linux-kernel - Re: [PATCH] virtio: remove virtio-pci root device

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Message-ID: <20110110120808.GA15554@redhat.com>
Date:	Mon, 10 Jan 2011 14:08:08 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Milton Miller <miltonm@....com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Anthony Liguori <aliguori@...ibm.com>,
	Jamie Lokier <jamie@...reable.org>,
	Thomas Weber <swirl@....li>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio: remove virtio-pci root device

On Mon, Jan 10, 2011 at 01:42:19PM +0200, Gleb Natapov wrote:
> On Mon, Jan 10, 2011 at 01:27:39PM +0200, Gleb Natapov wrote:
> > On Mon, Jan 10, 2011 at 01:22:05PM +0200, Michael S. Tsirkin wrote:
> > > On Mon, Jan 10, 2011 at 01:18:59PM +0200, Gleb Natapov wrote:
> > > > On Sun, Jan 09, 2011 at 05:18:21PM +0200, Michael S. Tsirkin wrote:
> > > > > On Fri, Jan 07, 2011 at 02:55:06AM -0600, Milton Miller wrote:
> > > > > > We sometimes need to map between the virtio device and
> > > > > > the given pci device. One such use is OS installer that
> > > > > > gets the boot pci device from BIOS and needs to
> > > > > > find the relevant block device. Since it can't,
> > > > > > installation fails.
> > > > > > 
> > > > > > Instead of creating a top-level devices/virtio-pci
> > > > > > directory, create each device under the corresponding
> > > > > > pci device node.  Symlinks to all virtio-pci
> > > > > > devices can be found under the pci driver link in
> > > > > > bus/pci/drivers/virtio-pci/devices, and all virtio
> > > > > > devices under drivers/bus/virtio/devices.
> > > > > > 
> > > > > > Signed-off-by: Milton Miller <miltonm@....com>
> > > > > 
> > > > > OK, this works fine for me.  I played with options to add compat
> > > > > softlinks under devices/virtio-pci but we still don't get exactly the
> > > > > same layout and since I don't think anyone actually uses them, it's
> > > > > probably ok to just to the simple thing.
> > > > > 
> > > > > Tested/Acked-by: Michael S. Tsirkin <mst@...hat.com>
> > > > > 
> > > > > Rusty, since this help fix at least one user, any chance this can be put
> > > > > in 2.6.38? OK to backport to -stable?
> > > > > 
> > > > > Gleb, could you try this out too?
> > > > > 
> > > > With this patch if I have 3 virtio disks for a VM I get:
> > > > /sys/devices/pci0000:00/0000:00:04.0/virtio0/block/vda
> > > > /sys/devices/pci0000:00/0000:00:05.0/virtio1/block/vdb
> > > > /sys/devices/pci0000:00/0000:00:06.0/virtio2/block/vdc
> > > > 
> > > > Number after virtio has no much sense. It either should be dropped at all
> > > > or be always zero in case we will support more then one virtio controller
> > > > per pci card. In that case each virtio controller will have directories
> > > > virtio0/virtio1/virtio2... under same pci device directory.
> > > 
> > > Yes. But this is the bus name.  It must be unique - all devices
> > > also appear under /sys/bus/virtio/devices.
> > > 
> > It is very strange king of bus that is spread over several PCI devices :)
> > It doesn't make much sense IMHO, but I can leave with it.
> > 
> I can't "leave" with it, but I can "live" with it.

The virtio bus is an attempt to make as many applications as
possible work transparently on any virtio system,
be it lguest, s390 or pci. Arbitrary IDs is just a hint to the
applications 'don't rely on the name at all'.

> --
> 			Gleb.
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