9pfs: fix 'total_open_fd' decrementation

According to 'man 2 close' errors returned by close() should only be used
for either diagnostic purposes or for catching data loss due to a previous
write error, as an error result of close() usually indicates a deferred
error of a previous write operation.

Therefore not decrementing 'total_open_fd' on a close() error is wrong
and would yield in a higher open file descriptor count than actually the
case, leading to 9p server reclaiming open file descriptors too soon.

Based-on: <20250312152933.383967-7-groug@kaod.org>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <E1tvEyJ-004dMa-So@kylie.crudebyte.com>

1 files changed, 9 insertions, 1 deletions

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index b22df3aa2b..8b001b9112 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -510,7 +510,15 @@ void coroutine_fn v9fs_reclaim_fd(V9fsPDU *pdu)
             err = (f->fid_type == P9_FID_DIR) ?
                 s->ops->closedir(&s->ctx, &f->fs_reclaim) :
                 s->ops->close(&s->ctx, &f->fs_reclaim);
-            if (!err) {
+
+            /* 'man 2 close' suggests to ignore close() errors except of EBADF */
+            if (unlikely(err && errno == EBADF)) {
+                /*
+                 * unexpected case as FIDs were picked above by having a valid
+                 * file descriptor
+                 */
+                error_report("9pfs: v9fs_reclaim_fd() WARNING: close() failed with EBADF");
+            } else {
                 /* total_open_fd must only be mutated on main thread */
                 nclosed++;
             }