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/ramfs.h>
  24 #include <linux/sched.h>
  25 #include <linux/slab.h>
  26 #include <linux/kthread.h>
  27
  28 static struct task_struct *thread;
  29
  30 #if defined CONFIG_DEVTMPFS_MOUNT
  31 static int mount_dev = 1;
  32 #else
  33 static int mount_dev;
  34 #endif
  35
  36 static DEFINE_SPINLOCK(req_lock);
  37
  38 static struct req {
  39         struct req *next;
  40         struct completion done;
  41         int err;
  42         const char *name;
  43         umode_t mode;   /* 0 => delete */
  44         struct device *dev;
  45 } *requests;
  46
  47 static int __init mount_param(char *str)
  48 {
  49         mount_dev = simple_strtoul(str, NULL, 0);
  50         return 1;
  51 }
  52 __setup("devtmpfs.mount=", mount_param);
  53
  54 static struct dentry *dev_mount(struct file_system_type *fs_type, int flags,
  55                       const char *dev_name, void *data)
  56 {
  57 #ifdef CONFIG_TMPFS
  58         return mount_single(fs_type, flags, data, shmem_fill_super);
  59 #else
  60         return mount_single(fs_type, flags, data, ramfs_fill_super);
  61 #endif
  62 }
  63
  64 static struct file_system_type dev_fs_type = {
  65         .name = "devtmpfs",
  66         .mount = dev_mount,
  67         .kill_sb = kill_litter_super,
  68 };
  69
  70 #ifdef CONFIG_BLOCK
  71 static inline int is_blockdev(struct device *dev)
  72 {
  73         return dev->class == &block_class;
  74 }
  75 #else
  76 static inline int is_blockdev(struct device *dev) { return 0; }
  77 #endif
  78
  79 int devtmpfs_create_node(struct device *dev)
  80 {
  81         const char *tmp = NULL;
  82         struct req req;
  83
  84         if (!thread)
  85                 return 0;
  86
  87         req.mode = 0;
  88         req.name = device_get_devnode(dev, &req.mode, &tmp);
  89         if (!req.name)
  90                 return -ENOMEM;
  91
  92         if (req.mode == 0)
  93                 req.mode = 0600;
  94         if (is_blockdev(dev))
  95                 req.mode |= S_IFBLK;
  96         else
  97                 req.mode |= S_IFCHR;
  98
  99         req.dev = dev;
 100
 101         init_completion(&req.done);
 102
 103         spin_lock(&req_lock);
 104         req.next = requests;
 105         requests = &req;
 106         spin_unlock(&req_lock);
 107
 108         wake_up_process(thread);
 109         wait_for_completion(&req.done);
 110
 111         kfree(tmp);
 112
 113         return req.err;
 114 }
 115
 116 int devtmpfs_delete_node(struct device *dev)
 117 {
 118         const char *tmp = NULL;
 119         struct req req;
 120
 121         if (!thread)
 122                 return 0;
 123
 124         req.name = device_get_devnode(dev, NULL, &tmp);
 125         if (!req.name)
 126                 return -ENOMEM;
 127
 128         req.mode = 0;
 129         req.dev = dev;
 130
 131         init_completion(&req.done);
 132
 133         spin_lock(&req_lock);
 134         req.next = requests;
 135         requests = &req;
 136         spin_unlock(&req_lock);
 137
 138         wake_up_process(thread);
 139         wait_for_completion(&req.done);
 140
 141         kfree(tmp);
 142         return req.err;
 143 }
 144
 145 static int dev_mkdir(const char *name, umode_t mode)
 146 {
 147         struct dentry *dentry;
 148         struct path path;
 149         int err;
 150
 151         dentry = kern_path_create(AT_FDCWD, name, &path, 1);
 152         if (IS_ERR(dentry))
 153                 return PTR_ERR(dentry);
 154
 155         err = vfs_mkdir(path.dentry->d_inode, dentry, mode);
 156         if (!err)
 157                 /* mark as kernel-created inode */
 158                 dentry->d_inode->i_private = &thread;
 159         dput(dentry);
 160         mutex_unlock(&path.dentry->d_inode->i_mutex);
 161         path_put(&path);
 162         return err;
 163 }
 164
 165 static int create_path(const char *nodepath)
 166 {
 167         char *path;
 168         char *s;
 169         int err = 0;
 170
 171         /* parent directories do not exist, create them */
 172         path = kstrdup(nodepath, GFP_KERNEL);
 173         if (!path)
 174                 return -ENOMEM;
 175
 176         s = path;
 177         for (;;) {
 178                 s = strchr(s, '/');
 179                 if (!s)
 180                         break;
 181                 s[0] = '\0';
 182                 err = dev_mkdir(path, 0755);
 183                 if (err && err != -EEXIST)
 184                         break;
 185                 s[0] = '/';
 186                 s++;
 187         }
 188         kfree(path);
 189         return err;
 190 }
 191
