff = __fuse_write_file_get(fc, fi);
  	err = fuse_flush_times(inode, ff);
  	if (ff)
  		fuse_file_put(ff, false, false);
  
  	return err;
  }
  
  static int fuse_writepage_locked(struct page *page)
  {
  	struct address_space *mapping = page->mapping;
  	struct inode *inode = mapping->host;
  	struct fuse_conn *fc = get_fuse_conn(inode);
  	struct fuse_inode *fi = get_fuse_inode(inode);
  	struct fuse_req *req;
  	struct page *tmp_page;
  	int error = -ENOMEM;
  
  	set_page_writeback(page);
  
  	req = fuse_request_alloc_nofs(1);
  	if (!req)
  		goto err;
  
  	/* writeback always goes to bg_queue */
  	__set_bit(FR_BACKGROUND, &req->flags);
  	tmp_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
  	if (!tmp_page)
  		goto err_free;
  
  	error = -EIO;
  	req->ff = fuse_write_file_get(fc, fi);
  	if (!req->ff)
  		goto err_nofile;
  
  	fuse_write_fill(req, req->ff, page_offset(page), 0);
  
  	copy_highpage(tmp_page, page);
  	req->misc.write.in.write_flags |= FUSE_WRITE_CACHE;
  	req->misc.write.next = NULL;
  	req->in.argpages = 1;
  	req->num_pages = 1;
  	req->pages[0] = tmp_page;
  	req->page_descs[0].offset = 0;
  	req->page_descs[0].length = PAGE_SIZE;
  	req->end = fuse_writepage_end;
  	req->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);
  	list_add(&req->writepages_entry, &fi->writepages);
  	list_add_tail(&req->list, &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:
  	fuse_request_free(req);
  err:
  	mapping_set_error(page->mapping, error);
  	end_page_writeback(page);
  	return error;
  }
  
  static int fuse_writepage(struct page *page, struct writeback_control *wbc)
  {
  	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);
  		return 0;
  	}
  
  	err = fuse_writepage_locked(page);
  	unlock_page(page);
  
  	return err;
  }
  
  struct fuse_fill_wb_data {
  	struct fuse_req *req;
  	struct fuse_file *ff;
  	struct inode *inode;
  	struct page **orig_pages;
  };
  
  static void fuse_writepages_send(struct fuse_fill_wb_data *data)
  {
  	struct fuse_req *req = data->req;
  	struct inode *inode = data->inode;
  	struct fuse_inode *fi = get_fuse_inode(inode);
  	int num_pages = req->num_pages;
  	int i;
  
  	req->ff = fuse_file_get(data->ff);
  	spin_lock(&fi->lock);
  	list_add_tail(&req->list, &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]);
  }
  
  /*
   * First recheck under fi->lock if the offending offset is still under
   * writeback.  If yes, then 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
   * copying the new page contents over to the old temporary page.
   */
  static bool fuse_writepage_in_flight(struct fuse_req *new_req,
  				     struct page *page)
  {
  	struct fuse_conn *fc = get_fuse_conn(new_req->inode);
  	struct fuse_inode *fi = get_fuse_inode(new_req->inode);
  	struct fuse_req *tmp;
  	struct fuse_req *old_req;
  
  	WARN_ON(new_req->num_pages != 0);
  
  	spin_lock(&fi->lock);
  	list_del(&new_req->writepages_entry);
  	old_req = fuse_find_writeback(fi, page->index, page->index);
  	if (!old_req) {
  		list_add(&new_req->writepages_entry, &fi->writepages);
  		spin_unlock(&fi->lock);
  		return false;
  	}
  
  	new_req->num_pages = 1;
  	for (tmp = old_req->misc.write.next; tmp; tmp = tmp->misc.write.next) {
  		pgoff_t curr_index;
  
