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 int __init mount_param(char *str)
  36 {
  37         dev_mount = simple_strtoul(str, NULL, 0);
  38         return 1;
  39 }
  40 __setup("devtmpfs.mount=", mount_param);
  41
  42 static int dev_get_sb(struct file_system_type *fs_type, int flags,
  43                       const char *dev_name, void *data, struct vfsmount *mnt)
  44 {
  45         return get_sb_single(fs_type, flags, data, shmem_fill_super, mnt);
  46 }
  47
  48 static struct file_system_type dev_fs_type = {
  49         .name = "devtmpfs",
  50         .get_sb = dev_get_sb,
  51         .kill_sb = kill_litter_super,
  52 };
  53
  54 #ifdef CONFIG_BLOCK
  55 static inline int is_blockdev(struct device *dev)
  56 {
  57         return dev->class == &block_class;
  58 }
  59 #else
  60 static inline int is_blockdev(struct device *dev) { return 0; }
  61 #endif
  62
  63 static int dev_mkdir(const char *name, mode_t mode)
  64 {
  65         struct nameidata nd;
  66         struct dentry *dentry;
  67         int err;
  68
  69         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
  70                               name, LOOKUP_PARENT, &nd);
  71         if (err)
  72                 return err;
  73
  74         dentry = lookup_create(&nd, 1);
  75         if (!IS_ERR(dentry)) {
  76                 err = vfs_mkdir(nd.path.dentry->d_inode, dentry, mode);
  77                 dput(dentry);
  78         } else {
  79                 err = PTR_ERR(dentry);
  80         }
  81         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
  82
  83         path_put(&nd.path);
  84         return err;
  85 }
  86
  87 static int create_path(const char *nodepath)
  88 {
  89         char *path;
  90         struct nameidata nd;
  91         int err = 0;
  92
  93         path = kstrdup(nodepath, GFP_KERNEL);
  94         if (!path)
  95                 return -ENOMEM;
  96
  97         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
  98                               path, LOOKUP_PARENT, &nd);
  99         if (err == 0) {
 100                 struct dentry *dentry;
 101
 102                 /* create directory right away */
 103                 dentry = lookup_create(&nd, 1);
 104                 if (!IS_ERR(dentry)) {
 105                         err = vfs_mkdir(nd.path.dentry->d_inode,
 106                                         dentry, 0755);
 107                         dput(dentry);
 108                 }
 109                 mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 110
 111                 path_put(&nd.path);
 112         } else if (err == -ENOENT) {
 113                 char *s;
 114
 115                 /* parent directories do not exist, create them */
 116                 s = path;
 117                 while (1) {
 118                         s = strchr(s, '/');
 119                         if (!s)
 120                                 break;
 121                         s[0] = '\0';
 122                         err = dev_mkdir(path, 0755);
 123                         if (err && err != -EEXIST)
 124                                 break;
 125                         s[0] = '/';
 126                         s++;
 127                 }
 128         }
 129
 130         kfree(path);
 131         return err;
 132 }
 133
 134 int devtmpfs_create_node(struct device *dev)
 135 {
 136         const char *tmp = NULL;
 137         const char *nodename;
 138         const struct cred *curr_cred;
 139         mode_t mode = 0;
 140         struct nameidata nd;
 141         struct dentry *dentry;
 142         int err;
 143
 144         if (!dev_mnt)
 145                 return 0;
 146
 147         nodename = device_get_devnode(dev, &mode, &tmp);
 148         if (!nodename)
 149                 return -ENOMEM;
 150
 151         if (mode == 0)
 152                 mode = 0600;
 153         if (is_blockdev(dev))
 154                 mode |= S_IFBLK;
 155         else
 156                 mode |= S_IFCHR;
 157
 158         curr_cred = override_creds(&init_cred);
 159         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 160                               nodename, LOOKUP_PARENT, &nd);
 161         if (err == -ENOENT) {
 162                 /* create missing parent directories */
 163                 create_path(nodename);
 164                 err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 165                                       nodename, LOOKUP_PARENT, &nd);
 166                 if (err)
 167                         goto out;
 168         }
 169
 170         dentry = lookup_create(&nd, 0);
 171         if (!IS_ERR(dentry)) {
 172                 int umask;
 173
 174                 umask = sys_umask(0000);
 175                 err = vfs_mknod(nd.path.dentry->d_inode,
 176                                 dentry, mode, dev->devt);
 177                 sys_umask(umask);
 178                 /* mark as kernel created inode */
 179                 if (!err)
 180                         dentry->d_inode->i_private = &dev_mnt;
 181                 dput(dentry);
 182         } else {
 183                 err = PTR_ERR(dentry);
 184         }
 185         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 186
 187         path_put(&nd.path);
 188 out:
 189         kfree(tmp);
 190         revert_creds(curr_cred);
 191         return err;
 192 }
 193
 194 static int dev_rmdir(const char *name)
 195 {
 196         struct nameidata nd;
 197         struct dentry *dentry;
 198         int err;
 199
 200         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 201                               name, LOOKUP_PARENT, &nd);
 202         if (err)
 203                 return err;
 204
 205         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 206         dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 207         if (!IS_ERR(dentry)) {
 208                 if (dentry->d_inode)
 209                         err = vfs_rmdir(nd.path.dentry->d_inode, dentry);
 210                 else
 211                         err = -ENOENT;