 192 static int handle_create(const char *nodename, umode_t mode, struct device *dev)
 193 {
 194         struct dentry *dentry;
 195         struct path path;
 196         int err;
 197
 198         dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 199         if (dentry == ERR_PTR(-ENOENT)) {
 200                 create_path(nodename);
 201                 dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 202         }
 203         if (IS_ERR(dentry))
 204                 return PTR_ERR(dentry);
 205
 206         err = vfs_mknod(path.dentry->d_inode,
 207                         dentry, mode, dev->devt);
 208         if (!err) {
 209                 struct iattr newattrs;
 210
 211                 /* fixup possibly umasked mode */
 212                 newattrs.ia_mode = mode;
 213                 newattrs.ia_valid = ATTR_MODE;
 214                 mutex_lock(&dentry->d_inode->i_mutex);
 215                 notify_change(dentry, &newattrs);
 216                 mutex_unlock(&dentry->d_inode->i_mutex);
 217
 218                 /* mark as kernel-created inode */
 219                 dentry->d_inode->i_private = &thread;
 220         }
 221         dput(dentry);
 222
 223         mutex_unlock(&path.dentry->d_inode->i_mutex);
 224         path_put(&path);
 225         return err;
 226 }
 227
 228 static int dev_rmdir(const char *name)
 229 {
 230         struct nameidata nd;
 231         struct dentry *dentry;
 232         int err;
 233
 234         err = kern_path_parent(name, &nd);
 235         if (err)
 236                 return err;
 237
 238         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 239         dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 240         if (!IS_ERR(dentry)) {
 241                 if (dentry->d_inode) {
 242                         if (dentry->d_inode->i_private == &thread)
 243                                 err = vfs_rmdir(nd.path.dentry->d_inode,
 244                                                 dentry);
 245                         else
 246                                 err = -EPERM;
 247                 } else {
 248                         err = -ENOENT;
 249                 }
 250                 dput(dentry);
 251         } else {
 252                 err = PTR_ERR(dentry);
 253         }
 254
 255         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 256         path_put(&nd.path);
 257         return err;
 258 }
 259
 260 static int delete_path(const char *nodepath)
 261 {
 262         const char *path;
 263         int err = 0;
 264
 265         path = kstrdup(nodepath, GFP_KERNEL);
 266         if (!path)
 267                 return -ENOMEM;
 268
 269         for (;;) {
 270                 char *base;
 271
 272                 base = strrchr(path, '/');
 273                 if (!base)
 274                         break;
 275                 base[0] = '\0';
 276                 err = dev_rmdir(path);
 277                 if (err)
 278                         break;
 279         }
 280
 281         kfree(path);
 282         return err;
 283 }
 284
 285 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 286 {
 287         /* did we create it */
 288         if (inode->i_private != &thread)
 289                 return 0;
 290
 291         /* does the dev_t match */
 292         if (is_blockdev(dev)) {
 293                 if (!S_ISBLK(stat->mode))
 294                         return 0;
 295         } else {
 296                 if (!S_ISCHR(stat->mode))
 297                         return 0;
 298         }
 299         if (stat->rdev != dev->devt)
 300                 return 0;
 301
 302         /* ours */
 303         return 1;
 304 }
 305
 306 static int handle_remove(const char *nodename, struct device *dev)
 307 {
 308         struct nameidata nd;
 309         struct dentry *dentry;
 310         struct kstat stat;
 311         int deleted = 1;
 312         int err;
 313
 314         err = kern_path_parent(nodename, &nd);
 315         if (err)
 316                 return err;
 317
 318         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 319         dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 320         if (!IS_ERR(dentry)) {
 321                 if (dentry->d_inode) {
 322                         err = vfs_getattr(nd.path.mnt, dentry, &stat);
 323                         if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {
 324                                 struct iattr newattrs;
 325                                 /*
 326                                  * before unlinking this node, reset permissions
 327                                  * of possible references like hardlinks
