drivers/base/devtmpfs.c

   1 /*
   2  * devtmpfs - kernel-maintained tmpfs-based /dev
   3  *
   4  * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
   5  *
   6  * During bootup, before any driver core device is registered,
   7  * devtmpfs, a tmpfs-based filesystem is created. Every driver-core
   8  * device which requests a device node, will add a node in this
   9  * filesystem.
  10  * By default, all devices are named after the the name of the
  11  * device, owned by root and have a default mode of 0600. Subsystems
  12  * can overwrite the default setting if needed.
  13  */
  14
  15 #include <linux/kernel.h>
  16 #include <linux/syscalls.h>
  17 #include <linux/mount.h>
  18 #include <linux/device.h>
  19 #include <linux/genhd.h>
  20 #include <linux/namei.h>
  21 #include <linux/fs.h>
  22 #include <linux/shmem_fs.h>
  23 #include <linux/cred.h>
  24 #include <linux/sched.h>
  25 #include <linux/init_task.h>
  26
  27 static struct vfsmount *dev_mnt;
  28
  29 #if defined CONFIG_DEVTMPFS_MOUNT
  30 static int dev_mount = 1;
  31 #else
  32 static int dev_mount;
  33 #endif
  34
  35 static DEFINE_MUTEX(dirlock);
  36
  37 static int __init mount_param(char *str)
  38 {
  39         dev_mount = simple_strtoul(str, NULL, 0);
  40         return 1;
  41 }
  42 __setup("devtmpfs.mount=", mount_param);
  43
  44 static int dev_get_sb(struct file_system_type *fs_type, int flags,
  45                       const char *dev_name, void *data, struct vfsmount *mnt)
  46 {
  47         return get_sb_single(fs_type, flags, data, shmem_fill_super, mnt);
  48 }
  49
  50 static struct file_system_type dev_fs_type = {
  51         .name = "devtmpfs",
  52         .get_sb = dev_get_sb,
  53         .kill_sb = kill_litter_super,
  54 };
  55
  56 #ifdef CONFIG_BLOCK
  57 static inline int is_blockdev(struct device *dev)
  58 {
  59         return dev->class == &block_class;
  60 }
  61 #else
  62 static inline int is_blockdev(struct device *dev) { return 0; }
  63 #endif
  64
  65 static int dev_mkdir(const char *name, mode_t mode)
  66 {
  67         struct nameidata nd;
  68         struct dentry *dentry;
  69         int err;
  70
  71         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
  72                               name, LOOKUP_PARENT, &nd);
  73         if (err)
  74                 return err;
  75
  76         dentry = lookup_create(&nd, 1);
  77         if (!IS_ERR(dentry)) {
  78                 err = vfs_mkdir(nd.path.dentry->d_inode, dentry, mode);
  79                 if (!err)
  80                         /* mark as kernel-created inode */
  81                         dentry->d_inode->i_private = &dev_mnt;
  82                 dput(dentry);
  83         } else {
  84                 err = PTR_ERR(dentry);
  85         }
  86
  87         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
  88         path_put(&nd.path);
  89         return err;
  90 }
  91
  92 static int create_path(const char *nodepath)
  93 {
  94         int err;
  95
  96         mutex_lock(&dirlock);
  97         err = dev_mkdir(nodepath, 0755);
  98         if (err == -ENOENT) {
  99                 char *path;
 100                 char *s;
 101
 102                 /* parent directories do not exist, create them */
 103                 path = kstrdup(nodepath, GFP_KERNEL);
 104                 if (!path) {
 105                         err = -ENOMEM;
 106                         goto out;
 107                 }
 108                 s = path;
 109                 for (;;) {
 110                         s = strchr(s, '/');
 111                         if (!s)
 112                                 break;
 113                         s[0] = '\0';
 114                         err = dev_mkdir(path, 0755);
 115                         if (err && err != -EEXIST)
 116                                 break;
 117                         s[0] = '/';
 118                         s++;
 119                 }
 120                 kfree(path);
 121         }
 122 out:
 123         mutex_unlock(&dirlock);
 124         return err;
 125 }
 126
 127 int devtmpfs_create_node(struct device *dev)
 128 {
 129         const char *tmp = NULL;
 130         const char *nodename;
 131         const struct cred *curr_cred;
 132         mode_t mode = 0;
 133         struct nameidata nd;
 134         struct dentry *dentry;
 135         int err;
 136
 137         if (!dev_mnt)
 138                 return 0;
 139
