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