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
  11 #include "sysfs.h"
  12
  13 static int object_depth(struct kobject * kobj)
  14 {
  15         struct kobject * p = kobj;
  16         int depth = 0;
  17         do { depth++; } while ((p = p->parent));
  18         return depth;
  19 }
  20
  21 static int object_path_length(struct kobject * kobj)
  22 {
  23         struct kobject * p = kobj;
  24         int length = 1;
  25         do {
  26                 length += strlen(kobject_name(p)) + 1;
  27                 p = p->parent;
  28         } while (p);
  29         return length;
  30 }
  31
  32 static void fill_object_path(struct kobject * kobj, char * buffer, int length)
  33 {
  34         struct kobject * p;
  35
  36         --length;
  37         for (p = kobj; p; p = p->parent) {
  38                 int cur = strlen(kobject_name(p));
  39
  40                 /* back up enough to print this bus id with '/' */
  41                 length -= cur;
  42                 strncpy(buffer + length,kobject_name(p),cur);
  43                 *(buffer + --length) = '/';
  44         }
  45 }
  46
  47 static int sysfs_add_link(struct dentry * parent, const char * name, struct kobject * target)
  48 {
  49         struct sysfs_dirent * parent_sd = parent->d_fsdata;
  50         struct sysfs_symlink * sl;
  51         int error = 0;
  52
  53         error = -ENOMEM;
  54         sl = kmalloc(sizeof(*sl), GFP_KERNEL);
  55         if (!sl)
  56                 goto exit1;
  57
  58         sl->link_name = kmalloc(strlen(name) + 1, GFP_KERNEL);
  59         if (!sl->link_name)
  60                 goto exit2;
  61
  62         strcpy(sl->link_name, name);
  63         sl->target_kobj = kobject_get(target);
  64
  65         error = sysfs_make_dirent(parent_sd, NULL, sl, S_IFLNK|S_IRWXUGO,
  66                                 SYSFS_KOBJ_LINK);
  67         if (!error)
  68                 return 0;
  69
  70         kobject_put(target);
  71         kfree(sl->link_name);
  72 exit2:
  73         kfree(sl);
  74 exit1:
  75         return error;
  76 }
  77
  78 /**
  79  *      sysfs_create_link - create symlink between two objects.
  80  *      @kobj:  object whose directory we're creating the link in.
  81  *      @target:        object we're pointing to.
  82  *      @name:          name of the symlink.
  83  */
  84 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
  85 {
  86         struct dentry *dentry = NULL;
  87         int error = -EEXIST;
  88
  89         BUG_ON(!name);
  90
  91         if (!kobj) {
  92                 if (sysfs_mount && sysfs_mount->mnt_sb)
  93                         dentry = sysfs_mount->mnt_sb->s_root;
  94         } else
  95                 dentry = kobj->dentry;
  96
  97         if (!dentry)
  98                 return -EFAULT;
  99
 100         mutex_lock(&dentry->d_inode->i_mutex);
 101         if (!sysfs_dirent_exist(dentry->d_fsdata, name))
 102                 error = sysfs_add_link(dentry, name, target);
 103         mutex_unlock(&dentry->d_inode->i_mutex);
 104         return error;
 105 }
 106
 107
 108 /**
 109  *      sysfs_remove_link - remove symlink in object's directory.
 110  *      @kobj:  object we're acting for.
 111  *      @name:  name of the symlink to remove.
 112  */
 113
 114 void sysfs_remove_link(struct kobject * kobj, const char * name)
 115 {
 116         sysfs_hash_and_remove(kobj->dentry,name);
 117 }
 118
 119 static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
 120                                  char *path)
 121 {
 122         char * s;
 123         int depth, size;
 124
 125         depth = object_depth(kobj);
 126         size = object_path_length(target) + depth * 3 - 1;
 127         if (size > PATH_MAX)
 128                 return -ENAMETOOLONG;
 129
 130         pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
 131
 132         for (s = path; depth--; s += 3)
 133                 strcpy(s,"../");
 134
 135         fill_object_path(target, path, size);
 136         pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
 137
 138         return 0;
 139 }
 140
 141 static int sysfs_getlink(struct dentry *dentry, char * path)
 142 {
 143         struct kobject *kobj, *target_kobj;
 144         int error = 0;
 145
 146         kobj = sysfs_get_kobject(dentry->d_parent);
 147         if (!kobj)
 148                 return -EINVAL;
 149
 150         target_kobj = sysfs_get_kobject(dentry);
 151         if (!target_kobj) {
 152                 kobject_put(kobj);
 153                 return -EINVAL;
 154         }
 155
 156         down_read(&sysfs_rename_sem);
 157         error = sysfs_get_target_path(kobj, target_kobj, path);
 158         up_read(&sysfs_rename_sem);
 159
 160         kobject_put(kobj);
 161         kobject_put(target_kobj);
 162         return error;
 163
 164 }
 165
 166 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 167 {
 168         int error = -ENOMEM;
 169         unsigned long page = get_zeroed_page(GFP_KERNEL);
 170         if (page)
 171                 error = sysfs_getlink(dentry, (char *) page);
 172         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 173         return NULL;
 174 }
 175
 176 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 177 {
 178         char *page = nd_get_link(nd);
 179         if (!IS_ERR(page))
 180                 free_page((unsigned long)page);
 181 }
 182
 183 struct inode_operations sysfs_symlink_inode_operations = {
 184         .readlink = generic_readlink,
 185         .follow_link = sysfs_follow_link,
 186         .put_link = sysfs_put_link,
 187 };
 188
 189
 190 EXPORT_SYMBOL_GPL(sysfs_create_link);
 191 EXPORT_SYMBOL_GPL(sysfs_remove_link);