linux/drivers/tty/tty_ldisc.c
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   1#include <linux/types.h>
   2#include <linux/errno.h>
   3#include <linux/kmod.h>
   4#include <linux/sched.h>
   5#include <linux/interrupt.h>
   6#include <linux/tty.h>
   7#include <linux/tty_driver.h>
   8#include <linux/file.h>
   9#include <linux/mm.h>
  10#include <linux/string.h>
  11#include <linux/slab.h>
  12#include <linux/poll.h>
  13#include <linux/proc_fs.h>
  14#include <linux/init.h>
  15#include <linux/module.h>
  16#include <linux/device.h>
  17#include <linux/wait.h>
  18#include <linux/bitops.h>
  19#include <linux/seq_file.h>
  20#include <linux/uaccess.h>
  21#include <linux/ratelimit.h>
  22
  23/*
  24 *      This guards the refcounted line discipline lists. The lock
  25 *      must be taken with irqs off because there are hangup path
  26 *      callers who will do ldisc lookups and cannot sleep.
  27 */
  28
  29static DEFINE_SPINLOCK(tty_ldisc_lock);
  30static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
  31/* Line disc dispatch table */
  32static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
  33
  34static inline struct tty_ldisc *get_ldisc(struct tty_ldisc *ld)
  35{
  36        if (ld)
  37                atomic_inc(&ld->users);
  38        return ld;
  39}
  40
  41static void put_ldisc(struct tty_ldisc *ld)
  42{
  43        unsigned long flags;
  44
  45        if (WARN_ON_ONCE(!ld))
  46                return;
  47
  48        /*
  49         * If this is the last user, free the ldisc, and
  50         * release the ldisc ops.
  51         *
  52         * We really want an "atomic_dec_and_lock_irqsave()",
  53         * but we don't have it, so this does it by hand.
  54         */
  55        local_irq_save(flags);
  56        if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) {
  57                struct tty_ldisc_ops *ldo = ld->ops;
  58
  59                ldo->refcount--;
  60                module_put(ldo->owner);
  61                spin_unlock_irqrestore(&tty_ldisc_lock, flags);
  62
  63                kfree(ld);
  64                return;
  65        }
  66        local_irq_restore(flags);
  67        wake_up(&ld->wq_idle);
  68}
  69
  70/**
  71 *      tty_register_ldisc      -       install a line discipline
  72 *      @disc: ldisc number
  73 *      @new_ldisc: pointer to the ldisc object
  74 *
  75 *      Installs a new line discipline into the kernel. The discipline
  76 *      is set up as unreferenced and then made available to the kernel
  77 *      from this point onwards.
  78 *
  79 *      Locking:
  80 *              takes tty_ldisc_lock to guard against ldisc races
  81 */
  82
  83int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
  84{
  85        unsigned long flags;
  86        int ret = 0;
  87
  88        if (disc < N_TTY || disc >= NR_LDISCS)
  89                return -EINVAL;
  90
  91        spin_lock_irqsave(&tty_ldisc_lock, flags);
  92        tty_ldiscs[disc] = new_ldisc;
  93        new_ldisc->num = disc;
  94        new_ldisc->refcount = 0;
  95        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
  96
  97        return ret;
  98}
  99EXPORT_SYMBOL(tty_register_ldisc);
 100
 101/**
 102 *      tty_unregister_ldisc    -       unload a line discipline
 103 *      @disc: ldisc number
 104 *      @new_ldisc: pointer to the ldisc object
 105 *
 106 *      Remove a line discipline from the kernel providing it is not
 107 *      currently in use.
