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 rwlock_t 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         read_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                         return -ENOMEM;
 106                 s = path;
 107                 for (;;) {
 108                         s = strchr(s, '/');
 109                         if (!s)
 110                                 break;
 111                         s[0] = '\0';
 112                         err = dev_mkdir(path, 0755);
 113                         if (err && err != -EEXIST)
 114                                 break;
 115                         s[0] = '/';
 116                         s++;
 117                 }
 118                 kfree(path);
 119         }
 120         read_unlock(&dirlock);
 121         return err;
 122 }
 123
 124 int devtmpfs_create_node(struct device *dev)
 125 {
 126         const char *tmp = NULL;
 127         const char *nodename;
 128         const struct cred *curr_cred;
 129         mode_t mode = 0;
 130         struct nameidata nd;
 131         struct dentry *dentry;
 132         int err;
 133
 134         if (!dev_mnt)
 135                 return 0;
 136
 137         nodename = device_get_devnode(dev, &mode, &tmp);
 138         if (!nodename)
 139                 return -ENOMEM;
 140
 141         if (mode == 0)
 142                 mode = 0600;
 143         if (is_blockdev(dev))
 144                 mode |= S_IFBLK;
 145         else
 146                 mode |= S_IFCHR;
 147
 148         curr_cred = override_creds(&init_cred);
 149
 150         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 151                               nodename, LOOKUP_PARENT, &nd);
 152         if (err == -ENOENT) {
 153                 create_path(nodename);
 154                 err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 155                                       nodename, LOOKUP_PARENT, &nd);
 156         }
 157         if (err)
 158                 goto out;
 159
 160         dentry = lookup_create(&nd, 0);
 161         if (!IS_ERR(dentry)) {
 162                 err = vfs_mknod(nd.path.dentry->d_inode,
 163                                 dentry, mode, dev->devt);
 164                 if (!err) {
 165                         struct iattr newattrs;
 166
 167                         /* fixup possibly umasked mode */
 168                         newattrs.ia_mode = mode;
 169                         newattrs.ia_valid = ATTR_MODE;
 170                         mutex_lock(&dentry->d_inode->i_mutex);
 171                         notify_change(dentry, &newattrs);
 172                         mutex_unlock(&dentry->d_inode->i_mutex);
 173
 174                         /* mark as kernel-created inode */
 175                         dentry->d_inode->i_private = &dev_mnt;
 176                 }
 177                 dput(dentry);
 178         } else {
 179                 err = PTR_ERR(dentry);
 180         }
 181
 182         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 183         path_put(&nd.path);
 184 out:
 185         kfree(tmp);
 186         revert_creds(curr_cred);
 187         return err;
 188 }
 189
 190 static int dev_rmdir(const char *name)
 191 {
 192         struct nameidata nd;
 193         struct dentry *dentry;
 194         int err;
 195
 196         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 197                               name, LOOKUP_PARENT, &nd);
 198         if (err)
 199                 return err;
 200
 201         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 202         dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 203         if (!IS_ERR(dentry)) {
 204                 if (dentry->d_inode) {
 205                         if (dentry->d_inode->i_private == &dev_mnt)
 206                                 err = vfs_rmdir(nd.path.dentry->d_inode,
 207                                                 dentry);
 208                         else
 209                                 err = -EPERM;
 210                 } else {
 211                         err = -ENOENT;
 212                 }
 213                 dput(dentry);
 214         } else {
 215                 err = PTR_ERR(dentry);
 216         }
 217
 218         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 219         path_put(&nd.path);
 220         return err;
 221 }
 222
 223 static int delete_path(const char *nodepath)
 224 {
 225         const char *path;
 226         int err = 0;
 227
 228         path = kstrdup(nodepath, GFP_KERNEL);
 229         if (!path)
 230                 return -ENOMEM;
 231
 232         write_lock(&dirlock);
