arch/um/os-Linux/sigio.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2002 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   4  */
   5
   6 #include <unistd.h>
   7 #include <errno.h>
   8 #include <fcntl.h>
   9 #include <poll.h>
  10 #include <pty.h>
  11 #include <sched.h>
  12 #include <signal.h>
  13 #include <string.h>
  14 #include <kern_util.h>
  15 #include <init.h>
  16 #include <os.h>
  17 #include <sigio.h>
  18 #include <um_malloc.h>
  19
  20 /*
  21  * Protected by sigio_lock(), also used by sigio_cleanup, which is an
  22  * exitcall.
  23  */
  24 static int write_sigio_pid = -1;
  25 static unsigned long write_sigio_stack;
  26
  27 /*
  28  * These arrays are initialized before the sigio thread is started, and
  29  * the descriptors closed after it is killed.  So, it can't see them change.
  30  * On the UML side, they are changed under the sigio_lock.
  31  */
  32 #define SIGIO_FDS_INIT {-1, -1}
  33
  34 static int write_sigio_fds[2] = SIGIO_FDS_INIT;
  35 static int sigio_private[2] = SIGIO_FDS_INIT;
  36
  37 struct pollfds {
  38         struct pollfd *poll;
  39         int size;
  40         int used;
  41 };
  42
  43 /*
  44  * Protected by sigio_lock().  Used by the sigio thread, but the UML thread
  45  * synchronizes with it.
  46  */
  47 static struct pollfds current_poll;
  48 static struct pollfds next_poll;
  49 static struct pollfds all_sigio_fds;
  50
  51 static int write_sigio_thread(void *unused)
  52 {
  53         struct pollfds *fds, tmp;
  54         struct pollfd *p;
  55         int i, n, respond_fd;
  56         char c;
  57
  58         os_fix_helper_signals();
  59         fds = &current_poll;
  60         while (1) {
  61                 n = poll(fds->poll, fds->used, -1);
  62                 if (n < 0) {
  63                         if (errno == EINTR)
  64                                 continue;
  65                         printk(UM_KERN_ERR "write_sigio_thread : poll returned "
  66                                "%d, errno = %d\n", n, errno);
  67                 }
  68                 for (i = 0; i < fds->used; i++) {
  69                         p = &fds->poll[i];
  70                         if (p->revents == 0)
  71                                 continue;
  72                         if (p->fd == sigio_private[1]) {
  73                                 CATCH_EINTR(n = read(sigio_private[1], &c,
  74                                                      sizeof(c)));
  75                                 if (n != sizeof(c))
  76                                         printk(UM_KERN_ERR
  77                                                "write_sigio_thread : "
  78                                                "read on socket failed, "
  79                                                "err = %d\n", errno);
  80                                 tmp = current_poll;
  81                                 current_poll = next_poll;
  82                                 next_poll = tmp;
  83                                 respond_fd = sigio_private[1];
  84                         }
  85                         else {
  86                                 respond_fd = write_sigio_fds[1];
  87                                 fds->used--;
  88                                 memmove(&fds->poll[i], &fds->poll[i + 1],
  89                                         (fds->used - i) * sizeof(*fds->poll));
  90                         }
  91
  92                         CATCH_EINTR(n = write(respond_fd, &c, sizeof(c)));
  93                         if (n != sizeof(c))
  94                                 printk(UM_KERN_ERR "write_sigio_thread : "
  95                                        "write on socket failed, err = %d\n",
  96                                        errno);
  97                 }
  98         }
  99
 100         return 0;
 101 }
 102
 103 static int need_poll(struct pollfds *polls, int n)
 104 {
 105         struct pollfd *new;
 106
 107         if (n <= polls->size)
 108                 return 0;
 109
 110         new = uml_kmalloc(n * sizeof(struct pollfd), UM_GFP_ATOMIC);
 111         if (new == NULL) {
 112                 printk(UM_KERN_ERR "need_poll : failed to allocate new "
 113                        "pollfds\n");
 114                 return -ENOMEM;
 115         }
 116
 117         memcpy(new, polls->poll, polls->used * sizeof(struct pollfd));
 118         kfree(polls->poll);
 119
 120         polls->poll = new;
 121         polls->size = n;
 122         return 0;
 123 }
 124
 125 /*
 126  * Must be called with sigio_lock held, because it's needed by the marked
 127  * critical section.
