kernfs: implement kernfs_root->supers list

Currently, there's no way to find out which super_blocks are
associated with a given kernfs_root.  Let's implement it - the planned
inotify extension to kernfs_notify() needs it.

Make kernfs_super_info point back to the super_block and chain it at
kernfs_root->supers.

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

3 files changed, 17 insertions, 0 deletions

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 78f3403300af..43aa97988c31 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -711,6 +711,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
                 return ERR_PTR(-ENOMEM);
 
         ida_init(&root->ino_ida);
+        INIT_LIST_HEAD(&root->supers);
 
         kn = __kernfs_new_node(root, "", S_IFDIR | S_IRUGO | S_IXUGO,
                                KERNFS_DIR);
diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index 8be13b2a079b..dc84a3ef9ca2 100644
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -49,6 +49,8 @@ static inline struct kernfs_root *kernfs_root(struct kernfs_node *kn)
  * mount.c
  */
 struct kernfs_super_info {
+        struct super_block      *sb;
+
         /*
          * The root associated with this super_block.  Each super_block is
          * identified by the root and ns it's associated with.
@@ -62,6 +64,9 @@ struct kernfs_super_info {
          * an array and compare kernfs_node tag against every entry.
          */
         const void              *ns;
+
+        /* anchored at kernfs_root->supers, protected by kernfs_mutex */
+        struct list_head        node;
 };
 #define kernfs_info(SB) ((struct kernfs_super_info *)(SB->s_fs_info))
 
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 6a5f04ac8704..f25a7c0c3cdc 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -68,6 +68,7 @@ static int kernfs_fill_super(struct super_block *sb)
         struct inode *inode;
         struct dentry *root;
 
+        info->sb = sb;
         sb->s_blocksize = PAGE_CACHE_SIZE;
         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
         sb->s_magic = SYSFS_MAGIC;
@@ -166,12 +167,18 @@ struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
                 *new_sb_created = !sb->s_root;
 
         if (!sb->s_root) {
+                struct kernfs_super_info *info = kernfs_info(sb);
+
                 error = kernfs_fill_super(sb);
                 if (error) {
                         deactivate_locked_super(sb);
                         return ERR_PTR(error);
                 }
                 sb->s_flags |= MS_ACTIVE;
+
+                mutex_lock(&kernfs_mutex);
+                list_add(&info->node, &root->supers);
+                mutex_unlock(&kernfs_mutex);
         }
 
         return dget(sb->s_root);
@@ -190,6 +197,10 @@ void kernfs_kill_sb(struct super_block *sb)
         struct kernfs_super_info *info = kernfs_info(sb);
         struct kernfs_node *root_kn = sb->s_root->d_fsdata;
 
+        mutex_lock(&kernfs_mutex);
+        list_del(&info->node);
+        mutex_unlock(&kernfs_mutex);
+
         /*
          * Remove the superblock from fs_supers/s_instances
          * so we can't find it, before freeing kernfs_super_info.