  		WARN_ON(tmp->inode != new_req->inode);
  		curr_index = tmp->misc.write.in.offset >> PAGE_SHIFT;
  		if (curr_index == page->index) {
  			WARN_ON(tmp->num_pages != 1);
  			WARN_ON(!test_bit(FR_PENDING, &tmp->flags));
  			swap(tmp->pages[0], new_req->pages[0]);
  			break;
  		}
  	}
  
  	if (!tmp) {
  		new_req->misc.write.next = old_req->misc.write.next;
  		old_req->misc.write.next = new_req;
  	}
  
  	spin_unlock(&fi->lock);
  
  	if (tmp) {
  		struct backing_dev_info *bdi = inode_to_bdi(new_req->inode);
  
  		dec_wb_stat(&bdi->wb, WB_WRITEBACK);
  		dec_node_page_state(new_req->pages[0], NR_WRITEBACK_TEMP);
  		wb_writeout_inc(&bdi->wb);
  		fuse_writepage_free(fc, new_req);
  		fuse_request_free(new_req);
  	}
  
  	return true;
  }
  
  static int fuse_writepages_fill(struct page *page,
  		struct writeback_control *wbc, void *_data)
  {
  	struct fuse_fill_wb_data *data = _data;
  	struct fuse_req *req = data->req;
  	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;
  	bool is_writeback;
  	int err;
  
  	if (!data->ff) {
  		err = -EIO;
  		data->ff = fuse_write_file_get(fc, get_fuse_inode(inode));
  		if (!data->ff)
  			goto out_unlock;
  	}
  
  	/*
  	 * 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.
  	 */
  	is_writeback = fuse_page_is_writeback(inode, page->index);
  
  	if (req && req->num_pages &&
  	    (is_writeback || req->num_pages == fc->max_pages ||
  	     (req->num_pages + 1) * PAGE_SIZE > fc->max_write ||
  	     data->orig_pages[req->num_pages - 1]->index + 1 != page->index)) {
  		fuse_writepages_send(data);
  		data->req = NULL;
  	} else if (req && req->num_pages == req->max_pages) {
  		if (!fuse_req_realloc_pages(fc, req, GFP_NOFS)) {
  			fuse_writepages_send(data);
  			req = data->req = 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 req->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->req == NULL) {
  		struct fuse_inode *fi = get_fuse_inode(inode);
  
  		err = -ENOMEM;
  		req = fuse_request_alloc_nofs(FUSE_REQ_INLINE_PAGES);
  		if (!req) {
  			__free_page(tmp_page);
  			goto out_unlock;
  		}
  
  		fuse_write_fill(req, data->ff, page_offset(page), 0);
  		req->misc.write.in.write_flags |= FUSE_WRITE_CACHE;
  		req->misc.write.next = NULL;
  		req->in.argpages = 1;
  		__set_bit(FR_BACKGROUND, &req->flags);
  		req->num_pages = 0;
  		req->end = fuse_writepage_end;
  		req->inode = inode;
  
  		spin_lock(&fi->lock);
  		list_add(&req->writepages_entry, &fi->writepages);
  		spin_unlock(&fi->lock);
  
  		data->req = req;
  	}
  	set_page_writeback(page);
  
  	copy_highpage(tmp_page, page);
  	req->pages[req->num_pages] = tmp_page;
  	req->page_descs[req->num_pages].offset = 0;
  	req->page_descs[req->num_pages].length = PAGE_SIZE;
  
  	inc_wb_stat(&inode_to_bdi(inode)->wb, WB_WRITEBACK);
  	inc_node_page_state(tmp_page, NR_WRITEBACK_TEMP);
  
  	err = 0;
  	if (is_writeback && fuse_writepage_in_flight(req, page)) {
  		end_page_writeback(page);
  		data->req = NULL;
  		goto out_unlock;
  	}
  	data->orig_pages[req->num_pages] = page;
  
  	/*
  	 * Protected by fi->lock against concurrent access by
  	 * fuse_page_is_writeback().
  	 */
  	spin_lock(&fi->lock);
  	req->num_pages++;
  	spin_unlock(&fi->lock);
  
  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 (is_bad_inode(inode))
  		goto out;
  
  	data.inode = inode;
  	data.req = 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.req) {
  		/* Ignore errors if we can write at least one page */
  		BUG_ON(!data.req->num_pages);
  		fuse_writepages_send(&data);
  		err = 0;
  	}
  	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, unsigned flags,
  		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, flags);
  	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;
  
  	if (!PageUptodate(page)) {
  		/* Zero any unwritten bytes at the end of the page */
  		size_t endoff = (pos + copied) & ~PAGE_MASK;
  		if (endoff)
  			zero_user_segment(page, endoff, PAGE_SIZE);
  		SetPageUptodate(page);
  	}
  
  	fuse_write_update_size(inode, pos + copied);
  	set_page_dirty(page);
  
  unlock:
  	unlock_page(page);
  	put_page(page);
  
  	return copied;
  }
  
  static int fuse_launder_page(struct page *page)
  {
  	int err = 0;
  	if (clear_page_dirty_for_io(page)) {
  		struct inode *inode = page->mapping->host;
  		err = fuse_writepage_locked(page);
  		if (!err)
  			fuse_wait_on_page_writeback(inode, page->index);
  	}
  	return err;
  }
  