 128  */
 129 static void update_thread(void)
 130 {
 131         unsigned long flags;
 132         int n;
 133         char c;
 134
 135         flags = set_signals_trace(0);
 136         CATCH_EINTR(n = write(sigio_private[0], &c, sizeof(c)));
 137         if (n != sizeof(c)) {
 138                 printk(UM_KERN_ERR "update_thread : write failed, err = %d\n",
 139                        errno);
 140                 goto fail;
 141         }
 142
 143         CATCH_EINTR(n = read(sigio_private[0], &c, sizeof(c)));
 144         if (n != sizeof(c)) {
 145                 printk(UM_KERN_ERR "update_thread : read failed, err = %d\n",
 146                        errno);
 147                 goto fail;
 148         }
 149
 150         set_signals_trace(flags);
 151         return;
 152  fail:
 153         /* Critical section start */
 154         if (write_sigio_pid != -1) {
 155                 os_kill_process(write_sigio_pid, 1);
 156                 free_stack(write_sigio_stack, 0);
 157         }
 158         write_sigio_pid = -1;
 159         close(sigio_private[0]);
 160         close(sigio_private[1]);
 161         close(write_sigio_fds[0]);
 162         close(write_sigio_fds[1]);
 163         /* Critical section end */
 164         set_signals_trace(flags);
 165 }
 166
 167 int __add_sigio_fd(int fd)
 168 {
 169         struct pollfd *p;
 170         int err, i, n;
 171
 172         for (i = 0; i < all_sigio_fds.used; i++) {
 173                 if (all_sigio_fds.poll[i].fd == fd)
 174                         break;
 175         }
 176         if (i == all_sigio_fds.used)
 177                 return -ENOSPC;
 178
 179         p = &all_sigio_fds.poll[i];
 180
 181         for (i = 0; i < current_poll.used; i++) {
 182                 if (current_poll.poll[i].fd == fd)
 183                         return 0;
 184         }
 185
 186         n = current_poll.used;
 187         err = need_poll(&next_poll, n + 1);
 188         if (err)
 189                 return err;
 190
 191         memcpy(next_poll.poll, current_poll.poll,
 192                current_poll.used * sizeof(struct pollfd));
 193         next_poll.poll[n] = *p;
 194         next_poll.used = n + 1;
 195         update_thread();
 196
 197         return 0;
 198 }
 199
 200
 201 int add_sigio_fd(int fd)
 202 {
 203         int err;
 204
 205         sigio_lock();
 206         err = __add_sigio_fd(fd);
 207         sigio_unlock();
 208
 209         return err;
 210 }
 211
 212 int __ignore_sigio_fd(int fd)
 213 {
 214         struct pollfd *p;
 215         int err, i, n = 0;
 216
 217         /*
 218          * This is called from exitcalls elsewhere in UML - if
 219          * sigio_cleanup has already run, then update_thread will hang
 220          * or fail because the thread is no longer running.
 221          */
 222         if (write_sigio_pid == -1)
 223                 return -EIO;
 224
 225         for (i = 0; i < current_poll.used; i++) {
 226                 if (current_poll.poll[i].fd == fd)
 227                         break;
 228         }
 229         if (i == current_poll.used)
 230                 return -ENOENT;
 231
 232         err = need_poll(&next_poll, current_poll.used - 1);
 233         if (err)
 234                 return err;
 235
 236         for (i = 0; i < current_poll.used; i++) {
 237                 p = &current_poll.poll[i];
 238                 if (p->fd != fd)
 239                         next_poll.poll[n++] = *p;
 240         }
 241         next_poll.used = current_poll.used - 1;
 242
 243         update_thread();
 244
 245         return 0;
 246 }
 247
 248 int ignore_sigio_fd(int fd)
 249 {
 250         int err;
 251
 252         sigio_lock();
 253         err = __ignore_sigio_fd(fd);
 254         sigio_unlock();
 255
 256         return err;
 257 }
 258
 259 static struct pollfd *setup_initial_poll(int fd)
 260 {
 261         struct pollfd *p;
 262
 263         p = uml_kmalloc(sizeof(struct pollfd), UM_GFP_KERNEL);
 264         if (p == NULL) {
 265                 printk(UM_KERN_ERR "setup_initial_poll : failed to allocate "
 266                        "poll\n");
 267                 return NULL;
 268         }
 269         *p = ((struct pollfd) { .fd             = fd,
 270                                 .events         = POLLIN,
 271                                 .revents        = 0 });
 272         return p;
 273 }
 274
 275 static void write_sigio_workaround(void)
 276 {
 277         struct pollfd *p;
 278         int err;
 279         int l_write_sigio_fds[2];
 280         int l_sigio_private[2];
 281         int l_write_sigio_pid;
 282
 283         /* We call this *tons* of times - and most ones we must just fail. */
 284         sigio_lock();
 285         l_write_sigio_pid = write_sigio_pid;
 286         sigio_unlock();
 287
 288         if (l_write_sigio_pid != -1)
 289                 return;
 290
 291         err = os_pipe(l_write_sigio_fds, 1, 1);
 292         if (err < 0) {
 293                 printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 1 failed, "
 294                        "err = %d\n", -err);
 295                 return;
 296         }
 297         err = os_pipe(l_sigio_private, 1, 1);
 298         if (err < 0) {
 299                 printk(UM_KERN_ERR "write_sigio_workaround - os_pipe 2 failed, "
 300                        "err = %d\n", -err);
 301                 goto out_close1;
 302         }
 303
 304         p = setup_initial_poll(l_sigio_private[1]);
 305         if (!p)
 306                 goto out_close2;
 307
 308         sigio_lock();
 309
 310         /*
 311          * Did we race? Don't try to optimize this, please, it's not so likely
 312          * to happen, and no more than once at the boot.