 108 *
 109 *      Locking:
 110 *              takes tty_ldisc_lock to guard against ldisc races
 111 */
 112
 113int tty_unregister_ldisc(int disc)
 114{
 115        unsigned long flags;
 116        int ret = 0;
 117
 118        if (disc < N_TTY || disc >= NR_LDISCS)
 119                return -EINVAL;
 120
 121        spin_lock_irqsave(&tty_ldisc_lock, flags);
 122        if (tty_ldiscs[disc]->refcount)
 123                ret = -EBUSY;
 124        else
 125                tty_ldiscs[disc] = NULL;
 126        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 127
 128        return ret;
 129}
 130EXPORT_SYMBOL(tty_unregister_ldisc);
 131
 132static struct tty_ldisc_ops *get_ldops(int disc)
 133{
 134        unsigned long flags;
 135        struct tty_ldisc_ops *ldops, *ret;
 136
 137        spin_lock_irqsave(&tty_ldisc_lock, flags);
 138        ret = ERR_PTR(-EINVAL);
 139        ldops = tty_ldiscs[disc];
 140        if (ldops) {
 141                ret = ERR_PTR(-EAGAIN);
 142                if (try_module_get(ldops->owner)) {
 143                        ldops->refcount++;
 144                        ret = ldops;
 145                }
 146        }
 147        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 148        return ret;
 149}
 150
 151static void put_ldops(struct tty_ldisc_ops *ldops)
 152{
 153        unsigned long flags;
 154
 155        spin_lock_irqsave(&tty_ldisc_lock, flags);
 156        ldops->refcount--;
 157        module_put(ldops->owner);
 158        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 159}
 160
 161/**
 162 *      tty_ldisc_get           -       take a reference to an ldisc
 163 *      @disc: ldisc number
 164 *
 165 *      Takes a reference to a line discipline. Deals with refcounts and
 166 *      module locking counts. Returns NULL if the discipline is not available.
 167 *      Returns a pointer to the discipline and bumps the ref count if it is
 168 *      available
 169 *
 170 *      Locking:
 171 *              takes tty_ldisc_lock to guard against ldisc races
 172 */
 173
 174static struct tty_ldisc *tty_ldisc_get(int disc)
 175{
 176        struct tty_ldisc *ld;
 177        struct tty_ldisc_ops *ldops;
 178
 179        if (disc < N_TTY || disc >= NR_LDISCS)
 180                return ERR_PTR(-EINVAL);
 181
 182        /*
 183         * Get the ldisc ops - we may need to request them to be loaded
 184         * dynamically and try again.
 185         */
 186        ldops = get_ldops(disc);
 187        if (IS_ERR(ldops)) {
 188                request_module("tty-ldisc-%d", disc);
 189                ldops = get_ldops(disc);
 190                if (IS_ERR(ldops))
 191                        return ERR_CAST(ldops);
 192        }
 193
 194        ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
 195        if (ld == NULL) {
 196                put_ldops(ldops);
 197                return ERR_PTR(-ENOMEM);
 198        }
 199
 200        ld->ops = ldops;
 201        atomic_set(&ld->users, 1);
 202        init_waitqueue_head(&ld->wq_idle);
 203
 204        return ld;
 205}
 206
 207static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
 208{
 209        return (*pos < NR_LDISCS) ? pos : NULL;
 210}
 211
 212static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
 213{
 214        (*pos)++;
 215        return (*pos < NR_LDISCS) ? pos : NULL;
 216}
 217
 218static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
 219{
 220}
 221
 222static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
 223{
 224        int i = *(loff_t *)v;
 225        struct tty_ldisc_ops *ldops;
 226
 227        ldops = get_ldops(i);
 228        if (IS_ERR(ldops))
 229                return 0;
 230        seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
 231        put_ldops(ldops);
 232        return 0;
 233}
 234
 235static const struct seq_operations tty_ldiscs_seq_ops = {
 236        .start  = tty_ldiscs_seq_start,
 237        .next   = tty_ldiscs_seq_next,
 238        .stop   = tty_ldiscs_seq_stop,
 239        .show   = tty_ldiscs_seq_show,
 240};
 241
 242static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
 243{
 244        return seq_open(file, &tty_ldiscs_seq_ops);
 245}
 246
 247const struct file_operations tty_ldiscs_proc_fops = {
 248        .owner          = THIS_MODULE,
 249        .open           = proc_tty_ldiscs_open,
 250        .read           = seq_read,
 251        .llseek         = seq_lseek,
 252        .release        = seq_release,
 253};
 254
 255/**
 256 *      tty_ldisc_assign        -       set ldisc on a tty
 257 *      @tty: tty to assign
 258 *      @ld: line discipline
 259 *
 260 *      Install an instance of a line discipline into a tty structure. The
 261 *      ldisc must have a reference count above zero to ensure it remains.
