/*
   * fs/kernfs/mount.c - kernfs mount implementation
   *
   * Copyright (c) 2001-3 Patrick Mochel
   * Copyright (c) 2007 SUSE Linux Products GmbH
   * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   *
   * This file is released under the GPLv2.
   */
  
  #include <linux/fs.h>
  #include <linux/mount.h>
  #include <linux/init.h>
  #include <linux/magic.h>
  #include <linux/slab.h>
  #include <linux/pagemap.h>
  
  #include "kernfs-internal.h"
  
  struct kmem_cache *kernfs_node_cache;
  
  static const struct super_operations kernfs_sops = {
  	.statfs		= simple_statfs,
  	.drop_inode	= generic_delete_inode,
  	.evict_inode	= kernfs_evict_inode,
  };
  
  static int kernfs_fill_super(struct super_block *sb)
  {
  	struct kernfs_super_info *info = kernfs_info(sb);
  	struct inode *inode;
  	struct dentry *root;
  
  	sb->s_blocksize = PAGE_CACHE_SIZE;
  	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
  	sb->s_magic = SYSFS_MAGIC;
  	sb->s_op = &kernfs_sops;
  	sb->s_time_gran = 1;
  
  	/* get root inode, initialize and unlock it */
  	mutex_lock(&kernfs_mutex);
  	inode = kernfs_get_inode(sb, info->root->kn);
  	mutex_unlock(&kernfs_mutex);
  	if (!inode) {
  		pr_debug("kernfs: could not get root inode
  ");
  		return -ENOMEM;
  	}
  
  	/* instantiate and link root dentry */
  	root = d_make_root(inode);
  	if (!root) {
  		pr_debug("%s: could not get root dentry!
  ", __func__);
  		return -ENOMEM;
  	}
  	kernfs_get(info->root->kn);
  	root->d_fsdata = info->root->kn;
  	sb->s_root = root;
  	sb->s_d_op = &kernfs_dops;
  	return 0;
  }
  
  static int kernfs_test_super(struct super_block *sb, void *data)
  {
  	struct kernfs_super_info *sb_info = kernfs_info(sb);
  	struct kernfs_super_info *info = data;
  
  	return sb_info->root == info->root && sb_info->ns == info->ns;
  }
  
  static int kernfs_set_super(struct super_block *sb, void *data)
  {
  	int error;
  	error = set_anon_super(sb, data);
  	if (!error)
  		sb->s_fs_info = data;
  	return error;
  }
  
  /**
   * kernfs_super_ns - determine the namespace tag of a kernfs super_block
   * @sb: super_block of interest
   *
   * Return the namespace tag associated with kernfs super_block @sb.
   */
  const void *kernfs_super_ns(struct super_block *sb)
  {
  	struct kernfs_super_info *info = kernfs_info(sb);
  
  	return info->ns;
  }
  
  /**
   * kernfs_mount_ns - kernfs mount helper
   * @fs_type: file_system_type of the fs being mounted
   * @flags: mount flags specified for the mount
   * @root: kernfs_root of the hierarchy being mounted
   * @new_sb_created: tell the caller if we allocated a new superblock
   * @ns: optional namespace tag of the mount
   *
   * This is to be called from each kernfs user's file_system_type->mount()
   * implementation, which should pass through the specified @fs_type and
   * @flags, and specify the hierarchy and namespace tag to mount via @root
   * and @ns, respectively.
   *
   * The return value can be passed to the vfs layer verbatim.
   */
  struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
  			       struct kernfs_root *root, bool *new_sb_created,
  			       const void *ns)
  {
  	struct super_block *sb;
  	struct kernfs_super_info *info;
  	int error;
  
  	info = kzalloc(sizeof(*info), GFP_KERNEL);
  	if (!info)
  		return ERR_PTR(-ENOMEM);
  
  	info->root = root;
  	info->ns = ns;
  
  	sb = sget(fs_type, kernfs_test_super, kernfs_set_super, flags, info);
  	if (IS_ERR(sb) || sb->s_fs_info != info)
  		kfree(info);
  	if (IS_ERR(sb))
  		return ERR_CAST(sb);
  
  	if (new_sb_created)
  		*new_sb_created = !sb->s_root;
  
  	if (!sb->s_root) {
  		error = kernfs_fill_super(sb);
  		if (error) {
  			deactivate_locked_super(sb);
  			return ERR_PTR(error);
  		}
  		sb->s_flags |= MS_ACTIVE;
  	}
  
  	return dget(sb->s_root);
  }
  
  /**
   * kernfs_kill_sb - kill_sb for kernfs
   * @sb: super_block being killed
   *
   * This can be used directly for file_system_type->kill_sb().  If a kernfs
   * user needs extra cleanup, it can implement its own kill_sb() and call
   * this function at the end.
   */
  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;
  
  	/*
  	 * Remove the superblock from fs_supers/s_instances
  	 * so we can't find it, before freeing kernfs_super_info.
  	 */
  	kill_anon_super(sb);
  	kfree(info);
  	kernfs_put(root_kn);
  }
  
  void __init kernfs_init(void)
  {
  	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
  					      sizeof(struct kernfs_node),
  					      0, SLAB_PANIC, NULL);
  	kernfs_inode_init();
  }