util/oslib-posix.c

   1 /*
   2  * os-posix-lib.c
   3  *
   4  * Copyright (c) 2003-2008 Fabrice Bellard
   5  * Copyright (c) 2010 Red Hat, Inc.
   6  *
   7  * QEMU library functions on POSIX which are shared between QEMU and
   8  * the QEMU tools.
   9  *
  10  * Permission is hereby granted, free of charge, to any person obtaining a copy
  11  * of this software and associated documentation files (the "Software"), to deal
  12  * in the Software without restriction, including without limitation the rights
  13  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  14  * copies of the Software, and to permit persons to whom the Software is
  15  * furnished to do so, subject to the following conditions:
  16  *
  17  * The above copyright notice and this permission notice shall be included in
  18  * all copies or substantial portions of the Software.
  19  *
  20  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  21  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  23  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  24  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  25  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  26  * THE SOFTWARE.
  27  */
  28
  29 #include "qemu/osdep.h"
  30 #include <termios.h>
  31
  32 #include <glib/gprintf.h>
  33
  34 #include "sysemu/sysemu.h"
  35 #include "trace.h"
  36 #include "qapi/error.h"
  37 #include "qemu/sockets.h"
  38 #include <libgen.h>
  39 #include <sys/signal.h>
  40 #include "qemu/cutils.h"
  41
  42 #ifdef CONFIG_LINUX
  43 #include <sys/syscall.h>
  44 #endif
  45
  46 #ifdef __FreeBSD__
  47 #include <sys/sysctl.h>
  48 #include <sys/user.h>
  49 #include <libutil.h>
  50 #endif
  51
  52 #ifdef __NetBSD__
  53 #include <sys/sysctl.h>
  54 #endif
  55
  56 #include "qemu/mmap-alloc.h"
  57
  58 #ifdef CONFIG_DEBUG_STACK_USAGE
  59 #include "qemu/error-report.h"
  60 #endif
  61
  62 #define MAX_MEM_PREALLOC_THREAD_COUNT 16
  63
  64 struct MemsetThread {
  65     char *addr;
  66     size_t numpages;
  67     size_t hpagesize;
  68     QemuThread pgthread;
  69     sigjmp_buf env;
  70 };
  71 typedef struct MemsetThread MemsetThread;
  72
  73 static MemsetThread *memset_thread;
  74 static int memset_num_threads;
  75 static bool memset_thread_failed;
  76
  77 int qemu_get_thread_id(void)
  78 {
  79 #if defined(__linux__)
  80     return syscall(SYS_gettid);
  81 #else
  82     return getpid();
  83 #endif
  84 }
  85
  86 int qemu_daemon(int nochdir, int noclose)
  87 {
  88     return daemon(nochdir, noclose);
  89 }
  90
  91 bool qemu_write_pidfile(const char *path, Error **errp)
  92 {
  93     int fd;
  94     char pidstr[32];
  95
  96     while (1) {
  97         struct stat a, b;
  98         struct flock lock = {
  99             .l_type = F_WRLCK,
 100             .l_whence = SEEK_SET,
 101             .l_len = 0,
 102         };
 103
 104         fd = qemu_open(path, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
 105         if (fd == -1) {
 106             error_setg_errno(errp, errno, "Cannot open pid file");
 107             return false;
 108         }
 109
 110         if (fstat(fd, &b) < 0) {
 111             error_setg_errno(errp, errno, "Cannot stat file");
 112             goto fail_close;
 113         }
 114
 115         if (fcntl(fd, F_SETLK, &lock)) {
 116             error_setg_errno(errp, errno, "Cannot lock pid file");
 117             goto fail_close;
 118         }
 119
 120         /*
 121          * Now make sure the path we locked is the same one that now
 122          * exists on the filesystem.
 123          */
 124         if (stat(path, &a) < 0) {
 125             /*
 126              * PID file disappeared, someone else must be racing with
 127              * us, so try again.
 128              */
 129             close(fd);
 130             continue;
 131         }
 132
 133         if (a.st_ino == b.st_ino) {
 134             break;
 135         }
 136
 137         /*
 138          * PID file was recreated, someone else must be racing with
 139          * us, so try again.