  /*
   * Write back dirty pages now, because there may not be any suitable
   * open files later
   */
  static void fuse_vma_close(struct vm_area_struct *vma)
  {
  	filemap_write_and_wait(vma->vm_file->f_mapping);
  }
  
  /*
   * Wait for writeback against this page to complete before allowing it
   * to be marked dirty again, and hence written back again, possibly
   * before the previous writepage completed.
   *
   * Block here, instead of in ->writepage(), so that the userspace fs
   * can only block processes actually operating on the filesystem.
   *
   * Otherwise unprivileged userspace fs would be able to block
   * unrelated:
   *
   * - page migration
   * - sync(2)
   * - try_to_free_pages() with order > PAGE_ALLOC_COSTLY_ORDER
   */
  static 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;
  
  	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->in.h.opcode = opcode;
  	args->in.h.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_conn *fc = get_fuse_conn(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(fc, &args);
  	if (!err)
  		err = convert_fuse_file_lock(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_conn *fc = get_fuse_conn(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, 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(fc, &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_conn *fc = get_fuse_conn(inode);
  	FUSE_ARGS(args);
  	struct fuse_bmap_in inarg;
  	struct fuse_bmap_out outarg;
  	int err;
  
  	if (!inode->i_sb->s_bdev || fc->no_bmap)
  		return 0;
  
  	memset(&inarg, 0, sizeof(inarg));
  	inarg.block = block;
  	inarg.blocksize = inode->i_sb->s_blocksize;
  	args.in.h.opcode = FUSE_BMAP;
  	args.in.h.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(fc, &args);
  	if (err == -ENOSYS)
  		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_conn *fc = get_fuse_conn(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 (fc->no_lseek)
  		goto fallback;
  
  	args.in.h.opcode = FUSE_LSEEK;
  	args.in.h.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(fc, &args);
  	if (err) {
  		if (err == -ENOSYS) {
  			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);
  	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);
  		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;
  }
  
  /*
   * CUSE servers compiled on 32bit broke on 64bit kernels because the
   * ABI was defined to be 'struct iovec' which is different on 32bit
   * and 64bit.  Fortunately we can determine which structure the server
   * used from the size of the reply.
   */
  static int fuse_copy_ioctl_iovec_old(struct iovec *dst, void *src,
  				     size_t transferred, unsigned count,
  				     bool is_compat)
  {
  #ifdef CONFIG_COMPAT
  	if (count * sizeof(struct compat_iovec) == transferred) {
  		struct compat_iovec *ciov = src;
  		unsigned i;
  
  		/*
  		 * With this interface a 32bit server cannot support
  		 * non-compat (i.e. ones coming from 64bit apps) ioctl
  		 * requests
  		 */
  		if (!is_compat)
  			return -EINVAL;
  
  		for (i = 0; i < count; i++) {
  			dst[i].iov_base = compat_ptr(ciov[i].iov_base);
  			dst[i].iov_len = ciov[i].iov_len;
  		}
  		return 0;
  	}
  #endif
  
  	if (count * sizeof(struct iovec) != transferred)
  		return -EIO;
  
  	memcpy(dst, src, transferred);
  	return 0;
  }
  
  /* Make sure iov_length() won't overflow */
  static int fuse_verify_ioctl_iov(struct fuse_conn *fc, struct iovec *iov,
  				 size_t count)
  {
  	size_t n;
  	u32 max = fc->max_pages << PAGE_SHIFT;
  
  	for (n = 0; n < count; n++, iov++) {
  		if (iov->iov_len > (size_t) max)
  			return -ENOMEM;
  		max -= iov->iov_len;
  	}
  	return 0;
  }
  
  static int fuse_copy_ioctl_iovec(struct fuse_conn *fc, struct iovec *dst,
  				 void *src, size_t transferred, unsigned count,
  				 bool is_compat)
  {
  	unsigned i;
  	struct fuse_ioctl_iovec *fiov = src;
  
