/*

   * fs/sysfs/symlink.c - sysfs symlink implementation
   *
   * Copyright (c) 2001-3 Patrick Mochel
   * Copyright (c) 2007 SUSE Linux Products GmbH
   * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
   *
   * This file is released under the GPLv2.
   *
   * Please see Documentation/filesystems/sysfs.txt for more information.

   */
  
  #include <linux/fs.h>

  #include <linux/gfp.h>

  #include <linux/mount.h>

  #include <linux/module.h>
  #include <linux/kobject.h>
  #include <linux/namei.h>

  #include <linux/mutex.h>

  #include <linux/security.h>

  
  #include "sysfs.h"

  static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
  				const char *name, int warn)

  {

  	struct sysfs_dirent *parent_sd = NULL;
  	struct sysfs_dirent *target_sd = NULL;

  	struct sysfs_dirent *sd = NULL;

  	struct sysfs_addrm_cxt acxt;

  	enum kobj_ns_type ns_type;

  	int error;

  	BUG_ON(!name);

  	if (!kobj)
  		parent_sd = &sysfs_root;
  	else

  		parent_sd = kobj->sd;

  	error = -EFAULT;

  	if (!parent_sd)

  		goto out_put;

  	/* target->sd can go away beneath us but is protected with

  	 * sysfs_assoc_lock.  Fetch target_sd from it.

  	 */

  	spin_lock(&sysfs_assoc_lock);

  	if (target->sd)
  		target_sd = sysfs_get(target->sd);

  	spin_unlock(&sysfs_assoc_lock);

  	error = -ENOENT;

  	if (!target_sd)

  		goto out_put;
  
  	error = -ENOMEM;
  	sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  	if (!sd)
  		goto out_put;

  	ns_type = sysfs_ns_type(parent_sd);
  	if (ns_type)

  		sd->s_ns = target->ktype->namespace(target);

  	sd->s_symlink.target_sd = target_sd;

  	target_sd = NULL;	/* reference is now owned by the symlink */

  	sysfs_addrm_start(&acxt, parent_sd);

  	/* Symlinks must be between directories with the same ns_type */

  	if (!ns_type ||
  	    (ns_type == sysfs_ns_type(sd->s_symlink.target_sd->s_parent))) {

  		if (warn)
  			error = sysfs_add_one(&acxt, sd);
  		else
  			error = __sysfs_add_one(&acxt, sd);
  	} else {
  		error = -EINVAL;
  		WARN(1, KERN_WARNING
  			"sysfs: symlink across ns_types %s/%s -> %s/%s
  ",
  			parent_sd->s_name,
  			sd->s_name,
  			sd->s_symlink.target_sd->s_parent->s_name,
  			sd->s_symlink.target_sd->s_name);
  	}

  	sysfs_addrm_finish(&acxt);

  	if (error)

  		goto out_put;

  
  	return 0;

   out_put:
  	sysfs_put(target_sd);
  	sysfs_put(sd);

  	return error;
  }

  /**

   *	sysfs_create_link - create symlink between two objects.
   *	@kobj:	object whose directory we're creating the link in.
   *	@target:	object we're pointing to.
   *	@name:		name of the symlink.
   */
  int sysfs_create_link(struct kobject *kobj, struct kobject *target,
  		      const char *name)
  {
  	return sysfs_do_create_link(kobj, target, name, 1);
  }
  
  /**
   *	sysfs_create_link_nowarn - create symlink between two objects.
   *	@kobj:	object whose directory we're creating the link in.
   *	@target:	object we're pointing to.
   *	@name:		name of the symlink.
   *
   *	This function does the same as sysf_create_link(), but it
   *	doesn't warn if the link already exists.
   */
  int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
  			     const char *name)
  {
  	return sysfs_do_create_link(kobj, target, name, 0);
  }
  
  /**

   *	sysfs_delete_link - remove symlink in object's directory.
   *	@kobj:	object we're acting for.
   *	@targ:	object we're pointing to.
   *	@name:	name of the symlink to remove.
   *
   *	Unlike sysfs_remove_link sysfs_delete_link has enough information
   *	to successfully delete symlinks in tagged directories.
   */
  void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
  			const char *name)
  {
  	const void *ns = NULL;
  	spin_lock(&sysfs_assoc_lock);

  	if (targ->sd && sysfs_ns_type(kobj->sd))

  		ns = targ->sd->s_ns;
  	spin_unlock(&sysfs_assoc_lock);
  	sysfs_hash_and_remove(kobj->sd, ns, name);
  }
  
