afs: Overhaul permit caching

Overhaul permit caching in AFS by making it per-vnode and sharing permit
lists where possible.

When most of the fileserver operations are called, they return a status
structure indicating the (revised) details of the vnode or vnodes involved
in the operation.  This includes the access mark derived from the ACL
(named CallerAccess in the protocol definition file).  This is cacheable
and if the ACL changes, the server will tell us that it is breaking the
callback promise, at which point we can discard the currently cached
permits.

With this patch, the afs_permits structure has, at the end, an array of
{ key, CallerAccess } elements, sorted by key pointer.  This is then cached
in a hash table so that it can be shared between vnodes with the same
access permits.

Permit lists can only be shared if they contain the exact same set of
key->CallerAccess mappings.

Note that that table is global rather than being per-net_ns.  If the keys
in a permit list cross net_ns boundaries, there is no problem sharing the
cached permits, since the permits are just integer masks.

Since permit lists pin keys, the permit cache also makes it easier for a
future patch to find all occurrences of a key and remove them by means of
setting the afs_permits::invalidated flag and then clearing the appropriate
key pointer.  In such an event, memory barriers will need adding.

Lastly, the permit caching is skipped if the server has sent either a
vnode-specific or an entire-server callback since the start of the
operation.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 4 insertions, 8 deletions

diff --git a/fs/afs/vnode.c b/fs/afs/vnode.c
index c1bf2124cef5..622e1100099b 100644
--- a/fs/afs/vnode.c
+++ b/fs/afs/vnode.c
@@ -88,11 +88,10 @@ static void afs_vnode_status_update_failed(struct afs_vnode *vnode, int ret)
  *   - there are any outstanding ops that will fetch the status
  * - TODO implement local caching
  */
-int afs_vnode_fetch_status(struct afs_vnode *vnode, struct afs_vnode *auth_vnode,
-			   struct key *key, bool force)
+int afs_vnode_fetch_status(struct afs_vnode *vnode, struct key *key, bool force)
 {
 	struct afs_server *server;
-	unsigned long acl_order;
+	unsigned int cb_break = 0;
 	int ret;
 
 	DECLARE_WAITQUEUE(myself, current);
@@ -113,9 +112,7 @@ int afs_vnode_fetch_status(struct afs_vnode *vnode, struct afs_vnode *auth_vnode
 		return -ENOENT;
 	}
 
-	acl_order = 0;
-	if (auth_vnode)
-		acl_order = auth_vnode->acl_order;
+	cb_break = vnode->cb_break + vnode->cb_s_break;
 
 	spin_lock(&vnode->lock);
 
@@ -192,8 +189,7 @@ get_anyway:
 	/* adjust the flags */
 	if (ret == 0) {
 		_debug("adjust");
-		if (auth_vnode)
-			afs_cache_permit(vnode, key, acl_order);
+		afs_cache_permit(vnode, key, cb_break);
 		afs_vnode_finalise_status_update(vnode, server);
 		afs_put_server(afs_v2net(vnode), server);
 	} else {