#include <stdio.h>
#include <errno.h>
#include <sys/statvfs.h>

int main(int argc, char *argv[]) {
    const char* path = argc > 1 ? argv[1] : "/writable";

    struct statvfs buf;
    if (statvfs(path, &buf) < 0) {
        perror("statvfs");
        return 1;
    }

    printf("%s has %lu blocks of %lu bytes available (~%0f%%)\n",
           path, buf.f_bavail, buf.f_bsize,
           100.*buf.f_bavail/buf.f_blocks*buf.f_bsize/buf.f_frsize);

    return 0;
}