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 kobject * kobj)
  15 {
  16         struct kobject * p = kobj;
  17         int depth = 0;
  18         do { depth++; } while ((p = p->parent));
  19         return depth;
  20 }
  21
  22 static int object_path_length(struct kobject * kobj)
  23 {
  24         struct kobject * p = kobj;
  25         int length = 1;
  26         do {
  27                 length += strlen(kobject_name(p)) + 1;
  28                 p = p->parent;
  29         } while (p);
  30         return length;
  31 }
  32
  33 static void fill_object_path(struct kobject * kobj, char * buffer, int length)
  34 {
  35         struct kobject * p;
  36
  37         --length;
  38         for (p = kobj; p; p = p->parent) {
  39                 int cur = strlen(kobject_name(p));
  40
  41                 /* back up enough to print this bus id with '/' */
  42                 length -= cur;
  43                 strncpy(buffer + length,kobject_name(p),cur);
  44                 *(buffer + --length) = '/';
  45         }
  46 }
  47
  48 static int sysfs_add_link(struct dentry * parent, const char * name, struct kobject * target)
  49 {
  50         struct sysfs_dirent * parent_sd = parent->d_fsdata;
  51         struct sysfs_symlink * sl;
  52         int error;
  53
  54         error = -ENOMEM;
  55         sl = kzalloc(sizeof(*sl), GFP_KERNEL);
  56         if (!sl)
  57                 goto err_out;
  58
  59         sl->link_name = kmalloc(strlen(name) + 1, GFP_KERNEL);
  60         if (!sl->link_name)
  61                 goto err_out;
  62
  63         strcpy(sl->link_name, name);
  64         sl->target_kobj = kobject_get(target);
  65
  66         error = sysfs_make_dirent(parent_sd, NULL, sl, S_IFLNK|S_IRWXUGO,
  67                                 SYSFS_KOBJ_LINK);
  68         if (error)
  69                 goto err_out;
  70
  71         return 0;
  72
  73  err_out:
  74         if (sl) {
  75                 kobject_put(sl->target_kobj);
  76                 kfree(sl->link_name);
  77                 kfree(sl);
  78         }
  79         return error;
  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, const char * name)
  89 {
  90         struct dentry *dentry = NULL;
  91         int error = -EEXIST;
  92
  93         BUG_ON(!name);
  94
  95         if (!kobj) {
  96                 if (sysfs_mount && sysfs_mount->mnt_sb)
  97                         dentry = sysfs_mount->mnt_sb->s_root;
  98         } else
  99                 dentry = kobj->dentry;
 100
 101         if (!dentry)
 102                 return -EFAULT;
 103
 104         mutex_lock(&dentry->d_inode->i_mutex);
 105         if (!sysfs_dirent_exist(dentry->d_fsdata, name))
 106                 error = sysfs_add_link(dentry, name, target);
 107         mutex_unlock(&dentry->d_inode->i_mutex);
 108         return error;
 109 }
 110
 111
 112 /**
 113  *      sysfs_remove_link - remove symlink in object's directory.
 114  *      @kobj:  object we're acting for.
 115  *      @name:  name of the symlink to remove.
 116  */
 117
 118 void sysfs_remove_link(struct kobject * kobj, const char * name)
 119 {
 120         sysfs_hash_and_remove(kobj->dentry,name);
 121 }
 122
 123 static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
 124                                  char *path)
 125 {
 126         char * s;
 127         int depth, size;
 128
 129         depth = object_depth(kobj);
 130         size = object_path_length(target) + depth * 3 - 1;
 131         if (size > PATH_MAX)
 132                 return -ENAMETOOLONG;
 133
 134         pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
 135
 136         for (s = path; depth--; s += 3)
 137                 strcpy(s,"../");
 138
 139         fill_object_path(target, path, size);
 140         pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
 141
 142         return 0;
 143 }
 144
 145 static int sysfs_getlink(struct dentry *dentry, char * path)
 146 {
 147         struct kobject *kobj, *target_kobj;
 148         int error = 0;
 149
 150         kobj = sysfs_get_kobject(dentry->d_parent);
 151         if (!kobj)
 152                 return -EINVAL;
 153
 154         target_kobj = sysfs_get_kobject(dentry);
 155         if (!target_kobj) {
 156                 kobject_put(kobj);
 157                 return -EINVAL;
 158         }
 159
 160         down_read(&sysfs_rename_sem);
 161         error = sysfs_get_target_path(kobj, target_kobj, path);
 162         up_read(&sysfs_rename_sem);
 163
 164         kobject_put(kobj);
 165         kobject_put(target_kobj);
 166         return error;
 167
 168 }
 169
 170 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 171 {
 172         int error = -ENOMEM;
 173         unsigned long page = get_zeroed_page(GFP_KERNEL);
 174         if (page)
 175                 error = sysfs_getlink(dentry, (char *) page);
 176         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 177         return NULL;
 178 }
 179
 180 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 181 {
 182         char *page = nd_get_link(nd);
 183         if (!IS_ERR(page))
 184                 free_page((unsigned long)page);
 185 }
 186
 187 const struct inode_operations sysfs_symlink_inode_operations = {
 188         .readlink = generic_readlink,
 189         .follow_link = sysfs_follow_link,
 190         .put_link = sysfs_put_link,
 191 };
 192
 193
 194 EXPORT_SYMBOL_GPL(sysfs_create_link);
 195 EXPORT_SYMBOL_GPL(sysfs_remove_link);