NFS: Add the mount option "nosharecache"

Prior to David Howell's mount changes in 2.6.18, users who mounted
different directories which happened to be from the same filesystem on the
server would get different super blocks, and hence could choose different
mount options. As long as there were no hard linked files that crossed from
one subtree to another, this was quite safe.
Post the changes, if the two directories are on the same filesystem (have
the same 'fsid'), they will share the same super block, and hence the same
mount options.

Add a flag to allow users to elect not to share the NFS super block with
another mount point, even if the fsids are the same. This will allow
users to set different mount options for the two different super blocks, as
was previously possible. It is still up to the user to ensure that there
are no cache coherency issues when doing this, however the default
behaviour will be to share super blocks whenever two paths result in
the same fsid.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 3 insertions, 1 deletions

diff --git a/include/linux/nfs4_mount.h b/include/linux/nfs4_mount.h
index d8d7480e5a47..a0dcf6655657 100644
--- a/include/linux/nfs4_mount.h
+++ b/include/linux/nfs4_mount.h
@@ -65,6 +65,7 @@ struct nfs4_mount_data {
 #define NFS4_MOUNT_NOCTO        0x0010  /* 1 */
 #define NFS4_MOUNT_NOAC         0x0020  /* 1 */
 #define NFS4_MOUNT_STRICTLOCK   0x1000  /* 1 */
-#define NFS4_MOUNT_FLAGMASK     0x1033
+#define NFS4_MOUNT_UNSHARED     0x8000  /* 1 */
+#define NFS4_MOUNT_FLAGMASK     0x9033
 
 #endif
diff --git a/include/linux/nfs_mount.h b/include/linux/nfs_mount.h
index 0b82a17c705b..a3ade89a64d2 100644
--- a/include/linux/nfs_mount.h
+++ b/include/linux/nfs_mount.h
@@ -62,6 +62,7 @@ struct nfs_mount_data {
 #define NFS_MOUNT_STRICTLOCK    0x1000  /* reserved for NFSv4 */
 #define NFS_MOUNT_SECFLAVOUR    0x2000  /* 5 */
 #define NFS_MOUNT_NORDIRPLUS    0x4000  /* 5 */
+#define NFS_MOUNT_UNSHARED      0x8000  /* 5 */
 #define NFS_MOUNT_FLAGMASK      0xFFFF
 
 #endif