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, 34 insertions, 0 deletions

diff --git a/fs/nfs/fscache-index.c b/fs/nfs/fscache-index.c
index ff14b032459b..a824050be807 100644
--- a/fs/nfs/fscache-index.c
+++ b/fs/nfs/fscache-index.c
@@ -112,3 +112,37 @@ const struct fscache_cookie_def nfs_fscache_server_index_def = {
         .type           = FSCACHE_COOKIE_TYPE_INDEX,
         .get_key        = nfs_server_get_key,
 };
+
+/*
+ * Generate a key to describe a superblock key in the main NFS index
+ */
+static uint16_t nfs_super_get_key(const void *cookie_netfs_data,
+                                  void *buffer, uint16_t bufmax)
+{
+        const struct nfs_fscache_key *key;
+        const struct nfs_server *nfss = cookie_netfs_data;
+        uint16_t len;
+
+        key = nfss->fscache_key;
+        len = sizeof(key->key) + key->key.uniq_len;
+        if (len > bufmax) {
+                len = 0;
+        } else {
+                memcpy(buffer, &key->key, sizeof(key->key));
+                memcpy(buffer + sizeof(key->key),
+                       key->key.uniquifier, key->key.uniq_len);
+        }
+
+        return len;
+}
+
+/*
+ * Define the superblock object for FS-Cache.  This is used to describe a
+ * superblock object to fscache_acquire_cookie().  It is keyed by all the NFS
+ * parameters that might cause a separate superblock.
+ */
+const struct fscache_cookie_def nfs_fscache_super_index_def = {
+        .name           = "NFS.super",
+        .type           = FSCACHE_COOKIE_TYPE_INDEX,
+        .get_key        = nfs_super_get_key,
+};