mxq_reaper.c

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/prctl.h>
#include <unistd.h>
#include <sys/resource.h>
#include <sys/time.h>
#include <sys/wait.h>
#include <errno.h>
#include <string.h>
#include <stdarg.h>

static const char REAPER_PNAME[] = "mxqd reaper";

__attribute__ ((noreturn))
__attribute__ ((format (printf, 1, 2)))
static void die(const char *restrict fmt, ...) {
    va_list ap;
    va_start(ap, fmt);
    vfprintf(stderr, fmt, ap);
    va_end(ap);
    _exit(1);
}

int main(int argc, char **argv) {

    if (argc < 5 || strcmp(argv[3], "--") != 0) {
        fprintf(stderr, "usage: %s UID SPOOLFILENAME -- CMD [ARGS...]\n", argv[0]);
        exit(1);
    }

    uid_t uid = atoi(argv[1]);
    char *spoolfilename = argv[2];
    char **user_argv = &argv[4];

    pid_t user_pid;
    int user_status = -1;
    struct rusage user_rusage;
    struct timeval user_time;

    struct timeval starttime;
    struct timeval endtime;

    if (prctl(PR_SET_NAME, REAPER_PNAME, NULL, NULL, NULL) == -1)
        die("PR_SET_NAME: %m\n");
    user_pid = fork();
    if (user_pid == 0) {
        if (setreuid(uid, uid) == -1)
            die("setreuid: %m\n");
        execvp(user_argv[0], user_argv);
        die("%s: %m\n", user_argv[0]);
    }
    if (user_pid == -1)
        die("fork: %m\n");
    if (gettimeofday(&starttime, NULL) == -1)
        die("gettimeofday: %m\n");
    while (1) {
        int status;
        pid_t pid = wait(&status);
        if (pid < 0 && errno == ECHILD)
            break;
        if (pid == user_pid)
            user_status = status;
    }
    if (gettimeofday(&endtime, NULL) == -1)
        die("gettimeofday: %m\n");
    timersub(&endtime, &starttime, &user_time);
    if (getrusage(RUSAGE_CHILDREN, &user_rusage) == -1)
        die("getrusage: %m\n");

   if (user_time.tv_sec<30) {
        int wait=30-user_time.tv_sec;
        sleep(wait);
    }

    while (1) {
        // if anything fails, do not write to stderr, as this is the users
        // stderr, just wait and retry.

        char *tmpfilename;
        if (asprintf(&tmpfilename, "%s.tmp", spoolfilename) == -1)
            goto retry_1;

        FILE *out = fopen(tmpfilename, "w");
        if (out == NULL)
            goto retry_2;
        if (fprintf(out,"1 %d %d %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld %ld\n",
                getpid(),
                user_status,
                user_time.tv_sec, user_time.tv_usec,
                user_rusage.ru_utime.tv_sec, user_rusage.ru_utime.tv_usec,
                user_rusage.ru_stime.tv_sec, user_rusage.ru_stime.tv_usec,
                user_rusage.ru_maxrss,
                user_rusage.ru_ixrss,
                user_rusage.ru_idrss,
                user_rusage.ru_isrss,
                user_rusage.ru_minflt,
                user_rusage.ru_majflt,
                user_rusage.ru_nswap,
                user_rusage.ru_inblock,
                user_rusage.ru_oublock,
                user_rusage.ru_msgsnd,
                user_rusage.ru_msgrcv,
                user_rusage.ru_nsignals,
                user_rusage.ru_nvcsw,
                user_rusage.ru_nivcsw) < 0)
            goto retry_3;
        if (fflush(out) == EOF)
            goto retry_3;
        if (fsync(fileno(out)) == -1)
            goto retry_3;
        if (fclose(out) == EOF)
            goto retry_2;
        if (rename(tmpfilename, spoolfilename) == -1)
            goto retry_2;
        break;

retry_3:
        fclose(out);
retry_2:
        free(tmpfilename);
retry_1:
        sleep(10);
    }
    return 0;
}