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_RAW_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_raw_lock_irqsave()",
  53         * but we don't have it, so this does it by hand.
  54         */
  55        raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
  56        if (atomic_dec_and_test(&ld->users)) {
  57                struct tty_ldisc_ops *ldo = ld->ops;
  58
  59                ldo->refcount--;
  60                module_put(ldo->owner);
  61                raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
  62
  63                kfree(ld);
  64                return;
  65        }
  66        raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
  67
  68        if (waitqueue_active(&ld->wq_idle))
  69                wake_up(&ld->wq_idle);
  70}
  71
  72/**
  73 *      tty_register_ldisc      -       install a line discipline
  74 *      @disc: ldisc number
  75 *      @new_ldisc: pointer to the ldisc object
  76 *
  77 *      Installs a new line discipline into the kernel. The discipline
  78 *      is set up as unreferenced and then made available to the kernel
  79 *      from this point onwards.
  80 *
  81 *      Locking:
  82 *              takes tty_ldisc_lock to guard against ldisc races
  83 */
  84
  85int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
  86{
  87        unsigned long flags;
  88        int ret = 0;
  89
  90        if (disc < N_TTY || disc >= NR_LDISCS)
  91                return -EINVAL;
  92
  93        raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
  94        tty_ldiscs[disc] = new_ldisc;
  95        new_ldisc->num = disc;
  96        new_ldisc->refcount = 0;
  97        raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
  98
  99        return ret;
 100}
 101EXPORT_SYMBOL(tty_register_ldisc);
 102
 103/**
 104 *      tty_unregister_ldisc    -       unload a line discipline
 105 *      @disc: ldisc number
 106 *      @new_ldisc: pointer to the ldisc object
 107 *
 108 *      Remove a line discipline from the kernel providing it is not
 109 *      currently in use.
 110 *
 111 *      Locking:
 112 *              takes tty_ldisc_lock to guard against ldisc races
 113 */
 114
 115int tty_unregister_ldisc(int disc)
 116{
 117        unsigned long flags;
 118        int ret = 0;
 119
 120        if (disc < N_TTY || disc >= NR_LDISCS)
 121                return -EINVAL;
 122
 123        raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
 124        if (tty_ldiscs[disc]->refcount)
 125                ret = -EBUSY;
 126        else
 127                tty_ldiscs[disc] = NULL;
 128        raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 129
 130        return ret;
 131}
 132EXPORT_SYMBOL(tty_unregister_ldisc);
 133
 134static struct tty_ldisc_ops *get_ldops(int disc)
 135{
 136        unsigned long flags;
 137        struct tty_ldisc_ops *ldops, *ret;
 138
 139        raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
 140        ret = ERR_PTR(-EINVAL);
 141        ldops = tty_ldiscs[disc];
 142        if (ldops) {
 143                ret = ERR_PTR(-EAGAIN);
 144                if (try_module_get(ldops->owner)) {
 145                        ldops->refcount++;
 146                        ret = ldops;
 147                }
 148        }
 149        raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 150        return ret;
 151}
 152
 153static void put_ldops(struct tty_ldisc_ops *ldops)
 154{
 155        unsigned long flags;
 156
 157        raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
 158        ldops->refcount--;
 159        module_put(ldops->owner);
 160        raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 161}
 162
 163/**
 164 *      tty_ldisc_get           -       take a reference to an ldisc
 165 *      @disc: ldisc number
 166 *
 167 *      Takes a reference to a line discipline. Deals with refcounts and
 168 *      module locking counts. Returns NULL if the discipline is not available.
 169 *      Returns a pointer to the discipline and bumps the ref count if it is
 170 *      available
 171 *
 172 *      Locking:
 173 *              takes tty_ldisc_lock to guard against ldisc races
 174 */
 175
 176static struct tty_ldisc *tty_ldisc_get(int disc)
 177{
 178        struct tty_ldisc *ld;
 179        struct tty_ldisc_ops *ldops;
 180
 181        if (disc < N_TTY || disc >= NR_LDISCS)
 182                return ERR_PTR(-EINVAL);
 183
 184        /*
 185         * Get the ldisc ops - we may need to request them to be loaded
 186         * dynamically and try again.