 140          */
 141         close(fd);
 142     }
 143
 144     if (ftruncate(fd, 0) < 0) {
 145         error_setg_errno(errp, errno, "Failed to truncate pid file");
 146         goto fail_unlink;
 147     }
 148
 149     snprintf(pidstr, sizeof(pidstr), FMT_pid "\n", getpid());
 150     if (write(fd, pidstr, strlen(pidstr)) != strlen(pidstr)) {
 151         error_setg(errp, "Failed to write pid file");
 152         goto fail_unlink;
 153     }
 154
 155     return true;
 156
 157 fail_unlink:
 158     unlink(path);
 159 fail_close:
 160     close(fd);
 161     return false;
 162 }
 163
 164 void *qemu_oom_check(void *ptr)
 165 {
 166     if (ptr == NULL) {
 167         fprintf(stderr, "Failed to allocate memory: %s\n", strerror(errno));
 168         abort();
 169     }
 170     return ptr;
 171 }
 172
 173 void *qemu_try_memalign(size_t alignment, size_t size)
 174 {
 175     void *ptr;
 176
 177     if (alignment < sizeof(void*)) {
 178         alignment = sizeof(void*);
 179     }
 180
 181 #if defined(CONFIG_POSIX_MEMALIGN)
 182     int ret;
 183     ret = posix_memalign(&ptr, alignment, size);
 184     if (ret != 0) {
 185         errno = ret;
 186         ptr = NULL;
 187     }
 188 #elif defined(CONFIG_BSD)
 189     ptr = valloc(size);
 190 #else
 191     ptr = memalign(alignment, size);
 192 #endif
 193     trace_qemu_memalign(alignment, size, ptr);
 194     return ptr;
 195 }
 196
 197 void *qemu_memalign(size_t alignment, size_t size)
 198 {
 199     return qemu_oom_check(qemu_try_memalign(alignment, size));
 200 }
 201
 202 /* alloc shared memory pages */
 203 void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared)
 204 {
 205     size_t align = QEMU_VMALLOC_ALIGN;
 206     void *ptr = qemu_ram_mmap(-1, size, align, shared);
 207
 208     if (ptr == MAP_FAILED) {
 209         return NULL;
 210     }
 211
 212     if (alignment) {
 213         *alignment = align;
 214     }
 215
 216     trace_qemu_anon_ram_alloc(size, ptr);
 217     return ptr;
 218 }
 219
 220 void qemu_vfree(void *ptr)
 221 {
 222     trace_qemu_vfree(ptr);
 223     free(ptr);
 224 }
 225
 226 void qemu_anon_ram_free(void *ptr, size_t size)
 227 {
 228     trace_qemu_anon_ram_free(ptr, size);
 229     qemu_ram_munmap(ptr, size);
 230 }
 231
 232 void qemu_set_block(int fd)
 233 {
 234     int f;
 235     f = fcntl(fd, F_GETFL);
 236     assert(f != -1);
 237     f = fcntl(fd, F_SETFL, f & ~O_NONBLOCK);
 238     assert(f != -1);
 239 }
 240
 241 void qemu_set_nonblock(int fd)
 242 {
 243     int f;
 244     f = fcntl(fd, F_GETFL);
 245     assert(f != -1);
 246     f = fcntl(fd, F_SETFL, f | O_NONBLOCK);
 247     assert(f != -1);
 248 }
 249
 250 int socket_set_fast_reuse(int fd)
 251 {
 252     int val = 1, ret;
 253
 254     ret = setsockopt(fd, SOL_SOCKET, SO_REUSEADDR,
 255                      (const char *)&val, sizeof(val));
 256
 257     assert(ret == 0);
 258
 259     return ret;
 260 }
 261
 262 void qemu_set_cloexec(int fd)
 263 {
 264     int f;
 265     f = fcntl(fd, F_GETFD);
 266     assert(f != -1);
 267     f = fcntl(fd, F_SETFD, f | FD_CLOEXEC);
 268     assert(f != -1);
 269 }
 270
 271 /*
 272  * Creates a pipe with FD_CLOEXEC set on both file descriptors
 273  */
 274 int qemu_pipe(int pipefd[2])
 275 {
 276     int ret;
 277
 278 #ifdef CONFIG_PIPE2
 279     ret = pipe2(pipefd, O_CLOEXEC);
 280     if (ret != -1 || errno != ENOSYS) {
 281         return ret;
 282     }
 283 #endif
 284     ret = pipe(pipefd);