 233         for (;;) {
 234                 char *base;
 235
 236                 base = strrchr(path, '/');
 237                 if (!base)
 238                         break;
 239                 base[0] = '\0';
 240                 err = dev_rmdir(path);
 241                 if (err)
 242                         break;
 243         }
 244         write_unlock(&dirlock);
 245
 246         kfree(path);
 247         return err;
 248 }
 249
 250 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 251 {
 252         /* did we create it */
 253         if (inode->i_private != &dev_mnt)
 254                 return 0;
 255
 256         /* does the dev_t match */
 257         if (is_blockdev(dev)) {
 258                 if (!S_ISBLK(stat->mode))
 259                         return 0;
 260         } else {
 261                 if (!S_ISCHR(stat->mode))
 262                         return 0;
 263         }
 264         if (stat->rdev != dev->devt)
 265                 return 0;
 266
 267         /* ours */
 268         return 1;
 269 }
 270
 271 int devtmpfs_delete_node(struct device *dev)
 272 {
 273         const char *tmp = NULL;
 274         const char *nodename;
 275         const struct cred *curr_cred;
 276         struct nameidata nd;
 277         struct dentry *dentry;
 278         struct kstat stat;
 279         int deleted = 1;
 280         int err;
 281
 282         if (!dev_mnt)
 283                 return 0;
 284
 285         nodename = device_get_devnode(dev, NULL, &tmp);
 286         if (!nodename)
 287                 return -ENOMEM;
 288
 289         curr_cred = override_creds(&init_cred);
 290         err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 291                               nodename, LOOKUP_PARENT, &nd);
 292         if (err)
 293                 goto out;
 294
 295         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 296         dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 297         if (!IS_ERR(dentry)) {
 298                 if (dentry->d_inode) {
 299                         err = vfs_getattr(nd.path.mnt, dentry, &stat);
 300                         if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {
 301                                 err = vfs_unlink(nd.path.dentry->d_inode,
 302                                                  dentry);
 303                                 if (!err || err == -ENOENT)
 304                                         deleted = 1;
 305                         }
 306                 } else {
 307                         err = -ENOENT;
 308                 }
 309                 dput(dentry);
 310         } else {
 311                 err = PTR_ERR(dentry);
 312         }
 313         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 314
 315         path_put(&nd.path);
 316         if (deleted && strchr(nodename, '/'))
 317                 delete_path(nodename);
 318 out:
 319         kfree(tmp);
 320         revert_creds(curr_cred);
 321         return err;
 322 }
 323
 324 /*
 325  * If configured, or requested by the commandline, devtmpfs will be
 326  * auto-mounted after the kernel mounted the root filesystem.
 327  */
 328 int devtmpfs_mount(const char *mntdir)
 329 {
 330         int err;
 331
 332         if (!dev_mount)
 333                 return 0;
 334
 335         if (!dev_mnt)
 336                 return 0;
 337
 338         err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
 339         if (err)
 340                 printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 341         else
 342                 printk(KERN_INFO "devtmpfs: mounted\n");
 343         return err;
 344 }
 345
 346 /*
 347  * Create devtmpfs instance, driver-core devices will add their device
 348  * nodes here.
 349  */
 350 int __init devtmpfs_init(void)
 351 {
 352         int err;
 353         struct vfsmount *mnt;
 354
 355         rwlock_init(&dirlock);
 356
 357         err = register_filesystem(&dev_fs_type);
 358         if (err) {
 359                 printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
 360                        "type %i\n", err);
 361                 return err;
 362         }
 363
 364         mnt = kern_mount_data(&dev_fs_type, "mode=0755");
 365         if (IS_ERR(mnt)) {
 366                 err = PTR_ERR(mnt);
 367                 printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
 368                 unregister_filesystem(&dev_fs_type);
 369                 return err;
 370         }
 371         dev_mnt = mnt;
 372
 373         printk(KERN_INFO "devtmpfs: initialized\n");
 374         return 0;
 375 }