fs/devpts/inode.c

   1 /* -*- linux-c -*- --------------------------------------------------------- *
   2  *
   3  * linux/fs/devpts/inode.c
   4  *
   5  *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
   6  *
   7  * This file is part of the Linux kernel and is made available under
   8  * the terms of the GNU General Public License, version 2, or at your
   9  * option, any later version, incorporated herein by reference.
  10  *
  11  * ------------------------------------------------------------------------- */
  12
  13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  14
  15 #include <linux/module.h>
  16 #include <linux/init.h>
  17 #include <linux/fs.h>
  18 #include <linux/sched.h>
  19 #include <linux/namei.h>
  20 #include <linux/slab.h>
  21 #include <linux/mount.h>
  22 #include <linux/tty.h>
  23 #include <linux/mutex.h>
  24 #include <linux/magic.h>
  25 #include <linux/idr.h>
  26 #include <linux/devpts_fs.h>
  27 #include <linux/parser.h>
  28 #include <linux/fsnotify.h>
  29 #include <linux/seq_file.h>
  30
  31 #define DEVPTS_DEFAULT_MODE 0600
  32 /*
  33  * ptmx is a new node in /dev/pts and will be unused in legacy (single-
  34  * instance) mode. To prevent surprises in user space, set permissions of
  35  * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
  36  * permissions.
  37  */
  38 #define DEVPTS_DEFAULT_PTMX_MODE 0000
  39 #define PTMX_MINOR      2
  40
  41 /*
  42  * sysctl support for setting limits on the number of Unix98 ptys allocated.
  43  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
  44  */
  45 static int pty_limit = NR_UNIX98_PTY_DEFAULT;
  46 static int pty_reserve = NR_UNIX98_PTY_RESERVE;
  47 static int pty_limit_min;
  48 static int pty_limit_max = INT_MAX;
  49 static int pty_count;
  50
  51 static struct ctl_table pty_table[] = {
  52         {
  53                 .procname       = "max",
  54                 .maxlen         = sizeof(int),
  55                 .mode           = 0644,
  56                 .data           = &pty_limit,
  57                 .proc_handler   = proc_dointvec_minmax,
  58                 .extra1         = &pty_limit_min,
  59                 .extra2         = &pty_limit_max,
  60         }, {
  61                 .procname       = "reserve",
  62                 .maxlen         = sizeof(int),
  63                 .mode           = 0644,
  64                 .data           = &pty_reserve,
  65                 .proc_handler   = proc_dointvec_minmax,
  66                 .extra1         = &pty_limit_min,
  67                 .extra2         = &pty_limit_max,
  68         }, {
  69                 .procname       = "nr",
  70                 .maxlen         = sizeof(int),
  71                 .mode           = 0444,
  72                 .data           = &pty_count,
  73                 .proc_handler   = proc_dointvec,
  74         },
  75         {}
  76 };
  77
  78 static struct ctl_table pty_kern_table[] = {
  79         {
  80                 .procname       = "pty",
  81                 .mode           = 0555,
  82                 .child          = pty_table,
  83         },
  84         {}
  85 };
  86
  87 static struct ctl_table pty_root_table[] = {
  88         {
  89                 .procname       = "kernel",
  90                 .mode           = 0555,
  91                 .child          = pty_kern_table,
  92         },
  93         {}
  94 };
  95
  96 static DEFINE_MUTEX(allocated_ptys_lock);
  97
  98 static struct vfsmount *devpts_mnt;
  99
 100 struct pts_mount_opts {
 101         int setuid;
 102         int setgid;
 103         kuid_t   uid;
 104         kgid_t   gid;
 105         umode_t mode;
 106         umode_t ptmxmode;
 107         int newinstance;
 108         int max;
 109 };
 110
 111 enum {
 112         Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,  Opt_max,
 113         Opt_err
 114 };
 115
 116 static const match_table_t tokens = {
 117         {Opt_uid, "uid=%u"},
 118         {Opt_gid, "gid=%u"},
 119         {Opt_mode, "mode=%o"},
 120 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 121         {Opt_ptmxmode, "ptmxmode=%o"},
 122         {Opt_newinstance, "newinstance"},
 123         {Opt_max, "max=%d"},
 124 #endif
 125         {Opt_err, NULL}
 126 };
 127
 128 struct pts_fs_info {
 129         struct ida allocated_ptys;
 130         struct pts_mount_opts mount_opts;
 131         struct dentry *ptmx_dentry;
 132 };
 133
 134 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
 135 {
 136         return sb->s_fs_info;
 137 }
 138
 139 static inline struct super_block *pts_sb_from_inode(struct inode *inode)
 140 {
 141 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 142         if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
 143                 return inode->i_sb;
 144 #endif
 145         return devpts_mnt->mnt_sb;
 146 }
 147
 148 #define PARSE_MOUNT     0
 149 #define PARSE_REMOUNT   1
 150
 151 /*
 152  * parse_mount_options():
 153  *      Set @opts to mount options specified in @data. If an option is not
 154  *      specified in @data, set it to its default value. The exception is
 155  *      'newinstance' option which can only be set/cleared on a mount (i.e.