  	if (fc->minor < 16) {
  		return fuse_copy_ioctl_iovec_old(dst, src, transferred,
  						 count, is_compat);
  	}
  
  	if (count * sizeof(struct fuse_ioctl_iovec) != transferred)
  		return -EIO;
  
  	for (i = 0; i < count; i++) {
  		/* Did the server supply an inappropriate value? */
  		if (fiov[i].base != (unsigned long) fiov[i].base ||
  		    fiov[i].len != (unsigned long) fiov[i].len)
  			return -EIO;
  
  		dst[i].iov_base = (void __user *) (unsigned long) fiov[i].base;
  		dst[i].iov_len = (size_t) fiov[i].len;
  
  #ifdef CONFIG_COMPAT
  		if (is_compat &&
  		    (ptr_to_compat(dst[i].iov_base) != fiov[i].base ||
  		     (compat_size_t) dst[i].iov_len != fiov[i].len))
  			return -EIO;
  #endif
  	}
  
  	return 0;
  }
  
  
  /*
   * For ioctls, there is no generic way to determine how much memory
   * needs to be read and/or written.  Furthermore, ioctls are allowed
   * to dereference the passed pointer, so the parameter requires deep
   * copying but FUSE has no idea whatsoever about what to copy in or
   * out.
   *
   * This is solved by allowing FUSE server to retry ioctl with
   * necessary in/out iovecs.  Let's assume the ioctl implementation
   * needs to read in the following structure.
   *
   * struct a {
   *	char	*buf;
   *	size_t	buflen;
   * }
   *
   * On the first callout to FUSE server, inarg->in_size and
   * inarg->out_size will be NULL; then, the server completes the ioctl
   * with FUSE_IOCTL_RETRY set in out->flags, out->in_iovs set to 1 and
   * the actual iov array to
   *
   * { { .iov_base = inarg.arg,	.iov_len = sizeof(struct a) } }
   *
   * which tells FUSE to copy in the requested area and retry the ioctl.
   * On the second round, the server has access to the structure and
   * from that it can tell what to look for next, so on the invocation,
   * it sets FUSE_IOCTL_RETRY, out->in_iovs to 2 and iov array to
   *
   * { { .iov_base = inarg.arg,	.iov_len = sizeof(struct a)	},
   *   { .iov_base = a.buf,	.iov_len = a.buflen		} }
   *
   * FUSE will copy both struct a and the pointed buffer from the
   * process doing the ioctl and retry ioctl with both struct a and the
   * buffer.
   *
   * This time, FUSE server has everything it needs and completes ioctl
   * without FUSE_IOCTL_RETRY which finishes the ioctl call.
   *
   * Copying data out works the same way.
   *
   * Note that if FUSE_IOCTL_UNRESTRICTED is clear, the kernel
   * automatically initializes in and out iovs by decoding @cmd with
   * _IOC_* macros and the server is not allowed to request RETRY.  This
   * limits ioctl data transfers to well-formed ioctls and is the forced
   * behavior for all FUSE servers.
   */
  long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
  		   unsigned int flags)
  {
  	struct fuse_file *ff = file->private_data;
  	struct fuse_conn *fc = ff->fc;
  	struct fuse_ioctl_in inarg = {
  		.fh = ff->fh,
  		.cmd = cmd,
  		.arg = arg,
  		.flags = flags
  	};
  	struct fuse_ioctl_out outarg;
  	struct fuse_req *req = NULL;
  	struct page **pages = NULL;
  	struct iovec *iov_page = NULL;
  	struct iovec *in_iov = NULL, *out_iov = NULL;
  	unsigned int in_iovs = 0, out_iovs = 0, num_pages = 0, max_pages;
  	size_t in_size, out_size, transferred, c;
  	int err, i;
  	struct iov_iter ii;
  
  #if BITS_PER_LONG == 32
  	inarg.flags |= FUSE_IOCTL_32BIT;
  #else
  	if (flags & FUSE_IOCTL_COMPAT)
  		inarg.flags |= FUSE_IOCTL_32BIT;
  #endif
  
  	/* assume all the iovs returned by client always fits in a page */
  	BUILD_BUG_ON(sizeof(struct fuse_ioctl_iovec) * FUSE_IOCTL_MAX_IOV > PAGE_SIZE);
  
  	err = -ENOMEM;
  	pages = kcalloc(fc->max_pages, sizeof(pages[0]), GFP_KERNEL);
  	iov_page = (struct iovec *) __get_free_page(GFP_KERNEL);
  	if (!pages || !iov_page)
  		goto out;
  
