cri-o/conmon/conmon.c

#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/prctl.h>
#include <sys/wait.h>
#include <termios.h>
#include <unistd.h>

#include <glib.h>

#define pexit(fmt, ...)                                                        \
	do {                                                                   \
		fprintf(stderr, "conmon: " fmt " %m\n", ##__VA_ARGS__);        \
		exit(EXIT_FAILURE);                                            \
	} while (0)

#define nexit(fmt, ...)                                                        \
	do {                                                                   \
		fprintf(stderr, "conmon: " fmt "\n", ##__VA_ARGS__);           \
		exit(EXIT_FAILURE);                                            \
	} while (0)

#define nwarn(fmt, ...)                                                        \
	do {                                                                   \
		fprintf(stderr, "conmon: " fmt "\n", ##__VA_ARGS__);           \
	} while (0)

#define _cleanup_(x) __attribute__((cleanup(x)))

static inline void freep(void *p) { free(*(void **)p); }

static inline void closep(int *fd) {
	if (*fd >= 0)
		close(*fd);
	*fd = -1;
}

#define _cleanup_free_ _cleanup_(freep)
#define _cleanup_close_ _cleanup_(closep)

struct termios tty_orig;

static void tty_restore(void)
{
	if (tcsetattr(STDIN_FILENO, TCSANOW, &tty_orig) == -1)
		pexit("tcsetattr");
}

#define BUF_SIZE 256
#define CMD_SIZE 1024
#define MAX_EVENTS 10

int main(int argc, char *argv[])
{
	int ret;
	const char *cid;
	char cmd[CMD_SIZE];
	GError *err = NULL;
	_cleanup_free_ char *contents;
	int cpid = -1;
	int status;
	pid_t pid;
	_cleanup_close_ int mfd = -1;
	_cleanup_close_ int epfd = -1;
	char slname[BUF_SIZE];
	char buf[BUF_SIZE];
	int num_read;
	struct termios t;
	struct epoll_event ev;
	struct epoll_event evlist[MAX_EVENTS];

	if (argc < 2) {
		nexit("Run as: conmon <id>");
	}

	/* Get the container id */
	cid = argv[1];

	/*
	 * Set self as subreaper so we can wait for container process
	 * and return its exit code.
	 */
	ret = prctl(PR_SET_CHILD_SUBREAPER, 1, 0, 0, 0);
	if (ret != 0) {
		pexit("Failed to set as subreaper");
	}

	/* Open the master pty */
	mfd = open("/dev/ptmx", O_RDWR | O_NOCTTY);
	if (mfd < 0)
		pexit("Failed to open console master pty");

	/* Grant access to the slave pty */
	if (grantpt(mfd) == -1)
		pexit("Failed to grant access to slave pty");

	/* Unlock the slave pty */
	if (unlockpt(mfd) == -1) {             /* Unlock slave pty */
		pexit("Failed to unlock the slave pty");
	}

	/* Get the slave pty name */
	ret = ptsname_r(mfd, slname, BUF_SIZE);
	if (ret != 0) {
		pexit("Failed to get the slave pty name");
	}

	/* Create the container */
	snprintf(cmd, CMD_SIZE, "runc create %s --pid-file pidfile --console %s", cid, slname);
	ret = system(cmd);
	if (ret != 0) {
		nexit("Failed to create container");
	}

	/* Read the pid so we can wait for the process to exit */
	g_file_get_contents("pidfile", &contents, NULL, &err);
	if (err) {
		fprintf(stderr, "Failed to read pidfile: %s\n", err->message);
		g_error_free(err);
		exit(1);
	}

	cpid = atoi(contents);
	printf("container PID: %d\n", cpid);

	/* Save exiting termios settings */
	if (tcgetattr(STDIN_FILENO, &tty_orig) == -1)
		pexit("tcegetattr");

	/* Settings for raw mode */
	t.c_lflag &= ~(ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHONL | IEXTEN);
	t.c_iflag &= ~(BRKINT | ICRNL | IGNBRK | IGNCR | INLCR | INPCK |
		       ISTRIP | IXON | IXOFF | IGNPAR | PARMRK);
	t.c_oflag &= ~OPOST;
	t.c_cc[VMIN] = 1;
	t.c_cc[VTIME] = 0;

	/* Set terminal to raw mode */
	if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &t) == -1)
		pexit("tcsetattr");

	/* Setup terminal restore on exit */
	if (atexit(tty_restore) != 0)
		pexit("atexit");

	epfd = epoll_create(5);
	if (epfd < 0)
		pexit("epoll_create");
	ev.events = EPOLLIN;
	ev.data.fd = STDIN_FILENO;
	if (epoll_ctl(epfd, EPOLL_CTL_ADD, STDIN_FILENO, &ev) < 0) {
		pexit("Failed to add stdin to epoll");
	}
	ev.data.fd = mfd;
	if (epoll_ctl(epfd, EPOLL_CTL_ADD, mfd, &ev) < 0) {
		pexit("Failed to add console master fd to epoll");
	}

	/* Copy data back and forth between STDIN and master fd */
	while (true) {
		int ready = epoll_wait(epfd, evlist, MAX_EVENTS, -1);
		for (int i = 0; i < ready; i++) {
			if (evlist[i].events & EPOLLIN) {
				if (evlist[i].data.fd == STDIN_FILENO) {
					num_read = read(STDIN_FILENO, buf, BUF_SIZE);
					if (num_read <= 0)
						goto out;

					if (write(mfd, buf, num_read) != num_read) {
						nwarn("partial/failed write (masterFd)");
						goto out;
					}
				} else if (evlist[i].data.fd == mfd) {
					num_read = read(mfd, buf, BUF_SIZE);
					if (num_read <= 0)
						goto out;

					if (write(STDOUT_FILENO, buf, num_read) != num_read) {
						nwarn("partial/failed write (STDOUT_FILENO)");
						goto out;
					}
				}
			} else if (evlist[i].events & (EPOLLHUP | EPOLLERR)) {
				printf("closing fd %d\n", evlist[i].data.fd);
				if (close(evlist[i].data.fd) < 0)
					pexit("close");
				goto out;
			}
		}
	}
out:
	tty_restore();

	/* Wait for the container process and record its exit code */
	while ((pid = waitpid(-1, &status, 0)) > 0) {
		printf("PID %d exited\n", pid);
		if (pid == cpid) {
			_cleanup_free_ char *status_str = NULL;
			ret = asprintf(&status_str, "%d", status);
			if (ret < 0) {
				pexit("Failed to allocate memory for status");
			}
			g_file_set_contents("exit", status_str, strlen(status_str), &err);
			if (err) {
				fprintf(stderr, "Failed to write %s to exit file: %s\n", status_str, err->message);
				g_error_free(err);
				exit(1);
			}
			break;
		}
	}

	return EXIT_SUCCESS;
}