 156  *      cannot be changed during remount).
 157  *
 158  * Note: @data may be NULL (in which case all options are set to default).
 159  */
 160 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
 161 {
 162         char *p;
 163         kuid_t uid;
 164         kgid_t gid;
 165
 166         opts->setuid  = 0;
 167         opts->setgid  = 0;
 168         opts->uid     = GLOBAL_ROOT_UID;
 169         opts->gid     = GLOBAL_ROOT_GID;
 170         opts->mode    = DEVPTS_DEFAULT_MODE;
 171         opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 172         opts->max     = NR_UNIX98_PTY_MAX;
 173
 174         /* newinstance makes sense only on initial mount */
 175         if (op == PARSE_MOUNT)
 176                 opts->newinstance = 0;
 177
 178         while ((p = strsep(&data, ",")) != NULL) {
 179                 substring_t args[MAX_OPT_ARGS];
 180                 int token;
 181                 int option;
 182
 183                 if (!*p)
 184                         continue;
 185
 186                 token = match_token(p, tokens, args);
 187                 switch (token) {
 188                 case Opt_uid:
 189                         if (match_int(&args[0], &option))
 190                                 return -EINVAL;
 191                         uid = make_kuid(current_user_ns(), option);
 192                         if (!uid_valid(uid))
 193                                 return -EINVAL;
 194                         opts->uid = uid;
 195                         opts->setuid = 1;
 196                         break;
 197                 case Opt_gid:
 198                         if (match_int(&args[0], &option))
 199                                 return -EINVAL;
 200                         gid = make_kgid(current_user_ns(), option);
 201                         if (!gid_valid(gid))
 202                                 return -EINVAL;
 203                         opts->gid = gid;
 204                         opts->setgid = 1;
 205                         break;
 206                 case Opt_mode:
 207                         if (match_octal(&args[0], &option))
 208                                 return -EINVAL;
 209                         opts->mode = option & S_IALLUGO;
 210                         break;
 211 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 212                 case Opt_ptmxmode:
 213                         if (match_octal(&args[0], &option))
 214                                 return -EINVAL;
 215                         opts->ptmxmode = option & S_IALLUGO;
 216                         break;
 217                 case Opt_newinstance:
 218                         /* newinstance makes sense only on initial mount */
 219                         if (op == PARSE_MOUNT)
 220                                 opts->newinstance = 1;
 221                         break;
 222                 case Opt_max:
 223                         if (match_int(&args[0], &option) ||
 224                             option < 0 || option > NR_UNIX98_PTY_MAX)
 225                                 return -EINVAL;
 226                         opts->max = option;
 227                         break;
 228 #endif
 229                 default:
 230                         pr_err("called with bogus options\n");
 231                         return -EINVAL;
 232                 }
 233         }
 234
 235         return 0;
 236 }
 237
 238 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 239 static int mknod_ptmx(struct super_block *sb)
 240 {
 241         int mode;
 242         int rc = -ENOMEM;
 243         struct dentry *dentry;
 244         struct inode *inode;
 245         struct dentry *root = sb->s_root;
 246         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 247         struct pts_mount_opts *opts = &fsi->mount_opts;
 248         kuid_t root_uid;
 249         kgid_t root_gid;
 250
 251         root_uid = make_kuid(current_user_ns(), 0);
 252         root_gid = make_kgid(current_user_ns(), 0);
 253         if (!uid_valid(root_uid) || !gid_valid(root_gid))
 254                 return -EINVAL;
 255
 256         mutex_lock(&d_inode(root)->i_mutex);
 257
 258         /* If we have already created ptmx node, return */
 259         if (fsi->ptmx_dentry) {
 260                 rc = 0;
 261                 goto out;
 262         }
 263
 264         dentry = d_alloc_name(root, "ptmx");
 265         if (!dentry) {
 266                 pr_err("Unable to alloc dentry for ptmx node\n");
 267                 goto out;
 268         }
 269
 270         /*
 271          * Create a new 'ptmx' node in this mount of devpts.