 328                                  */
 329                                 newattrs.ia_uid = 0;
 330                                 newattrs.ia_gid = 0;
 331                                 newattrs.ia_mode = stat.mode & ~0777;
 332                                 newattrs.ia_valid =
 333                                         ATTR_UID|ATTR_GID|ATTR_MODE;
 334                                 mutex_lock(&dentry->d_inode->i_mutex);
 335                                 notify_change(dentry, &newattrs);
 336                                 mutex_unlock(&dentry->d_inode->i_mutex);
 337                                 err = vfs_unlink(nd.path.dentry->d_inode,
 338                                                  dentry);
 339                                 if (!err || err == -ENOENT)
 340                                         deleted = 1;
 341                         }
 342                 } else {
 343                         err = -ENOENT;
 344                 }
 345                 dput(dentry);
 346         } else {
 347                 err = PTR_ERR(dentry);
 348         }
 349         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 350
 351         path_put(&nd.path);
 352         if (deleted && strchr(nodename, '/'))
 353                 delete_path(nodename);
 354         return err;
 355 }
 356
 357 /*
 358  * If configured, or requested by the commandline, devtmpfs will be
 359  * auto-mounted after the kernel mounted the root filesystem.
 360  */
 361 int devtmpfs_mount(const char *mntdir)
 362 {
 363         int err;
 364
 365         if (!mount_dev)
 366                 return 0;
 367
 368         if (!thread)
 369                 return 0;
 370
 371         err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
 372         if (err)
 373                 printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 374         else
 375                 printk(KERN_INFO "devtmpfs: mounted\n");
 376         return err;
 377 }
 378
 379 static DECLARE_COMPLETION(setup_done);
 380
 381 static int handle(const char *name, umode_t mode, struct device *dev)
 382 {
 383         if (mode)
 384                 return handle_create(name, mode, dev);
 385         else
 386                 return handle_remove(name, dev);
 387 }
 388
 389 static int devtmpfsd(void *p)
 390 {
 391         char options[] = "mode=0755";
 392         int *err = p;
 393         *err = sys_unshare(CLONE_NEWNS);
 394         if (*err)
 395                 goto out;
 396         *err = sys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
 397         if (*err)
 398                 goto out;
 399         sys_chdir("/.."); /* will traverse into overmounted root */
 400         sys_chroot(".");
 401         complete(&setup_done);
 402         while (1) {
 403                 spin_lock(&req_lock);
 404                 while (requests) {
 405                         struct req *req = requests;
 406                         requests = NULL;
 407                         spin_unlock(&req_lock);
 408                         while (req) {
 409                                 struct req *next = req->next;
 410                                 req->err = handle(req->name, req->mode, req->dev);
 411                                 complete(&req->done);
 412                                 req = next;
 413                         }
 414                         spin_lock(&req_lock);
 415                 }
 416                 __set_current_state(TASK_INTERRUPTIBLE);
 417                 spin_unlock(&req_lock);
 418                 schedule();
 419         }
 420         return 0;
 421 out:
 422         complete(&setup_done);
 423         return *err;
 424 }
 425
 426 /*
 427  * Create devtmpfs instance, driver-core devices will add their device
 428  * nodes here.
 429  */
 430 int __init devtmpfs_init(void)
 431 {
 432         int err = register_filesystem(&dev_fs_type);
 433         if (err) {
 434                 printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
 435                        "type %i\n", err);
 436                 return err;
 437         }
 438
 439         thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
 440         if (!IS_ERR(thread)) {
 441                 wait_for_completion(&setup_done);
 442         } else {
 443                 err = PTR_ERR(thread);
 444                 thread = NULL;
 445         }
 446
 447         if (err) {
 448                 printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
 449                 unregister_filesystem(&dev_fs_type);
 450                 return err;
 451         }
 452
 453         printk(KERN_INFO "devtmpfs: initialized\n");
 454         return 0;
 455 }