 212                 dput(dentry);
 213         } else {
 214                 err = PTR_ERR(dentry);
 215         }
 216         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 217
 218         path_put(&nd.path);
 219         return err;
 220 }
 221
 222 static int delete_path(const char *nodepath)
 223 {
 224         const char *path;
 225         int err = 0;
 226
 227         path = kstrdup(nodepath, GFP_KERNEL);
 228         if (!path)
 229                 return -ENOMEM;
 230
 231         while (1) {
 232                 char *base;
 233
 234                 base = strrchr(path, '/');
 235                 if (!base)
 236                         break;
 237                 base[0] = '\0';
 238                 err = dev_rmdir(path);
 239                 if (err)
 240                         break;
 241         }
 242
 243         kfree(path);
 244         return err;
 245 }
 246
 247 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 248 {
 249         /* did we create it */
 250         if (inode->i_private != &dev_mnt)
 251                 return 0;
 252
 253         /* does the dev_t match */
 254         if (is_blockdev(dev)) {
 255                 if (!S_ISBLK(stat->mode))
 256                         return 0;
 257         } else {
 258                 if (!S_ISCHR(stat->mode))
 259                         return 0;
 260         }
 261         if (stat->rdev != dev->devt)
 262                 return 0;
 263
 264         /* ours */
 265         return 1;
 266 }
 267
 268 int devtmpfs_delete_node(struct device *dev)
 269 {
 270         const char *tmp = NULL;
 271         const char *nodename;
 272         const struct cred *curr_cred;
 273         struct nameidata nd;
 274         struct dentry *dentry;
 275         struct kstat stat;
 276         int deleted = 1;
 277         int err;
 278
 279         if (!dev_mnt)
 280                 return 0;
 281
 282         nodename = device_get_devnode(dev, NULL, &tmp);
 283         if (!nodename)
 284                 return -ENOMEM;
 285
 286         curr_cred = override_creds(&init_cred);
 287         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 288                               nodename, LOOKUP_PARENT, &nd);
 289         if (err)
 290                 goto out;
 291
 292         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 293         dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 294         if (!IS_ERR(dentry)) {
 295                 if (dentry->d_inode) {
 296                         err = vfs_getattr(nd.path.mnt, dentry, &stat);
 297                         if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {
 298                                 struct iattr newattrs;
 299                                 /*
 300                                  * before unlinking this node, reset permissions
 301                                  * of possible references like hardlinks
 302                                  */
 303                                 newattrs.ia_uid = 0;
 304                                 newattrs.ia_gid = 0;
 305                                 newattrs.ia_mode = stat.mode & ~0777;
 306                                 newattrs.ia_valid =
 307                                         ATTR_UID|ATTR_GID|ATTR_MODE;
 308                                 mutex_lock(&dentry->d_inode->i_mutex);
 309                                 notify_change(dentry, &newattrs);
 310                                 mutex_unlock(&dentry->d_inode->i_mutex);
 311                                 err = vfs_unlink(nd.path.dentry->d_inode,
 312                                                  dentry);
 313                                 if (!err || err == -ENOENT)
 314                                         deleted = 1;
 315                         }
 316                 } else {
 317                         err = -ENOENT;
 318                 }
 319                 dput(dentry);
 320         } else {
 321                 err = PTR_ERR(dentry);
 322         }
 323         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 324
 325         path_put(&nd.path);
 326         if (deleted && strchr(nodename, '/'))
 327                 delete_path(nodename);
 328 out:
 329         kfree(tmp);
 330         revert_creds(curr_cred);
 331         return err;
 332 }
 333
 334 /*
 335  * If configured, or requested by the commandline, devtmpfs will be
 336  * auto-mounted after the kernel mounted the root filesystem.
 337  */
 338 int devtmpfs_mount(const char *mountpoint)
 339 {
 340         struct path path;
 341         int err;
 342
 343         if (!dev_mount)
 344                 return 0;
 345
 346         if (!dev_mnt)
 347                 return 0;
 348
 349         err = kern_path(mountpoint, LOOKUP_FOLLOW, &path);
 350         if (err)
 351                 return err;
 352         err = do_add_mount(dev_mnt, &path, 0, NULL);
 353         if (err)
 354                 printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 355         else
 356                 printk(KERN_INFO "devtmpfs: mounted\n");
 357         path_put(&path);
 358         return err;
 359 }
 360
 361 /*
 362  * Create devtmpfs instance, driver-core devices will add their device
 363  * nodes here.
 364  */
 365 int __init devtmpfs_init(void)
 366 {
 367         int err;
 368         struct vfsmount *mnt;
 369         char options[] = "mode=0755";
 370
 371         err = register_filesystem(&dev_fs_type);
 372         if (err) {
 373                 printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
 374                        "type %i\n", err);
 375                 return err;
 376         }
 377
 378         mnt = kern_mount_data(&dev_fs_type, options);
 379         if (IS_ERR(mnt)) {
 380                 err = PTR_ERR(mnt);
 381                 printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
 382                 unregister_filesystem(&dev_fs_type);
 383                 return err;
 384         }
 385         dev_mnt = mnt;
 386
 387         printk(KERN_INFO "devtmpfs: initialized\n");
 388         return 0;
 389 }