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Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target |
Date: |
Wed, 18 Jun 2014 18:26:05 +0300 |
On Wed, Jun 18, 2014 at 05:14:17PM +0200, Alexander Graf wrote:
>
> On 18.06.14 17:12, Michael S. Tsirkin wrote:
> >On Wed, Jun 18, 2014 at 02:35:21PM +0200, Greg Kurz wrote:
> >>On Wed, 18 Jun 2014 18:38:14 +0800
> >>Stefan Hajnoczi <address@hidden> wrote:
> >>
> >>>On Tue, Jun 17, 2014 at 09:40:19AM +0200, Alexander Graf wrote:
> >>>>On 17.06.14 09:36, Stefan Hajnoczi wrote:
> >>>>>On Fri, Jun 13, 2014 at 01:18:00PM +0200, Greg Kurz wrote:
> >>>>>>This version merges the changes requested during the v7 review, remarks
> >>>>>>from
> >>>>>>ppc64 dump support review (yes, we talked about virtio there) and the
> >>>>>>work on
> >>>>>>virtio subsections migration. Also two new patches have been added:
> >>>>>>- patch #1 is a preliminary fix for virtio-serial posted by Alexander
> >>>>>>Graf
> >>>>>>- patch #9 prepares the work on the virtio_is_big_endian() helper
> >>>>>>
> >>>>>>The most significant changes are:
> >>>>>>- introduction of a new CPU method for virtio
> >>>>>>- endianness is taken from CPU that resets the device
> >>>>>>- fastpath virtio memory accessors for fixed endian targets
> >>>>>>- VMState based virtio subsections (compatibility friendly)
> >>>>>I'm surprised it's not enough for the virtio device to have an
> >>>>>endianness field (big/little). It seems these patches make endianness
> >>>>>depend on the CPUState through which the device is being accessed.
> >>>>>
> >>>>>Can you explain why it's necessary to check the CPUState?
> >>>>They only check CPUState at the point in time of reset, as that's the only
> >>>>case where we can derive the implicit endian configuration from :).
> >>>What bothers me is that real hardware can't do this. Given that VIRTIO
> >>>1.0 is always little-endian I guess this is just a temporary hack for
> >>>ppc little-endian. Would be nice to add a comment so it's clear why
> >>>this approach is being taken instead of a cleaner solution.
> >>>
> >>>Stefan
> >>Hi Stefan,
> >>
> >>Previous versions of this patch set had such comments:
> >>
> >>"virtio data structures are defined as "target endian", which assumes
> >>that's a fixed value. In fact, that actually means it's platform-specific.
> >>The OASIS virtio 1.0 spec will fix this, by making all little endian.
> >>
> >>We need to support both implementations and we want to share as much code
> >>as possible."
> >>
> >>but these lines got lost between v6 and v7... my bad... :-\
> >>
> >>I agree all of this is a hack but:
> >>- it has been on the table for nearly a year
> >>- ppc LE distros are already available
> >>- the memory accessors part makes sense for 1.0
> >>
> >>and, speaking of 1.0, I couldn't find any clue about when QEMU would support
> >>this (Cc'ing Rusty for his input), but we (IBM and distro partners) need
> >>ppc LE support now.
> >>
> >>Cheers.
> >QEMU 2.2 I think.
> >
> >One disadvantage of this work is that it removes some of the stimulus
> >for people to work on 1.0, replacing it with hacks. Hmm.
>
> If you prefer I can also apply these patches and send a pull request for
> them.
>
>
> Alex
Not yet, please. v8 still got some comments, so we need to get v9.
Then give people a bit of time to review. If everyone's happy it should
be mergeable in about a week from now. Also there are Paolo's patches
already in queue which will conflict, not sure it's a good time for you
to step up and start merging virtio patches.
I'm not nacking, chill :)
I know you want these patches very much, but they aren't yet 100% ready anyway
and I don't see why, meanwhile, I shouldn't mention the downsides for
others to consider.
--
MST
- [Qemu-devel] [PATCH v8 20/20] target-ppc: enable virtio endian ambivalent support, (continued)
- Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target, Peter Maydell, 2014/06/18
- Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target, Michael S. Tsirkin, 2014/06/18
- Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target, Greg Kurz, 2014/06/18
- Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target, Michael S. Tsirkin, 2014/06/18
- Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target, Peter Maydell, 2014/06/18
- Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target, Alexander Graf, 2014/06/18
- Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target, Peter Maydell, 2014/06/18
- Re: [Qemu-devel] [PATCH v8 00/20] virtio endian-ambivalent target, Alexander Graf, 2014/06/18