  	/*
  	 * If restricted, initialize IO parameters as encoded in @cmd.
  	 * RETRY from server is not allowed.
  	 */
  	if (!(flags & FUSE_IOCTL_UNRESTRICTED)) {
  		struct iovec *iov = iov_page;
  
  		iov->iov_base = (void __user *)arg;
  		iov->iov_len = _IOC_SIZE(cmd);
  
  		if (_IOC_DIR(cmd) & _IOC_WRITE) {
  			in_iov = iov;
  			in_iovs = 1;
  		}
  
  		if (_IOC_DIR(cmd) & _IOC_READ) {
  			out_iov = iov;
  			out_iovs = 1;
  		}
  	}
  
   retry:
  	inarg.in_size = in_size = iov_length(in_iov, in_iovs);
  	inarg.out_size = out_size = iov_length(out_iov, out_iovs);
  
  	/*
  	 * Out data can be used either for actual out data or iovs,
  	 * make sure there always is at least one page.
  	 */
  	out_size = max_t(size_t, out_size, PAGE_SIZE);
  	max_pages = DIV_ROUND_UP(max(in_size, out_size), PAGE_SIZE);
  
  	/* make sure there are enough buffer pages and init request with them */
  	err = -ENOMEM;
  	if (max_pages > fc->max_pages)
  		goto out;
  	while (num_pages < max_pages) {
  		pages[num_pages] = alloc_page(GFP_KERNEL | __GFP_HIGHMEM);
  		if (!pages[num_pages])
  			goto out;
  		num_pages++;
  	}
  
  	req = fuse_get_req(fc, num_pages);
  	if (IS_ERR(req)) {
  		err = PTR_ERR(req);
  		req = NULL;
  		goto out;
  	}
  	memcpy(req->pages, pages, sizeof(req->pages[0]) * num_pages);
  	req->num_pages = num_pages;
  	fuse_page_descs_length_init(req, 0, req->num_pages);
  
  	/* okay, let's send it to the client */
  	req->in.h.opcode = FUSE_IOCTL;
  	req->in.h.nodeid = ff->nodeid;
  	req->in.numargs = 1;
  	req->in.args[0].size = sizeof(inarg);
  	req->in.args[0].value = &inarg;
  	if (in_size) {
  		req->in.numargs++;
  		req->in.args[1].size = in_size;
  		req->in.argpages = 1;
  
  		err = -EFAULT;
  		iov_iter_init(&ii, WRITE, in_iov, in_iovs, in_size);
  		for (i = 0; iov_iter_count(&ii) && !WARN_ON(i >= num_pages); i++) {
  			c = copy_page_from_iter(pages[i], 0, PAGE_SIZE, &ii);
  			if (c != PAGE_SIZE && iov_iter_count(&ii))
  				goto out;
  		}
  	}
  
  	req->out.numargs = 2;
  	req->out.args[0].size = sizeof(outarg);
  	req->out.args[0].value = &outarg;
  	req->out.args[1].size = out_size;
  	req->out.argpages = 1;
  	req->out.argvar = 1;
  
  	fuse_request_send(fc, req);
  	err = req->out.h.error;
  	transferred = req->out.args[1].size;
  	fuse_put_request(fc, req);
  	req = NULL;
  	if (err)
  		goto out;
  
  	/* did it ask for retry? */
  	if (outarg.flags & FUSE_IOCTL_RETRY) {
  		void *vaddr;
  
  		/* no retry if in restricted mode */
  		err = -EIO;
  		if (!(flags & FUSE_IOCTL_UNRESTRICTED))
  			goto out;
  
  		in_iovs = outarg.in_iovs;
  		out_iovs = outarg.out_iovs;
  
