Re: [PATCH] kvm tools: adds a PCI device that exports a host shared segment as a PCI BAR in the guest

[Sasha Levin <levinsasha928@gmail.com>]

On Thu, 2011-08-25 at 14:30 +0300, Avi Kivity wrote:
> On 08/25/2011 02:15 PM, Pekka Enberg wrote:
> > On Thu, Aug 25, 2011 at 1:59 PM, Stefan Hajnoczi<stefanha@gmail.com>  wrote:
> > >  Introducing yet another non-standard and non-Linux interface doesn't
> > >  help though.  If there is no significant improvement over ivshmem then
> > >  it makes sense to let ivshmem gain critical mass and more users
> > >  instead of fragmenting the space.
> >
> > Look, I'm not going to require QEMU compatibility from tools/kvm
> > contributors. If you guys really feel that strongly about the
> > interface, then either
> >
> >    - Get Rusty's "virtio spec pixie pee" for ivshmem
> 
> It's not a virtio device (doesn't do dma).  It does have a spec in 
> qemu.git/docs/specs.

Please note that the spec you have in /docs/specs is different from what
Cam has in his git tree
(https://gitorious.org/nahanni/guest-code/blobs/master/device_spec.txt
).

If we are going to add it to KVM tool maybe it's a good time to move it
out of QEMU tree and make it less QEMU specific?

> 
> >    - Get the Linux driver merged to linux-next
> 
> ivshmem uses uio, so it doesn't need an in-kernel driver, IIRC.  Map 
> your BAR from sysfs and go.
> 
> >    - Help out David and Sasha to change interface
> >
> > But don't ask me to block clean code from inclusion to tools/kvm
> > because it doesn't have a QEMU-capable interface.
> 
> A lot of thought has gone into the design and implementation of 
> ivshmem.  But don't let that stop you from merging clean code.

Theres a big difference in requiring it to be ivshmem compatible because
ivshmem is good and requiring it to be ivshmem compatible because thats
what QEMU is doing.

Looking at the comments in this thread I would have expected to see much
more comments regarding the technical supremacy of ivshmem over a simple
memory shared block instead of the argument that KVM tools has to
conform to QEMU standards.

-- 

Sasha.