sunrpc: create a new dummy pipe for gssd to hold open

rpc.gssd will naturally hold open any pipe named */clnt*/gssd that shows
up under rpc_pipefs. That behavior gives us a reliable mechanism to tell
whether it's actually running or not.

Create a new toplevel "gssd" directory in rpc_pipefs when it's mounted.
Under that directory create another directory called "clntXX", and then
within that a pipe called "gssd".

We'll never send an upcall along that pipe, and any downcall written to
it will just return -EINVAL.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 90 insertions, 3 deletions

diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index bf04b30a788a..c23458b464c4 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -38,7 +38,7 @@
 #define NET_NAME(net)   ((net == &init_net) ? " (init_net)" : "")
 
 static struct file_system_type rpc_pipe_fs_type;
-
+static const struct rpc_pipe_ops gssd_dummy_pipe_ops;
 
 static struct kmem_cache *rpc_inode_cachep __read_mostly;
 
@@ -1159,6 +1159,7 @@ enum {
         RPCAUTH_nfsd4_cb,
         RPCAUTH_cache,
         RPCAUTH_nfsd,
+        RPCAUTH_gssd,
         RPCAUTH_RootEOF
 };
 
@@ -1195,6 +1196,10 @@ static const struct rpc_filelist files[] = {
                 .name = "nfsd",
                 .mode = S_IFDIR | S_IRUGO | S_IXUGO,
         },
+        [RPCAUTH_gssd] = {
+                .name = "gssd",
+                .mode = S_IFDIR | S_IRUGO | S_IXUGO,
+        },
 };
 
 /*
@@ -1208,13 +1213,25 @@ struct dentry *rpc_d_lookup_sb(const struct super_block *sb,
 }
 EXPORT_SYMBOL_GPL(rpc_d_lookup_sb);
 
-void rpc_pipefs_init_net(struct net *net)
+int rpc_pipefs_init_net(struct net *net)
 {
         struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
 
+        sn->gssd_dummy = rpc_mkpipe_data(&gssd_dummy_pipe_ops, 0);
+        if (IS_ERR(sn->gssd_dummy))
+                return PTR_ERR(sn->gssd_dummy);
+
         mutex_init(&sn->pipefs_sb_lock);
         sn->gssd_running = 1;
         sn->pipe_version = -1;
+        return 0;
+}
+
+void rpc_pipefs_exit_net(struct net *net)
+{
+        struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
+
+        rpc_destroy_pipe_data(sn->gssd_dummy);
 }
 
 /*
@@ -1244,11 +1261,73 @@ void rpc_put_sb_net(const struct net *net)
 }
 EXPORT_SYMBOL_GPL(rpc_put_sb_net);
 
+static const struct rpc_filelist gssd_dummy_clnt_dir[] = {
+        [0] = {
+                .name = "clntXX",
+                .mode = S_IFDIR | S_IRUGO | S_IXUGO,
+        },
+};
+
+static ssize_t
+dummy_downcall(struct file *filp, const char __user *src, size_t len)
+{
+        return -EINVAL;
+}
+
+static const struct rpc_pipe_ops gssd_dummy_pipe_ops = {
+        .upcall         = rpc_pipe_generic_upcall,
+        .downcall       = dummy_downcall,
+};
+
+/**
+ * rpc_gssd_dummy_populate - create a dummy gssd pipe
+ * @root:       root of the rpc_pipefs filesystem
+ * @pipe_data:  pipe data created when netns is initialized
+ *
+ * Create a dummy set of directories and a pipe that gssd can hold open to
+ * indicate that it is up and running.
+ */
+static struct dentry *
+rpc_gssd_dummy_populate(struct dentry *root, struct rpc_pipe *pipe_data)
+{
+        int ret = 0;
+        struct dentry *gssd_dentry;
+        struct dentry *clnt_dentry = NULL;
+        struct dentry *pipe_dentry = NULL;
+        struct qstr q = QSTR_INIT(files[RPCAUTH_gssd].name,
+                                  strlen(files[RPCAUTH_gssd].name));
+
+        /* We should never get this far if "gssd" doesn't exist */
+        gssd_dentry = d_hash_and_lookup(root, &q);
+        if (!gssd_dentry)
+                return ERR_PTR(-ENOENT);
+
+        ret = rpc_populate(gssd_dentry, gssd_dummy_clnt_dir, 0, 1, NULL);
+        if (ret) {
+                pipe_dentry = ERR_PTR(ret);
+                goto out;
+        }
+
+        q.name = gssd_dummy_clnt_dir[0].name;
+        q.len = strlen(gssd_dummy_clnt_dir[0].name);
+        clnt_dentry = d_hash_and_lookup(gssd_dentry, &q);
+        if (!clnt_dentry) {
+                pipe_dentry = ERR_PTR(-ENOENT);
+                goto out;
+        }
+
+        pipe_dentry = rpc_mkpipe_dentry(clnt_dentry, "gssd", NULL, pipe_data);
+out:
+        dput(clnt_dentry);
+        dput(gssd_dentry);
+        return pipe_dentry;
+}
+
 static int
 rpc_fill_super(struct super_block *sb, void *data, int silent)
 {
         struct inode *inode;
-        struct dentry *root;
+        struct dentry *root, *gssd_dentry;
         struct net *net = data;
         struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
         int err;
@@ -1266,6 +1345,13 @@ rpc_fill_super(struct super_block *sb, void *data, int silent)
                 return -ENOMEM;
         if (rpc_populate(root, files, RPCAUTH_lockd, RPCAUTH_RootEOF, NULL))
                 return -ENOMEM;
+
+        gssd_dentry = rpc_gssd_dummy_populate(root, sn->gssd_dummy);
+        if (IS_ERR(gssd_dentry)) {
+                __rpc_depopulate(root, files, RPCAUTH_lockd, RPCAUTH_RootEOF);
+                return PTR_ERR(gssd_dentry);
+        }
+
         dprintk("RPC:       sending pipefs MOUNT notification for net %p%s\n",
                 net, NET_NAME(net));
         mutex_lock(&sn->pipefs_sb_lock);
@@ -1280,6 +1366,7 @@ rpc_fill_super(struct super_block *sb, void *data, int silent)
         return 0;
 
 err_depopulate:
+        dput(gssd_dentry);
         blocking_notifier_call_chain(&rpc_pipefs_notifier_list,
                                            RPC_PIPEFS_UMOUNT,
                                            sb);