  		/*
  		 * Make sure things are in boundary, separate checks
  		 * are to protect against overflow.
  		 */
  		err = -ENOMEM;
  		if (in_iovs > FUSE_IOCTL_MAX_IOV ||
  		    out_iovs > FUSE_IOCTL_MAX_IOV ||
  		    in_iovs + out_iovs > FUSE_IOCTL_MAX_IOV)
  			goto out;
  
  		vaddr = kmap_atomic(pages[0]);
  		err = fuse_copy_ioctl_iovec(fc, iov_page, vaddr,
  					    transferred, in_iovs + out_iovs,
  					    (flags & FUSE_IOCTL_COMPAT) != 0);
  		kunmap_atomic(vaddr);
  		if (err)
  			goto out;
  
  		in_iov = iov_page;
  		out_iov = in_iov + in_iovs;
  
  		err = fuse_verify_ioctl_iov(fc, in_iov, in_iovs);
  		if (err)
  			goto out;
  
  		err = fuse_verify_ioctl_iov(fc, out_iov, out_iovs);
  		if (err)
  			goto out;
  
  		goto retry;
  	}
  
  	err = -EIO;
  	if (transferred > inarg.out_size)
  		goto out;
  
  	err = -EFAULT;
  	iov_iter_init(&ii, READ, out_iov, out_iovs, transferred);
  	for (i = 0; iov_iter_count(&ii) && !WARN_ON(i >= num_pages); i++) {
  		c = copy_page_to_iter(pages[i], 0, PAGE_SIZE, &ii);
  		if (c != PAGE_SIZE && iov_iter_count(&ii))
  			goto out;
  	}
  	err = 0;
   out:
  	if (req)
  		fuse_put_request(fc, req);
  	free_page((unsigned long) iov_page);
  	while (num_pages)
  		__free_page(pages[--num_pages]);
  	kfree(pages);
  
  	return err ? err : outarg.result;
  }
  EXPORT_SYMBOL_GPL(fuse_do_ioctl);
  
  long fuse_ioctl_common(struct file *file, unsigned int cmd,
  		       unsigned long arg, unsigned int flags)
  {
  	struct inode *inode = file_inode(file);
  	struct fuse_conn *fc = get_fuse_conn(inode);
  
  	if (!fuse_allow_current_process(fc))
  		return -EACCES;
  
  	if (is_bad_inode(inode))
  		return -EIO;
  
  	return fuse_do_ioctl(file, cmd, arg, flags);
  }
  
  static long fuse_file_ioctl(struct file *file, unsigned int cmd,
  			    unsigned long arg)
  {
  	return fuse_ioctl_common(file, cmd, arg, 0);
  }
  
  static long fuse_file_compat_ioctl(struct file *file, unsigned int cmd,
  				   unsigned long arg)
  {
  	return fuse_ioctl_common(file, cmd, arg, FUSE_IOCTL_COMPAT);
  }
  
  /*
   * All files which have been polled are linked to RB tree
   * fuse_conn->polled_files which is indexed by kh.  Walk the tree and
   * find the matching one.
   */
  static struct rb_node **fuse_find_polled_node(struct fuse_conn *fc, u64 kh,
  					      struct rb_node **parent_out)
  {
  	struct rb_node **link = &fc->polled_files.rb_node;
  	struct rb_node *last = NULL;
  
  	while (*link) {
  		struct fuse_file *ff;
  
  		last = *link;
  		ff = rb_entry(last, struct fuse_file, polled_node);
  
  		if (kh < ff->kh)
  			link = &last->rb_left;
  		else if (kh > ff->kh)
  			link = &last->rb_right;
  		else
  			return link;
  	}
  
  	if (parent_out)
  		*parent_out = last;
  	return link;
  }
  
  /*
   * The file is about to be polled.  Make sure it's on the polled_files
   * RB tree.  Note that files once added to the polled_files tree are
   * not removed before the file is released.  This is because a file
   * polled once is likely to be polled again.
   */
  static void fuse_register_polled_file(struct fuse_conn *fc,
  				      struct fuse_file *ff)
  {
  	spin_lock(&fc->lock);
  	if (RB_EMPTY_NODE(&ff->polled_node)) {
  		struct rb_node **link, *uninitialized_var(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_conn *fc = ff->fc;
  	struct fuse_poll_in inarg = { .fh = ff->fh, .kh = ff->kh };
  	struct fuse_poll_out outarg;
  	FUSE_ARGS(args);
  	int err;
  
  	if (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(fc, ff);
  	}
  
  	args.in.h.opcode = FUSE_POLL;
  	args.in.h.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(fc, &args);
  
  	if (!err)
  		return demangle_poll(outarg.revents);
  	if (err == -ENOSYS) {
  		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;
  	bool async_dio = ff->fc->async_dio;
  	loff_t pos = 0;
  	struct inode *inode;
  	loff_t i_size;
  	size_t count = iov_iter_count(iter);
  	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;
  
