#include <fcntl.h>
#include <limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>

// musl forbids include/linux
#define RNDADDENTROPY   _IOW( 'R', 0x03, int [2] )

#define RAND_POOL_SIZE 512

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fputs("usage: load-random-seed FILE\n", stderr);
        exit(1);
    }

    int seed_fd = open(argv[1], O_RDONLY);
    if (seed_fd == -1) {
        perror("error opening seed file");
        exit(1);
    }
    struct {
        int entropy_count;
        int buf_size;
        char buf[RAND_POOL_SIZE];
    } rpi = {
        .entropy_count = RAND_POOL_SIZE * CHAR_BIT,
        .buf_size = RAND_POOL_SIZE
    };
    size_t sz = 0;
    do {
        ssize_t r = read(seed_fd, &rpi.buf[sz], RAND_POOL_SIZE - sz);
        if (r == -1) {
            perror("error reading seed file");
            exit(1);
        }
        sz += r;
    } while (sz < RAND_POOL_SIZE);

    if (close(seed_fd) == -1) {
        perror("error closing seed file");
        exit(1);
    }

    int urandom_fd = open("/dev/urandom", O_RDWR);
    if (urandom_fd == -1) {
        perror("error opening /dev/urandom");
        exit(1);
    }
    if (ioctl(urandom_fd, RNDADDENTROPY, &rpi) == -1) {
        perror("error adding entropy");
        exit(1);
    }
    if (close(urandom_fd) == -1) {
        perror("error closing /dev/urandom");
        exit(1);
    }

    return 0;
}