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From: Richard Weinberger <richard@nod.at>
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Subject: Re: [RFC v2 17/37] lkl tools: host lib: virtio devices
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To: Johannes Berg <johannes@sipsolutions.net>
Cc: Hajime Tazaki <thehajime@gmail.com>, linux-arch <linux-arch@vger.kernel.org>, cem <cem@freebsd.org>, tavi purdila <tavi.purdila@gmail.com>, linux-um <linux-um@lists.infradead.org>, retrage01 <retrage01@gmail.com>, linux-kernel-library@freelists.org, pscollins <pscollins@google.com>, sigmaepsilon92 <sigmaepsilon92@gmail.com>, liuyuan <liuyuan@google.com>

----- Ursprüngliche Mail -----
> Von: "Johannes Berg" <johannes@sipsolutions.net>
> An: "Richard Weinberger" <richard.weinberger@gmail.com>, "Hajime Tazaki" <thehajime@gmail.com>
> CC: "linux-arch" <linux-arch@vger.kernel.org>, "cem" <cem@freebsd.org>, "tavi purdila" <tavi.purdila@gmail.com>,
> "linux-um" <linux-um@lists.infradead.org>, "retrage01" <retrage01@gmail.com>, linux-kernel-library@freelists.org,
> "pscollins" <pscollins@google.com>, "sigmaepsilon92" <sigmaepsilon92@gmail.com>, "liuyuan" <liuyuan@google.com>
> Gesendet: Dienstag, 26. November 2019 09:43:36
> Betreff: Re: [RFC v2 17/37] lkl tools: host lib: virtio devices

> On Mon, 2019-11-25 at 23:07 +0100, Richard Weinberger wrote:
>> On Fri, Nov 8, 2019 at 6:03 AM Hajime Tazaki <thehajime@gmail.com> wrote:
>> > From: Octavian Purdila <tavi.purdila@gmail.com>
>> > 
>> > Add helpers for implementing host virtio devices. It uses the memory
>> > mapped I/O helpers to interact with the Linux MMIO virtio transport
>> > driver and offers support to setup and add a new virtio device,
>> > dispatch requests from the incoming queues as well as support for
>> > completing requests.
>> > 
>> > All added virtio devices are stored in lkl_virtio_devs as strings, per
>> > the Linux MMIO virtio transport driver command line specification.
>> 
>> Did you checkout arch/um/drivers/virtio_uml.c?
>> Why is this driver needed?
> 
> This isn't really a driver, this is virtio *device-side* code. Our
> virtio_uml is *guest-side* code, and only speaks vhost-user.

Sorry, bad wording from my side. I meant with "driver" a kernel component.
 
> I'm not sure how MMIO devices could possibly work though, does LKL
> intercept MMIO somehow?

My point is that UML and LKL should try to do use the same concept/code
regarding virtio. At the end of day both use virtual devices which use
facilities from the host.
If this is really not possible it needs a good explanation.

Thanks,
//richard