 285     if (ret == 0) {
 286         qemu_set_cloexec(pipefd[0]);
 287         qemu_set_cloexec(pipefd[1]);
 288     }
 289
 290     return ret;
 291 }
 292
 293 char *
 294 qemu_get_local_state_pathname(const char *relative_pathname)
 295 {
 296     return g_strdup_printf("%s/%s", CONFIG_QEMU_LOCALSTATEDIR,
 297                            relative_pathname);
 298 }
 299
 300 void qemu_set_tty_echo(int fd, bool echo)
 301 {
 302     struct termios tty;
 303
 304     tcgetattr(fd, &tty);
 305
 306     if (echo) {
 307         tty.c_lflag |= ECHO | ECHONL | ICANON | IEXTEN;
 308     } else {
 309         tty.c_lflag &= ~(ECHO | ECHONL | ICANON | IEXTEN);
 310     }
 311
 312     tcsetattr(fd, TCSANOW, &tty);
 313 }
 314
 315 static char exec_dir[PATH_MAX];
 316
 317 void qemu_init_exec_dir(const char *argv0)
 318 {
 319     char *dir;
 320     char *p = NULL;
 321     char buf[PATH_MAX];
 322
 323     assert(!exec_dir[0]);
 324
 325 #if defined(__linux__)
 326     {
 327         int len;
 328         len = readlink("/proc/self/exe", buf, sizeof(buf) - 1);
 329         if (len > 0) {
 330             buf[len] = 0;
 331             p = buf;
 332         }
 333     }
 334 #elif defined(__FreeBSD__) \
 335       || (defined(__NetBSD__) && defined(KERN_PROC_PATHNAME))
 336     {
 337 #if defined(__FreeBSD__)
 338         static int mib[4] = {CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1};
 339 #else
 340         static int mib[4] = {CTL_KERN, KERN_PROC_ARGS, -1, KERN_PROC_PATHNAME};
 341 #endif
 342         size_t len = sizeof(buf) - 1;
 343
 344         *buf = '\0';
 345         if (!sysctl(mib, ARRAY_SIZE(mib), buf, &len, NULL, 0) &&
 346             *buf) {
 347             buf[sizeof(buf) - 1] = '\0';
 348             p = buf;
 349         }
 350     }
 351 #endif
 352     /* If we don't have any way of figuring out the actual executable
 353        location then try argv[0].  */
 354     if (!p) {
 355         if (!argv0) {
 356             return;
 357         }
 358         p = realpath(argv0, buf);
 359         if (!p) {
 360             return;
 361         }
 362     }
 363     dir = g_path_get_dirname(p);
 364
 365     pstrcpy(exec_dir, sizeof(exec_dir), dir);
 366
 367     g_free(dir);
 368 }
 369
 370 char *qemu_get_exec_dir(void)
 371 {
 372     return g_strdup(exec_dir);
 373 }
 374
 375 static void sigbus_handler(int signal)
 376 {
 377     int i;
 378     if (memset_thread) {
 379         for (i = 0; i < memset_num_threads; i++) {
 380             if (qemu_thread_is_self(&memset_thread[i].pgthread)) {
 381                 siglongjmp(memset_thread[i].env, 1);
 382             }
 383         }
 384     }
 385 }
 386
 387 static void *do_touch_pages(void *arg)
 388 {
 389     MemsetThread *memset_args = (MemsetThread *)arg;
 390     sigset_t set, oldset;
 391
 392     /* unblock SIGBUS */
 393     sigemptyset(&set);
 394     sigaddset(&set, SIGBUS);
 395     pthread_sigmask(SIG_UNBLOCK, &set, &oldset);
 396
 397     if (sigsetjmp(memset_args->env, 1)) {
 398         memset_thread_failed = true;
 399     } else {
 400         char *addr = memset_args->addr;
 401         size_t numpages = memset_args->numpages;
 402         size_t hpagesize = memset_args->hpagesize;
 403         size_t i;
 404         for (i = 0; i < numpages; i++) {
 405             /*
 406              * Read & write back the same value, so we don't
 407              * corrupt existing user/app data that might be
 408              * stored.