 272          */
 273         inode = new_inode(sb);
 274         if (!inode) {
 275                 pr_err("Unable to alloc inode for ptmx node\n");
 276                 dput(dentry);
 277                 goto out;
 278         }
 279
 280         inode->i_ino = 2;
 281         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 282
 283         mode = S_IFCHR|opts->ptmxmode;
 284         init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
 285         inode->i_uid = root_uid;
 286         inode->i_gid = root_gid;
 287
 288         d_add(dentry, inode);
 289
 290         fsi->ptmx_dentry = dentry;
 291         rc = 0;
 292 out:
 293         mutex_unlock(&d_inode(root)->i_mutex);
 294         return rc;
 295 }
 296
 297 static void update_ptmx_mode(struct pts_fs_info *fsi)
 298 {
 299         struct inode *inode;
 300         if (fsi->ptmx_dentry) {
 301                 inode = d_inode(fsi->ptmx_dentry);
 302                 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
 303         }
 304 }
 305 #else
 306 static inline void update_ptmx_mode(struct pts_fs_info *fsi)
 307 {
 308         return;
 309 }
 310 #endif
 311
 312 static int devpts_remount(struct super_block *sb, int *flags, char *data)
 313 {
 314         int err;
 315         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 316         struct pts_mount_opts *opts = &fsi->mount_opts;
 317
 318         sync_filesystem(sb);
 319         err = parse_mount_options(data, PARSE_REMOUNT, opts);
 320
 321         /*
 322          * parse_mount_options() restores options to default values
 323          * before parsing and may have changed ptmxmode. So, update the
 324          * mode in the inode too. Bogus options don't fail the remount,
 325          * so do this even on error return.
 326          */
 327         update_ptmx_mode(fsi);
 328
 329         return err;
 330 }
 331
 332 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
 333 {
 334         struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
 335         struct pts_mount_opts *opts = &fsi->mount_opts;
 336
 337         if (opts->setuid)
 338                 seq_printf(seq, ",uid=%u",
 339                            from_kuid_munged(&init_user_ns, opts->uid));
 340         if (opts->setgid)
 341                 seq_printf(seq, ",gid=%u",
 342                            from_kgid_munged(&init_user_ns, opts->gid));
 343         seq_printf(seq, ",mode=%03o", opts->mode);
 344 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 345         seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
 346         if (opts->max < NR_UNIX98_PTY_MAX)
 347                 seq_printf(seq, ",max=%d", opts->max);
 348 #endif
 349
 350         return 0;
 351 }
 352
 353 static const struct super_operations devpts_sops = {
 354         .statfs         = simple_statfs,
 355         .remount_fs     = devpts_remount,
 356         .show_options   = devpts_show_options,
 357 };
 358
 359 static void *new_pts_fs_info(void)
 360 {
 361         struct pts_fs_info *fsi;
 362
 363         fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
 364         if (!fsi)
 365                 return NULL;
 366
 367         ida_init(&fsi->allocated_ptys);
 368         fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
 369         fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 370
 371         return fsi;
 372 }
 373
 374 static int
 375 devpts_fill_super(struct super_block *s, void *data, int silent)
 376 {
 377         struct inode *inode;
 378
 379         s->s_blocksize = 1024;
 380         s->s_blocksize_bits = 10;
 381         s->s_magic = DEVPTS_SUPER_MAGIC;
 382         s->s_op = &devpts_sops;
 383         s->s_time_gran = 1;
 384
 385         s->s_fs_info = new_pts_fs_info();
 386         if (!s->s_fs_info)
 387                 goto fail;
 388
 389         inode = new_inode(s);
 390         if (!inode)
 391                 goto fail;
 392         inode->i_ino = 1;
 393         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 394         inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
 395         inode->i_op = &simple_dir_inode_operations;
 396         inode->i_fop = &simple_dir_operations;
 397         set_nlink(inode, 2);
 398
 399         s->s_root = d_make_root(inode);
 400         if (s->s_root)
 401                 return 0;
 402
 403         pr_err("get root dentry failed\n");
 404
 405 fail:
 406         return -ENOMEM;
 407 }
 408
 409 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 410 static int compare_init_pts_sb(struct super_block *s, void *p)
 411 {
 412         if (devpts_mnt)
 413                 return devpts_mnt->mnt_sb == s;
 414         return 0;
 415 }
 416
 417 /*
 418  * devpts_mount()
 419  *
 420  *     If the '-o newinstance' mount option was specified, mount a new
 421  *     (private) instance of devpts.  PTYs created in this instance are
 422  *     independent of the PTYs in other devpts instances.