 262 *      The tty instance refcount starts at zero.
 263 *
 264 *      Locking:
 265 *              Caller must hold references
 266 */
 267
 268static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
 269{
 270        tty->ldisc = ld;
 271}
 272
 273/**
 274 *      tty_ldisc_try           -       internal helper
 275 *      @tty: the tty
 276 *
 277 *      Make a single attempt to grab and bump the refcount on
 278 *      the tty ldisc. Return 0 on failure or 1 on success. This is
 279 *      used to implement both the waiting and non waiting versions
 280 *      of tty_ldisc_ref
 281 *
 282 *      Locking: takes tty_ldisc_lock
 283 */
 284
 285static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
 286{
 287        unsigned long flags;
 288        struct tty_ldisc *ld;
 289
 290        spin_lock_irqsave(&tty_ldisc_lock, flags);
 291        ld = NULL;
 292        if (test_bit(TTY_LDISC, &tty->flags))
 293                ld = get_ldisc(tty->ldisc);
 294        spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 295        return ld;
 296}
 297
 298/**
 299 *      tty_ldisc_ref_wait      -       wait for the tty ldisc
 300 *      @tty: tty device
 301 *
 302 *      Dereference the line discipline for the terminal and take a
 303 *      reference to it. If the line discipline is in flux then
 304 *      wait patiently until it changes.
 305 *
 306 *      Note: Must not be called from an IRQ/timer context. The caller
 307 *      must also be careful not to hold other locks that will deadlock
 308 *      against a discipline change, such as an existing ldisc reference
 309 *      (which we check for)
 310 *
 311 *      Locking: call functions take tty_ldisc_lock
 312 */
 313
 314struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
 315{
 316        struct tty_ldisc *ld;
 317
 318        /* wait_event is a macro */
 319        wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
 320        return ld;
 321}
 322EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
 323
 324/**
 325 *      tty_ldisc_ref           -       get the tty ldisc
 326 *      @tty: tty device
 327 *
 328 *      Dereference the line discipline for the terminal and take a
 329 *      reference to it. If the line discipline is in flux then
 330 *      return NULL. Can be called from IRQ and timer functions.
 331 *
 332 *      Locking: called functions take tty_ldisc_lock
 333 */
 334
 335struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
 336{
 337        return tty_ldisc_try(tty);
 338}
 339EXPORT_SYMBOL_GPL(tty_ldisc_ref);
 340
 341/**
 342 *      tty_ldisc_deref         -       free a tty ldisc reference
 343 *      @ld: reference to free up
 344 *
 345 *      Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
 346 *      be called in IRQ context.
 347 *
 348 *      Locking: takes tty_ldisc_lock
 349 */
 350
 351void tty_ldisc_deref(struct tty_ldisc *ld)
 352{
 353        put_ldisc(ld);
 354}
 355EXPORT_SYMBOL_GPL(tty_ldisc_deref);
 356
 357static inline void tty_ldisc_put(struct tty_ldisc *ld)
 358{
 359        put_ldisc(ld);
 360}
 361
 362/**
 363 *      tty_ldisc_enable        -       allow ldisc use
 364 *      @tty: terminal to activate ldisc on
 365 *
 366 *      Set the TTY_LDISC flag when the line discipline can be called
 367 *      again. Do necessary wakeups for existing sleepers. Clear the LDISC
 368 *      changing flag to indicate any ldisc change is now over.
 369 *
 370 *      Note: nobody should set the TTY_LDISC bit except via this function.
 371 *      Clearing directly is allowed.
 372 */
 373
 374void tty_ldisc_enable(struct tty_struct *tty)
 375{
 376        set_bit(TTY_LDISC, &tty->flags);
 377        clear_bit(TTY_LDISC_CHANGING, &tty->flags);
 378        wake_up(&tty_ldisc_wait);
 379}
 380
 381/**
 382 *      tty_ldisc_flush -       flush line discipline queue
 383 *      @tty: tty
 384 *
 385 *      Flush the line discipline queue (if any) for this tty. If there
 386 *      is no line discipline active this is a no-op.
