sysfs, kernfs: prepare mount path for kernfs

We're in the process of separating out core sysfs functionality into
kernfs which will deal with sysfs_dirents directly.  This patch
rearranges mount path so that the kernfs and sysfs parts are separate.

* As sysfs_super_info won't be visible outside kernfs proper,
  kernfs_super_ns() is added to allow kernfs users to access a
  super_block's namespace tag.

* Generic mount operation is separated out into kernfs_mount_ns().
  sysfs_mount() now just performs sysfs-specific permission check,
  acquires namespace tag, and invokes kernfs_mount_ns().

* Generic superblock release is separated out into kernfs_kill_sb()
  which can be used directly as file_system_type->kill_sb().  As sysfs
  needs to put the namespace tag, sysfs_kill_sb() wraps
  kernfs_kill_sb() with ns tag put.

* sysfs_dir_cachep init and sysfs_inode_init() are separated out into
  kernfs_init().  kernfs_init() uses only small amount of memory and
  trying to handle and propagate kernfs_init() failure doesn't make
  much sense.  Use SLAB_PANIC for sysfs_dir_cachep and make
  sysfs_inode_init() panic on failure.

  After this change, kernfs_init() should be called before
  sysfs_init(), fs/namespace.c::mnt_init() modified accordingly.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index fad8b986800f..75fcbe5c9d65 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -18,6 +18,8 @@ struct file;
 struct iattr;
 struct seq_file;
 struct vm_area_struct;
+struct super_block;
+struct file_system_type;
 
 struct sysfs_dirent;
 
@@ -109,6 +111,13 @@ void kernfs_enable_ns(struct sysfs_dirent *sd);
 int kernfs_setattr(struct sysfs_dirent *sd, const struct iattr *iattr);
 void kernfs_notify(struct sysfs_dirent *sd);
 
+const void *kernfs_super_ns(struct super_block *sb);
+struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
+                               struct kernfs_root *root, const void *ns);
+void kernfs_kill_sb(struct super_block *sb);
+
+void kernfs_init(void);
+
 #else   /* CONFIG_SYSFS */
 
 static inline struct sysfs_dirent *
@@ -160,6 +169,18 @@ static inline int kernfs_setattr(struct sysfs_dirent *sd,
 
 static inline void kernfs_notify(struct sysfs_dirent *sd) { }
 
+static inline const void *kernfs_super_ns(struct super_block *sb)
+{ return NULL; }
+
+static inline struct dentry *
+kernfs_mount_ns(struct file_system_type *fs_type, int flags,
+                struct kernfs_root *root, const void *ns)
+{ return ERR_PTR(-ENOSYS); }
+
+static inline void kernfs_kill_sb(struct super_block *sb) { }
+
+static inline void kernfs_init(void) { }
+
 #endif  /* CONFIG_SYSFS */
 
 static inline struct sysfs_dirent *
@@ -201,4 +222,11 @@ static inline int kernfs_remove_by_name(struct sysfs_dirent *parent,
         return kernfs_remove_by_name_ns(parent, name, NULL);
 }
 
+static inline struct dentry *
+kernfs_mount(struct file_system_type *fs_type, int flags,
+             struct kernfs_root *root)
+{
+        return kernfs_mount_ns(fs_type, flags, root, NULL);
+}
+
 #endif  /* __LINUX_KERNFS_H */