Re: [Qemu-devel] [PATCH v7 1/8] virtio: endian-ambivalent targets using legacy virtio

[Greg Kurz]

On Wed, 16 Apr 2014 20:32:07 +0300
"Michael S. Tsirkin" <address@hidden> wrote:

> On Wed, Apr 16, 2014 at 05:42:22PM +0100, Peter Maydell wrote:
> > On 16 April 2014 17:34, Michael S. Tsirkin <address@hidden> wrote:
> > > so it looks like virtio is currently compiled per-target.
> > > So why isn't it reasonable to keep it per-target for
> > > purpose of this enhancement?
> > > What am I missing?
> > 
> > "virtio" is more than one C file. Currently per-target:
> > hw/virtio/virtio.c
> > hw/virtio/virtio-balloon.c
> > hw/scsi/virtio-scsi.c
> > hw/block/virtio-blk.c
> > hw/char/virtio-serial-bus.c
> > hw/net/virtio-net.c
> > 
> > Currently built once:
> > hw/char/virtio-console.c
> > hw/virtio/virtio-bus.c
> > hw/virtio/virtio-mmio.c
> > hw/virtio/virtio-pci.c
> > hw/virtio/virtio-rng.c
> > 
> > If we can move files from the first group to the second
> > that's cool.
> 
> But doesn't have to be part of this series, yes?
> I would say let's at least have virtio 1.0 out
> and implemented in qemu and linux guests, then
> we can start deprecate virtio 0.X in favor of it.
> 
> > Moving files from the second to the first is
> > what I'd like to avoid...
> > 
> > thanks
> > -- PMM
> 
> Absolutely.
> 
> Looks like we are in agreement after all.
> 
> So as far as I could see the only issue is with config access
> e.g. in virtio-pci?
> That one already has a branch around virtio_is_big_endian,
> so it's not a problem, there's no need to optimize that.
> 

It is because you haven't looked at the other patches... When
the whole serie is applied, all virtio files use inlined helpers
from virtio-access.h to access memory and fix endianness. That is
why we'd rather not add target dependency here...

This being said, if you have an insight to have branch-less code
for fixed endian targets, and dedicated code for ambivalent endian
targets, please send something.

Cheers.

--
Greg