 387 */
 388
 389void tty_ldisc_flush(struct tty_struct *tty)
 390{
 391        struct tty_ldisc *ld = tty_ldisc_ref(tty);
 392        if (ld) {
 393                if (ld->ops->flush_buffer)
 394                        ld->ops->flush_buffer(tty);
 395                tty_ldisc_deref(ld);
 396        }
 397        tty_buffer_flush(tty);
 398}
 399EXPORT_SYMBOL_GPL(tty_ldisc_flush);
 400
 401/**
 402 *      tty_set_termios_ldisc           -       set ldisc field
 403 *      @tty: tty structure
 404 *      @num: line discipline number
 405 *
 406 *      This is probably overkill for real world processors but
 407 *      they are not on hot paths so a little discipline won't do
 408 *      any harm.
 409 *
 410 *      Locking: takes termios_mutex
 411 */
 412
 413static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
 414{
 415        mutex_lock(&tty->termios_mutex);
 416        tty->termios.c_line = num;
 417        mutex_unlock(&tty->termios_mutex);
 418}
 419
 420/**
 421 *      tty_ldisc_open          -       open a line discipline
 422 *      @tty: tty we are opening the ldisc on
 423 *      @ld: discipline to open
 424 *
 425 *      A helper opening method. Also a convenient debugging and check
 426 *      point.
 427 *
 428 *      Locking: always called with BTM already held.
 429 */
 430
 431static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 432{
 433        WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
 434        if (ld->ops->open) {
 435                int ret;
 436                /* BTM here locks versus a hangup event */
 437                ret = ld->ops->open(tty);
 438                if (ret)
 439                        clear_bit(TTY_LDISC_OPEN, &tty->flags);
 440                return ret;
 441        }
 442        return 0;
 443}
 444
 445/**
 446 *      tty_ldisc_close         -       close a line discipline
 447 *      @tty: tty we are opening the ldisc on
 448 *      @ld: discipline to close
 449 *
 450 *      A helper close method. Also a convenient debugging and check
 451 *      point.
 452 */
 453
 454static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
 455{
 456        WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
 457        clear_bit(TTY_LDISC_OPEN, &tty->flags);
 458        if (ld->ops->close)
 459                ld->ops->close(tty);
 460}
 461
 462/**
 463 *      tty_ldisc_restore       -       helper for tty ldisc change
 464 *      @tty: tty to recover
 465 *      @old: previous ldisc
 466 *
 467 *      Restore the previous line discipline or N_TTY when a line discipline
 468 *      change fails due to an open error
 469 */
 470
 471static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
 472{
 473        char buf[64];
 474        struct tty_ldisc *new_ldisc;
 475        int r;
 476
 477        /* There is an outstanding reference here so this is safe */
 478        old = tty_ldisc_get(old->ops->num);
 479        WARN_ON(IS_ERR(old));
 480        tty_ldisc_assign(tty, old);
 481        tty_set_termios_ldisc(tty, old->ops->num);
 482        if (tty_ldisc_open(tty, old) < 0) {
 483                tty_ldisc_put(old);
 484                /* This driver is always present */
 485                new_ldisc = tty_ldisc_get(N_TTY);
 486                if (IS_ERR(new_ldisc))
 487                        panic("n_tty: get");
 488                tty_ldisc_assign(tty, new_ldisc);
 489                tty_set_termios_ldisc(tty, N_TTY);
 490                r = tty_ldisc_open(tty, new_ldisc);
 491                if (r < 0)
 492                        panic("Couldn't open N_TTY ldisc for "
 493                              "%s --- error %d.",
 494                              tty_name(tty, buf), r);
 495        }
 496}
 497
 498/**
 499 *      tty_ldisc_halt          -       shut down the line discipline
 500 *      @tty: tty device
 501 *
 502 *      Shut down the line discipline and work queue for this tty device.
 503 *      The TTY_LDISC flag being cleared ensures no further references can
 504 *      be obtained while the delayed work queue halt ensures that no more
 505 *      data is fed to the ldisc.
 506 *
 507 *      You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
 508 *      in order to make sure any currently executing ldisc work is also
 509 *      flushed.
