[PATCH v2 2/9] netfs: Fix unbuffered/DIO write partial transfer error return

[David Howells <dhowells@redhat.com>]

Fix unbuffered/DIO write to return the amount of data transferred in
preference to an error if a partial transfer has been achieved, and to
prefer an error stashed in the request over the one returned by
netfs_unbuffered_write() (likely -EINTR or -ERESTARTSYS).

Fixes: a0b4c7a49137e ("netfs: Fix unbuffered/DIO writes to dispatch subrequests in strict sequence")
Link: https://sashiko.dev/#/patchset/20260824120224.504575-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Paulo Alcantara <pc@manguebit.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/netfs/direct_write.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
index b04019097ab8..544a4243fc59 100644
--- a/fs/netfs/direct_write.c
+++ b/fs/netfs/direct_write.c
@@ -139,13 +139,11 @@ static int netfs_unbuffered_write(struct netfs_io_request *wreq)
 		if (test_bit(NETFS_SREQ_NEED_RETRY, &subreq->flags)) {
 			retry = true;
 		} else if (test_bit(NETFS_SREQ_FAILED, &subreq->flags)) {
-			ret = subreq->error;
-			wreq->error = ret;
+			wreq->error = subreq->error;
 			netfs_see_subrequest(subreq, netfs_sreq_trace_see_failed);
 			subreq = NULL;
 			break;
 		}
-		ret = 0;
 
 		if (!retry) {
 			netfs_unbuffered_write_collect(wreq, stream, subreq);
@@ -288,11 +286,11 @@ ssize_t netfs_unbuffered_write_iter_locked(struct kiocb *iocb, struct iov_iter *
 		ret = -EIOCBQUEUED;
 	} else {
 		ret = netfs_unbuffered_write(wreq);
-		if (ret < 0) {
-			_debug("begin = %zd", ret);
-		} else {
+		if (wreq->transferred) {
 			iocb->ki_pos += wreq->transferred;
-			ret = wreq->transferred ?: wreq->error;
+			ret = wreq->transferred;
+		} else if (wreq->error) {
+			ret = wreq->error;
 		}
 
 		netfs_put_request(wreq, netfs_rreq_trace_put_complete);