 409              *
 410              * 'volatile' to stop compiler optimizing this away
 411              * to a no-op
 412              *
 413              * TODO: get a better solution from kernel so we
 414              * don't need to write at all so we don't cause
 415              * wear on the storage backing the region...
 416              */
 417             *(volatile char *)addr = *addr;
 418             addr += hpagesize;
 419         }
 420     }
 421     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 422     return NULL;
 423 }
 424
 425 static inline int get_memset_num_threads(int smp_cpus)
 426 {
 427     long host_procs = sysconf(_SC_NPROCESSORS_ONLN);
 428     int ret = 1;
 429
 430     if (host_procs > 0) {
 431         ret = MIN(MIN(host_procs, MAX_MEM_PREALLOC_THREAD_COUNT), smp_cpus);
 432     }
 433     /* In case sysconf() fails, we fall back to single threaded */
 434     return ret;
 435 }
 436
 437 static bool touch_all_pages(char *area, size_t hpagesize, size_t numpages,
 438                             int smp_cpus)
 439 {
 440     size_t numpages_per_thread;
 441     size_t size_per_thread;
 442     char *addr = area;
 443     int i = 0;
 444
 445     memset_thread_failed = false;
 446     memset_num_threads = get_memset_num_threads(smp_cpus);
 447     memset_thread = g_new0(MemsetThread, memset_num_threads);
 448     numpages_per_thread = (numpages / memset_num_threads);
 449     size_per_thread = (hpagesize * numpages_per_thread);
 450     for (i = 0; i < memset_num_threads; i++) {
 451         memset_thread[i].addr = addr;
 452         memset_thread[i].numpages = (i == (memset_num_threads - 1)) ?
 453                                     numpages : numpages_per_thread;
 454         memset_thread[i].hpagesize = hpagesize;
 455         qemu_thread_create(&memset_thread[i].pgthread, "touch_pages",
 456                            do_touch_pages, &memset_thread[i],
 457                            QEMU_THREAD_JOINABLE);
 458         addr += size_per_thread;
 459         numpages -= numpages_per_thread;
 460     }
 461     for (i = 0; i < memset_num_threads; i++) {
 462         qemu_thread_join(&memset_thread[i].pgthread);
 463     }
 464     g_free(memset_thread);
 465     memset_thread = NULL;
 466
 467     return memset_thread_failed;
 468 }
 469
 470 void os_mem_prealloc(int fd, char *area, size_t memory, int smp_cpus,
 471                      Error **errp)
 472 {
 473     int ret;
 474     struct sigaction act, oldact;
 475     size_t hpagesize = qemu_fd_getpagesize(fd);
 476     size_t numpages = DIV_ROUND_UP(memory, hpagesize);
 477
 478     memset(&act, 0, sizeof(act));
 479     act.sa_handler = &sigbus_handler;
 480     act.sa_flags = 0;
 481
 482     ret = sigaction(SIGBUS, &act, &oldact);
 483     if (ret) {
 484         error_setg_errno(errp, errno,
 485             "os_mem_prealloc: failed to install signal handler");
 486         return;
 487     }
 488
 489     /* touch pages simultaneously */
 490     if (touch_all_pages(area, hpagesize, numpages, smp_cpus)) {
 491         error_setg(errp, "os_mem_prealloc: Insufficient free host memory "
 492             "pages available to allocate guest RAM");
 493     }
 494
 495     ret = sigaction(SIGBUS, &oldact, NULL);
 496     if (ret) {
 497         /* Terminate QEMU since it can't recover from error */
 498         perror("os_mem_prealloc: failed to reinstall signal handler");
 499         exit(1);
 500     }
 501 }
 502
 503
 504 char *qemu_get_pid_name(pid_t pid)
 505 {
 506     char *name = NULL;
 507
 508 #if defined(__FreeBSD__)
 509     /* BSDs don't have /proc, but they provide a nice substitute */
 510     struct kinfo_proc *proc = kinfo_getproc(pid);
 511
 512     if (proc) {
 513         name = g_strdup(proc->ki_comm);
 514         free(proc);
 515     }
 516 #else
 517     /* Assume a system with reasonable procfs */
 518     char *pid_path;
 519     size_t len;
 520
 521     pid_path = g_strdup_printf("/proc/%d/cmdline", pid);
 522     g_file_get_contents(pid_path, &name, &len, NULL);
 523     g_free(pid_path);
 524 #endif
 525
 526     return name;
 527 }
 528
 529
 530 pid_t qemu_fork(Error **errp)
 531 {
 532     sigset_t oldmask, newmask;
 533     struct sigaction sig_action;
 534     int saved_errno;
 535     pid_t pid;
 536
 537     /*
 538      * Need to block signals now, so that child process can safely
 539      * kill off caller's signal handlers without a race.
