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Date: Fri, 28 May 2010 08:16:29 -0500
From: Ryan Harper <ryanh@us.ibm.com>
Subject: Re: [Qemu-devel] [PATCH 0/4] Add virtio disk identification support
Message-ID: <20100528131629.GD29645@us.ibm.com>
References: <4BAAF541.4090605@redhat.com>
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To: john cooper <john.cooper@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>, Marc Haber <mh+qemu-devel@zugschlus.de>, qemu-devel@nongnu.org

* john cooper <john.cooper@redhat.com> [2010-03-25 00:45]:
> This series adds the minimal support to qemu and virtio_blk
> to support passing of a virtio_blk serial id string from qemu
> through the guest driver and to the guest userland.
> 
> This is derived in part from a patch set posted by Rusty some
> time ago, but has been minimized to remove support for prior
> versions which attempted to provide the same functionality via
> pci config/io space.  This version rather uses a virtio request
> as proposed in Rusty's example.
> 
> Also removed is the packaging of the serial/id string within
> the glorious bag of bits returned by the ATA_IDENTIFY command.
> Here we transfer only the 20 bytes of serial/id string from
> qemu to the guest userland.  In the proposed interface, this
> is made available by an ioctl() into the virtio_blk driver
> however other interfaces (eg: /sys) have also been proposed.
> A code snippet is attached below as an example of ioctl usage.
> 
> The resulting code is quite minimal and I believe it addresses
> all concerns raised in prior versions.
> 
> -john
> 
> 
> 
> #include <stdio.h>
> #include <strings.h>
> #include <sys/types.h>
> #include <fcntl.h>
> #include <linux/hdreg.h>
> 
> #define IOCTL_CMD	'VBID'
> 
> main()
> {
> 	int fd, rv;
> 	char buf[512];
> 
> 	bzero(buf, sizeof (buf));
> 	if ((fd = open("/dev/vda", O_RDONLY)) < 0)
> 		perror("open");
> 	else if (ioctl(fd, IOCTL_CMD, buf) < 0)
> 		perror("ioctl");
> 	else
> 		printf("[%s]\n", buf);
> }

Would we want to patch up blkid command to use this so distro stacks can
extract the serial and build the typical /dev/disk/by-id/ links ?


-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@us.ibm.com