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