 510 */
 511
 512static int tty_ldisc_halt(struct tty_struct *tty)
 513{
 514        clear_bit(TTY_LDISC, &tty->flags);
 515        return cancel_work_sync(&tty->buf.work);
 516}
 517
 518/**
 519 *      tty_ldisc_flush_works   -       flush all works of a tty
 520 *      @tty: tty device to flush works for
 521 *
 522 *      Sync flush all works belonging to @tty.
 523 */
 524static void tty_ldisc_flush_works(struct tty_struct *tty)
 525{
 526        flush_work(&tty->hangup_work);
 527        flush_work(&tty->SAK_work);
 528        flush_work(&tty->buf.work);
 529}
 530
 531/**
 532 *      tty_ldisc_wait_idle     -       wait for the ldisc to become idle
 533 *      @tty: tty to wait for
 534 *      @timeout: for how long to wait at most
 535 *
 536 *      Wait for the line discipline to become idle. The discipline must
 537 *      have been halted for this to guarantee it remains idle.
 538 */
 539static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
 540{
 541        long ret;
 542        ret = wait_event_timeout(tty->ldisc->wq_idle,
 543                        atomic_read(&tty->ldisc->users) == 1, timeout);
 544        return ret > 0 ? 0 : -EBUSY;
 545}
 546
 547/**
 548 *      tty_set_ldisc           -       set line discipline
 549 *      @tty: the terminal to set
 550 *      @ldisc: the line discipline
 551 *
 552 *      Set the discipline of a tty line. Must be called from a process
 553 *      context. The ldisc change logic has to protect itself against any
 554 *      overlapping ldisc change (including on the other end of pty pairs),
 555 *      the close of one side of a tty/pty pair, and eventually hangup.
 556 *
 557 *      Locking: takes tty_ldisc_lock, termios_mutex
 558 */
 559
 560int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 561{
 562        int retval;
 563        struct tty_ldisc *o_ldisc, *new_ldisc;
 564        int work, o_work = 0;
 565        struct tty_struct *o_tty;
 566
 567        new_ldisc = tty_ldisc_get(ldisc);
 568        if (IS_ERR(new_ldisc))
 569                return PTR_ERR(new_ldisc);
 570
 571        tty_lock(tty);
 572        /*
 573         *      We need to look at the tty locking here for pty/tty pairs
 574         *      when both sides try to change in parallel.
 575         */
 576
 577        o_tty = tty->link;      /* o_tty is the pty side or NULL */
 578
 579
 580        /*
 581         *      Check the no-op case
 582         */
 583
 584        if (tty->ldisc->ops->num == ldisc) {
 585                tty_unlock(tty);
 586                tty_ldisc_put(new_ldisc);
 587                return 0;
 588        }
 589
 590        tty_unlock(tty);
 591        /*
 592         *      Problem: What do we do if this blocks ?
 593         *      We could deadlock here
 594         */
 595
 596        tty_wait_until_sent(tty, 0);
 597
 598        tty_lock(tty);
 599        mutex_lock(&tty->ldisc_mutex);
 600
 601        /*
 602         *      We could be midstream of another ldisc change which has
 603         *      dropped the lock during processing. If so we need to wait.
 604         */
 605
 606        while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
 607                mutex_unlock(&tty->ldisc_mutex);
 608                tty_unlock(tty);
 609                wait_event(tty_ldisc_wait,
 610                        test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
 611                tty_lock(tty);
 612                mutex_lock(&tty->ldisc_mutex);
 613        }
 614
 615        set_bit(TTY_LDISC_CHANGING, &tty->flags);
 616
 617        /*
 618         *      No more input please, we are switching. The new ldisc
 619         *      will update this value in the ldisc open function
 620         */
 621
 622        tty->receive_room = 0;
 623
 624        o_ldisc = tty->ldisc;
 625
 626        tty_unlock(tty);
 627        /*
 628         *      Make sure we don't change while someone holds a
 629         *      reference to the line discipline. The TTY_LDISC bit
 630         *      prevents anyone taking a reference once it is clear.
 631         *      We need the lock to avoid racing reference takers.
