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 = 0;
  53
  54         error = -ENOMEM;
  55         sl = kmalloc(sizeof(*sl), GFP_KERNEL);
  56         if (!sl)
  57                 goto exit1;
  58
  59         sl->link_name = kmalloc(strlen(name) + 1, GFP_KERNEL);
  60         if (!sl->link_name)
  61                 goto exit2;
  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                 return 0;
  70
  71         kobject_put(target);
  72         kfree(sl->link_name);
  73 exit2:
  74         kfree(sl);
  75 exit1:
  76         return error;
  77 }
  78
  79 /**
  80  *      sysfs_create_link - create symlink between two objects.
  81  *      @kobj:  object whose directory we're creating the link in.
  82  *      @target:        object we're pointing to.
  83  *      @name:          name of the symlink.
  84  */
  85 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
  86 {
  87         struct dentry *dentry = NULL;
  88         int error = -EEXIST;
  89
  90         BUG_ON(!name);
  91
  92         if (!kobj) {
  93                 if (sysfs_mount && sysfs_mount->mnt_sb)
  94                         dentry = sysfs_mount->mnt_sb->s_root;
  95         } else
  96                 dentry = kobj->dentry;
  97
  98         if (!dentry)
  99                 return -EFAULT;
 100
 101         mutex_lock(&dentry->d_inode->i_mutex);
 102         if (!sysfs_dirent_exist(dentry->d_fsdata, name))
 103                 error = sysfs_add_link(dentry, name, target);
 104         mutex_unlock(&dentry->d_inode->i_mutex);
 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 kobject * kobj, struct kobject * target,
 121                                  char *path)
 122 {
 123         char * s;
 124         int depth, size;
 125
 126         depth = object_depth(kobj);
 127         size = object_path_length(target) + 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, 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 kobject *kobj, *target_kobj;
 145         int error = 0;
 146
 147         kobj = sysfs_get_kobject(dentry->d_parent);
 148         if (!kobj)
 149                 return -EINVAL;
 150
 151         target_kobj = sysfs_get_kobject(dentry);
 152         if (!target_kobj) {
 153                 kobject_put(kobj);
 154                 return -EINVAL;
 155         }
 156
 157         down_read(&sysfs_rename_sem);
 158         error = sysfs_get_target_path(kobj, target_kobj, path);
 159         up_read(&sysfs_rename_sem);
 160
 161         kobject_put(kobj);
 162         kobject_put(target_kobj);
 163         return error;
 164
 165 }
 166
 167 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 168 {
 169         int error = -ENOMEM;
 170         unsigned long page = get_zeroed_page(GFP_KERNEL);
 171         if (page)
 172                 error = sysfs_getlink(dentry, (char *) page);
 173         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 174         return NULL;
 175 }
 176
 177 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 178 {
 179         char *page = nd_get_link(nd);
 180         if (!IS_ERR(page))
 181                 free_page((unsigned long)page);
 182 }
 183
 184 const struct inode_operations sysfs_symlink_inode_operations = {
 185         .readlink = generic_readlink,
 186         .follow_link = sysfs_follow_link,
 187         .put_link = sysfs_put_link,
 188 };
 189
 190
 191 EXPORT_SYMBOL_GPL(sysfs_create_link);
 192 EXPORT_SYMBOL_GPL(sysfs_remove_link);