// SPDX-License-Identifier: GPL-2.0-only

  /*
   * 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>

   */

  
  #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 <linux/namei.h>

  #include <linux/seq_file.h>

  #include <linux/exportfs.h>

  
  #include "kernfs-internal.h"

  struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;

  static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
  {

  	struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));

  	struct kernfs_syscall_ops *scops = root->syscall_ops;
  
  	if (scops && scops->show_options)
  		return scops->show_options(sf, root);
  	return 0;
  }

  static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
  {

  	struct kernfs_node *node = kernfs_dentry_node(dentry);

  	struct kernfs_root *root = kernfs_root(node);
  	struct kernfs_syscall_ops *scops = root->syscall_ops;
  
  	if (scops && scops->show_path)
  		return scops->show_path(sf, node, root);

  	seq_dentry(sf, dentry, " \t
  \\");
  	return 0;

  }

  const struct super_operations kernfs_sops = {

  	.statfs		= simple_statfs,
  	.drop_inode	= generic_delete_inode,

  	.evict_inode	= kernfs_evict_inode,

  	.show_options	= kernfs_sop_show_options,

  	.show_path	= kernfs_sop_show_path,

  };

  static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
  			    struct inode *parent)

  {

  	struct kernfs_node *kn = inode->i_private;

  	if (*max_len < 2) {
  		*max_len = 2;
  		return FILEID_INVALID;
  	}

  	*max_len = 2;
  	*(u64 *)fh = kn->id;
  	return FILEID_KERNFS;
  }
  
  static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
  					    struct fid *fid, int fh_len,
  					    int fh_type, bool get_parent)
  {
  	struct kernfs_super_info *info = kernfs_info(sb);
  	struct kernfs_node *kn;
  	struct inode *inode;
  	u64 id;
  
  	if (fh_len < 2)
  		return NULL;
  
  	switch (fh_type) {
  	case FILEID_KERNFS:
  		id = *(u64 *)fid;
  		break;
  	case FILEID_INO32_GEN:
  	case FILEID_INO32_GEN_PARENT:
  		/*

  		 * blk_log_action() exposes "LOW32,HIGH32" pair without
  		 * type and userland can call us with generic fid
  		 * constructed from them.  Combine it back to ID.  See
  		 * blk_log_action().

  		 */
  		id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
  		break;
  	default:
  		return NULL;
  	}
  
  	kn = kernfs_find_and_get_node_by_id(info->root, id);

  	if (!kn)
  		return ERR_PTR(-ESTALE);

  
  	if (get_parent) {
  		struct kernfs_node *parent;
  
  		parent = kernfs_get_parent(kn);
  		kernfs_put(kn);
  		kn = parent;
  		if (!kn)
  			return ERR_PTR(-ESTALE);
  	}

  	inode = kernfs_get_inode(sb, kn);
  	kernfs_put(kn);

  	if (!inode)
  		return ERR_PTR(-ESTALE);

  	return d_obtain_alias(inode);

  }

  static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
  					  struct fid *fid, int fh_len,
  					  int fh_type)

  {

  	return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);

  }

  static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
  					  struct fid *fid, int fh_len,
  					  int fh_type)

  {

  	return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);

  }
  
  static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
  {
  	struct kernfs_node *kn = kernfs_dentry_node(child);
  
  	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
  }
  
  static const struct export_operations kernfs_export_ops = {

  	.encode_fh	= kernfs_encode_fh,

  	.fh_to_dentry	= kernfs_fh_to_dentry,
  	.fh_to_parent	= kernfs_fh_to_parent,
  	.get_parent	= kernfs_get_parent_dentry,
  };

  /**
   * kernfs_root_from_sb - determine kernfs_root associated with a super_block
   * @sb: the super_block in question
   *
   * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
   * %NULL is returned.
   */
  struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
  {
  	if (sb->s_op == &kernfs_sops)
  		return kernfs_info(sb)->root;
  	return NULL;
  }

  /*
   * find the next ancestor in the path down to @child, where @parent was the
   * ancestor whose descendant we want to find.
   *
   * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
   * node.  If @parent is b, then we return the node for c.
   * Passing in d as @parent is not ok.
   */
  static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
  					      struct kernfs_node *parent)
  {
  	if (child == parent) {
  		pr_crit_once("BUG in find_next_ancestor: called with parent == child");
  		return NULL;
  	}
  
  	while (child->parent != parent) {
  		if (!child->parent)
  			return NULL;
  		child = child->parent;
  	}
  
  	return child;
  }
  
  /**
   * kernfs_node_dentry - get a dentry for the given kernfs_node
   * @kn: kernfs_node for which a dentry is needed
   * @sb: the kernfs super_block
   */
  struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
  				  struct super_block *sb)
  {
  	struct dentry *dentry;
  	struct kernfs_node *knparent = NULL;
  
