/*
 * pipetest.c - Minimal CRIU reproducer: open a pipe, checkpoint, then
 * re-open the read end via /proc/self/fd/<n> after restore.
 *
 * Steps to reproduce:
 *   1. Build:   gcc -o pipetest pipetest.c
 *   2. Run:     ./pipetest &
 *   3. In another terminal, checkpoint:
 *        criu dump -t $(pgrep pipetest) -D /tmp/pipetest-img --shell-job
 *   4. Restore:
 *        criu restore -D /tmp/pipetest-img --shell-job
 *
 * Expected: open(/proc/self/fd/<read_end>) succeeds after restore.
 * Observed: open() fails with Permission denied.
 */

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

int main(void)
{
    int fds[2];

    if (pipe(fds) < 0) {
        perror("pipe");
        return 1;
    }

    printf("pipe read_fd=%d write_fd=%d\n", fds[0], fds[1]);
    printf("sleeping 20s — checkpoint pid %d now\n", getpid());
    fflush(stdout);

    sleep(20);
    printf("Continuing.  5 seconds of sleep for debug.\n");
    sleep(5);

    /* After restore, attempt to open the read end via /proc/self/fd */
    char path[64];
    snprintf(path, sizeof(path), "/proc/%d/fd/%d", getpid(), fds[0]);

    printf("re-opening pipe read end via %s\n", path);
    fflush(stdout);

    int reopen_fd = open(path, O_RDONLY);
    if (reopen_fd < 0) {
        fprintf(stderr, "open(%s) failed: %s\n", path, strerror(errno));
        return 1;
    }

    printf("open succeeded: new_fd=%d\n", reopen_fd);

    /* Quick sanity check: write to write end, read from re-opened fd */
    const char msg[] = "hello through pipe\n";
    if (write(fds[1], msg, sizeof(msg) - 1) < 0) {
        perror("write");
        return 1;
    }

    char buf[64] = {0};
    ssize_t n = read(reopen_fd, buf, sizeof(buf) - 1);
    if (n < 0) {
        perror("read");
        return 1;
    }

    printf("read %zd bytes: %s", n, buf);

    close(reopen_fd);
    close(fds[0]);
    close(fds[1]);
    return 0;
}