 632         *
 633         *      We must clear the TTY_LDISC bit here to avoid a livelock
 634         *      with a userspace app continually trying to use the tty in
 635         *      parallel to the change and re-referencing the tty.
 636         */
 637
 638        work = tty_ldisc_halt(tty);
 639        if (o_tty)
 640                o_work = tty_ldisc_halt(o_tty);
 641
 642        /*
 643         * Wait for ->hangup_work and ->buf.work handlers to terminate.
 644         * We must drop the mutex here in case a hangup is also in process.
 645         */
 646
 647        mutex_unlock(&tty->ldisc_mutex);
 648
 649        tty_ldisc_flush_works(tty);
 650
 651        retval = tty_ldisc_wait_idle(tty, 5 * HZ);
 652
 653        tty_lock(tty);
 654        mutex_lock(&tty->ldisc_mutex);
 655
 656        /* handle wait idle failure locked */
 657        if (retval) {
 658                tty_ldisc_put(new_ldisc);
 659                goto enable;
 660        }
 661
 662        if (test_bit(TTY_HUPPING, &tty->flags)) {
 663                /* We were raced by the hangup method. It will have stomped
 664                   the ldisc data and closed the ldisc down */
 665                clear_bit(TTY_LDISC_CHANGING, &tty->flags);
 666                mutex_unlock(&tty->ldisc_mutex);
 667                tty_ldisc_put(new_ldisc);
 668                tty_unlock(tty);
 669                return -EIO;
 670        }
 671
 672        /* Shutdown the current discipline. */
 673        tty_ldisc_close(tty, o_ldisc);
 674
 675        /* Now set up the new line discipline. */
 676        tty_ldisc_assign(tty, new_ldisc);
 677        tty_set_termios_ldisc(tty, ldisc);
 678
 679        retval = tty_ldisc_open(tty, new_ldisc);
 680        if (retval < 0) {
 681                /* Back to the old one or N_TTY if we can't */
 682                tty_ldisc_put(new_ldisc);
 683                tty_ldisc_restore(tty, o_ldisc);
 684        }
 685
 686        /* At this point we hold a reference to the new ldisc and a
 687           a reference to the old ldisc. If we ended up flipping back
 688           to the existing ldisc we have two references to it */
 689
 690        if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
 691                tty->ops->set_ldisc(tty);
 692
 693        tty_ldisc_put(o_ldisc);
 694
 695enable:
 696        /*
 697         *      Allow ldisc referencing to occur again
 698         */
 699
 700        tty_ldisc_enable(tty);
 701        if (o_tty)
 702                tty_ldisc_enable(o_tty);
 703
 704        /* Restart the work queue in case no characters kick it off. Safe if
 705           already running */
 706        if (work)
 707                schedule_work(&tty->buf.work);
 708        if (o_work)
 709                schedule_work(&o_tty->buf.work);
 710        mutex_unlock(&tty->ldisc_mutex);
 711        tty_unlock(tty);
 712        return retval;
 713}
 714
 715/**
 716 *      tty_reset_termios       -       reset terminal state
 717 *      @tty: tty to reset
 718 *
 719 *      Restore a terminal to the driver default state.
 720 */
 721
 722static void tty_reset_termios(struct tty_struct *tty)
 723{
 724        mutex_lock(&tty->termios_mutex);
 725        tty->termios = tty->driver->init_termios;
 726        tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
 727        tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
 728        mutex_unlock(&tty->termios_mutex);
 729}
 730
 731
 732/**
 733 *      tty_ldisc_reinit        -       reinitialise the tty ldisc
 734 *      @tty: tty to reinit
 735 *      @ldisc: line discipline to reinitialize
 736 *
 737 *      Switch the tty to a line discipline and leave the ldisc
 738 *      state closed
 739 */
 740
 741static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
 742{
 743        struct tty_ldisc *ld = tty_ldisc_get(ldisc);
 744
 745        if (IS_ERR(ld))
 746                return -1;
 747
 748        tty_ldisc_close(tty, tty->ldisc);
 749        tty_ldisc_put(tty->ldisc);
 750        tty->ldisc = NULL;
 751        /*
 752         *      Switch the line discipline back
 753         */
 754        tty_ldisc_assign(tty, ld);
 755        tty_set_termios_ldisc(tty, ldisc);
 756
 757        return 0;
 758}
 759
 760/**
 761 *      tty_ldisc_hangup                -       hangup ldisc reset
 762 *      @tty: tty being hung up
 763 *
 764 *      Some tty devices reset their termios when they receive a hangup
 765 *      event. In that situation we must also switch back to N_TTY properly
 766 *      before we reset the termios data.
