source: azure_iot_hub/trunk/musl-1.1.18/src/process/system.c@ 388

#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/wait.h>
#include <spawn.h>
#include <errno.h>
#include "pthread_impl.h"
#include "libc.h"

extern char **__environ;

int system(const char *cmd)
{
        pid_t pid;
        sigset_t old, reset;
        struct sigaction sa = { .sa_handler = SIG_IGN }, oldint, oldquit;
        int status = 0x7f00, ret;
        posix_spawnattr_t attr;

        pthread_testcancel();

        if (!cmd) return 1;

        sigaction(SIGINT, &sa, &oldint);
        sigaction(SIGQUIT, &sa, &oldquit);
        sigaddset(&sa.sa_mask, SIGCHLD);
        sigprocmask(SIG_BLOCK, &sa.sa_mask, &old);

        sigemptyset(&reset);
        if (oldint.sa_handler != SIG_IGN) sigaddset(&reset, SIGINT);
        if (oldquit.sa_handler != SIG_IGN) sigaddset(&reset, SIGQUIT);
        posix_spawnattr_init(&attr);
        posix_spawnattr_setsigmask(&attr, &old);
        posix_spawnattr_setsigdefault(&attr, &reset);
        posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSIGDEF|POSIX_SPAWN_SETSIGMASK);
        ret = posix_spawn(&pid, "/bin/sh", 0, &attr,
                (char *[]){"sh", "-c", (char *)cmd, 0}, __environ);
        posix_spawnattr_destroy(&attr);

        if (!ret) while (waitpid(pid, &status, 0)<0 && errno == EINTR);
        sigaction(SIGINT, &oldint, NULL);
        sigaction(SIGQUIT, &oldquit, NULL);
        sigprocmask(SIG_SETMASK, &old, NULL);

        if (ret) errno = ret;
        return status;
}