 313          */
 314         if (write_sigio_pid != -1)
 315                 goto out_free;
 316
 317         current_poll = ((struct pollfds) { .poll        = p,
 318                                            .used        = 1,
 319                                            .size        = 1 });
 320
 321         if (write_sigio_irq(l_write_sigio_fds[0]))
 322                 goto out_clear_poll;
 323
 324         memcpy(write_sigio_fds, l_write_sigio_fds, sizeof(l_write_sigio_fds));
 325         memcpy(sigio_private, l_sigio_private, sizeof(l_sigio_private));
 326
 327         write_sigio_pid = run_helper_thread(write_sigio_thread, NULL,
 328                                             CLONE_FILES | CLONE_VM,
 329                                             &write_sigio_stack);
 330
 331         if (write_sigio_pid < 0)
 332                 goto out_clear;
 333
 334         sigio_unlock();
 335         return;
 336
 337 out_clear:
 338         write_sigio_pid = -1;
 339         write_sigio_fds[0] = -1;
 340         write_sigio_fds[1] = -1;
 341         sigio_private[0] = -1;
 342         sigio_private[1] = -1;
 343 out_clear_poll:
 344         current_poll = ((struct pollfds) { .poll        = NULL,
 345                                            .size        = 0,
 346                                            .used        = 0 });
 347 out_free:
 348         sigio_unlock();
 349         kfree(p);
 350 out_close2:
 351         close(l_sigio_private[0]);
 352         close(l_sigio_private[1]);
 353 out_close1:
 354         close(l_write_sigio_fds[0]);
 355         close(l_write_sigio_fds[1]);
 356 }
 357
 358 void sigio_broken(int fd)
 359 {
 360         int err;
 361
 362         write_sigio_workaround();
 363
 364         sigio_lock();
 365         err = need_poll(&all_sigio_fds, all_sigio_fds.used + 1);
 366         if (err) {
 367                 printk(UM_KERN_ERR "maybe_sigio_broken - failed to add pollfd "
 368                        "for descriptor %d\n", fd);
 369                 goto out;
 370         }
 371
 372         all_sigio_fds.poll[all_sigio_fds.used++] =
 373                 ((struct pollfd) { .fd          = fd,
 374                                    .events      = POLLIN,
 375                                    .revents     = 0 });
 376 out:
 377         sigio_unlock();
 378 }
 379
 380 /* Changed during early boot */
 381 static int pty_output_sigio;
 382
 383 void maybe_sigio_broken(int fd)
 384 {
 385         if (!isatty(fd))
 386                 return;
 387
 388         if (pty_output_sigio)
 389                 return;
 390
 391         sigio_broken(fd);
 392 }
 393
 394 static void sigio_cleanup(void)
 395 {
 396         if (write_sigio_pid == -1)
 397                 return;
 398
 399         os_kill_process(write_sigio_pid, 1);
 400         free_stack(write_sigio_stack, 0);
 401         write_sigio_pid = -1;
 402 }
 403
 404 __uml_exitcall(sigio_cleanup);
 405
 406 /* Used as a flag during SIGIO testing early in boot */
 407 static int got_sigio;
 408
 409 static void __init handler(int sig)
 410 {
 411         got_sigio = 1;
 412 }
 413
 414 struct openpty_arg {
 415         int master;
 416         int slave;
 417         int err;
 418 };
 419
 420 static void openpty_cb(void *arg)
 421 {
 422         struct openpty_arg *info = arg;
 423
 424         info->err = 0;
 425         if (openpty(&info->master, &info->slave, NULL, NULL, NULL))
 426                 info->err = -errno;
 427 }
 428
 429 static int async_pty(int master, int slave)
 430 {
 431         int flags;
 432
 433         flags = fcntl(master, F_GETFL);
 434         if (flags < 0)
 435                 return -errno;
 436
 437         if ((fcntl(master, F_SETFL, flags | O_NONBLOCK | O_ASYNC) < 0) ||
 438             (fcntl(master, F_SETOWN, os_getpid()) < 0))