 767 *
 768 *      Locking: We can take the ldisc mutex as the rest of the code is
 769 *      careful to allow for this.
 770 *
 771 *      In the pty pair case this occurs in the close() path of the
 772 *      tty itself so we must be careful about locking rules.
 773 */
 774
 775void tty_ldisc_hangup(struct tty_struct *tty)
 776{
 777        struct tty_ldisc *ld;
 778        int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
 779        int err = 0;
 780
 781        /*
 782         * FIXME! What are the locking issues here? This may me overdoing
 783         * things... This question is especially important now that we've
 784         * removed the irqlock.
 785         */
 786        ld = tty_ldisc_ref(tty);
 787        if (ld != NULL) {
 788                /* We may have no line discipline at this point */
 789                if (ld->ops->flush_buffer)
 790                        ld->ops->flush_buffer(tty);
 791                tty_driver_flush_buffer(tty);
 792                if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
 793                    ld->ops->write_wakeup)
 794                        ld->ops->write_wakeup(tty);
 795                if (ld->ops->hangup)
 796                        ld->ops->hangup(tty);
 797                tty_ldisc_deref(ld);
 798        }
 799        /*
 800         * FIXME: Once we trust the LDISC code better we can wait here for
 801         * ldisc completion and fix the driver call race
 802         */
 803        wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
 804        wake_up_interruptible_poll(&tty->read_wait, POLLIN);
 805        /*
 806         * Shutdown the current line discipline, and reset it to
 807         * N_TTY if need be.
 808         *
 809         * Avoid racing set_ldisc or tty_ldisc_release
 810         */
 811        mutex_lock(&tty->ldisc_mutex);
 812
 813        /*
 814         * this is like tty_ldisc_halt, but we need to give up
 815         * the BTM before calling cancel_work_sync, which may
 816         * need to wait for another function taking the BTM
 817         */
 818        clear_bit(TTY_LDISC, &tty->flags);
 819        tty_unlock(tty);
 820        cancel_work_sync(&tty->buf.work);
 821        mutex_unlock(&tty->ldisc_mutex);
 822retry:
 823        tty_lock(tty);
 824        mutex_lock(&tty->ldisc_mutex);
 825
 826        /* At this point we have a closed ldisc and we want to
 827           reopen it. We could defer this to the next open but
 828           it means auditing a lot of other paths so this is
 829           a FIXME */
 830        if (tty->ldisc) {       /* Not yet closed */
 831                if (atomic_read(&tty->ldisc->users) != 1) {
 832                        char cur_n[TASK_COMM_LEN], tty_n[64];
 833                        long timeout = 3 * HZ;
 834                        tty_unlock(tty);
 835
 836                        while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
 837                                timeout = MAX_SCHEDULE_TIMEOUT;
 838                                printk_ratelimited(KERN_WARNING
 839                                        "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
 840                                        __func__, get_task_comm(cur_n, current),
 841                                        tty_name(tty, tty_n));
 842                        }
 843                        mutex_unlock(&tty->ldisc_mutex);
 844                        goto retry;
 845                }
 846
 847                if (reset == 0) {
 848
 849                        if (!tty_ldisc_reinit(tty, tty->termios.c_line))
 850                                err = tty_ldisc_open(tty, tty->ldisc);
 851                        else
 852                                err = 1;
 853                }
 854                /* If the re-open fails or we reset then go to N_TTY. The
 855                   N_TTY open cannot fail */
 856                if (reset || err) {
 857                        BUG_ON(tty_ldisc_reinit(tty, N_TTY));
 858                        WARN_ON(tty_ldisc_open(tty, tty->ldisc));
 859                }
 860                tty_ldisc_enable(tty);
 861        }
 862        mutex_unlock(&tty->ldisc_mutex);
 863        if (reset)
 864                tty_reset_termios(tty);
 865}
 866
 867/**
 868 *      tty_ldisc_setup                 -       open line discipline
 869 *      @tty: tty being shut down
 870 *      @o_tty: pair tty for pty/tty pairs
 871 *
 872 *      Called during the initial open of a tty/pty pair in order to set up the
 873 *      line disciplines and bind them to the tty. This has no locking issues
 874 *      as the device isn't yet active.