 540      */
 541     sigfillset(&newmask);
 542     if (pthread_sigmask(SIG_SETMASK, &newmask, &oldmask) != 0) {
 543         error_setg_errno(errp, errno,
 544                          "cannot block signals");
 545         return -1;
 546     }
 547
 548     pid = fork();
 549     saved_errno = errno;
 550
 551     if (pid < 0) {
 552         /* attempt to restore signal mask, but ignore failure, to
 553          * avoid obscuring the fork failure */
 554         (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 555         error_setg_errno(errp, saved_errno,
 556                          "cannot fork child process");
 557         errno = saved_errno;
 558         return -1;
 559     } else if (pid) {
 560         /* parent process */
 561
 562         /* Restore our original signal mask now that the child is
 563          * safely running. Only documented failures are EFAULT (not
 564          * possible, since we are using just-grabbed mask) or EINVAL
 565          * (not possible, since we are using correct arguments).  */
 566         (void)pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 567     } else {
 568         /* child process */
 569         size_t i;
 570
 571         /* Clear out all signal handlers from parent so nothing
 572          * unexpected can happen in our child once we unblock
 573          * signals */
 574         sig_action.sa_handler = SIG_DFL;
 575         sig_action.sa_flags = 0;
 576         sigemptyset(&sig_action.sa_mask);
 577
 578         for (i = 1; i < NSIG; i++) {
 579             /* Only possible errors are EFAULT or EINVAL The former
 580              * won't happen, the latter we expect, so no need to check
 581              * return value */
 582             (void)sigaction(i, &sig_action, NULL);
 583         }
 584
 585         /* Unmask all signals in child, since we've no idea what the
 586          * caller's done with their signal mask and don't want to
 587          * propagate that to children */
 588         sigemptyset(&newmask);
 589         if (pthread_sigmask(SIG_SETMASK, &newmask, NULL) != 0) {
 590             Error *local_err = NULL;
 591             error_setg_errno(&local_err, errno,
 592                              "cannot unblock signals");
 593             error_report_err(local_err);
 594             _exit(1);
 595         }
 596     }
 597     return pid;
 598 }
 599
 600 void *qemu_alloc_stack(size_t *sz)
 601 {
 602     void *ptr, *guardpage;
 603     int flags;
 604 #ifdef CONFIG_DEBUG_STACK_USAGE
 605     void *ptr2;
 606 #endif
 607     size_t pagesz = getpagesize();
 608 #ifdef _SC_THREAD_STACK_MIN
 609     /* avoid stacks smaller than _SC_THREAD_STACK_MIN */
 610     long min_stack_sz = sysconf(_SC_THREAD_STACK_MIN);
 611     *sz = MAX(MAX(min_stack_sz, 0), *sz);
 612 #endif
 613     /* adjust stack size to a multiple of the page size */
 614     *sz = ROUND_UP(*sz, pagesz);
 615     /* allocate one extra page for the guard page */
 616     *sz += pagesz;
 617
 618     flags = MAP_PRIVATE | MAP_ANONYMOUS;
 619 #if defined(MAP_STACK) && defined(__OpenBSD__)
 620     /* Only enable MAP_STACK on OpenBSD. Other OS's such as
 621      * Linux/FreeBSD/NetBSD have a flag with the same name
 622      * but have differing functionality. OpenBSD will SEGV
 623      * if it spots execution with a stack pointer pointing
 624      * at memory that was not allocated with MAP_STACK.
