#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>

/**
 * NOTE: requires fdescfs to be mounted to run interpreted files (starting with #!)
 */

char *args[] = { "batchrun", NULL };

int
main(int argc, char **argv)
{
	char buf[2];
	ssize_t ret;
	int tries = 0;
	int fd = 3;

	if (argc > 1) {
		fd = atoi(argv[1]);
	}

retry:
	if (tries++ >= 3)
		errx(1, "Failed to read file header");

	ret = pread(fd, buf, sizeof(buf), 0);
	if (ret == 2) {
		if (strncmp(buf, "#!", 2) != 0) {
			fcntl(3, F_SETFD, FD_CLOEXEC);
		}
	} else if (ret == -1) {
		if (errno == EINTR)
			goto retry;
	} else if (ret != 0) {
		goto retry;
	}

	fexecve(fd, args, NULL);
	err(1, "fexecve()");
}