namespaces: move proc_net_get_sb to a generic fs/super.c helper

The mqueuefs filesystem will use this helper as well.  Proc's main get_sb
could also be made to use it, but that will require a bit more rework.

Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 43 insertions, 0 deletions

diff --git a/fs/super.c b/fs/super.c
index 77cb4ec919b9..786fe7d72790 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -771,6 +771,46 @@ void kill_litter_super(struct super_block *sb)
 
 EXPORT_SYMBOL(kill_litter_super);
 
+static int ns_test_super(struct super_block *sb, void *data)
+{
+        return sb->s_fs_info == data;
+}
+
+static int ns_set_super(struct super_block *sb, void *data)
+{
+        sb->s_fs_info = data;
+        return set_anon_super(sb, NULL);
+}
+
+int get_sb_ns(struct file_system_type *fs_type, int flags, void *data,
+        int (*fill_super)(struct super_block *, void *, int),
+        struct vfsmount *mnt)
+{
+        struct super_block *sb;
+
+        sb = sget(fs_type, ns_test_super, ns_set_super, data);
+        if (IS_ERR(sb))
+                return PTR_ERR(sb);
+
+        if (!sb->s_root) {
+                int err;
+                sb->s_flags = flags;
+                err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
+                if (err) {
+                        up_write(&sb->s_umount);
+                        deactivate_super(sb);
+                        return err;
+                }
+
+                sb->s_flags |= MS_ACTIVE;
+        }
+
+        simple_set_mnt(mnt, sb);
+        return 0;
+}
+
+EXPORT_SYMBOL(get_sb_ns);
+
 #ifdef CONFIG_BLOCK
 static int set_bdev_super(struct super_block *s, void *data)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bce40a2207ee..562d2855cf30 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1699,6 +1699,9 @@ struct file_system_type {
         struct lock_class_key i_alloc_sem_key;
 };
 
+extern int get_sb_ns(struct file_system_type *fs_type, int flags, void *data,
+        int (*fill_super)(struct super_block *, void *, int),
+        struct vfsmount *mnt);
 extern int get_sb_bdev(struct file_system_type *fs_type,
         int flags, const char *dev_name, void *data,
         int (*fill_super)(struct super_block *, void *, int),