 140         nodename = device_get_devnode(dev, &mode, &tmp);
 141         if (!nodename)
 142                 return -ENOMEM;
 143
 144         if (mode == 0)
 145                 mode = 0600;
 146         if (is_blockdev(dev))
 147                 mode |= S_IFBLK;
 148         else
 149                 mode |= S_IFCHR;
 150
 151         curr_cred = override_creds(&init_cred);
 152
 153         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 154                               nodename, LOOKUP_PARENT, &nd);
 155         if (err == -ENOENT) {
 156                 create_path(nodename);
 157                 err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 158                                       nodename, LOOKUP_PARENT, &nd);
 159         }
 160         if (err)
 161                 goto out;
 162
 163         dentry = lookup_create(&nd, 0);
 164         if (!IS_ERR(dentry)) {
 165                 err = vfs_mknod(nd.path.dentry->d_inode,
 166                                 dentry, mode, dev->devt);
 167                 if (!err) {
 168                         struct iattr newattrs;
 169
 170                         /* fixup possibly umasked mode */
 171                         newattrs.ia_mode = mode;
 172                         newattrs.ia_valid = ATTR_MODE;
 173                         mutex_lock(&dentry->d_inode->i_mutex);
 174                         notify_change(dentry, &newattrs);
 175                         mutex_unlock(&dentry->d_inode->i_mutex);
 176
 177                         /* mark as kernel-created inode */
 178                         dentry->d_inode->i_private = &dev_mnt;
 179                 }
 180                 dput(dentry);
 181         } else {
 182                 err = PTR_ERR(dentry);
 183         }
 184
 185         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 186         path_put(&nd.path);
 187 out:
 188         kfree(tmp);
 189         revert_creds(curr_cred);
 190         return err;
 191 }
 192
 193 static int dev_rmdir(const char *name)
 194 {
 195         struct nameidata nd;
 196         struct dentry *dentry;
 197         int err;
 198
 199         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 200                               name, LOOKUP_PARENT, &nd);
 201         if (err)
 202                 return err;
 203
 204         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 205         dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 206         if (!IS_ERR(dentry)) {
 207                 if (dentry->d_inode) {
 208                         if (dentry->d_inode->i_private == &dev_mnt)
 209                                 err = vfs_rmdir(nd.path.dentry->d_inode,
 210                                                 dentry);
 211                         else
 212                                 err = -EPERM;
 213                 } else {
 214                         err = -ENOENT;
 215                 }
 216                 dput(dentry);
 217         } else {
 218                 err = PTR_ERR(dentry);
 219         }
 220
 221         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 222         path_put(&nd.path);
 223         return err;
 224 }
 225
 226 static int delete_path(const char *nodepath)
 227 {
 228         const char *path;
 229         int err = 0;
 230
 231         path = kstrdup(nodepath, GFP_KERNEL);
 232         if (!path)
 233                 return -ENOMEM;
 234
 235         mutex_lock(&dirlock);
 236         for (;;) {
 237                 char *base;
 238
 239                 base = strrchr(path, '/');
 240                 if (!base)
 241                         break;
 242                 base[0] = '\0';
 243                 err = dev_rmdir(path);
 244                 if (err)
 245                         break;
 246         }
 247         mutex_unlock(&dirlock);
 248
 249         kfree(path);
 250         return err;
 251 }
 252
 253 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 254 {
 255         /* did we create it */
 256         if (inode->i_private != &dev_mnt)
 257                 return 0;
 258
 259         /* does the dev_t match */
 260         if (is_blockdev(dev)) {
 261                 if (!S_ISBLK(stat->mode))
 262                         return 0;
 263         } else {
 264                 if (!S_ISCHR(stat->mode))
 265                         return 0;
 266         }
 267         if (stat->rdev != dev->devt)
 268                 return 0;
 269
 270         /* ours */
