Re: [Qemu-devel] [PATCH v3] net: Adding netmap network backend

[Anthony Liguori]

On Mon, Nov 4, 2013 at 11:51 AM, Luigi Rizzo <address@hidden> wrote:
> On Mon, Nov 04, 2013 at 10:20:12AM -0800, Anthony Liguori wrote:
>> On Mon, Nov 4, 2013 at 10:08 AM, Luigi Rizzo <address@hidden> wrote:
> ...
>> >> On Tue, Oct 29, 2013 at 3:12 AM, Vincenzo Maffione <address@hidden>
>> >> wrote:
>> >> > This patch adds support for a network backend based on netmap.
>> >> > netmap is a framework for high speed packet I/O. You can use it
>> >> > to build extremely fast traffic generators, monitors, software
>> >> > switches or network middleboxes. Its companion software switch
>> >> > VALE lets you interconnect virtual machines.
>> >> > netmap and VALE are implemented as a non intrusive kernel module,
>> >> > support NICs from multiple vendors, are part of standard FreeBSD
>> >> > distributions and available in source format for Linux too.
>> >>
>> >> I don't think it's a good idea to support this on Linux hosts.  This
>> >> is an out of tree module that most likely will never go upstream.
>> >>
>> >> I don't want to live through another kqemu with this if it eventually
>> >> starts to bit-rot.
>> >
>> >
>> > I believe this is very different from kqemu.
>> >
>> > For first, it is just a one-file backend (the patches
>> > to other files are just because there is not yet a way
>> > to automatically generate them; but i am sure qemu
>> > will get there). Getting rid of it, should the code
>> > bit-rot, is completely trivial.
>> >
>> > Second, there is nothing linux specific here. Unless configure
>> > determines that the (possibly out of tree, as in Linux,
>> > or in-tree, as in FreeBSD) netmap headers are
>> > installed, it just won't build the backend.
>>
>> Without being in upstream Linux, we have no guarantee that the API/ABI
>> will be stable over time.  I suspect it's also very unlikely that any
>> many stream distro will include these patches meaning that the number
>> of users that will test this is very low.
>>
>> I don't think just adding another backend because we can helps us out
>> in the long term.  Either this is the Right Approach to networking and
>> we should focus on getting proper kernel support or if that's not
>> worth it, then there's no reason to include this in QEMU either.
>
> anthony,
> i'd still like you to answer the question that i asked before:
>
>         are you opposed to netmap support just for linux, or you
>         oppose to it in general (despite netmap being already
>         upstream in FreeBSD) ?
>
> Your reasoning seems along the lines "if feature X is not upstream
> in linux we do not want to support it".

Yes.  This is the historic policy we have taken for any feature.  I
have no problem with netmap being used on FreeBSD hosts but I think it
should not be enabled on Linux hosts.

Regards,

Anthony Liguori