source: tools/watchdog.c @ 30ee9efc

#include <errno.h>
#include <fcntl.h>
#include <getopt.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

char * this_cmd = NULL;

void parse_args(int argc, char * argv[]);
int run();
void printcmd();

int main(int argc, char * argv[]) {
        parse_args(argc, argv);

        int retcode = run();
        if( !WIFEXITED(retcode) ) {
                printf("Child Error : %d ", retcode); printcmd();
                return retcode;
        }

        printf("Child exited normally "); printcmd();
        return 0;
}

void usage( FILE * out, int code ) {
        fprintf(out, "%s [OPTION] [--] N CMD\n", this_cmd);
        fprintf(out, "Run command, killing it if it doesn't print for more than 5 continuous seconds\n\n");
        fprintf(out, "\t-h,--help\tprint this usage message\n");
        exit(code);
}

char ** cmd_to_run = NULL;
pid_t child_pid = 0;
int pipe_fds[2];

void arg_error(void) {
        fprintf(stderr,"\n");
        usage(stderr, 1);
}

void parse_args(int argc, char * argv[]) {
        this_cmd = argv[0];

        enum { Help, };
        static struct option long_opts[] = {
                { "help", no_argument, 0, Help },
                { 0, 0, 0, 0 }
        }; // long_opts
        int long_index;

        int c;
        while ( (c = getopt_long( argc, argv, "h", long_opts, &long_index)) != -1 ) {
                switch ( c ) {
                        case Help:
                        case 'h':
                                usage(stdout, 0);
                                break;
                        default:
                                arg_error();
                                break;
                } // switch
        } // while

        if( argc < optind + 1 ) {
                fprintf(stderr, "Too few arguments\n");
                arg_error();
        }

        cmd_to_run = argv + optind;
}

static void exit_handler (__attribute__((unused)) int a, __attribute__((unused)) void * b) {
        close(pipe_fds[0]);
        if(child_pid != 0) kill(child_pid, SIGKILL);
}

#define checked(call, ...) ({int ret = call(__VA_ARGS__); if (ret == -1) { perror(#call); exit(1); } ret;})

void run_child();
void make_noblock(int fd);
void sink(int fd);
int waitfd(int fd);

int run() {
        on_exit(exit_handler, NULL);
        checked(pipe, pipe_fds);

        printf("Watching command: "); printcmd();

        child_pid = checked(fork);
        if (child_pid == 0) { run_child(); }

        close(pipe_fds[1]);
        make_noblock(pipe_fds[0]);

        int status;
        while(waitpid(child_pid, &status, WNOHANG) == 0) {
                if(waitfd(pipe_fds[0]) == 0) {
                        printf("Child Deadlocked "); printcmd();
                        exit(127);
                }
                sink(pipe_fds[0]);
        }

        child_pid = 0;
        return status;

        return 0;
}

void make_noblock(int fd) {
        int flags = fcntl(fd, F_GETFL);
        flags |= O_NONBLOCK;
        fcntl(fd, F_SETFL, flags );
}

void sink(int fd) {
        char buff[100];
        int len = 100;
        int rv;
        do {
                rv = read( fd, buff, len );
        }
        while(rv > 0);
}

int waitfd(int fd) {
        fd_set set;
        FD_ZERO(&set);
        FD_SET(fd, &set);

        struct timeval timeout;
        timeout.tv_sec = 5;
        timeout.tv_usec = 0;

        int rv = select(fd + 1, &set, NULL, NULL, &timeout);
        if(rv == -1) {
                perror("select\n");
                exit(1);
        }
        return rv;
}

void run_child() {
        /* This is the child process. */
        while ((dup2(pipe_fds[1], STDOUT_FILENO) == -1) && (errno == EINTR));

        close(pipe_fds[1]);
        close(pipe_fds[0]);

        execvp ( *cmd_to_run, cmd_to_run);

        /* The execvp  function returns only if an error occurs.  */
        fprintf(stderr, "an error occurred in execvp\n");
        abort ();
}

void printcmd() {
        if(!cmd_to_run) return;
        char ** cmd = cmd_to_run;
        while (*cmd) {
                printf("%s ", *cmd);
                cmd++;
        }
        printf("\n");
}