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[Qemu-devel] Re: [PATCH 0/2] fix virtio_blk serial pci config breakage


From: Anthony Liguori
Subject: [Qemu-devel] Re: [PATCH 0/2] fix virtio_blk serial pci config breakage
Date: Tue, 29 Sep 2009 08:55:20 -0500
User-agent: Thunderbird 2.0.0.23 (X11/20090825)

Michael S. Tsirkin wrote:
On Tue, Sep 29, 2009 at 09:22:53AM +0200, Avi Kivity wrote:
On 09/29/2009 08:58 AM, Michael S. Tsirkin wrote:
Using bar per feature we'll quickly run out of BARs.
We already use a BAR for MSI-X - let's add
ATA identity there?
Mixing unrelated features will quickly cause confusion.

Note if we ever switch to 64 bit BARs, we'll only have 3 of these
available, so the ID would be using the last free one.
We can just as well plan ahead for when we'll add another feature?

I agree fixed offsets are messy though.  I previously proposed storing
the offset to the identity data in an i/o register. This will let each
implementation lay out this data in an optimal manner, without
confusion.

1) There's no need to make the identity page separate from the config space. The real problem is the config space is too small. We can fix that without making any changes to virtio-blk by putting the config space in a separate BAR.

2) Passing an ATA identity page is goofy. We should just pass the serial number and let Linux generate the identity page. Just because Linux requires this as it's user space interface, that doesn't mean that other guests will (like Windows). Instead of exposing an opaque blob, we should expose the information we need in a structured way.

Regards,

Anthony Liguori




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