 625      */
 626     flags |= MAP_STACK;
 627 #endif
 628
 629     ptr = mmap(NULL, *sz, PROT_READ | PROT_WRITE, flags, -1, 0);
 630     if (ptr == MAP_FAILED) {
 631         perror("failed to allocate memory for stack");
 632         abort();
 633     }
 634
 635 #if defined(HOST_IA64)
 636     /* separate register stack */
 637     guardpage = ptr + (((*sz - pagesz) / 2) & ~pagesz);
 638 #elif defined(HOST_HPPA)
 639     /* stack grows up */
 640     guardpage = ptr + *sz - pagesz;
 641 #else
 642     /* stack grows down */
 643     guardpage = ptr;
 644 #endif
 645     if (mprotect(guardpage, pagesz, PROT_NONE) != 0) {
 646         perror("failed to set up stack guard page");
 647         abort();
 648     }
 649
 650 #ifdef CONFIG_DEBUG_STACK_USAGE
 651     for (ptr2 = ptr + pagesz; ptr2 < ptr + *sz; ptr2 += sizeof(uint32_t)) {
 652         *(uint32_t *)ptr2 = 0xdeadbeaf;
 653     }
 654 #endif
 655
 656     return ptr;
 657 }
 658
 659 #ifdef CONFIG_DEBUG_STACK_USAGE
 660 static __thread unsigned int max_stack_usage;
 661 #endif
 662
 663 void qemu_free_stack(void *stack, size_t sz)
 664 {
 665 #ifdef CONFIG_DEBUG_STACK_USAGE
 666     unsigned int usage;
 667     void *ptr;
 668
 669     for (ptr = stack + getpagesize(); ptr < stack + sz;
 670          ptr += sizeof(uint32_t)) {
 671         if (*(uint32_t *)ptr != 0xdeadbeaf) {
 672             break;
 673         }
 674     }
 675     usage = sz - (uintptr_t) (ptr - stack);
 676     if (usage > max_stack_usage) {
 677         error_report("thread %d max stack usage increased from %u to %u",
 678                      qemu_get_thread_id(), max_stack_usage, usage);
 679         max_stack_usage = usage;
 680     }
 681 #endif
 682
 683     munmap(stack, sz);
 684 }
 685
 686 void sigaction_invoke(struct sigaction *action,
 687                       struct qemu_signalfd_siginfo *info)
 688 {
 689     siginfo_t si = {};
 690     si.si_signo = info->ssi_signo;
 691     si.si_errno = info->ssi_errno;
 692     si.si_code = info->ssi_code;
 693
 694     /* Convert the minimal set of fields defined by POSIX.
 695      * Positive si_code values are reserved for kernel-generated
 696      * signals, where the valid siginfo fields are determined by
 697      * the signal number.  But according to POSIX, it is unspecified
 698      * whether SI_USER and SI_QUEUE have values less than or equal to
 699      * zero.
 700      */
 701     if (info->ssi_code == SI_USER || info->ssi_code == SI_QUEUE ||
 702         info->ssi_code <= 0) {
 703         /* SIGTERM, etc.  */
 704         si.si_pid = info->ssi_pid;
 705         si.si_uid = info->ssi_uid;
 706     } else if (info->ssi_signo == SIGILL || info->ssi_signo == SIGFPE ||
 707                info->ssi_signo == SIGSEGV || info->ssi_signo == SIGBUS) {
 708         si.si_addr = (void *)(uintptr_t)info->ssi_addr;
 709     } else if (info->ssi_signo == SIGCHLD) {
 710         si.si_pid = info->ssi_pid;
 711         si.si_status = info->ssi_status;
 712         si.si_uid = info->ssi_uid;
 713     }
 714     action->sa_sigaction(info->ssi_signo, &si, NULL);
 715 }