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