Function subd

lightningd/subd.c:202–301

We use sockets, not pipes, because fds are bidir. */

/* We use sockets, not pipes, because fds are bidir. */
static int subd(const char *path, const char *name,
		const char *debug_subdaemon,
		int *msgfd,
		bool io_logging,
		va_list *ap)
{
	int childmsg[2], execfail[2];
	pid_t childpid;
	int err, *fd;

	if (socketpair(AF_LOCAL, SOCK_STREAM, 0, childmsg) != 0)
		goto fail;

	if (pipe(execfail) != 0)
		goto close_msgfd_fail;

	if (fcntl(execfail[1], F_SETFD, fcntl(execfail[1], F_GETFD)
		  | FD_CLOEXEC) < 0)
		goto close_execfail_fail;

	childpid = fork();
	if (childpid < 0)
		goto close_execfail_fail;

	if (childpid == 0) {
		size_t num_args;
		char *args[] = { NULL, NULL, NULL, NULL };
		int **fds = tal_arr(tmpctx, int *, 3);
		int stdoutfd = STDOUT_FILENO, stderrfd = STDERR_FILENO;

		close(childmsg[0]);
		close(execfail[0]);

		/* msg = STDIN (0) */
		fds[0] = &childmsg[1];
		/* These are untouched */
		fds[1] = &stdoutfd;
		fds[2] = &stderrfd;

		while ((fd = va_arg(*ap, int *)) != NULL) {
			assert(*fd != -1);
			tal_arr_expand(&fds, fd);
		}

		/* Finally, the fd to report exec errors on */
		tal_arr_expand(&fds, &execfail[1]);

		if (!shuffle_fds(fds, tal_count(fds)))
			goto child_errno_fail;

		/* Make (fairly!) sure all other fds are closed. */
		closefrom(tal_count(fds));

		num_args = 0;
		args[num_args++] = tal_strdup(NULL, path);
		if (io_logging)
			args[num_args++] = "--log-io";
#if DEVELOPER