Implemented a mount option "nocto" that disables cache coherency

checking at open time.  It may improve performance for read-only
NFS mounts.  Use deliberately.

MFC after:	1 week
Reviewed by:	rmacklem, jhb (earlier version)

2 files changed, 5 insertions, 2 deletions

diff --git a/sys/fs/nfsclient/nfs_clvfsops.c b/sys/fs/nfsclient/nfs_clvfsops.c
index 9280f41..8b4fc6a 100644
--- a/sys/fs/nfsclient/nfs_clvfsops.c
+++ b/sys/fs/nfsclient/nfs_clvfsops.c
@@ -716,7 +716,7 @@ static const char *nfs_opts[] = { "from", "nfs_args",
     "retrans", "acregmin", "acregmax", "acdirmin", "acdirmax", "resvport",
     "readahead", "hostname", "timeout", "addr", "fh", "nfsv3", "sec",
     "principal", "nfsv4", "gssname", "allgssname", "dirpath",
-    "negnametimeo",
+    "negnametimeo", "nocto",
     NULL };
 
 /*
@@ -833,6 +833,8 @@ nfs_mount(struct mount *mp)
 	}
 	if (vfs_getopt(mp->mnt_optnew, "allgssname", NULL, NULL) == 0)
 		args.flags |= NFSMNT_ALLGSSNAME;
+	if (vfs_getopt(mp->mnt_optnew, "nocto", NULL, NULL) == 0)
+		args.flags |= NFSMNT_NOCTO;
 	if (vfs_getopt(mp->mnt_optnew, "readdirsize", (void **)&opt, NULL) == 0) {
 		if (opt == NULL) { 
 			vfs_mount_error(mp, "illegal readdirsize");
diff --git a/sys/fs/nfsclient/nfs_clvnops.c b/sys/fs/nfsclient/nfs_clvnops.c
index cc9563a..6dc709f 100644
--- a/sys/fs/nfsclient/nfs_clvnops.c
+++ b/sys/fs/nfsclient/nfs_clvnops.c
@@ -1026,7 +1026,8 @@ nfs_lookup(struct vop_lookup_args *ap)
 		 */
 		newvp = *vpp;
 		newnp = VTONFS(newvp);
-		if ((flags & (ISLASTCN | ISOPEN)) == (ISLASTCN | ISOPEN) &&
+		if (!(nmp->nm_flag & NFSMNT_NOCTO) &&
+		    (flags & (ISLASTCN | ISOPEN)) == (ISLASTCN | ISOPEN) &&
 		    !(newnp->n_flag & NMODIFIED)) {
 			mtx_lock(&newnp->n_mtx);
 			newnp->n_attrstamp = 0;