  	BUG_ON(sb->s_op != &kernfs_sops);
  
  	dentry = dget(sb->s_root);
  
  	/* Check if this is the root kernfs_node */
  	if (!kn->parent)
  		return dentry;
  
  	knparent = find_next_ancestor(kn, NULL);

  	if (WARN_ON(!knparent)) {
  		dput(dentry);

  		return ERR_PTR(-EINVAL);

  	}

  
  	do {
  		struct dentry *dtmp;
  		struct kernfs_node *kntmp;
  
  		if (kn == knparent)
  			return dentry;
  		kntmp = find_next_ancestor(kn, knparent);

  		if (WARN_ON(!kntmp)) {
  			dput(dentry);

  			return ERR_PTR(-EINVAL);

  		}

  		dtmp = lookup_positive_unlocked(kntmp->name, dentry,

  					       strlen(kntmp->name));

  		dput(dentry);
  		if (IS_ERR(dtmp))
  			return dtmp;
  		knparent = kntmp;
  		dentry = dtmp;
  	} while (true);
  }

  static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)

  {

  	struct kernfs_super_info *info = kernfs_info(sb);

  	struct inode *inode;
  	struct dentry *root;

  	info->sb = sb;

  	/* Userspace would break if executables or devices appear on sysfs */
  	sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;

  	sb->s_blocksize = PAGE_SIZE;
  	sb->s_blocksize_bits = PAGE_SHIFT;

  	sb->s_magic = kfc->magic;

  	sb->s_op = &kernfs_sops;

  	sb->s_xattr = kernfs_xattr_handlers;

  	if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
  		sb->s_export_op = &kernfs_export_ops;

  	sb->s_time_gran = 1;

  	/* sysfs dentries and inodes don't require IO to create */
  	sb->s_shrink.seeks = 0;

  	/* 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;
  	}

  	sb->s_root = root;

  	sb->s_d_op = &kernfs_dops;

  	return 0;
  }

  static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)

  {

  	struct kernfs_super_info *sb_info = kernfs_info(sb);

  	struct kernfs_super_info *info = fc->s_fs_info;

  
  	return sb_info->root == info->root && sb_info->ns == info->ns;
  }

  static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)

  {

  	struct kernfs_fs_context *kfc = fc->fs_private;
  
  	kfc->ns_tag = NULL;
  	return set_anon_super_fc(sb, fc);

  }
  
  /**
   * 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_get_tree - kernfs filesystem access/retrieval helper
   * @fc: The filesystem context.

   *

   * This is to be called from each kernfs user's fs_context->ops->get_tree()
   * implementation, which should set the specified ->@fs_type and ->@flags, and
   * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
   * respectively.

   */

  int kernfs_get_tree(struct fs_context *fc)

  {

  	struct kernfs_fs_context *kfc = fc->fs_private;

  	struct super_block *sb;

  	struct kernfs_super_info *info;

  	int error;
  
  	info = kzalloc(sizeof(*info), GFP_KERNEL);
  	if (!info)

  		return -ENOMEM;

  	info->root = kfc->root;
  	info->ns = kfc->ns_tag;

  	INIT_LIST_HEAD(&info->node);

  	fc->s_fs_info = info;
  	sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);

  	if (IS_ERR(sb))

  		return PTR_ERR(sb);

  	if (!sb->s_root) {

  		struct kernfs_super_info *info = kernfs_info(sb);

  		kfc->new_sb_created = true;
  
  		error = kernfs_fill_super(sb, kfc);

  		if (error) {
  			deactivate_locked_super(sb);

  			return error;

  		}

  		sb->s_flags |= SB_ACTIVE;

  
  		mutex_lock(&kernfs_mutex);

  		list_add(&info->node, &info->root->supers);

  		mutex_unlock(&kernfs_mutex);

  	}

  	fc->root = dget(sb->s_root);
  	return 0;
  }
  
  void kernfs_free_fs_context(struct fs_context *fc)
  {
  	/* Note that we don't deal with kfc->ns_tag here. */
  	kfree(fc->s_fs_info);
  	fc->s_fs_info = NULL;

  }
  
  /**
   * 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);

  	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.

  	 */
  	kill_anon_super(sb);
  	kfree(info);

  }
  
  void __init kernfs_init(void)
  {

  	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",

  					      sizeof(struct kernfs_node),

  					      0, SLAB_PANIC, NULL);

  
  	/* Creates slab cache for kernfs inode attributes */
  	kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
  					      sizeof(struct kernfs_iattrs),
  					      0, SLAB_PANIC, NULL);

  }