[PATCH 12/12] sunrpc: make rpc_pipefs be mountable multiple times

["Kirill A. Shutsemov" <kirill@shutemov.name>]

From: Kirill A. Shutemov <kirill@shutemov.name>

To support containers, allow multiple independent instances of
rpc_pipefs. Use '-o newinstance' to create new of the filesystem.
The same semantics as with devpts.

Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
---
 net/sunrpc/rpc_pipe.c |   80 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 79 insertions(+), 1 deletions(-)

diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index c48f7a5..836e725 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -16,6 +16,7 @@
 #include <linux/namei.h>
 #include <linux/fsnotify.h>
 #include <linux/kernel.h>
+#include <linux/parser.h>
 
 #include <asm/ioctls.h>
 #include <linux/fs.h>
@@ -38,6 +39,49 @@ static struct kmem_cache *rpc_inode_cachep __read_mostly;
 
 #define RPC_UPCALL_TIMEOUT (30*HZ)
 
+struct rpc_mount_opts {
+	int newinstance;
+};
+
+enum {
+	Opt_newinstance,
+
+	Opt_err
+};
+
+static const match_table_t tokens = {
+	{Opt_newinstance, "newinstance"},
+
+	{Opt_err, NULL}
+};
+
+static int
+parse_mount_options(char *data, struct rpc_mount_opts *opts)
+{
+	char *p;
+
+	opts->newinstance = 0;
+
+	while ((p = strsep(&data, ",")) != NULL) {
+		substring_t args[MAX_OPT_ARGS];
+		int token;
+
+		if (!*p)
+			continue;
+
+		token = match_token(p, tokens, args);
+		switch (token) {
+		case Opt_newinstance:
+			opts->newinstance = 1;
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
 static void rpc_purge_list(struct rpc_inode *rpci, struct list_head *head,
 		void (*destroy_msg)(struct rpc_pipe_msg *), int err)
 {
@@ -1025,11 +1069,45 @@ rpc_fill_super(struct super_block *sb, void *data, int silent)
 	return 0;
 }
 
+static int
+compare_rpc_mnt_sb(struct super_block *s, void *p)
+{
+	if (init_rpc_pipefs)
+		return init_rpc_pipefs->mnt_sb == s;
+	return 0;
+}
+
 static struct dentry *
 rpc_mount(struct file_system_type *fs_type,
 		int flags, const char *dev_name, void *data)
 {
-	return mount_single(fs_type, flags, data, rpc_fill_super);
+	int error;
+	struct rpc_mount_opts opts;
+	struct super_block *s;
+
+	error = parse_mount_options(data, &opts);
+	if (error)
+		return ERR_PTR(error);
+
+	if (opts.newinstance)
+		s = sget(fs_type, NULL, set_anon_super, NULL);
+	else
+		s = sget(fs_type, compare_rpc_mnt_sb, set_anon_super, NULL);
+
+	if (IS_ERR(s))
+		return ERR_CAST(s);
+
+	if (!s->s_root) {
+		s->s_flags = flags;
+		error = rpc_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
+		if (error) {
+			deactivate_locked_super(s);
+			return ERR_PTR(error);
+		}
+		s->s_flags |= MS_ACTIVE;
+	}
+
+	return dget(s->s_root);
 }
 
 static struct file_system_type rpc_pipe_fs_type = {
-- 
1.7.3.4