 271         return 1;
 272 }
 273
 274 int devtmpfs_delete_node(struct device *dev)
 275 {
 276         const char *tmp = NULL;
 277         const char *nodename;
 278         const struct cred *curr_cred;
 279         struct nameidata nd;
 280         struct dentry *dentry;
 281         struct kstat stat;
 282         int deleted = 1;
 283         int err;
 284
 285         if (!dev_mnt)
 286                 return 0;
 287
 288         nodename = device_get_devnode(dev, NULL, &tmp);
 289         if (!nodename)
 290                 return -ENOMEM;
 291
 292         curr_cred = override_creds(&init_cred);
 293         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 294                               nodename, LOOKUP_PARENT, &nd);
 295         if (err)
 296                 goto out;
 297
 298         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 299         dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 300         if (!IS_ERR(dentry)) {
 301                 if (dentry->d_inode) {
 302                         err = vfs_getattr(nd.path.mnt, dentry, &stat);
 303                         if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {
 304                                 struct iattr newattrs;
 305                                 /*
 306                                  * before unlinking this node, reset permissions
 307                                  * of possible references like hardlinks
 308                                  */
 309                                 newattrs.ia_uid = 0;
 310                                 newattrs.ia_gid = 0;
 311                                 newattrs.ia_mode = stat.mode & ~0777;
 312                                 newattrs.ia_valid =
 313                                         ATTR_UID|ATTR_GID|ATTR_MODE;
 314                                 mutex_lock(&dentry->d_inode->i_mutex);
 315                                 notify_change(dentry, &newattrs);
 316                                 mutex_unlock(&dentry->d_inode->i_mutex);
 317                                 err = vfs_unlink(nd.path.dentry->d_inode,
 318                                                  dentry);
 319                                 if (!err || err == -ENOENT)
 320                                         deleted = 1;
 321                         }
 322                 } else {
 323                         err = -ENOENT;
 324                 }
 325                 dput(dentry);
 326         } else {
 327                 err = PTR_ERR(dentry);
 328         }
 329         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 330
 331         path_put(&nd.path);
 332         if (deleted && strchr(nodename, '/'))
 333                 delete_path(nodename);
 334 out:
 335         kfree(tmp);
 336         revert_creds(curr_cred);
 337         return err;
 338 }
 339
 340 /*
 341  * If configured, or requested by the commandline, devtmpfs will be
 342  * auto-mounted after the kernel mounted the root filesystem.
 343  */
 344 int devtmpfs_mount(const char *mntdir)
 345 {
 346         int err;
 347
 348         if (!dev_mount)
 349                 return 0;
 350
 351         if (!dev_mnt)
 352                 return 0;
 353
 354         err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
 355         if (err)
 356                 printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 357         else
 358                 printk(KERN_INFO "devtmpfs: mounted\n");
 359         return err;
 360 }
 361
 362 /*
 363  * Create devtmpfs instance, driver-core devices will add their device
 364  * nodes here.
 365  */
 366 int __init devtmpfs_init(void)
 367 {
 368         int err;
 369         struct vfsmount *mnt;
 370         char options[] = "mode=0755";
 371
 372         err = register_filesystem(&dev_fs_type);
 373         if (err) {
 374                 printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
 375                        "type %i\n", err);
 376                 return err;
 377         }
 378
 379         mnt = kern_mount_data(&dev_fs_type, options);
 380         if (IS_ERR(mnt)) {
 381                 err = PTR_ERR(mnt);
 382                 printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
 383                 unregister_filesystem(&dev_fs_type);
 384                 return err;
 385         }
 386         dev_mnt = mnt;
 387
 388         printk(KERN_INFO "devtmpfs: initialized\n");
 389         return 0;
 390 }