sunrpc: add an "info" file for the dummy gssd pipe

rpc.gssd expects to see an "info" file in each clntXX dir. Since adding
the dummy gssd pipe, users that run rpc.gssd see a lot of these messages
spamming the logs:

    rpc.gssd[508]: ERROR: can't open /var/lib/nfs/rpc_pipefs/gssd/clntXX/info: No such file or directory
    rpc.gssd[508]: ERROR: failed to read service info

Add a dummy gssd/clntXX/info file to help silence these messages.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

net/sunrpc/rpc_pipe.c

@@ -17,6 +17,7 @@
 #include <linux/fsnotify.h>
 #include <linux/kernel.h>
 #include <linux/rcupdate.h>
+#include <linux/utsname.h>
 
 #include <asm/ioctls.h>
 #include <linux/poll.h>
@@ -1275,6 +1276,44 @@ static const struct rpc_pipe_ops gssd_dummy_pipe_ops = {
 	.downcall	= dummy_downcall,
 };
 
+/*
+ * Here we present a bogus "info" file to keep rpc.gssd happy. We don't expect
+ * that it will ever use this info to handle an upcall, but rpc.gssd expects
+ * that this file will be there and have a certain format.
+ */
+static int
+rpc_show_dummy_info(struct seq_file *m, void *v)
+{
+	seq_printf(m, "RPC server: %s\n", utsname()->nodename);
+	seq_printf(m, "service: foo (1) version 0\n");
+	seq_printf(m, "address: 127.0.0.1\n");
+	seq_printf(m, "protocol: tcp\n");
+	seq_printf(m, "port: 0\n");
+	return 0;
+}
+
+static int
+rpc_dummy_info_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, rpc_show_dummy_info, NULL);
+}
+
+static const struct file_operations rpc_dummy_info_operations = {
+	.owner		= THIS_MODULE,
+	.open		= rpc_dummy_info_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static const struct rpc_filelist gssd_dummy_info_file[] = {
+	[0] = {
+		.name = "info",
+		.i_fop = &rpc_dummy_info_operations,
+		.mode = S_IFREG | S_IRUSR,
+	},
+};
+
 /**
  * rpc_gssd_dummy_populate - create a dummy gssd pipe
  * @root:	root of the rpc_pipefs filesystem
@@ -1312,9 +1351,18 @@ rpc_gssd_dummy_populate(struct dentry *root, struct rpc_pipe *pipe_data)
 		goto out;
 	}
 
+	ret = rpc_populate(clnt_dentry, gssd_dummy_info_file, 0, 1, NULL);
+	if (ret) {
+		__rpc_depopulate(gssd_dentry, gssd_dummy_clnt_dir, 0, 1);
+		pipe_dentry = ERR_PTR(ret);
+		goto out;
+	}
+
 	pipe_dentry = rpc_mkpipe_dentry(clnt_dentry, "gssd", NULL, pipe_data);
-	if (IS_ERR(pipe_dentry))
+	if (IS_ERR(pipe_dentry)) {
+		__rpc_depopulate(clnt_dentry, gssd_dummy_info_file, 0, 1);
 		__rpc_depopulate(gssd_dentry, gssd_dummy_clnt_dir, 0, 1);
+	}
 out:
 	dput(clnt_dentry);
 	dput(gssd_dentry);