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Date: Thu, 28 Jan 2010 13:43:27 +0100
From: Christoph Hellwig <hch@lst.de>
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Subject: [Qemu-devel] future of the virtio-blk serial number support
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To: qemu-devel@nongnu.org
Cc: john cooper <john.cooper@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Anthony Liguori <aliguori@us.ibm.com>, Rusty Russell <rusty@rustcorp.com.au>, "Michael S. Tsirkin" <mst@redhat.com>

Back iSeptember 2007 Michael made the serial number support in qemu
optional and off by default, and in October 2009 Rusty reverted the
Linux virtio-blk support for it.  Given that I can't find support in
any other virtio implementation that makes the feature look essentially
dead.

How should we proceed with adding more fields to struct virtio_blk_config?
I would suggest removing the identity field, declaring
VIRTIO_BLK_F_IDENTIFY officially deprecated and adding the new fields
directly after blk_size again, maybe with a comment that these new
features can't be advertized together with VIRTIO_BLK_F_IDENTIFY.

I need to add a new optiomal_io_size field soon to support the block
topology information when using virtio which is quite important when
using RAID arrays as backend, and I'd prefer to do it in a way that's
compatibly with the PCI spec.