 187         */
 188        ldops = get_ldops(disc);
 189        if (IS_ERR(ldops)) {
 190                request_module("tty-ldisc-%d", disc);
 191                ldops = get_ldops(disc);
 192                if (IS_ERR(ldops))
 193                        return ERR_CAST(ldops);
 194        }
 195
 196        ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
 197        if (ld == NULL) {
 198                put_ldops(ldops);
 199                return ERR_PTR(-ENOMEM);
 200        }
 201
 202        ld->ops = ldops;
 203        atomic_set(&ld->users, 1);
 204        init_waitqueue_head(&ld->wq_idle);
 205
 206        return ld;
 207}
 208
 209static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos)
 210{
 211        return (*pos < NR_LDISCS) ? pos : NULL;
 212}
 213
 214static void *tty_ldiscs_seq_next(struct seq_file *m, void *v, loff_t *pos)
 215{
 216        (*pos)++;
 217        return (*pos < NR_LDISCS) ? pos : NULL;
 218}
 219
 220static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
 221{
 222}
 223
 224static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
 225{
 226        int i = *(loff_t *)v;
 227        struct tty_ldisc_ops *ldops;
 228
 229        ldops = get_ldops(i);
 230        if (IS_ERR(ldops))
 231                return 0;
 232        seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
 233        put_ldops(ldops);
 234        return 0;
 235}
 236
 237static const struct seq_operations tty_ldiscs_seq_ops = {
 238        .start  = tty_ldiscs_seq_start,
 239        .next   = tty_ldiscs_seq_next,
 240        .stop   = tty_ldiscs_seq_stop,
 241        .show   = tty_ldiscs_seq_show,
 242};
 243
 244static int proc_tty_ldiscs_open(struct inode *inode, struct file *file)
 245{
 246        return seq_open(file, &tty_ldiscs_seq_ops);
 247}
 248
 249const struct file_operations tty_ldiscs_proc_fops = {
 250        .owner          = THIS_MODULE,
 251        .open           = proc_tty_ldiscs_open,
 252        .read           = seq_read,
 253        .llseek         = seq_lseek,
 254        .release        = seq_release,
 255};
 256
 257/**
 258 *      tty_ldisc_assign        -       set ldisc on a tty
 259 *      @tty: tty to assign
 260 *      @ld: line discipline
 261 *
 262 *      Install an instance of a line discipline into a tty structure. The
 263 *      ldisc must have a reference count above zero to ensure it remains.
 264 *      The tty instance refcount starts at zero.
 265 *
 266 *      Locking:
 267 *              Caller must hold references
 268 */
 269
 270static void tty_ldisc_assign(struct tty_struct *tty, struct tty_ldisc *ld)
 271{
 272        tty->ldisc = ld;
 273}
 274
 275/**
 276 *      tty_ldisc_try           -       internal helper
 277 *      @tty: the tty
 278 *
 279 *      Make a single attempt to grab and bump the refcount on
 280 *      the tty ldisc. Return 0 on failure or 1 on success. This is
 281 *      used to implement both the waiting and non waiting versions
 282 *      of tty_ldisc_ref
 283 *
 284 *      Locking: takes tty_ldisc_lock
 285 */
 286
 287static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
 288{
 289        unsigned long flags;
 290        struct tty_ldisc *ld;
 291
 292        raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
 293        ld = NULL;
 294        if (test_bit(TTY_LDISC, &tty->flags))
 295                ld = get_ldisc(tty->ldisc);
 296        raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
 297        return ld;
 298}
 299
 300/**
 301 *      tty_ldisc_ref_wait      -       wait for the tty ldisc
 302 *      @tty: tty device
 303 *
 304 *      Dereference the line discipline for the terminal and take a
 305 *      reference to it. If the line discipline is in flux then
 306 *      wait patiently until it changes.
