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 /**
  48  *      sysfs_create_link - create symlink between two objects.
  49  *      @kobj:  object whose directory we're creating the link in.
  50  *      @target:        object we're pointing to.
  51  *      @name:          name of the symlink.
  52  */
  53 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
  54 {
  55         struct sysfs_dirent *parent_sd = NULL;
  56         struct sysfs_dirent *target_sd = NULL;
  57         struct sysfs_dirent *sd = NULL;
  58         struct sysfs_addrm_cxt acxt;
  59         int error;
  60
  61         BUG_ON(!name);
  62
  63         if (!kobj) {
  64                 if (sysfs_mount && sysfs_mount->mnt_sb)
  65                         parent_sd = sysfs_mount->mnt_sb->s_root->d_fsdata;
  66         } else
  67                 parent_sd = kobj->sd;
  68
  69         error = -EFAULT;
  70         if (!parent_sd)
  71                 goto out_put;
  72
  73         /* target->sd can go away beneath us but is protected with
  74          * sysfs_assoc_lock.  Fetch target_sd from it.
  75          */
  76         spin_lock(&sysfs_assoc_lock);
  77         if (target->sd)
  78                 target_sd = sysfs_get(target->sd);
  79         spin_unlock(&sysfs_assoc_lock);
  80
  81         error = -ENOENT;
  82         if (!target_sd)
  83                 goto out_put;
  84
  85         error = -ENOMEM;
  86         sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  87         if (!sd)
  88                 goto out_put;
  89
  90         sd->s_elem.symlink.target_sd = target_sd;
  91         target_sd = NULL;       /* reference is now owned by the symlink */
  92
  93         sysfs_addrm_start(&acxt, parent_sd);
  94
  95         if (!sysfs_find_dirent(parent_sd, name)) {
  96                 sysfs_add_one(&acxt, sd);
  97                 sysfs_link_sibling(sd);
  98         }
  99
 100         if (!sysfs_addrm_finish(&acxt)) {
 101                 error = -EEXIST;
 102                 goto out_put;
 103         }
 104
 105         return 0;
 106
 107  out_put:
 108         sysfs_put(target_sd);
 109         sysfs_put(sd);
 110         return error;
 111 }
 112
 113
 114 /**
 115  *      sysfs_remove_link - remove symlink in object's directory.
 116  *      @kobj:  object we're acting for.
 117  *      @name:  name of the symlink to remove.
 118  */
 119
 120 void sysfs_remove_link(struct kobject * kobj, const char * name)
 121 {
 122         sysfs_hash_and_remove(kobj->sd, name);
 123 }
 124
 125 static int sysfs_get_target_path(struct sysfs_dirent * parent_sd,
 126                                  struct sysfs_dirent * target_sd, char *path)
 127 {
 128         char * s;
 129         int depth, size;
 130
 131         depth = object_depth(parent_sd);
 132         size = object_path_length(target_sd) + depth * 3 - 1;
 133         if (size > PATH_MAX)
 134                 return -ENAMETOOLONG;
 135
 136         pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
 137
 138         for (s = path; depth--; s += 3)
 139                 strcpy(s,"../");
 140
 141         fill_object_path(target_sd, path, size);
 142         pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
 143
 144         return 0;
 145 }
 146
 147 static int sysfs_getlink(struct dentry *dentry, char * path)
 148 {
 149         struct sysfs_dirent *sd = dentry->d_fsdata;
 150         struct sysfs_dirent *parent_sd = sd->s_parent;
 151         struct sysfs_dirent *target_sd = sd->s_elem.symlink.target_sd;
 152         int error;
 153
 154         mutex_lock(&sysfs_mutex);
 155         error = sysfs_get_target_path(parent_sd, target_sd, path);
 156         mutex_unlock(&sysfs_mutex);
 157
 158         return error;
 159 }
 160
 161 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 162 {
 163         int error = -ENOMEM;
 164         unsigned long page = get_zeroed_page(GFP_KERNEL);
 165         if (page)
 166                 error = sysfs_getlink(dentry, (char *) page);
 167         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 168         return NULL;
 169 }
 170
 171 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 172 {
 173         char *page = nd_get_link(nd);
 174         if (!IS_ERR(page))
 175                 free_page((unsigned long)page);
 176 }
 177
 178 const struct inode_operations sysfs_symlink_inode_operations = {
 179         .readlink = generic_readlink,
 180         .follow_link = sysfs_follow_link,
 181         .put_link = sysfs_put_link,
 182 };
 183
 184
 185 EXPORT_SYMBOL_GPL(sysfs_create_link);
 186 EXPORT_SYMBOL_GPL(sysfs_remove_link);