fs/sysfs/symlink.c

   1 /*
   2  * symlink.c - operations for sysfs symlinks.
   3  */
   4
   5 #include <linux/fs.h>
   6 #include <linux/mount.h>
   7 #include <linux/module.h>
   8 #include <linux/kobject.h>
   9 #include <linux/namei.h>
  10 #include <asm/semaphore.h>
  11
  12 #include "sysfs.h"
  13
  14 static int object_depth(struct sysfs_dirent *sd)
  15 {
  16         int depth = 0;
  17
  18         for (; sd->s_parent; sd = sd->s_parent)
  19                 depth++;
  20
  21         return depth;
  22 }
  23
  24 static int object_path_length(struct sysfs_dirent * sd)
  25 {
  26         int length = 1;
  27
  28         for (; sd->s_parent; sd = sd->s_parent)
  29                 length += strlen(sd->s_name) + 1;
  30
  31         return length;
  32 }
  33
  34 static void fill_object_path(struct sysfs_dirent *sd, char *buffer, int length)
  35 {
  36         --length;
  37         for (; sd->s_parent; sd = sd->s_parent) {
  38                 int cur = strlen(sd->s_name);
  39
  40                 /* back up enough to print this bus id with '/' */
  41                 length -= cur;
  42                 strncpy(buffer + length, sd->s_name, cur);
  43                 *(buffer + --length) = '/';
  44         }
  45 }
  46
  47 static int sysfs_add_link(struct sysfs_dirent * parent_sd, const char * name,
  48                           struct sysfs_dirent * target_sd)
  49 {
  50         struct sysfs_dirent * sd;
  51
  52         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  53         if (!sd)
  54                 return -ENOMEM;
  55
  56         sd->s_elem.symlink.target_sd = target_sd;
  57         sysfs_attach_dirent(sd, parent_sd, NULL);
  58         return 0;
  59 }
  60
  61 /**
  62  *      sysfs_create_link - create symlink between two objects.
  63  *      @kobj:  object whose directory we're creating the link in.
  64  *      @target:        object we're pointing to.
  65  *      @name:          name of the symlink.
  66  */
  67 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
  68 {
  69         struct dentry *dentry = NULL;
  70         struct sysfs_dirent *parent_sd = NULL;
  71         struct sysfs_dirent *target_sd = NULL;
  72         int error = -EEXIST;
  73
  74         BUG_ON(!name);
  75
  76         if (!kobj) {
  77                 if (sysfs_mount && sysfs_mount->mnt_sb)
  78                         dentry = sysfs_mount->mnt_sb->s_root;
  79         } else
  80                 dentry = kobj->dentry;
  81
  82         if (!dentry)
  83                 return -EFAULT;
  84         parent_sd = dentry->d_fsdata;
  85
  86         /* target->dentry can go away beneath us but is protected with
  87          * kobj_sysfs_assoc_lock.  Fetch target_sd from it.
  88          */
  89         spin_lock(&kobj_sysfs_assoc_lock);
  90         if (target->dentry)
  91                 target_sd = sysfs_get(target->dentry->d_fsdata);
  92         spin_unlock(&kobj_sysfs_assoc_lock);
  93
  94         if (!target_sd)
  95                 return -ENOENT;
  96
  97         mutex_lock(&dentry->d_inode->i_mutex);
  98         if (!sysfs_find_dirent(dentry->d_fsdata, name))
  99                 error = sysfs_add_link(parent_sd, name, target_sd);
 100         mutex_unlock(&dentry->d_inode->i_mutex);
 101
 102         if (error)
 103                 sysfs_put(target_sd);
 104
 105         return error;
 106 }
 107
 108
 109 /**
 110  *      sysfs_remove_link - remove symlink in object's directory.
 111  *      @kobj:  object we're acting for.
 112  *      @name:  name of the symlink to remove.
 113  */
 114
 115 void sysfs_remove_link(struct kobject * kobj, const char * name)
 116 {
 117         sysfs_hash_and_remove(kobj->dentry,name);
 118 }
 119
 120 static int sysfs_get_target_path(struct sysfs_dirent * parent_sd,
 121                                  struct sysfs_dirent * target_sd, char *path)
 122 {
 123         char * s;
 124         int depth, size;
 125
 126         depth = object_depth(parent_sd);
 127         size = object_path_length(target_sd) + depth * 3 - 1;
 128         if (size > PATH_MAX)
 129                 return -ENAMETOOLONG;
 130
 131         pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
 132
 133         for (s = path; depth--; s += 3)
 134                 strcpy(s,"../");
 135
 136         fill_object_path(target_sd, path, size);
 137         pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
 138
 139         return 0;
 140 }
 141
 142 static int sysfs_getlink(struct dentry *dentry, char * path)
 143 {
 144         struct sysfs_dirent *sd = dentry->d_fsdata;
 145         struct sysfs_dirent *parent_sd = sd->s_parent;
 146         struct sysfs_dirent *target_sd = sd->s_elem.symlink.target_sd;
 147         int error;
 148
 149         down_read(&sysfs_rename_sem);
 150         error = sysfs_get_target_path(parent_sd, target_sd, path);
 151         up_read(&sysfs_rename_sem);
 152
 153         return error;
 154 }
 155
 156 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 157 {
 158         int error = -ENOMEM;
 159         unsigned long page = get_zeroed_page(GFP_KERNEL);
 160         if (page)
 161                 error = sysfs_getlink(dentry, (char *) page);
 162         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 163         return NULL;
 164 }
 165
 166 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 167 {
 168         char *page = nd_get_link(nd);
 169         if (!IS_ERR(page))
 170                 free_page((unsigned long)page);
 171 }
 172
 173 const struct inode_operations sysfs_symlink_inode_operations = {
 174         .readlink = generic_readlink,
 175         .follow_link = sysfs_follow_link,
 176         .put_link = sysfs_put_link,
 177 };
 178
 179
 180 EXPORT_SYMBOL_GPL(sysfs_create_link);
 181 EXPORT_SYMBOL_GPL(sysfs_remove_link);