linux-kernel - Re: [RFC v1 01/10] roadtest: import libvhost-user from QEMU

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Date:   Tue, 5 Apr 2022 15:54:12 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     Johannes Berg <johannes@...solutions.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kernel <kernel@...s.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
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        "shuah@...nel.org" <shuah@...nel.org>,
        "brendanhiggins@...gle.com" <brendanhiggins@...gle.com>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "jic23@...nel.org" <jic23@...nel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
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        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [RFC v1 01/10] roadtest: import libvhost-user from QEMU

On Thu, Mar 24, 2022 at 02:00:10PM +0100, Johannes Berg wrote:
> On Fri, 2022-03-11 at 17:24 +0100, Vincent Whitchurch wrote:
> > Import the libvhost-user from QEMU for use in the implementation of the
> > virtio devices in the roadtest backend.
> 
> So hm, I wonder if this is the sensible thing to do?
> 
> Not that I mind importing qemu code, but:
> 
>  1) the implementation is rather complex in some places, and has support
>     for a LOT of virtio/vhost-user features that are really not needed
>     in these cases, for performance etc. It's also close to 4k LOC.

Is this really a problem given that the code is imported as-is?  The
intention is not to have to make a lot of local modifications to it in
the kernel tree.  The code is stable and presumably well-tested
upstream, and upstream maintains it as a separate library (in the QEMU
source tree though) to encourage reuse.

>  2) the implementation doesn't support time-travel mode which might come
>     in handy

True, but I don't see the external time-travel controller stuff being
too useful for the kinds of tests this framework is targeting.