 307 *
 308 *      Note: Must not be called from an IRQ/timer context. The caller
 309 *      must also be careful not to hold other locks that will deadlock
 310 *      against a discipline change, such as an existing ldisc reference
 311 *      (which we check for)
 312 *
 313 *      Locking: call functions take tty_ldisc_lock
 314 */
 315
 316struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
 317{
 318        struct tty_ldisc *ld;
 319
 320        /* wait_event is a macro */
 321        wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL);
 322        return ld;
 323}
 324EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
 325
 326/**
 327 *      tty_ldisc_ref           -       get the tty ldisc
 328 *      @tty: tty device
 329 *
 330 *      Dereference the line discipline for the terminal and take a
 331 *      reference to it. If the line discipline is in flux then
 332 *      return NULL. Can be called from IRQ and timer functions.
 333 *
 334 *      Locking: called functions take tty_ldisc_lock
 335 */
 336
 337struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty)
 338{
 339        return tty_ldisc_try(tty);
 340}
 341EXPORT_SYMBOL_GPL(tty_ldisc_ref);
 342
 343/**
 344 *      tty_ldisc_deref         -       free a tty ldisc reference
 345 *      @ld: reference to free up
 346 *
 347 *      Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May
 348 *      be called in IRQ context.
 349 *
 350 *      Locking: takes tty_ldisc_lock
 351 */
 352
 353void tty_ldisc_deref(struct tty_ldisc *ld)
 354{
 355        put_ldisc(ld);
 356}
 357EXPORT_SYMBOL_GPL(tty_ldisc_deref);
 358
 359static inline void tty_ldisc_put(struct tty_ldisc *ld)
 360{
 361        put_ldisc(ld);
 362}
 363
 364/**
 365 *      tty_ldisc_enable        -       allow ldisc use
 366 *      @tty: terminal to activate ldisc on
 367 *
 368 *      Set the TTY_LDISC flag when the line discipline can be called
 369 *      again. Do necessary wakeups for existing sleepers. Clear the LDISC
 370 *      changing flag to indicate any ldisc change is now over.
 371 *
 372 *      Note: nobody should set the TTY_LDISC bit except via this function.
 373 *      Clearing directly is allowed.
 374 */
 375
 376void tty_ldisc_enable(struct tty_struct *tty)
 377{
 378        set_bit(TTY_LDISC, &tty->flags);
 379        clear_bit(TTY_LDISC_CHANGING, &tty->flags);
 380        wake_up(&tty_ldisc_wait);
 381}
 382
 383/**
 384 *      tty_ldisc_flush -       flush line discipline queue
 385 *      @tty: tty
 386 *
 387 *      Flush the line discipline queue (if any) for this tty. If there
 388 *      is no line discipline active this is a no-op.
 389 */
 390
 391void tty_ldisc_flush(struct tty_struct *tty)
 392{
 393        struct tty_ldisc *ld = tty_ldisc_ref(tty);
 394        if (ld) {
 395                if (ld->ops->flush_buffer)
 396                        ld->ops->flush_buffer(tty);
 397                tty_ldisc_deref(ld);
 398        }
 399        tty_buffer_flush(tty);
 400}
 401EXPORT_SYMBOL_GPL(tty_ldisc_flush);
 402
 403/**
 404 *      tty_set_termios_ldisc           -       set ldisc field
 405 *      @tty: tty structure
 406 *      @num: line discipline number
 407 *
 408 *      This is probably overkill for real world processors but
 409 *      they are not on hot paths so a little discipline won't do
 410 *      any harm.
 411 *
 412 *      Locking: takes termios_mutex
 413 */
 414
 415static void tty_set_termios_ldisc(struct tty_struct *tty, int num)
 416{
 417        mutex_lock(&tty->termios_mutex);
 418        tty->termios.c_line = num;
 419        mutex_unlock(&tty->termios_mutex);
 420}
 421
 422/**
 423 *      tty_ldisc_open          -       open a line discipline
 424 *      @tty: tty we are opening the ldisc on
 425 *      @ld: discipline to open
 426 *
 427 *      A helper opening method. Also a convenient debugging and check
 428 *      point.
