#define _POSIX_C_SOURCE 200112L
#include <assert.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>

void usage() {
    fputs("usage: nureadahead-preload DEVICE < file\n", stderr);
}

int main(int argc, char *argv[]) {
    if (argc != 2 || argv[1][0] == '-' || argv[1][0] == '\0') {
        usage();
        exit(1);
    }

    int fd = open(argv[1], O_RDONLY);
    if (fd == -1) {
        perror("nureadahead-preload");
        exit(1);
    }

    while (1) {
        unsigned long long start, end;
        switch (scanf("%llu %llu\n", &start, &end)) {
            case 2:
                if (posix_fadvise(fd, start * 512, (end - start + 1) * 512, POSIX_FADV_WILLNEED) == -1) {
                    perror("nureadahead-preload: readahead");
                    exit(1);
                }
                break;
            case EOF:
                exit(0);
            default:
                fputs("nureadahead-preload: invalid input\n", stderr);
        }
    }
}