Add serial number support for virtio_blk, V2

[Resend of earlier patch: 1/2 rebased to qemu-kvm, 2/2 minor tweak]

This patch allows passing of a virtio_blk drive serial number from qemu into a guest's virtio_blk driver, and provides a means to access the serial number from a guest's userspace.

Equivalent functionality currently exists for IDE and SCSI, however it is not yet implemented for virtio. Scenarios exist where guest code relies on a unique drive serial number to correctly identify the machine environment in which it exists.

The following two patches implement the above:

qemu-vblk-serial-2.patch

which provides the qemu missing bits to interpret a '-drive .. serial=XYZ ..' flag, and:

virtio_blk-serial-2.patch

which extracts this information and makes it available to guest userspace via ioctl.

Attached to this patch header is a trivial example program which retrieves the serial number from guest userspace.

The above patches are relative to qemu-kvm.git and 2.6.29.3 respectively.

-john

[email protected]

/* 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);
}

patch 1/2 seems to be missing.

So why can't we re-use the existing interfaces instead of inventing a new one?

It is in the kvm and qemu-devel list archives:

http://www.spinics.net/lists/kvm/maillist.html
http://lists.gnu.org/archive/html/qemu-devel/2009-05/msg00661.html

I'm unclear to what specifically you're referring -- the ioctl() used to retrieve the serial number in the guest?

-john

[email protected]

Ah, it got posted as reply to the previous submission, not with this one.

Well, there's not specific ioctl to get a serial number for scsi, but given that we now have SG_IO passthrough in virtio-blk it should be easy enough to provide inquiry data and the device identification VPD page by that way. Not sure how it's handled for ide, maybe that way is even easier.

IDE has "identify" command which return various info including 20 byte serial number.

--
Gleb.

Yea, I'm hardly in enamored with the IDE/ATA diatribe. But in this case displacing the new ioctl with HDIO_GET_IDENTITY seemed the most straightforward means to provide access within an existing interface. Updated patch follows.

-john

[email protected]