NFS: Added support to turn off the NFSv3 READDIRPLUS RPC.

READDIRPLUS can be a performance hindrance when the client is working with
large directories. In addition, some servers still have bugs in their
implementations (e.g. Tru64 returns wrong values for the fsid).

Add a mount flag to enable users to turn it off at mount time following the
implementation in Apple's NFS client.
Signed-off-by: NSteve Dickson <steved@redhat.com>
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/client.c

@@ -618,7 +618,8 @@ static int nfs_init_server(struct nfs_server *server, const struct nfs_mount_dat
 	if (clp->cl_nfsversion == 3) {
 		if (server->namelen == 0 || server->namelen > NFS3_MAXNAMLEN)
 			server->namelen = NFS3_MAXNAMLEN;
-		server->caps |= NFS_CAP_READDIRPLUS;
+		if (!(data->flags & NFS_MOUNT_NORDIRPLUS))
+			server->caps |= NFS_CAP_READDIRPLUS;
 	} else {
 		if (server->namelen == 0 || server->namelen > NFS2_MAXNAMLEN)
 			server->namelen = NFS2_MAXNAMLEN;

fs/nfs/super.c

@@ -290,6 +290,7 @@ static void nfs_show_mount_options(struct seq_file *m, struct nfs_server *nfss,
 		{ NFS_MOUNT_NOAC, ",noac", "" },
 		{ NFS_MOUNT_NONLM, ",nolock", "" },
 		{ NFS_MOUNT_NOACL, ",noacl", "" },
+		{ NFS_MOUNT_NORDIRPLUS, ",nordirplus", "" },
 		{ 0, NULL, NULL }
 	};
 	const struct proc_nfs_info *nfs_infop;

include/linux/nfs_mount.h

@@ -61,6 +61,7 @@ struct nfs_mount_data {
 #define NFS_MOUNT_NOACL		0x0800	/* 4 */
 #define NFS_MOUNT_STRICTLOCK	0x1000	/* reserved for NFSv4 */
 #define NFS_MOUNT_SECFLAVOUR	0x2000	/* 5 */
+#define NFS_MOUNT_NORDIRPLUS	0x4000	/* 5 */
 #define NFS_MOUNT_FLAGMASK	0xFFFF
 
 #endif