  	/* optimization for short read */
  	if (async_dio && iov_iter_rw(iter) != WRITE && offset + count > i_size) {
  		if (offset >= i_size)
  			return 0;
  		iov_iter_truncate(iter, fuse_round_up(ff->fc, i_size - offset));
  		count = iov_iter_count(iter);
  	}
  
  	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 = async_dio;
  	io->iocb = iocb;
  	io->blocking = is_sync_kiocb(iocb);
  
  	/*
  	 * 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) && iov_iter_rw(iter) == 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(inode);
  	} else {
  		ret = __fuse_direct_read(io, iter, &pos);
  	}
  
  	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) {
  		if (ret > 0)
  			fuse_write_update_size(inode, pos);
  		else if (ret < 0 && offset + count > i_size)
  			fuse_do_truncate(file);
  	}
  
  	return ret;
  }
  
  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_conn *fc = ff->fc;
  	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);
  
  	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
  		return -EOPNOTSUPP;
  
  	if (fc->no_fallocate)
  		return -EOPNOTSUPP;
  
  	if (lock_inode) {
  		inode_lock(inode);
  		if (mode & FALLOC_FL_PUNCH_HOLE) {
  			loff_t endbyte = offset + length - 1;
  			err = filemap_write_and_wait_range(inode->i_mapping,
  							   offset, endbyte);
  			if (err)
  				goto out;
  
  			fuse_sync_writes(inode);
  		}
  	}
  
  	if (!(mode & FALLOC_FL_KEEP_SIZE))
  		set_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
  
  	args.in.h.opcode = FUSE_FALLOCATE;
  	args.in.h.nodeid = ff->nodeid;
  	args.in.numargs = 1;
  	args.in.args[0].size = sizeof(inarg);
  	args.in.args[0].value = &inarg;
  	err = fuse_simple_request(fc, &args);
  	if (err == -ENOSYS) {
  		fc->no_fallocate = 1;
  		err = -EOPNOTSUPP;
  	}
  	if (err)
  		goto out;
  
  	/* we could have extended the file */
  	if (!(mode & FALLOC_FL_KEEP_SIZE)) {
  		bool changed = fuse_write_update_size(inode, offset + length);
  
  		if (changed && fc->writeback_cache)
  			file_update_time(file);
  	}
  
  	if (mode & FALLOC_FL_PUNCH_HOLE)
  		truncate_pagecache_range(inode, offset, offset + length - 1);
  
  	fuse_invalidate_attr(inode);
  
  out:
  	if (!(mode & FALLOC_FL_KEEP_SIZE))
  		clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
  
  	if (lock_inode)
  		inode_unlock(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_out = file_inode(file_out);
  	struct fuse_inode *fi_out = get_fuse_inode(inode_out);
  	struct fuse_conn *fc = ff_in->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;
  
  	inode_lock(inode_out);
  
  	if (fc->writeback_cache) {
  		err = filemap_write_and_wait_range(inode_out->i_mapping,
  						   pos_out, pos_out + len);
  		if (err)
  			goto out;
  
  		fuse_sync_writes(inode_out);
  	}
  
  	if (is_unstable)
  		set_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);
  
  	args.in.h.opcode = FUSE_COPY_FILE_RANGE;
  	args.in.h.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(fc, &args);
  	if (err == -ENOSYS) {
  		fc->no_copy_file_range = 1;
  		err = -EOPNOTSUPP;
  	}
  	if (err)
  		goto out;
  
  	if (fc->writeback_cache) {
  		fuse_write_update_size(inode_out, pos_out + outarg.size);
  		file_update_time(file_out);
  	}
  
  	fuse_invalidate_attr(inode_out);
  
  	err = outarg.size;
  out:
  	if (is_unstable)
  		clear_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);
  
  	inode_unlock(inode_out);
  
  	return err;
  }
  
  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,
  	.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  = {
  	.readpage	= fuse_readpage,
  	.writepage	= fuse_writepage,
  	.writepages	= fuse_writepages,
  	.launder_page	= fuse_launder_page,
  	.readpages	= fuse_readpages,
  	.set_page_dirty	= __set_page_dirty_nobuffers,
  	.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)
  {
  	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);
  	INIT_LIST_HEAD(&fi->writepages);
  }
  