sysfs, kernfs: make super_blocks bind to different kernfs_roots

kernfs is being updated to allow multiple sysfs_dirent hierarchies so
that it can also be used by other users.  Currently, sysfs
super_blocks are always attached to one kernfs_root - sysfs_root - and
distinguished only by their namespace tags.

This patch adds sysfs_super_info->root and update
sysfs_fill/test_super() so that super_blocks are identified by the
combination of both the associated kernfs_root and namespace tag.
This allows mounting different kernfs hierarchies.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 12 insertions, 4 deletions

diff --git a/fs/sysfs/mount.c b/fs/sysfs/mount.c
index 0b5661b462f7..f143b203a7e6 100644
--- a/fs/sysfs/mount.c
+++ b/fs/sysfs/mount.c
@@ -37,6 +37,7 @@ struct sysfs_dirent *sysfs_root_sd;
 
 static int sysfs_fill_super(struct super_block *sb)
 {
+        struct sysfs_super_info *info = sysfs_info(sb);
         struct inode *inode;
         struct dentry *root;
 
@@ -48,7 +49,7 @@ static int sysfs_fill_super(struct super_block *sb)
 
         /* get root inode, initialize and unlock it */
         mutex_lock(&sysfs_mutex);
-        inode = sysfs_get_inode(sb, sysfs_root_sd);
+        inode = sysfs_get_inode(sb, info->root->sd);
         mutex_unlock(&sysfs_mutex);
         if (!inode) {
                 pr_debug("sysfs: could not get root inode\n");
@@ -61,8 +62,8 @@ static int sysfs_fill_super(struct super_block *sb)
                 pr_debug("%s: could not get root dentry!\n", __func__);
                 return -ENOMEM;
         }
-        kernfs_get(sysfs_root_sd);
-        root->d_fsdata = sysfs_root_sd;
+        kernfs_get(info->root->sd);
+        root->d_fsdata = info->root->sd;
         sb->s_root = root;
         sb->s_d_op = &sysfs_dentry_ops;
         return 0;
@@ -73,7 +74,7 @@ static int sysfs_test_super(struct super_block *sb, void *data)
         struct sysfs_super_info *sb_info = sysfs_info(sb);
         struct sysfs_super_info *info = data;
 
-        return sb_info->ns == info->ns;
+        return sb_info->root == info->root && sb_info->ns == info->ns;
 }
 
 static int sysfs_set_super(struct super_block *sb, void *data)
@@ -110,6 +111,7 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type,
         if (!info)
                 return ERR_PTR(-ENOMEM);
 
+        info->root = sysfs_root;
         info->ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
 
         sb = sget(fs_type, sysfs_test_super, sysfs_set_super, flags, info);
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 2b217cef90be..93b4b68458ad 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -20,6 +20,12 @@
 
 struct sysfs_super_info {
         /*
+         * The root associated with this super_block.  Each super_block is
+         * identified by the root and ns it's associated with.
+         */
+        struct kernfs_root      *root;
+
+        /*
          * Each sb is associated with one namespace tag, currently the network
          * namespace of the task which mounted this sysfs instance.  If multiple
          * tags become necessary, make the following an array and compare