NFS: DNS resolver PipeFS notifier introduced

This patch subscribes DNS resolver caches to RPC pipefs notifications. Notifier
is registering on NFS module load. This notifier callback is responsible for
creation/destruction of PipeFS DNS resolver cache directory.
Note that no locking required in notifier callback because PipeFS superblock
pointer is passed as an argument from it's creation or destruction routine and
thus we can be sure about it's validity.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 37 insertions, 1 deletions

diff --git a/fs/nfs/dns_resolve.c b/fs/nfs/dns_resolve.c
index 9aea78ab86ac..200eb67c95d9 100644
--- a/fs/nfs/dns_resolve.c
+++ b/fs/nfs/dns_resolve.c
@@ -40,6 +40,7 @@ ssize_t nfs_dns_resolve_name(struct net *net, char *name, size_t namelen,
 #include <linux/sunrpc/clnt.h>
 #include <linux/sunrpc/cache.h>
 #include <linux/sunrpc/svcauth.h>
+#include <linux/sunrpc/rpc_pipe_fs.h>
 
 #include "dns_resolve.h"
 #include "cache_lib.h"
@@ -400,12 +401,47 @@ void nfs_dns_resolver_cache_destroy(struct net *net)
         kfree(cd);
 }
 
+static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
+                           void *ptr)
+{
+        struct super_block *sb = ptr;
+        struct net *net = sb->s_fs_info;
+        struct nfs_net *nn = net_generic(net, nfs_net_id);
+        struct cache_detail *cd = nn->nfs_dns_resolve;
+        int ret = 0;
+
+        if (cd == NULL)
+                return 0;
+
+        if (!try_module_get(THIS_MODULE))
+                return 0;
+
+        switch (event) {
+        case RPC_PIPEFS_MOUNT:
+                ret = nfs_cache_register_sb(sb, cd);
+                break;
+        case RPC_PIPEFS_UMOUNT:
+                nfs_cache_unregister_sb(sb, cd);
+                break;
+        default:
+                ret = -ENOTSUPP;
+                break;
+        }
+        module_put(THIS_MODULE);
+        return ret;
+}
+
+static struct notifier_block nfs_dns_resolver_block = {
+        .notifier_call  = rpc_pipefs_event,
+};
+
 int nfs_dns_resolver_init(void)
 {
-        return 0;
+        return rpc_pipefs_notifier_register(&nfs_dns_resolver_block);
 }
 
 void nfs_dns_resolver_destroy(void)
 {
+        rpc_pipefs_notifier_unregister(&nfs_dns_resolver_block);
 }
 #endif