  /**

   *	sysfs_remove_link - remove symlink in object's directory.
   *	@kobj:	object we're acting for.
   *	@name:	name of the symlink to remove.
   */

  void sysfs_remove_link(struct kobject * kobj, const char * name)

  {

  	struct sysfs_dirent *parent_sd = NULL;
  
  	if (!kobj)
  		parent_sd = &sysfs_root;
  	else
  		parent_sd = kobj->sd;

  	sysfs_hash_and_remove(parent_sd, NULL, name);

  }

  /**
   *	sysfs_rename_link - rename symlink in object's directory.
   *	@kobj:	object we're acting for.
   *	@targ:	object we're pointing to.
   *	@old:	previous name of the symlink.
   *	@new:	new name of the symlink.
   *
   *	A helper function for the common rename symlink idiom.
   */
  int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
  			const char *old, const char *new)
  {
  	struct sysfs_dirent *parent_sd, *sd = NULL;

  	const void *old_ns = NULL, *new_ns = NULL;

  	int result;
  
  	if (!kobj)
  		parent_sd = &sysfs_root;
  	else
  		parent_sd = kobj->sd;

  	if (targ->sd)
  		old_ns = targ->sd->s_ns;

  	result = -ENOENT;

  	sd = sysfs_get_dirent(parent_sd, old_ns, old);

  	if (!sd)
  		goto out;
  
  	result = -EINVAL;
  	if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
  		goto out;
  	if (sd->s_symlink.target_sd->s_dir.kobj != targ)
  		goto out;

  	if (sysfs_ns_type(parent_sd))
  		new_ns = targ->ktype->namespace(targ);
  
  	result = sysfs_rename(sd, parent_sd, new_ns, new);

  
  out:
  	sysfs_put(sd);
  	return result;
  }

  static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
  				 struct sysfs_dirent *target_sd, char *path)

  {

  	struct sysfs_dirent *base, *sd;
  	char *s = path;
  	int len = 0;
  
  	/* go up to the root, stop at the base */
  	base = parent_sd;
  	while (base->s_parent) {
  		sd = target_sd->s_parent;
  		while (sd->s_parent && base != sd)
  			sd = sd->s_parent;
  
  		if (base == sd)
  			break;
  
  		strcpy(s, "../");
  		s += 3;
  		base = base->s_parent;
  	}
  
  	/* determine end of target string for reverse fillup */
  	sd = target_sd;
  	while (sd->s_parent && sd != base) {
  		len += strlen(sd->s_name) + 1;
  		sd = sd->s_parent;
  	}

  	/* check limits */
  	if (len < 2)
  		return -EINVAL;
  	len--;
  	if ((s - path) + len > PATH_MAX)

  		return -ENAMETOOLONG;

  	/* reverse fillup of target string from target to base */
  	sd = target_sd;
  	while (sd->s_parent && sd != base) {
  		int slen = strlen(sd->s_name);

  		len -= slen;
  		strncpy(s + len, sd->s_name, slen);
  		if (len)
  			s[--len] = '/';

  		sd = sd->s_parent;
  	}

  
  	return 0;
  }
  
  static int sysfs_getlink(struct dentry *dentry, char * path)
  {

  	struct sysfs_dirent *sd = dentry->d_fsdata;
  	struct sysfs_dirent *parent_sd = sd->s_parent;

  	struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;

  	int error;

  	mutex_lock(&sysfs_mutex);

  	error = sysfs_get_target_path(parent_sd, target_sd, path);

  	mutex_unlock(&sysfs_mutex);

  	return error;

  }

  static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)

  {
  	int error = -ENOMEM;
  	unsigned long page = get_zeroed_page(GFP_KERNEL);

  	if (page) {

  		error = sysfs_getlink(dentry, (char *) page); 

  		if (error < 0)
  			free_page((unsigned long)page);
  	}

  	nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);

  	return NULL;

  }

  static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)

  {
  	char *page = nd_get_link(nd);
  	if (!IS_ERR(page))
  		free_page((unsigned long)page);
  }

  const struct inode_operations sysfs_symlink_inode_operations = {

  	.setxattr	= sysfs_setxattr,
  	.readlink	= generic_readlink,
  	.follow_link	= sysfs_follow_link,
  	.put_link	= sysfs_put_link,

  	.setattr	= sysfs_setattr,
  	.getattr	= sysfs_getattr,
  	.permission	= sysfs_permission,

  };
  
  
  EXPORT_SYMBOL_GPL(sysfs_create_link);
  EXPORT_SYMBOL_GPL(sysfs_remove_link);

  EXPORT_SYMBOL_GPL(sysfs_rename_link);