 429 *
 430 *      Locking: always called with BTM already held.
 431 */
 432
 433static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)
 434{
 435        WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags));
 436        if (ld->ops->open) {
 437                int ret;
 438                /* BTM here locks versus a hangup event */
 439                ret = ld->ops->open(tty);
 440                if (ret)
 441                        clear_bit(TTY_LDISC_OPEN, &tty->flags);
 442                return ret;
 443        }
 444        return 0;
 445}
 446
 447/**
 448 *      tty_ldisc_close         -       close a line discipline
 449 *      @tty: tty we are opening the ldisc on
 450 *      @ld: discipline to close
 451 *
 452 *      A helper close method. Also a convenient debugging and check
 453 *      point.
 454 */
 455
 456static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
 457{
 458        WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
 459        clear_bit(TTY_LDISC_OPEN, &tty->flags);
 460        if (ld->ops->close)
 461                ld->ops->close(tty);
 462}
 463
 464/**
 465 *      tty_ldisc_restore       -       helper for tty ldisc change
 466 *      @tty: tty to recover
 467 *      @old: previous ldisc
 468 *
 469 *      Restore the previous line discipline or N_TTY when a line discipline
 470 *      change fails due to an open error
 471 */
 472
 473static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
 474{
 475        char buf[64];
 476        struct tty_ldisc *new_ldisc;
 477        int r;
 478
 479        /* There is an outstanding reference here so this is safe */
 480        old = tty_ldisc_get(old->ops->num);
 481        WARN_ON(IS_ERR(old));
 482        tty_ldisc_assign(tty, old);
 483        tty_set_termios_ldisc(tty, old->ops->num);
 484        if (tty_ldisc_open(tty, old) < 0) {
 485                tty_ldisc_put(old);
 486                /* This driver is always present */
 487                new_ldisc = tty_ldisc_get(N_TTY);
 488                if (IS_ERR(new_ldisc))
 489                        panic("n_tty: get");
 490                tty_ldisc_assign(tty, new_ldisc);
 491                tty_set_termios_ldisc(tty, N_TTY);
 492                r = tty_ldisc_open(tty, new_ldisc);
 493                if (r < 0)
 494                        panic("Couldn't open N_TTY ldisc for "
 495                              "%s --- error %d.",
 496                              tty_name(tty, buf), r);
 497        }
 498}
 499
 500/**
 501 *      tty_ldisc_halt          -       shut down the line discipline
 502 *      @tty: tty device
 503 *
 504 *      Shut down the line discipline and work queue for this tty device.
 505 *      The TTY_LDISC flag being cleared ensures no further references can
 506 *      be obtained while the delayed work queue halt ensures that no more
 507 *      data is fed to the ldisc.
 508 *
 509 *      You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex)
 510 *      in order to make sure any currently executing ldisc work is also
 511 *      flushed.
 512 */
 513
 514static int tty_ldisc_halt(struct tty_struct *tty)
 515{
 516        clear_bit(TTY_LDISC, &tty->flags);
 517        return cancel_work_sync(&tty->port->buf.work);
 518}
 519
 520/**
 521 *      tty_ldisc_flush_works   -       flush all works of a tty
 522 *      @tty: tty device to flush works for
 523 *
 524 *      Sync flush all works belonging to @tty.
 525 */
 526static void tty_ldisc_flush_works(struct tty_struct *tty)
 527{
 528        flush_work(&tty->hangup_work);
 529        flush_work(&tty->SAK_work);
 530        flush_work(&tty->port->buf.work);
 531}
 532
 533/**
 534 *      tty_ldisc_wait_idle     -       wait for the ldisc to become idle
 535 *      @tty: tty to wait for
 536 *      @timeout: for how long to wait at most
 537 *
 538 *      Wait for the line discipline to become idle. The discipline must
 539 *      have been halted for this to guarantee it remains idle.
