#include <stdio.h>
#include <dirent.h>
#include <sys/stat.h>

int main(int argc, char **argv)
{
    struct stat root, block;
    char path[128];
    struct dirent *e;
    DIR *d;

    if (stat(argv[1], &root))
        return 1;

    if (!(d = opendir("/dev")))
        return 1;

    while ((e = readdir(d)) != NULL)
    {
        snprintf(path, sizeof(path), "/dev/%s", e->d_name);

        if (lstat(path, &block) || !S_ISBLK(block.st_mode) || block.st_rdev != root.st_dev)
            continue;

        printf("Rootdev is %s\n", path);
        break;
    }

    closedir(d);
    return 0;
}