Re: [Qemu-devel] virtio block device and sysfs

[john cooper <john.cooper@third-harmonic.com>]

Marc Haber wrote:
> Hi,
> 
> On Mon, Mar 22, 2010 at 02:26:11AM -0400, john cooper wrote:
>> This is a tad ironic as that is how this saga begun.  Namely stuffing
>> 20 bytes of serial number string into the virtio-blk PCI config space
>> on qemu's side and pushing it over to the guest driver.  I exposed this
>> to the guest app via a new ioctl cmd which itself was the original
>> point of contention.  Someone took issue with introducing a new
>> interface citing the existence of ATA and SCSI counterparts.  However
>> dragging in the associated baggage in order to emulate those interfaces
>> unintentionally bloated usage of the config space to the point of breakage.
>> To address this I'd moved from using config space to an unused BAR which
>> (understandably) didn't go over too well.  Somewhere along the line Rusty
>> posted a minimal alternative version which directly used a virtio request
>> to retrieve the data from qemu which is arguably the right way to do the
>> job.
> 
> *argh* That sounds like politics.

Well, maybe.  But it is hard to argue with anyone calling the
ATA_IDENTIFY interface ugly -- it is.

Concerning qemu->virtio_blk communication, I don't think an
argument to use PCI config space exists after one looks at
the implementation of adding a new virtio request.

>> That said we still had a dispute over what interface would be used to
>> pass the S/N back to the guest: a new interface or reuse of an existing
>> interface (eg: ATA IDENTIFY).  That's where things fizzled when we
>> couldn't immediately resolve the issue.  So publishing the S/N in
>> /sys would seem to side step this snag.
> 
> Re-using an existing interface would probable make it easier for
> non-Linux OSses to also take advantage of this, since their ATA driver
> is already there.

Exactly my singular motivation and honestly the only redeeming
quality of propagating that crusty interface.

>> I could have swore I sent out a guest-driver-app-interface-less
>> version of the patch using virtio to pass the S/N but didn't find it in
>> the archives.  I did however locate it and can bring it forward as a
>> reference for the above if interest exists.
> 
> If it brings the issue forward and gives me hope to be able to do what
> I want to do in a reasonable time frame, why not.

Just time.  But I'll resurrect the patch so we don't have to go through
all of this again.

-john


-- 
john.cooper@third-harmonic.com