 540 */
 541static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
 542{
 543        long ret;
 544        ret = wait_event_timeout(tty->ldisc->wq_idle,
 545                        atomic_read(&tty->ldisc->users) == 1, timeout);
 546        return ret > 0 ? 0 : -EBUSY;
 547}
 548
 549/**
 550 *      tty_set_ldisc           -       set line discipline
 551 *      @tty: the terminal to set
 552 *      @ldisc: the line discipline
 553 *
 554 *      Set the discipline of a tty line. Must be called from a process
 555 *      context. The ldisc change logic has to protect itself against any
 556 *      overlapping ldisc change (including on the other end of pty pairs),
 557 *      the close of one side of a tty/pty pair, and eventually hangup.
 558 *
 559 *      Locking: takes tty_ldisc_lock, termios_mutex
 560 */
 561
 562int tty_set_ldisc(struct tty_struct *tty, int ldisc)
 563{
 564        int retval;
 565        struct tty_ldisc *o_ldisc, *new_ldisc;
 566        int work, o_work = 0;
 567        struct tty_struct *o_tty;
 568
 569        new_ldisc = tty_ldisc_get(ldisc);
 570        if (IS_ERR(new_ldisc))
 571                return PTR_ERR(new_ldisc);
 572
 573        tty_lock(tty);
 574        /*
 575         *      We need to look at the tty locking here for pty/tty pairs
 576         *      when both sides try to change in parallel.
 577         */
 578
 579        o_tty = tty->link;      /* o_tty is the pty side or NULL */
 580
 581
 582        /*
 583         *      Check the no-op case
 584         */
 585
 586        if (tty->ldisc->ops->num == ldisc) {
 587                tty_unlock(tty);
 588                tty_ldisc_put(new_ldisc);
 589                return 0;
 590        }
 591
 592        tty_unlock(tty);
 593        /*
 594         *      Problem: What do we do if this blocks ?
 595         *      We could deadlock here
 596         */
 597
 598        tty_wait_until_sent(tty, 0);
 599
 600        tty_lock(tty);
 601        mutex_lock(&tty->ldisc_mutex);
 602
 603        /*
 604         *      We could be midstream of another ldisc change which has
 605         *      dropped the lock during processing. If so we need to wait.
 606         */
 607
 608        while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) {
 609                mutex_unlock(&tty->ldisc_mutex);
 610                tty_unlock(tty);
 611                wait_event(tty_ldisc_wait,
 612                        test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0);
 613                tty_lock(tty);
 614                mutex_lock(&tty->ldisc_mutex);
 615        }
 616
 617        set_bit(TTY_LDISC_CHANGING, &tty->flags);
 618
 619        /*
 620         *      No more input please, we are switching. The new ldisc
 621         *      will update this value in the ldisc open function
 622         */
 623
 624        tty->receive_room = 0;
 625
 626        o_ldisc = tty->ldisc;
 627
 628        tty_unlock(tty);
 629        /*
 630         *      Make sure we don't change while someone holds a
 631         *      reference to the line discipline. The TTY_LDISC bit
 632         *      prevents anyone taking a reference once it is clear.
 633         *      We need the lock to avoid racing reference takers.
 634         *
 635         *      We must clear the TTY_LDISC bit here to avoid a livelock
 636         *      with a userspace app continually trying to use the tty in
 637         *      parallel to the change and re-referencing the tty.
 638         */
 639
 640        work = tty_ldisc_halt(tty);
 641        if (o_tty)
 642                o_work = tty_ldisc_halt(o_tty);
 643
 644        /*
 645         * Wait for ->hangup_work and ->buf.work handlers to terminate.
 646         * We must drop the mutex here in case a hangup is also in process.
