[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: Re: [virtio-comment] virtio and endian-ness
Cornelia Huck <cornelia.huck@de.ibm.com> writes: > On Mon, 19 Aug 2013 12:27:53 +0300 > "Michael S. Tsirkin" <mst@redhat.com> wrote: > >> On Mon, Aug 19, 2013 at 11:09:44AM +0200, Cornelia Huck wrote: >> > On Mon, 19 Aug 2013 12:08:35 +0300 >> > "Michael S. Tsirkin" <mst@redhat.com> wrote: >> > >> > > On Mon, Aug 19, 2013 at 05:17:30PM +0930, Rusty Russell wrote: >> > > > "Michael S. Tsirkin" <mst@redhat.com> writes: >> > > > > On Mon, Aug 19, 2013 at 12:21:03PM +0930, Rusty Russell wrote: >> > > > >> "Michael S. Tsirkin" <mst@redhat.com> writes: >> > > > >> > During the last TC meeting, we discussed making virtio little endian. >> > > > >> > It was suggested that a feature bit can be used for this, >> > > > >> > but I now think I see two problems: >> > > > >> > >> > > > >> > >> > > > >> > 1. Features are optional, >> > > > >> > in that there's no way for device to communicate to >> > > > >> > guest that guest must ack a feature bit, and e.g. fail >> > > > >> > if guest does not ack. >> > > > >> > >> > > > >> > On the other hand, it seems likely >> > > > >> > that a hardware virtio device might want to *only* implement >> > > > >> > little endian format and not both big and little endian. >> > > > >> > >> > > > >> > In other words this would be something Paolo once called >> > > > >> > a "negative feature". >> > > > >> > >> > > > >> > 2. With virtio-pci we are running out of transport bits, >> > > > >> > and need a new config space layout to add extra feature bits. > > Just as point of data: For virtio-ccw we should be able to easily > extend feature bits. Yes, I think virtio-ccw and virtio-mmio could simply add a new feature bit to say "1.0 compliant". In 20 years time that might look a bit awkward, but that's probably OK unless there's an obvious out-of-band mechanism to use. BTW "standards compliant" for proposals so far means: 1) config fields are LE. 2) device-specfic headers are LE (eg. virtio_net_hdr). 3) fields in the ring are LE. For virtio-ccw, the actual commands to manipulate the virtio devices and bus (ie. struct ccw1) would remain BE, because that's the nature of CCW. > Regarding little-endian rings, we could probably hack up some code to > measure the overhead that would give us. That would be great! Thanks, Rusty.
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]