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         struct sysfs_dirent * sd;
  53         int error;
  54
  55         error = -ENOMEM;
  56         sl = kzalloc(sizeof(*sl), GFP_KERNEL);
  57         if (!sl)
  58                 goto err_out;
  59
  60         sl->target_kobj = kobject_get(target);
  61
  62         sd = sysfs_new_dirent(name, sl, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
  63         if (!sd)
  64                 goto err_out;
  65         sysfs_attach_dirent(sd, parent_sd, NULL);
  66
  67         return 0;
  68
  69  err_out:
  70         if (sl) {
  71                 kobject_put(sl->target_kobj);
  72                 kfree(sl);
  73         }
  74         return error;
  75 }
  76
  77 /**
  78  *      sysfs_create_link - create symlink between two objects.
  79  *      @kobj:  object whose directory we're creating the link in.
  80  *      @target:        object we're pointing to.
  81  *      @name:          name of the symlink.
  82  */
  83 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
  84 {
  85         struct dentry *dentry = NULL;
  86         int error = -EEXIST;
  87
  88         BUG_ON(!name);
  89
  90         if (!kobj) {
  91                 if (sysfs_mount && sysfs_mount->mnt_sb)
  92                         dentry = sysfs_mount->mnt_sb->s_root;
  93         } else
  94                 dentry = kobj->dentry;
  95
  96         if (!dentry)
  97                 return -EFAULT;
  98
  99         mutex_lock(&dentry->d_inode->i_mutex);
 100         if (!sysfs_dirent_exist(dentry->d_fsdata, name))
 101                 error = sysfs_add_link(dentry, name, target);
 102         mutex_unlock(&dentry->d_inode->i_mutex);
 103         return error;
 104 }
 105
 106
 107 /**
 108  *      sysfs_remove_link - remove symlink in object's directory.
 109  *      @kobj:  object we're acting for.
 110  *      @name:  name of the symlink to remove.
 111  */
 112
 113 void sysfs_remove_link(struct kobject * kobj, const char * name)
 114 {
 115         sysfs_hash_and_remove(kobj->dentry,name);
 116 }
 117
 118 static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
 119                                  char *path)
 120 {
 121         char * s;
 122         int depth, size;
 123
 124         depth = object_depth(kobj);
 125         size = object_path_length(target) + depth * 3 - 1;
 126         if (size > PATH_MAX)
 127                 return -ENAMETOOLONG;
 128
 129         pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
 130
 131         for (s = path; depth--; s += 3)
 132                 strcpy(s,"../");
 133
 134         fill_object_path(target, path, size);
 135         pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
 136
 137         return 0;
 138 }
 139
 140 static int sysfs_getlink(struct dentry *dentry, char * path)
 141 {
 142         struct kobject *kobj, *target_kobj;
 143         int error = 0;
 144
 145         kobj = sysfs_get_kobject(dentry->d_parent);
 146         if (!kobj)
 147                 return -EINVAL;
 148
 149         target_kobj = sysfs_get_kobject(dentry);
 150         if (!target_kobj) {
 151                 kobject_put(kobj);
 152                 return -EINVAL;
 153         }
 154
 155         down_read(&sysfs_rename_sem);
 156         error = sysfs_get_target_path(kobj, target_kobj, path);
 157         up_read(&sysfs_rename_sem);
 158
 159         kobject_put(kobj);
 160         kobject_put(target_kobj);
 161         return error;
 162
 163 }
 164
 165 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 166 {
 167         int error = -ENOMEM;
 168         unsigned long page = get_zeroed_page(GFP_KERNEL);
 169         if (page)
 170                 error = sysfs_getlink(dentry, (char *) page);
 171         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 172         return NULL;
 173 }
 174
 175 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
 176 {
 177         char *page = nd_get_link(nd);
 178         if (!IS_ERR(page))
 179                 free_page((unsigned long)page);
 180 }
 181
 182 const struct inode_operations sysfs_symlink_inode_operations = {
 183         .readlink = generic_readlink,
 184         .follow_link = sysfs_follow_link,
 185         .put_link = sysfs_put_link,
 186 };
 187
 188
 189 EXPORT_SYMBOL_GPL(sysfs_create_link);
 190 EXPORT_SYMBOL_GPL(sysfs_remove_link);