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

[john cooper]

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


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