fs/sysfs/symlink.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * fs/sysfs/symlink.c - sysfs symlink implementation
   4  *
   5  * Copyright (c) 2001-3 Patrick Mochel
   6  * Copyright (c) 2007 SUSE Linux Products GmbH
   7  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
   8  *
   9  * Please see Documentation/filesystems/sysfs.txt for more information.
  10  */
  11
  12 #include <linux/fs.h>
  13 #include <linux/module.h>
  14 #include <linux/kobject.h>
  15 #include <linux/mutex.h>
  16 #include <linux/security.h>
  17
  18 #include "sysfs.h"
  19
  20 static int sysfs_do_create_link_sd(struct kernfs_node *parent,
  21                                    struct kobject *target_kobj,
  22                                    const char *name, int warn)
  23 {
  24         struct kernfs_node *kn, *target = NULL;
  25
  26         BUG_ON(!name || !parent);
  27
  28         /*
  29          * We don't own @target_kobj and it may be removed at any time.
  30          * Synchronize using sysfs_symlink_target_lock.  See
  31          * sysfs_remove_dir() for details.
  32          */
  33         spin_lock(&sysfs_symlink_target_lock);
  34         if (target_kobj->sd) {
  35                 target = target_kobj->sd;
  36                 kernfs_get(target);
  37         }
  38         spin_unlock(&sysfs_symlink_target_lock);
  39
  40         if (!target)
  41                 return -ENOENT;
  42
  43         kn = kernfs_create_link(parent, name, target);
  44         kernfs_put(target);
  45
  46         if (!IS_ERR(kn))
  47                 return 0;
  48
  49         if (warn && PTR_ERR(kn) == -EEXIST)
  50                 sysfs_warn_dup(parent, name);
  51         return PTR_ERR(kn);
  52 }
  53
  54 /**
  55  *      sysfs_create_link_sd - create symlink to a given object.
  56  *      @kn:            directory we're creating the link in.
  57  *      @target:        object we're pointing to.
  58  *      @name:          name of the symlink.
  59  */
  60 int sysfs_create_link_sd(struct kernfs_node *kn, struct kobject *target,
  61                          const char *name)
  62 {
  63         return sysfs_do_create_link_sd(kn, target, name, 1);
  64 }
  65
  66 static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
  67                                 const char *name, int warn)
  68 {
  69         struct kernfs_node *parent = NULL;
  70
  71         if (!kobj)
  72                 parent = sysfs_root_kn;
  73         else
  74                 parent = kobj->sd;
  75
  76         if (!parent)
  77                 return -EFAULT;
  78
  79         return sysfs_do_create_link_sd(parent, target, name, warn);
  80 }
  81
  82 /**
  83  *      sysfs_create_link - create symlink between two objects.
  84  *      @kobj:  object whose directory we're creating the link in.
  85  *      @target:        object we're pointing to.
  86  *      @name:          name of the symlink.
  87  */
  88 int sysfs_create_link(struct kobject *kobj, struct kobject *target,
  89                       const char *name)
  90 {
  91         return sysfs_do_create_link(kobj, target, name, 1);
  92 }
  93 EXPORT_SYMBOL_GPL(sysfs_create_link);
  94
  95 /**
  96  *      sysfs_create_link_nowarn - create symlink between two objects.
  97  *      @kobj:  object whose directory we're creating the link in.
  98  *      @target:        object we're pointing to.
  99  *      @name:          name of the symlink.
 100  *
 101  *      This function does the same as sysfs_create_link(), but it
 102  *      doesn't warn if the link already exists.
 103  */
 104 int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
 105                              const char *name)
 106 {
 107         return sysfs_do_create_link(kobj, target, name, 0);
 108 }
 109
 110 /**
 111  *      sysfs_delete_link - remove symlink in object's directory.
 112  *      @kobj:  object we're acting for.
 113  *      @targ:  object we're pointing to.
 114  *      @name:  name of the symlink to remove.
 115  *
 116  *      Unlike sysfs_remove_link sysfs_delete_link has enough information
 117  *      to successfully delete symlinks in tagged directories.
 118  */
 119 void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
 120                         const char *name)
 121 {
 122         const void *ns = NULL;
 123
 124         /*
 125          * We don't own @target and it may be removed at any time.
 126          * Synchronize using sysfs_symlink_target_lock.  See
 127          * sysfs_remove_dir() for details.
 128          */
 129         spin_lock(&sysfs_symlink_target_lock);
 130         if (targ->sd && kernfs_ns_enabled(kobj->sd))
 131                 ns = targ->sd->ns;
 132         spin_unlock(&sysfs_symlink_target_lock);
 133         kernfs_remove_by_name_ns(kobj->sd, name, ns);
 134 }
 135
 136 /**
 137  *      sysfs_remove_link - remove symlink in object's directory.
 138  *      @kobj:  object we're acting for.
 139  *      @name:  name of the symlink to remove.
 140  */
 141 void sysfs_remove_link(struct kobject *kobj, const char *name)
 142 {
 143         struct kernfs_node *parent = NULL;
 144
 145         if (!kobj)
 146                 parent = sysfs_root_kn;
 147         else
 148                 parent = kobj->sd;
 149
 150         kernfs_remove_by_name(parent, name);
 151 }
 152 EXPORT_SYMBOL_GPL(sysfs_remove_link);
 153
 154 /**
 155  *      sysfs_rename_link_ns - rename symlink in object's directory.
 156  *      @kobj:  object we're acting for.
 157  *      @targ:  object we're pointing to.
 158  *      @old:   previous name of the symlink.
 159  *      @new:   new name of the symlink.
 160  *      @new_ns: new namespace of the symlink.
 161  *
 162  *      A helper function for the common rename symlink idiom.
 163  */
 164 int sysfs_rename_link_ns(struct kobject *kobj, struct kobject *targ,
 165                          const char *old, const char *new, const void *new_ns)
 166 {
 167         struct kernfs_node *parent, *kn = NULL;
 168         const void *old_ns = NULL;
 169         int result;
 170
 171         if (!kobj)
 172                 parent = sysfs_root_kn;
 173         else
 174                 parent = kobj->sd;
 175
 176         if (targ->sd)
 177                 old_ns = targ->sd->ns;
 178
 179         result = -ENOENT;
 180         kn = kernfs_find_and_get_ns(parent, old, old_ns);
 181         if (!kn)
 182                 goto out;
 183
 184         result = -EINVAL;
 185         if (kernfs_type(kn) != KERNFS_LINK)
 186                 goto out;
 187         if (kn->symlink.target_kn->priv != targ)
 188                 goto out;
 189
 190         result = kernfs_rename_ns(kn, parent, new, new_ns);
 191
 192 out:
 193         kernfs_put(kn);
 194         return result;
 195 }
 196 EXPORT_SYMBOL_GPL(sysfs_rename_link_ns);