#define _GNU_SOURCE
#define _FILE_OFFSET_BITS	64

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <errno.h>

#define SECTOR_SHIFT	9

int main(int argc, char **argv)
{
	int f, r;
	unsigned long size;
	unsigned long bufsize;
	unsigned int pagesize;
	off_t offset;
	char *endptr;
	char *buffer;
	int mode = 'z';

	if (argc > 1 && argv[1][0] == '-') {
		mode = argv[1][1];
		argv++;
		argc--;
	}

	if (argc < 3)
		return 1;

	size = strtol(argv[2], &endptr, 10);
	if (*endptr || !size || size > 4096)
		return 1;
	size <<= SECTOR_SHIFT;
	bufsize = (size + pagesize - 1) & ~(pagesize - 1);

	if (argc >= 4) {
		offset = (off_t)strtoll(argv[3], &endptr, 10);
		if (*endptr)
			return 1;
		offset <<= SECTOR_SHIFT;
	} else
		offset = 0;

	f = open(argv[1], ((mode == 'w' || mode == 'z') ? O_WRONLY : O_RDONLY) | O_DIRECT | O_SYNC);
	if (f < 0) {
		perror("fopen");
		return 1;
	}

	if (offset) {
		if (lseek(f, offset, SEEK_SET) != offset) {
			perror("lseek");
			return 1;
		}
	}

	buffer = mmap(NULL, bufsize, PROT_READ | PROT_WRITE,
	              MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
	if (!buffer) {
		perror("mmap");
		close(f);
		return 1;
	}

	if (mode == 'z')
		memset(buffer, 0, size);
	else if (mode == 'w')
		read(0, buffer, size);

	if (mode == 'z' || mode == 'w')
		r = write(f, buffer, size);
	else if (mode == 'v' || mode == 'r')
		r = read(f, buffer, size);

	if (mode == 'v') {
		char *start = buffer;
		char *end = buffer + size;
		while(start != end)
			if (*start++) {
				fprintf(stderr, "Verify failed at %08x\n", (start - buffer) - 1);
				break;
			}
	} else if (mode == 'r')
		write(1, buffer, size);

	munmap(buffer, bufsize);
	close(f);

	if (r < 0) {
		perror("write");
		return 1;
	}

	fprintf(stderr, "Result: %d\n", r);

	return 0;
}