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