 647         */
 648
 649        mutex_unlock(&tty->ldisc_mutex);
 650
 651        tty_ldisc_flush_works(tty);
 652
 653        retval = tty_ldisc_wait_idle(tty, 5 * HZ);
 654
 655        tty_lock(tty);
 656        mutex_lock(&tty->ldisc_mutex);
 657
 658        /* handle wait idle failure locked */
 659        if (retval) {
 660                tty_ldisc_put(new_ldisc);
 661                goto enable;
 662        }
 663
 664        if (test_bit(TTY_HUPPING, &tty->flags)) {
 665                /* We were raced by the hangup method. It will have stomped
 666                   the ldisc data and closed the ldisc down */
 667                clear_bit(TTY_LDISC_CHANGING, &tty->flags);
 668                mutex_unlock(&tty->ldisc_mutex);
 669                tty_ldisc_put(new_ldisc);
 670                tty_unlock(tty);
 671                return -EIO;
 672        }
 673
 674        /* Shutdown the current discipline. */
 675        tty_ldisc_close(tty, o_ldisc);
 676
 677        /* Now set up the new line discipline. */
 678        tty_ldisc_assign(tty, new_ldisc);
 679        tty_set_termios_ldisc(tty, ldisc);
 680
 681        retval = tty_ldisc_open(tty, new_ldisc);
 682        if (retval < 0) {
 683                /* Back to the old one or N_TTY if we can't */
 684                tty_ldisc_put(new_ldisc);
 685                tty_ldisc_restore(tty, o_ldisc);
 686        }
 687
 688        /* At this point we hold a reference to the new ldisc and a
 689           a reference to the old ldisc. If we ended up flipping back
 690           to the existing ldisc we have two references to it */
 691
 692        if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc)
 693                tty->ops->set_ldisc(tty);
 694
 695        tty_ldisc_put(o_ldisc);
 696
 697enable:
 698        /*
 699         *      Allow ldisc referencing to occur again
 700         */
 701
 702        tty_ldisc_enable(tty);
 703        if (o_tty)
 704                tty_ldisc_enable(o_tty);
 705
 706        /* Restart the work queue in case no characters kick it off. Safe if
 707           already running */
 708        if (work)
 709                schedule_work(&tty->port->buf.work);
 710        if (o_work)
 711                schedule_work(&o_tty->port->buf.work);
 712        mutex_unlock(&tty->ldisc_mutex);
 713        tty_unlock(tty);
 714        return retval;
 715}
 716
 717/**
 718 *      tty_reset_termios       -       reset terminal state
 719 *      @tty: tty to reset
 720 *
 721 *      Restore a terminal to the driver default state.
 722 */
 723
 724static void tty_reset_termios(struct tty_struct *tty)
 725{
 726        mutex_lock(&tty->termios_mutex);
 727        tty->termios = tty->driver->init_termios;
 728        tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios);
 729        tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios);
 730        mutex_unlock(&tty->termios_mutex);
 731}
 732
 733
 734/**
 735 *      tty_ldisc_reinit        -       reinitialise the tty ldisc
 736 *      @tty: tty to reinit
 737 *      @ldisc: line discipline to reinitialize
 738 *
 739 *      Switch the tty to a line discipline and leave the ldisc
 740 *      state closed
 741 */
 742
 743static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc)
 744{
 745        struct tty_ldisc *ld = tty_ldisc_get(ldisc);
 746
 747        if (IS_ERR(ld))
 748                return -1;
 749
 750        tty_ldisc_close(tty, tty->ldisc);
 751        tty_ldisc_put(tty->ldisc);
 752        tty->ldisc = NULL;
 753        /*
 754         *      Switch the line discipline back
 755         */
 756        tty_ldisc_assign(tty, ld);
 757        tty_set_termios_ldisc(tty, ldisc);
 758
 759        return 0;
 760}
 761
 762/**
 763 *      tty_ldisc_hangup                -       hangup ldisc reset
 764 *      @tty: tty being hung up
 765 *
 766 *      Some tty devices reset their termios when they receive a hangup
 767 *      event. In that situation we must also switch back to N_TTY properly
 768 *      before we reset the termios data.
 769 *
 770 *      Locking: We can take the ldisc mutex as the rest of the code is
 771 *      careful to allow for this.
 772 *
 773 *      In the pty pair case this occurs in the close() path of the
 774 *      tty itself so we must be careful about locking rules.
