#include <sys/file.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/wait.h>

#ifndef linux
#define fstat64(fd, st) fstat(fd, st)
#endif

int
run_child(char *filename)
{
    int fd = -1, ret = -1;

    fd = open(filename, O_RDWR);
    if (fd < 0) {
        fprintf(stderr, "open failed (%s)\n", strerror(errno));
        goto out;
    }

    ret = flock(fd, LOCK_EX | LOCK_NB);
    if ((ret == 0) || (errno != EWOULDBLOCK)) {
        fprintf(stderr,
                "no locks present, though parent has held "
                "one\n");
        ret = -1;
        goto out;
    }

    ret = 0;
out:
    return ret;
}

int
main(int argc, char *argv[])
{
    int fd = -1, ret = -1, status = 0;
    char *filename = NULL, *cmd = NULL;
    struct stat stbuf = {
        0,
    };

    if (argc != 3) {
        fprintf(stderr,
                "Usage: %s <filename> "
                "<gluster-cmd-to-trigger-graph-switch>\n",
                argv[0]);
        goto out;
    }

    filename = argv[1];
    cmd = argv[2];

    fd = open(filename, O_RDWR | O_CREAT, 0);
    if (fd < 0) {
        fprintf(stderr, "open (%s) failed (%s)\n", filename, strerror(errno));
        goto out;
    }

    ret = flock(fd, LOCK_EX);
    if (ret < 0) {
        fprintf(stderr, "flock failed (%s)\n", strerror(errno));
        goto out;
    }

    system(cmd);

    /* wait till graph switch completes */
    ret = fstat64(fd, &stbuf);
    if (ret < 0) {
        fprintf(stderr, "fstat64 failure (%s)\n", strerror(errno));
        goto out;
    }

    sleep(10);

    /* By now old-graph would be disconnected and locks should be cleaned
     * up if they are not migrated. Check that by trying to acquire a lock
     * on a new fd opened by another process on same file
     */
    ret = fork();
    if (ret == 0) {
        ret = run_child(filename);
    } else {
        wait(&status);
        if (WIFEXITED(status)) {
            ret = WEXITSTATUS(status);
        } else {
            ret = 0;
        }
    }

out:
    return ret;
}