Commit 0b8def9d authored by Al Viro's avatar Al Viro
Browse files

__generic_file_write_iter: keep ->ki_pos and return value consistent 



A side effect worth noting: in O_APPEND case we set ->ki_pos early,
so if it turns out to be an error or a zero-length write, we'll
end up with ->ki_pos modified.  Safe, since all callers never
look at the ->ki_pos after the call of __generic_file_write_iter()
returning non-positive, all the way to caller of ->write_iter() and
those discard ->ki_pos when getting that.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent e9d1593d

mm/filemap.c

+10 −14
Original line number Diff line number Diff line
@@ -2557,7 +2557,6 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from) 
	struct file *file = iocb->ki_filp;

	struct address_space * mapping = file->f_mapping;

	struct inode 	*inode = mapping->host;

	loff_t		pos = iocb->ki_pos;

	ssize_t		written = 0;

	ssize_t		err;

	ssize_t		status;
@@ -2565,7 +2564,7 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from) 


	/* We can write back this queue in page reclaim */

	current->backing_dev_info = inode_to_bdi(inode);

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

	err = generic_write_checks(file, &iocb->ki_pos, &count, S_ISBLK(inode->i_mode));

	if (err)

		goto out;
@@ -2583,9 +2582,9 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from) 
		goto out;



	if (io_is_direct(file)) {

		loff_t endbyte;

		loff_t pos, endbyte;



		written = generic_file_direct_write(iocb, from, pos);

		written = generic_file_direct_write(iocb, from, iocb->ki_pos);

		/*

		 * If the write stopped short of completing, fall back to

		 * buffered writes.  Some filesystems do this for writes to
@@ -2593,13 +2592,10 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from) 
		 * not succeed (even if it did, DAX does not handle dirty

		 * page-cache pages correctly).

		 */

		if (written < 0 || written == count || IS_DAX(inode))

		if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))

			goto out;



		pos += written;

		count -= written;



		status = generic_perform_write(file, from, pos);

		status = generic_perform_write(file, from, pos = iocb->ki_pos);

		/*

		 * If generic_perform_write() returned a synchronous error

		 * then we want to return the number of bytes which were
@@ -2611,15 +2607,15 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from) 
			err = status;

			goto out;

		}

		iocb->ki_pos = pos + status;

		/*

		 * We need to ensure that the page cache pages are written to

		 * disk and invalidated to preserve the expected O_DIRECT

		 * semantics.

		 */

		endbyte = pos + status - 1;

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

		err = filemap_write_and_wait_range(mapping, pos, endbyte);

		if (err == 0) {

			iocb->ki_pos = endbyte + 1;

			written += status;

			invalidate_mapping_pages(mapping,

						 pos >> PAGE_CACHE_SHIFT,
@@ -2631,9 +2627,9 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from) 
			 */

		}

	} else {

		written = generic_perform_write(file, from, pos);

		if (likely(written >= 0))

			iocb->ki_pos = pos + written;

		written = generic_perform_write(file, from, iocb->ki_pos);

		if (likely(written > 0))

			iocb->ki_pos += written;

	}

out:

	current->backing_dev_info = NULL;

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