 775 */
 776
 777void tty_ldisc_hangup(struct tty_struct *tty)
 778{
 779        struct tty_ldisc *ld;
 780        int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
 781        int err = 0;
 782
 783        /*
 784         * FIXME! What are the locking issues here? This may me overdoing
 785         * things... This question is especially important now that we've
 786         * removed the irqlock.
 787         */
 788        ld = tty_ldisc_ref(tty);
 789        if (ld != NULL) {
 790                /* We may have no line discipline at this point */
 791                if (ld->ops->flush_buffer)
 792                        ld->ops->flush_buffer(tty);
 793                tty_driver_flush_buffer(tty);
 794                if ((test_bit(TTY_DO_WRITE_WAKEUP, &tty->flags)) &&
 795                    ld->ops->write_wakeup)
 796                        ld->ops->write_wakeup(tty);
 797                if (ld->ops->hangup)
 798                        ld->ops->hangup(tty);
 799                tty_ldisc_deref(ld);
 800        }
 801        /*
 802         * FIXME: Once we trust the LDISC code better we can wait here for
 803         * ldisc completion and fix the driver call race
 804         */
 805        wake_up_interruptible_poll(&tty->write_wait, POLLOUT);
 806        wake_up_interruptible_poll(&tty->read_wait, POLLIN);
 807        /*
 808         * Shutdown the current line discipline, and reset it to
 809         * N_TTY if need be.
 810         *
 811         * Avoid racing set_ldisc or tty_ldisc_release
 812         */
 813        mutex_lock(&tty->ldisc_mutex);
 814
 815        /*
 816         * this is like tty_ldisc_halt, but we need to give up
 817         * the BTM before calling cancel_work_sync, which may
 818         * need to wait for another function taking the BTM
 819         */
 820        clear_bit(TTY_LDISC, &tty->flags);
 821        tty_unlock(tty);
 822        cancel_work_sync(&tty->port->buf.work);
 823        mutex_unlock(&tty->ldisc_mutex);
 824retry:
 825        tty_lock(tty);
 826        mutex_lock(&tty->ldisc_mutex);
 827
 828        /* At this point we have a closed ldisc and we want to
 829           reopen it. We could defer this to the next open but
 830           it means auditing a lot of other paths so this is
 831           a FIXME */
 832        if (tty->ldisc) {       /* Not yet closed */
 833                if (atomic_read(&tty->ldisc->users) != 1) {
 834                        char cur_n[TASK_COMM_LEN], tty_n[64];
 835                        long timeout = 3 * HZ;
 836                        tty_unlock(tty);
 837
 838                        while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) {
 839                                timeout = MAX_SCHEDULE_TIMEOUT;
 840                                printk_ratelimited(KERN_WARNING
 841                                        "%s: waiting (%s) for %s took too long, but we keep waiting...\n",
 842                                        __func__, get_task_comm(cur_n, current),
 843                                        tty_name(tty, tty_n));
 844                        }
 845                        mutex_unlock(&tty->ldisc_mutex);
 846                        goto retry;
 847                }
 848
 849                if (reset == 0) {
 850
 851                        if (!tty_ldisc_reinit(tty, tty->termios.c_line))
 852                                err = tty_ldisc_open(tty, tty->ldisc);
 853                        else
 854                                err = 1;
 855                }
 856                /* If the re-open fails or we reset then go to N_TTY. The
 857                   N_TTY open cannot fail */
 858                if (reset || err) {
 859                        BUG_ON(tty_ldisc_reinit(tty, N_TTY));
 860                        WARN_ON(tty_ldisc_open(tty, tty->ldisc));
 861                }
 862                tty_ldisc_enable(tty);
 863        }
 864        mutex_unlock(&tty->ldisc_mutex);
 865        if (reset)
 866                tty_reset_termios(tty);
 867}
 868
 869/**
 870 *      tty_ldisc_setup                 -       open line discipline
 871 *      @tty: tty being shut down
 872 *      @o_tty: pair tty for pty/tty pairs
 873 *
 874 *      Called during the initial open of a tty/pty pair in order to set up the
 875 *      line disciplines and bind them to the tty. This has no locking issues
 876 *      as the device isn't yet active.