 875 */
 876
 877int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
 878{
 879        struct tty_ldisc *ld = tty->ldisc;
 880        int retval;
 881
 882        retval = tty_ldisc_open(tty, ld);
 883        if (retval)
 884                return retval;
 885
 886        if (o_tty) {
 887                retval = tty_ldisc_open(o_tty, o_tty->ldisc);
 888                if (retval) {
 889                        tty_ldisc_close(tty, ld);
 890                        return retval;
 891                }
 892                tty_ldisc_enable(o_tty);
 893        }
 894        tty_ldisc_enable(tty);
 895        return 0;
 896}
 897
 898static void tty_ldisc_kill(struct tty_struct *tty)
 899{
 900        mutex_lock(&tty->ldisc_mutex);
 901        /*
 902         * Now kill off the ldisc
 903         */
 904        tty_ldisc_close(tty, tty->ldisc);
 905        tty_ldisc_put(tty->ldisc);
 906        /* Force an oops if we mess this up */
 907        tty->ldisc = NULL;
 908
 909        /* Ensure the next open requests the N_TTY ldisc */
 910        tty_set_termios_ldisc(tty, N_TTY);
 911        mutex_unlock(&tty->ldisc_mutex);
 912}
 913
 914/**
 915 *      tty_ldisc_release               -       release line discipline
 916 *      @tty: tty being shut down
 917 *      @o_tty: pair tty for pty/tty pairs
 918 *
 919 *      Called during the final close of a tty/pty pair in order to shut down
 920 *      the line discpline layer. On exit the ldisc assigned is N_TTY and the
 921 *      ldisc has not been opened.
 922 */
 923
 924void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
 925{
 926        /*
 927         * Prevent flush_to_ldisc() from rescheduling the work for later.  Then
 928         * kill any delayed work. As this is the final close it does not
 929         * race with the set_ldisc code path.
 930         */
 931
 932        tty_lock_pair(tty, o_tty);
 933        tty_ldisc_halt(tty);
 934        tty_ldisc_flush_works(tty);
 935        if (o_tty) {
 936                tty_ldisc_halt(o_tty);
 937                tty_ldisc_flush_works(o_tty);
 938        }
 939
 940        /* This will need doing differently if we need to lock */
 941        tty_ldisc_kill(tty);
 942
 943        if (o_tty)
 944                tty_ldisc_kill(o_tty);
 945
 946        tty_unlock_pair(tty, o_tty);
 947        /* And the memory resources remaining (buffers, termios) will be
 948           disposed of when the kref hits zero */
 949}
 950
 951/**
 952 *      tty_ldisc_init          -       ldisc setup for new tty
 953 *      @tty: tty being allocated
 954 *
 955 *      Set up the line discipline objects for a newly allocated tty. Note that
 956 *      the tty structure is not completely set up when this call is made.
 957 */
 958
 959void tty_ldisc_init(struct tty_struct *tty)
 960{
 961        struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
 962        if (IS_ERR(ld))
 963                panic("n_tty: init_tty");
 964        tty_ldisc_assign(tty, ld);
 965}
 966
 967/**
 968 *      tty_ldisc_init          -       ldisc cleanup for new tty
 969 *      @tty: tty that was allocated recently
 970 *
 971 *      The tty structure must not becompletely set up (tty_ldisc_setup) when
 972 *      this call is made.
 973 */
 974void tty_ldisc_deinit(struct tty_struct *tty)
 975{
 976        put_ldisc(tty->ldisc);
 977        tty_ldisc_assign(tty, NULL);
 978}
 979
 980void tty_ldisc_begin(void)
 981{
 982        /* Setup the default TTY line discipline. */
 983        (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
 984}
 985
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