[PATCH 5/5] 9p: Use length of data written to the server in preference to error

[David Howells]

In v9fs_upload_to_server(), we pass the error to netfslib to terminate the
subreq rather than the amount of data written - even if we did actually
write something.

Further, we assume that the write is always entirely done if successful -
but it might have been partially complete - as returned by
p9_client_write(), but we ignore that.

Fix this by indicating the amount written by preference and only returning
the error if we didn't write anything.

(We might want to return both in future if both are available as this
might be useful as to whether we retry or not.)

Suggested-by: Dominique Martinet <asmadeus at codewreck.org>
Link: https://lore.kernel.org/r/ZZULNQAZ0n0WQv7p@codewreck.org/
Signed-off-by: David Howells <dhowells at redhat.com>
cc: Eric Van Hensbergen <ericvh at kernel.org>
cc: Latchesar Ionkov <lucho at ionkov.net>
cc: Christian Schoenebeck <linux_oss at crudebyte.com>
cc: v9fs at lists.linux.dev
cc: linux-cachefs at redhat.com
cc: linux-fsdevel at vger.kernel.org
---
 fs/9p/vfs_addr.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index f7f83eec3bcc..047855033d32 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -29,12 +29,11 @@
 static void v9fs_upload_to_server(struct netfs_io_subrequest *subreq)
 {
 	struct p9_fid *fid = subreq->rreq->netfs_priv;
-	int err;
+	int err, len;
 
 	trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
-	p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
-	netfs_write_subrequest_terminated(subreq, err < 0 ? err : subreq->len,
-					  false);
+	len = p9_client_write(fid, subreq->start, &subreq->io_iter, &err);
+	netfs_write_subrequest_terminated(subreq, len ?: err, false);
 }
 
 static void v9fs_upload_to_server_worker(struct work_struct *work)