 439                 return -errno;
 440
 441         if ((fcntl(slave, F_SETFL, flags | O_NONBLOCK) < 0))
 442                 return -errno;
 443
 444         return 0;
 445 }
 446
 447 static void __init check_one_sigio(void (*proc)(int, int))
 448 {
 449         struct sigaction old, new;
 450         struct openpty_arg pty = { .master = -1, .slave = -1 };
 451         int master, slave, err;
 452
 453         initial_thread_cb(openpty_cb, &pty);
 454         if (pty.err) {
 455                 printk(UM_KERN_ERR "check_one_sigio failed, errno = %d\n",
 456                        -pty.err);
 457                 return;
 458         }
 459
 460         master = pty.master;
 461         slave = pty.slave;
 462
 463         if ((master == -1) || (slave == -1)) {
 464                 printk(UM_KERN_ERR "check_one_sigio failed to allocate a "
 465                        "pty\n");
 466                 return;
 467         }
 468
 469         /* Not now, but complain so we now where we failed. */
 470         err = raw(master);
 471         if (err < 0) {
 472                 printk(UM_KERN_ERR "check_one_sigio : raw failed, errno = %d\n",
 473                       -err);
 474                 return;
 475         }
 476
 477         err = async_pty(master, slave);
 478         if (err < 0) {
 479                 printk(UM_KERN_ERR "check_one_sigio : sigio_async failed, "
 480                        "err = %d\n", -err);
 481                 return;
 482         }
 483
 484         if (sigaction(SIGIO, NULL, &old) < 0) {
 485                 printk(UM_KERN_ERR "check_one_sigio : sigaction 1 failed, "
 486                        "errno = %d\n", errno);
 487                 return;
 488         }
 489
 490         new = old;
 491         new.sa_handler = handler;
 492         if (sigaction(SIGIO, &new, NULL) < 0) {
 493                 printk(UM_KERN_ERR "check_one_sigio : sigaction 2 failed, "
 494                        "errno = %d\n", errno);
 495                 return;
 496         }
 497
 498         got_sigio = 0;
 499         (*proc)(master, slave);
 500
 501         close(master);
 502         close(slave);
 503
 504         if (sigaction(SIGIO, &old, NULL) < 0)
 505                 printk(UM_KERN_ERR "check_one_sigio : sigaction 3 failed, "
 506                        "errno = %d\n", errno);
 507 }
 508
 509 static void tty_output(int master, int slave)
 510 {
 511         int n;
 512         char buf[512];
 513
 514         printk(UM_KERN_INFO "Checking that host ptys support output SIGIO...");
 515
 516         memset(buf, 0, sizeof(buf));
 517
 518         while (write(master, buf, sizeof(buf)) > 0) ;
 519         if (errno != EAGAIN)
 520                 printk(UM_KERN_ERR "tty_output : write failed, errno = %d\n",
 521                        errno);
 522         while (((n = read(slave, buf, sizeof(buf))) > 0) &&
 523                !({ barrier(); got_sigio; }))
 524                 ;
 525
 526         if (got_sigio) {
 527                 printk(UM_KERN_CONT "Yes\n");
 528                 pty_output_sigio = 1;
 529         } else if (n == -EAGAIN)
 530                 printk(UM_KERN_CONT "No, enabling workaround\n");
 531         else
 532                 printk(UM_KERN_CONT "tty_output : read failed, err = %d\n", n);
 533 }
 534
 535 static void __init check_sigio(void)
 536 {
 537         if ((access("/dev/ptmx", R_OK) < 0) &&
 538             (access("/dev/ptyp0", R_OK) < 0)) {
 539                 printk(UM_KERN_WARNING "No pseudo-terminals available - "
 540                        "skipping pty SIGIO check\n");
 541                 return;
 542         }
 543         check_one_sigio(tty_output);
 544 }
 545
 546 /* Here because it only does the SIGIO testing for now */
 547 void __init os_check_bugs(void)
 548 {
 549         check_sigio();
 550 }