 423  *
 424  *     If the '-o newinstance' option was not specified, mount/remount the
 425  *     initial kernel mount of devpts.  This type of mount gives the
 426  *     legacy, single-instance semantics.
 427  *
 428  *     The 'newinstance' option is needed to support multiple namespace
 429  *     semantics in devpts while preserving backward compatibility of the
 430  *     current 'single-namespace' semantics. i.e all mounts of devpts
 431  *     without the 'newinstance' mount option should bind to the initial
 432  *     kernel mount, like mount_single().
 433  *
 434  *     Mounts with 'newinstance' option create a new, private namespace.
 435  *
 436  *     NOTE:
 437  *
 438  *     For single-mount semantics, devpts cannot use mount_single(),
 439  *     because mount_single()/sget() find and use the super-block from
 440  *     the most recent mount of devpts. But that recent mount may be a
 441  *     'newinstance' mount and mount_single() would pick the newinstance
 442  *     super-block instead of the initial super-block.
 443  */
 444 static struct dentry *devpts_mount(struct file_system_type *fs_type,
 445         int flags, const char *dev_name, void *data)
 446 {
 447         int error;
 448         struct pts_mount_opts opts;
 449         struct super_block *s;
 450
 451         error = parse_mount_options(data, PARSE_MOUNT, &opts);
 452         if (error)
 453                 return ERR_PTR(error);
 454
 455         /* Require newinstance for all user namespace mounts to ensure
 456          * the mount options are not changed.
 457          */
 458         if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
 459                 return ERR_PTR(-EINVAL);
 460
 461         if (opts.newinstance)
 462                 s = sget(fs_type, NULL, set_anon_super, flags, NULL);
 463         else
 464                 s = sget(fs_type, compare_init_pts_sb, set_anon_super, flags,
 465                          NULL);
 466
 467         if (IS_ERR(s))
 468                 return ERR_CAST(s);
 469
 470         if (!s->s_root) {
 471                 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
 472                 if (error)
 473                         goto out_undo_sget;
 474                 s->s_flags |= MS_ACTIVE;
 475         }
 476
 477         memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
 478
 479         error = mknod_ptmx(s);
 480         if (error)
 481                 goto out_undo_sget;
 482
 483         return dget(s->s_root);
 484
 485 out_undo_sget:
 486         deactivate_locked_super(s);
 487         return ERR_PTR(error);
 488 }
 489
 490 #else
 491 /*
 492  * This supports only the legacy single-instance semantics (no
 493  * multiple-instance semantics)
 494  */
 495 static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
 496                 const char *dev_name, void *data)
 497 {
 498         return mount_single(fs_type, flags, data, devpts_fill_super);
 499 }
 500 #endif
 501
 502 static void devpts_kill_sb(struct super_block *sb)
 503 {
 504         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 505
 506         ida_destroy(&fsi->allocated_ptys);
 507         kfree(fsi);
 508         kill_litter_super(sb);
 509 }
 510
 511 static struct file_system_type devpts_fs_type = {
 512         .name           = "devpts",
 513         .mount          = devpts_mount,
 514         .kill_sb        = devpts_kill_sb,
 515 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 516         .fs_flags       = FS_USERNS_MOUNT | FS_USERNS_DEV_MOUNT,
 517 #endif
 518 };
 519
 520 /*
 521  * The normal naming convention is simply /dev/pts/<number>; this conforms
 522  * to the System V naming convention
 523  */
 524
 525 int devpts_new_index(struct inode *ptmx_inode)
 526 {
 527         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 528         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 529         int index;
 530         int ida_ret;
 531
 532 retry:
 533         if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
 534                 return -ENOMEM;
 535
 536         mutex_lock(&allocated_ptys_lock);
 537         if (pty_count >= pty_limit -
 538                         (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
 539                 mutex_unlock(&allocated_ptys_lock);
 540                 return -ENOSPC;
 541         }
 542
 543         ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
 544         if (ida_ret < 0) {
 545                 mutex_unlock(&allocated_ptys_lock);
 546                 if (ida_ret == -EAGAIN)
 547                         goto retry;
 548                 return -EIO;
 549         }
 550
 551         if (index >= fsi->mount_opts.max) {
 552                 ida_remove(&fsi->allocated_ptys, index);
 553                 mutex_unlock(&allocated_ptys_lock);
 554                 return -ENOSPC;
 555         }
 556         pty_count++;
 557         mutex_unlock(&allocated_ptys_lock);
