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Date: Thu, 12 Jul 2018 21:20:41 -0400 From: "Samudrala, Sridhar" <sridhar.samudrala@...el.com> To: Siwei Liu <loseweigh@...il.com>, "Michael S. Tsirkin" <mst@...hat.com> Cc: Cornelia Huck <cohuck@...hat.com>, si-wei liu <si-wei.liu@...cle.com>, Roman Kagan <rkagan@...tuozzo.com>, Venu Busireddy <venu.busireddy@...cle.com>, Marcel Apfelbaum <marcel@...hat.com>, virtio-dev@...ts.oasis-open.org, qemu-devel@...gnu.org, Alexander Duyck <alexander.h.duyck@...el.com>, Netdev <netdev@...r.kernel.org> Subject: Re: [virtio-dev] Re: [Qemu-devel] [PATCH v3 0/3] Use of unique identifier for pairing virtio and passthrough devices... On 7/12/2018 6:19 PM, Siwei Liu wrote: > On Thu, Jul 12, 2018 at 2:00 PM, Michael S. Tsirkin <mst@...hat.com> wrote: >> On Thu, Jul 12, 2018 at 01:52:53PM -0700, Siwei Liu wrote: >>> The definition is incomplete due to lack of spec. There's no "host" >>> part defined yet in the host-guest interface. If match by MAC is an >>> interface, the same must be done on the host(device) side as well, >>> which has been agreed not the way to go. However, I don't think that's >>> what the author intends to do by interpreting his QEMU patch - it >>> missed the other parts as well, such as the feature negotiation and >>> how it interacts with the paired device. >>> >>> What I said is that match by MAC is just a guest implementation that >>> one can change at any time. We now have the group ID on QEMU, why >>> still sticking to matching by MAC? It shoulnd't be a host-guest >>> interface in the first place anyway. >> I think that match by MAC is a simple portable way to match devices. >> E.g. it will work seamlessly with niche things like zPCI. However > That's a good point. I'm not sure if it's a valid assumption that zPCI > should always use the same MAC address as that of virtio. Someone > who's more familiar with the use case may decide and work on that. It > means VFIO device has to take in the MAC address as an identifier to > the "-device vfio-pci,.." QEMU option. I think there's no point to > match device using group ID in QEMU while using MAC in the guest. > Based on that assumption, I'd go with making VIRTIO_NET_F_STANDBY to > match device based on group ID, while someone may come up with another > feature bit later, say VIRTIO_NET_F_STANDBY_BY_MAC when its QEMU > support is available. Would it make sense? VIRTIO_NET_F_STANDBY as defined in the guest virtio_net driver supports match by MAC address. I think we should add support for this feature bit in QEMU. If submitting a patch to update the spec is a pre-requisite to add this feature bit to QEMU, i can do that. As far as i understand, group id patches to QEMU are still under review. Matching by group ID can be another feature bit that could support matching by group id as well as MAC. > -Siwei > >> there are other niche use-cases that aren't addressed by match by MAC >> such as PF pass-through as a primary, and the pci bridge trick addresses >> that at cost of some portability. >> >> So I see no issues supporting both mechanisms, but others on the TC >> might feel differently. >> >> -- >> MST
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