 877 */
 878
 879int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty)
 880{
 881        struct tty_ldisc *ld = tty->ldisc;
 882        int retval;
 883
 884        retval = tty_ldisc_open(tty, ld);
 885        if (retval)
 886                return retval;
 887
 888        if (o_tty) {
 889                retval = tty_ldisc_open(o_tty, o_tty->ldisc);
 890                if (retval) {
 891                        tty_ldisc_close(tty, ld);
 892                        return retval;
 893                }
 894                tty_ldisc_enable(o_tty);
 895        }
 896        tty_ldisc_enable(tty);
 897        return 0;
 898}
 899
 900static void tty_ldisc_kill(struct tty_struct *tty)
 901{
 902        /* There cannot be users from userspace now. But there still might be
 903         * drivers holding a reference via tty_ldisc_ref. Do not steal them the
 904         * ldisc until they are done. */
 905        tty_ldisc_wait_idle(tty, MAX_SCHEDULE_TIMEOUT);
 906
 907        mutex_lock(&tty->ldisc_mutex);
 908        /*
 909         * Now kill off the ldisc
 910         */
 911        tty_ldisc_close(tty, tty->ldisc);
 912        tty_ldisc_put(tty->ldisc);
 913        /* Force an oops if we mess this up */
 914        tty->ldisc = NULL;
 915
 916        /* Ensure the next open requests the N_TTY ldisc */
 917        tty_set_termios_ldisc(tty, N_TTY);
 918        mutex_unlock(&tty->ldisc_mutex);
 919}
 920
 921/**
 922 *      tty_ldisc_release               -       release line discipline
 923 *      @tty: tty being shut down
 924 *      @o_tty: pair tty for pty/tty pairs
 925 *
 926 *      Called during the final close of a tty/pty pair in order to shut down
 927 *      the line discpline layer. On exit the ldisc assigned is N_TTY and the
 928 *      ldisc has not been opened.
 929 */
 930
 931void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty)
 932{
 933        /*
 934         * Prevent flush_to_ldisc() from rescheduling the work for later.  Then
 935         * kill any delayed work. As this is the final close it does not
 936         * race with the set_ldisc code path.
 937         */
 938
 939        tty_ldisc_halt(tty);
 940        if (o_tty)
 941                tty_ldisc_halt(o_tty);
 942
 943        tty_ldisc_flush_works(tty);
 944        if (o_tty)
 945                tty_ldisc_flush_works(o_tty);
 946
 947        tty_lock_pair(tty, o_tty);
 948        /* This will need doing differently if we need to lock */
 949        tty_ldisc_kill(tty);
 950        if (o_tty)
 951                tty_ldisc_kill(o_tty);
 952
 953        tty_unlock_pair(tty, o_tty);
 954        /* And the memory resources remaining (buffers, termios) will be
 955           disposed of when the kref hits zero */
 956}
 957
 958/**
 959 *      tty_ldisc_init          -       ldisc setup for new tty
 960 *      @tty: tty being allocated
 961 *
 962 *      Set up the line discipline objects for a newly allocated tty. Note that
 963 *      the tty structure is not completely set up when this call is made.
 964 */
 965
 966void tty_ldisc_init(struct tty_struct *tty)
 967{
 968        struct tty_ldisc *ld = tty_ldisc_get(N_TTY);
 969        if (IS_ERR(ld))
 970                panic("n_tty: init_tty");
 971        tty_ldisc_assign(tty, ld);
 972}
 973
 974/**
 975 *      tty_ldisc_init          -       ldisc cleanup for new tty
 976 *      @tty: tty that was allocated recently
 977 *
 978 *      The tty structure must not becompletely set up (tty_ldisc_setup) when
 979 *      this call is made.
 980 */
 981void tty_ldisc_deinit(struct tty_struct *tty)
 982{
 983        put_ldisc(tty->ldisc);
 984        tty_ldisc_assign(tty, NULL);
 985}
 986
 987void tty_ldisc_begin(void)
 988{
 989        /* Setup the default TTY line discipline. */
 990        (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY);
 991}
 992
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