 558         return index;
 559 }
 560
 561 void devpts_kill_index(struct inode *ptmx_inode, int idx)
 562 {
 563         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 564         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 565
 566         mutex_lock(&allocated_ptys_lock);
 567         ida_remove(&fsi->allocated_ptys, idx);
 568         pty_count--;
 569         mutex_unlock(&allocated_ptys_lock);
 570 }
 571
 572 /*
 573  * pty code needs to hold extra references in case of last /dev/tty close
 574  */
 575
 576 void devpts_add_ref(struct inode *ptmx_inode)
 577 {
 578         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 579
 580         atomic_inc(&sb->s_active);
 581         ihold(ptmx_inode);
 582 }
 583
 584 void devpts_del_ref(struct inode *ptmx_inode)
 585 {
 586         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 587
 588         iput(ptmx_inode);
 589         deactivate_super(sb);
 590 }
 591
 592 /**
 593  * devpts_pty_new -- create a new inode in /dev/pts/
 594  * @ptmx_inode: inode of the master
 595  * @device: major+minor of the node to be created
 596  * @index: used as a name of the node
 597  * @priv: what's given back by devpts_get_priv
 598  *
 599  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
 600  */
 601 struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
 602                 void *priv)
 603 {
 604         struct dentry *dentry;
 605         struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 606         struct inode *inode;
 607         struct dentry *root = sb->s_root;
 608         struct pts_fs_info *fsi = DEVPTS_SB(sb);
 609         struct pts_mount_opts *opts = &fsi->mount_opts;
 610         char s[12];
 611
 612         inode = new_inode(sb);
 613         if (!inode)
 614                 return ERR_PTR(-ENOMEM);
 615
 616         inode->i_ino = index + 3;
 617         inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
 618         inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
 619         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 620         init_special_inode(inode, S_IFCHR|opts->mode, device);
 621         inode->i_private = priv;
 622
 623         sprintf(s, "%d", index);
 624
 625         mutex_lock(&d_inode(root)->i_mutex);
 626
 627         dentry = d_alloc_name(root, s);
 628         if (dentry) {
 629                 d_add(dentry, inode);
 630                 fsnotify_create(d_inode(root), dentry);
 631         } else {
 632                 iput(inode);
 633                 inode = ERR_PTR(-ENOMEM);
 634         }
 635
 636         mutex_unlock(&d_inode(root)->i_mutex);
 637
 638         return inode;
 639 }
 640
 641 /**
 642  * devpts_get_priv -- get private data for a slave
 643  * @pts_inode: inode of the slave
 644  *
 645  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
 646  */
 647 void *devpts_get_priv(struct inode *pts_inode)
 648 {
 649         struct dentry *dentry;
 650         void *priv = NULL;
 651
 652         BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
 653
 654         /* Ensure dentry has not been deleted by devpts_pty_kill() */
 655         dentry = d_find_alias(pts_inode);
 656         if (!dentry)
 657                 return NULL;
 658
 659         if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
 660                 priv = pts_inode->i_private;
 661
 662         dput(dentry);
 663
 664         return priv;
 665 }
 666
 667 /**
 668  * devpts_pty_kill -- remove inode form /dev/pts/
 669  * @inode: inode of the slave to be removed
 670  *
 671  * This is an inverse operation of devpts_pty_new.
 672  */
 673 void devpts_pty_kill(struct inode *inode)
 674 {
 675         struct super_block *sb = pts_sb_from_inode(inode);
 676         struct dentry *root = sb->s_root;
 677         struct dentry *dentry;
 678
 679         BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
 680
 681         mutex_lock(&d_inode(root)->i_mutex);
 682
 683         dentry = d_find_alias(inode);
 684
 685         drop_nlink(inode);
 686         d_delete(dentry);
 687         dput(dentry);   /* d_alloc_name() in devpts_pty_new() */
 688         dput(dentry);           /* d_find_alias above */
 689
 690         mutex_unlock(&d_inode(root)->i_mutex);
 691 }
 692
 693 static int __init init_devpts_fs(void)
 694 {
 695         int err = register_filesystem(&devpts_fs_type);
 696         struct ctl_table_header *table;
 697
 698         if (!err) {
 699                 table = register_sysctl_table(pty_root_table);
 700                 devpts_mnt = kern_mount(&devpts_fs_type);
 701                 if (IS_ERR(devpts_mnt)) {
 702                         err = PTR_ERR(devpts_mnt);
 703                         unregister_filesystem(&devpts_fs_type);
 704                         unregister_sysctl_table(table);
 705                 }
 706         }
 707         return err;
 708 }
 709 module_init(init_devpts_fs)