NFS: Define and create superblock-level objects

Define and create superblock-level cache index objects (as managed by
nfs_server structs).

Each superblock object is created in a server level index object and is itself
an index into which inode-level objects are inserted.

Ideally there would be one superblock-level object per server, and the former
would be folded into the latter; however, since the "nosharecache" option
exists this isn't possible.

The superblock object key is a sequence consisting of:

 (1) Certain superblock s_flags.

 (2) Various connection parameters that serve to distinguish superblocks for
     sget().

 (3) The volume FSID.

 (4) The security flavour.

 (5) The uniquifier length.

 (6) The uniquifier text.  This is normally an empty string, unless the fsc=xyz
     mount option was used to explicitly specify a uniquifier.

The key blob is of variable length, depending on the length of (6).

The superblock object is given no coherency data to carry in the auxiliary data
permitted by the cache.  It is assumed that the superblock is always coherent.

This patch also adds uniquification handling such that two otherwise identical
superblocks, at least one of which is marked "nosharecache", won't end up
trying to share the on-disk cache.  It will be possible to manually provide a
uniquifier through a mount option with a later patch to avoid the error
otherwise produced.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 0a374b9c5093..6ad75948cbf7 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -108,6 +108,11 @@ struct nfs_server {
         unsigned long           mount_time;     /* when this fs was mounted */
         dev_t                   s_dev;          /* superblock dev numbers */
 
+#ifdef CONFIG_NFS_FSCACHE
+        struct nfs_fscache_key  *fscache_key;   /* unique key for superblock */
+        struct fscache_cookie   *fscache;       /* superblock cookie */
+#endif
+
 #ifdef CONFIG_NFS_V4
         u32                     attr_bitmask[2];/* V4 bitmask representing the set
                                                    of attributes supported on this