Add O_NONBLOCK to the vn_open_cred() flags for NFS client locking when

opening the POSIX fifo; convert ENXIO error returns to EOPNOTSUPP.

This improves handling of the case where the /var/run/lock fifo exists
but there is no listener: we immediately return EOPNOTSUPP rather
than blocking until a listener turns up.  This could occur during a
diskless boot before rpc.lockd is loaded, or if the lock file persists
across a reboot following the disabling of rpc.lockd.  This may have
suddenly started to occur due to fifo blocking fixes--previously it
looks like attempts to read on a fifo with no listener would time out
due to insufficient resources.

Reviewed by:	alfred

1 files changed, 13 insertions, 3 deletions

diff --git a/sys/nfsclient/nfs_lock.c b/sys/nfsclient/nfs_lock.c
index 67f049a..550a133 100644
--- a/sys/nfsclient/nfs_lock.c
+++ b/sys/nfsclient/nfs_lock.c
@@ -143,10 +143,20 @@ nfs_dolock(struct vop_advlock_args *ap)
 	 */
 	NDINIT(&nd, LOOKUP, FOLLOW, UIO_SYSSPACE, _PATH_LCKFIFO, td);
 
-	fmode = FFLAGS(O_WRONLY);
+	fmode = FFLAGS(O_WRONLY | O_NONBLOCK);
 	error = vn_open_cred(&nd, &fmode, 0, thread0.td_ucred);
-	if (error != 0) {
-		return (error == ENOENT ? EOPNOTSUPP : error);
+	switch (error) {
+	case ENOENT:
+	case ENXIO:
+		/*
+		 * Map a failure to find the fifo or no listener on the
+		 * fifo to locking not being supported.
+		 */
+		return (EOPNOTSUPP);
+	case 0:
+		break;
+	default:
+		return (error);
 	}
 	wvp = nd.ni_vp;
 	VOP_UNLOCK(wvp, 0, td);		/* vn_open leaves it locked */