fuse: update ki_pos in fuse_perform_write

Both callers of fuse_perform_write need to updated ki_pos, move it into
common code.

Link: https://lkml.kernel.org/r/20230601145904.1385409-11-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Anna Schumaker <anna@kernel.org>
Cc: Chao Yu <chao@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/fuse/file.c

@@ -1329,7 +1329,10 @@ static ssize_t fuse_perform_write(struct kiocb *iocb,
 	fuse_write_update_attr(inode, pos, res);
 	clear_bit(FUSE_I_SIZE_UNSTABLE, &fi->state);
 
-	return res > 0 ? res : err;
+	if (!res)
+		return err;
+	iocb->ki_pos += res;
+	return res;
 }
 
 static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
@@ -1341,7 +1344,6 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	struct inode *inode = mapping->host;
 	ssize_t err;
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	loff_t endbyte = 0;
 
 	if (fc->writeback_cache) {
 		/* Update size (EOF optimization) and mode (SUID clearing) */
@@ -1375,19 +1377,20 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		goto out;
 
 	if (iocb->ki_flags & IOCB_DIRECT) {
-		loff_t pos = iocb->ki_pos;
+		loff_t pos, endbyte;
+
 		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);
+		written_buffered = fuse_perform_write(iocb, mapping, from,
+						      iocb->ki_pos);
 		if (written_buffered < 0) {
 			err = written_buffered;
 			goto out;
 		}
-		endbyte = pos + written_buffered - 1;
+		pos = iocb->ki_pos - written_buffered;
+		endbyte = iocb->ki_pos - 1;
 
 		err = filemap_write_and_wait_range(file->f_mapping, pos,
 						   endbyte);
@@ -1399,11 +1402,8 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 					 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:
 	inode_unlock(inode);