[PATCH/RFC v3 10/10] New mount option for volatile filehandle recovery

[Matthew Treinish <treinish@linux.vnet.ibm.com>]

The new 'vfhretry' mount option will be used to enable the volatile filehandle
recovery routines in the client. On an expired filehandle recover the client
will attempt to recover by performing a lookup on the name of the file.

This option enables volatile filehandle recovery by re-lookup on FHEXPIRED
errors. Only use this mount option if the filenames/paths on the server are not
going to change from the initial expiration until all the recovery operations
complete. Otherwise the validity of the files recovered from the server can not
be guaranteed. It can only truly be considered safe to use this recovery
mechanism on a linux server, if the filesystem is read-only.

This mechanism of recovery isn't necessarily safe for a posix filesystem so
using the mount option will allow the user to enable this at their own risk.
If the mount option is not turned on, the FHEXPIRED error will be converted to
ESTALE.

Signed-off-by: Matthew Treinish <treinish@linux.vnet.ibm.com>
---
 fs/nfs/super.c            |    6 ++++++
 include/linux/nfs_mount.h |    1 +
 2 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 6708f30..6c0be34e 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -87,6 +87,7 @@ enum {
 	Opt_sharecache, Opt_nosharecache,
 	Opt_resvport, Opt_noresvport,
 	Opt_fscache, Opt_nofscache,
+	Opt_vfhretry,
 
 	/* Mount options that take integer arguments */
 	Opt_port,
@@ -151,6 +152,7 @@ static const match_table_t nfs_mount_option_tokens = {
 	{ Opt_noresvport, "noresvport" },
 	{ Opt_fscache, "fsc" },
 	{ Opt_nofscache, "nofsc" },
+	{ Opt_vfhretry, "vfhretry" },
 
 	{ Opt_port, "port=%s" },
 	{ Opt_rsize, "rsize=%s" },
@@ -652,6 +654,7 @@ static void nfs_show_mount_options(struct seq_file *m, struct nfs_server *nfss,
 		{ NFS_MOUNT_NORDIRPLUS, ",nordirplus", "" },
 		{ NFS_MOUNT_UNSHARED, ",nosharecache", "" },
 		{ NFS_MOUNT_NORESVPORT, ",noresvport", "" },
+		{ NFS_MOUNT_VFHRETRY, ",vfhretry", ""},
 		{ 0, NULL, NULL }
 	};
 	const struct proc_nfs_info *nfs_infop;
@@ -1230,6 +1233,9 @@ static int nfs_parse_mount_options(char *raw,
 			kfree(mnt->fscache_uniq);
 			mnt->fscache_uniq = NULL;
 			break;
+		case Opt_vfhretry:
+			mnt->flags |= NFS_MOUNT_VFHRETRY;
+			break;
 
 		/*
 		 * options that take numeric values
diff --git a/include/linux/nfs_mount.h b/include/linux/nfs_mount.h
index 576bddd..dba0e23 100644
--- a/include/linux/nfs_mount.h
+++ b/include/linux/nfs_mount.h
@@ -73,5 +73,6 @@ struct nfs_mount_data {
 
 #define NFS_MOUNT_LOCAL_FLOCK	0x100000
 #define NFS_MOUNT_LOCAL_FCNTL	0x200000
+#define NFS_MOUNT_VFHRETRY	0x400000
 
 #endif
-- 
1.7.4.4