bdcmp.c

#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define REPORT_BLOCKS 1024
#define BLOCK_SIZE 65536
#define SUB_BLOCK_SIZE 8192

char ba[BLOCK_SIZE];
char bb[BLOCK_SIZE];

int
open_block_device(const char* path)
{
        int fd;

        fd = open(path, O_RDONLY);
        if (fd < 0) {
                fprintf(stderr, "Unable to open block device: %s\n", path);
                exit(1);
        }
        return fd;
}

int
main(int argc, char* argv[])
{
        size_t blocknum = 0;
        size_t diff_blocks = 0;
        size_t diff_sub_blocks = 0;
        int fa, fb;

        fa = open_block_device(argv[1]);
        fb = open_block_device(argv[2]);

        while (true) {
                if (blocknum % REPORT_BLOCKS == 0) {
                        printf("\rblock number: %zu", blocknum);
                }

                if (read(fa, ba, BLOCK_SIZE) != BLOCK_SIZE) {
                        break;
                }
                if (read(fb, bb, BLOCK_SIZE) != BLOCK_SIZE) {
                        break;
                }

                bool block_differs = false;
                bool sub_block_differs = false;
                for (size_t i = 0; i < BLOCK_SIZE; ++i) {
                        if (i % SUB_BLOCK_SIZE == 0) {
                                sub_block_differs = false;
                        }

                        if (ba[i] != bb[i]) {
                                if (!block_differs) {
                                        block_differs = true;
                                        ++diff_blocks;
                                }
                                if (!sub_block_differs) {
                                        sub_block_differs = true;
                                        ++diff_sub_blocks;
                                }
                        }
                }

                ++blocknum;
        }
        printf("\nTotal blocks counted: %zu\n", blocknum);
        printf("Differing blocks: %zu\n", diff_blocks);
        printf("Differing sub-blocks: %zu\n", diff_sub_blocks);

        return 0;
}