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)

sbin/mount_nfs/mount_nfs.8

@@ -28,7 +28,7 @@
 .\"	@(#)mount_nfs.8	8.3 (Berkeley) 3/29/95
 .\" $FreeBSD$
 .\"
-.Dd April 27, 2011
+.Dd May 3, 2011
 .Dt MOUNT_NFS 8
 .Os
 .Sh NAME
@@ -180,6 +180,17 @@ NFS port number 2049 or replies to requests using a different IP address
 Setting the
 .Va vfs.nfs.nfs_ip_paranoia
 sysctl to 0 will make this option the default.
+.It Cm nocto
+Normally, NFS clients maintain the close-to-open cache coherency.
+This works by flushing at close time and checking at open time.
+Checking at open time is implemented by getting attributes from
+the server and purging the data cache if they do not match
+attributes cached by the client.
+.Pp
+This option disables checking at open time.
+It may improve performance for read-only mounts,
+but should only be used if the data on the server changes rarely.
+Be sure to understand the consequences before enabling this option.
 .It Cm noinet4 , noinet6
 Disables
 .Dv AF_INET

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");

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;

sys/nfs/nfs_diskless.c

@@ -112,6 +112,8 @@ nfs_parse_options(const char *envopts, struct nfs_args *nd)
 			nd->flags |= NFSMNT_NOCONN;
 		else if (strcmp(o, "nolockd") == 0)
 			nd->flags |= NFSMNT_NOLOCKD;
+		else if (strcmp(o, "nocto") == 0)
+			nd->flags |= NFSMNT_NOCTO;
 		else if (strcmp(o, "nfsv2") == 0)
 			nd->flags &= ~(NFSMNT_NFSV3 | NFSMNT_NFSV4);
 		else if (strcmp(o, "nfsv3") == 0) {

sys/nfsclient/nfs_vfsops.c

@@ -786,7 +786,7 @@ static const char *nfs_opts[] = { "from", "nfs_args",
     "readahead", "readdirsize", "soft", "hard", "mntudp", "tcp", "udp",
     "wsize", "rsize", "retrans", "acregmin", "acregmax", "acdirmin",
     "acdirmax", "deadthresh", "hostname", "timeout", "addr", "fh", "nfsv3",
-    "sec", "maxgroups", "principal", "negnametimeo",
+    "sec", "maxgroups", "principal", "negnametimeo", "nocto",
     NULL };
 
 /*
@@ -901,6 +901,8 @@ nfs_mount(struct mount *mp)
 		args.sotype = SOCK_STREAM;
 	if (vfs_getopt(mp->mnt_optnew, "nfsv3", NULL, NULL) == 0)
 		args.flags |= NFSMNT_NFSV3;
+	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");

sys/nfsclient/nfs_vnops.c

@@ -960,7 +960,8 @@ 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;

sys/nfsclient/nfsargs.h

@@ -97,5 +97,6 @@ struct nfs_args {
 #define	NFSMNT_PRIVACY		0x04000000 /* Use privacy with RPCSEC_GSS */
 #define	NFSMNT_ALLGSSNAME	0x08000000 /* Use principal for all accesses */
 #define	NFSMNT_STRICT3530	0x10000000 /* Adhere strictly to RFC3530 */
+#define	NFSMNT_NOCTO		0x20000000 /* Don't flush attrcache on open */
 
 #endif