/* example: retrieve serial number from virtio block device
 */
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <linux/virtio_blk.h>

#define iswhite(c)	(!('!' <= (c) && (c) <= '~'))

#ifndef VBLK_GET_SN
#define VBLK_GET_SN ((unsigned int)('V' << 24 | 'B' << 16 | 'L' << 8 | 'K'))
#endif

/* get virtblk drive serial#
 */
int main(int ac, char ***av)
{
	int fd, nb, i;
	unsigned char sn[30];
	unsigned char *p;

	sn[0] = sizeof (sn);
	if ((fd = open("/dev/vda", O_RDONLY)) < 0)
		perror("can't open device"), exit(1);
	else if ((nb = ioctl(fd, VBLK_GET_SN, &sn)) < 0)
		perror("can't ioctl device"), exit(1);
	printf("returned %d bytes:\n", nb);
	for (p = sn, i = nb; 0 <= --i; ++p)
		printf("%02x%c", *p, i ? ' ' : '\t');
	for (p = sn, i = nb; 0 <= --i; ++p)
		printf("%c%s", iswhite(*p) ? '.' : *p, i ? "" : "\n");
	return (0);
}