linux-kernel - Re: [PATCH] um: virt-pci: set device ready in probe()

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Date:   Sun, 12 Jun 2022 10:08:17 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Vincent Whitchurch <vincent.whitchurch@...s.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        kernel@...s.com, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Jason Wang <jasowang@...hat.com>, linux-um@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] um: virt-pci: set device ready in probe()

On Sun, Jun 12, 2022 at 10:58:20AM +0200, Johannes Berg wrote:
> On Fri, 2022-06-10 at 20:34 -0400, Michael S. Tsirkin wrote:
> > 
> > Also fixes this commit:
> > 
> > commit 68f5d3f3b6543266b29e047cfaf9842333019b4c
> > Author: Johannes Berg <johannes.berg@...el.com>
> > Date:   Fri Mar 5 13:19:58 2021 +0100
> > 
> >     um: add PCI over virtio emulation driver
> 
> Hm, why? It worked before the harden change.

Worked on a specific hypervisor. It was out of spec though.

> > BTW Johannes I think you need to spec this device and get
> > an ID - what's the plan for that? Current hack of punting
> > this to userspace isn't really any good long term.
> 
> Yeah, agree, it dropped off my radar (and the process is a bit
> cumbersome IMHO).

Hmm.

So right the recommended way is:
post patch
open github issue
send an email requesting vote

I guess we can switch request for vote to the github issue
to streamline this a bit - do you think that will help?




> But I'm not quite sure what you mean wrt. "punting to userspace", here
> in the virt-pci code I'm punting to the Kconfig :-)
> 
> Did you just mix that up, or was there some additional userspace thing
> you're thinking of?

Right, I meant "punting it to the user".

> The only userspace thing I can think of it is in virtio_uml where you
> have the ID on the command-line, but that's because it implements the
> virtio device bus over vhost-user which doesn't have ID discoverability
> in the protocol. That could also be fixed I guess, but it's a bit of a
> chicken & egg problem, if you don't have the ID and discovering it were
> not supported, you'd end up with an unusable device unless you specified
> the ID, in which case you don't need to discover it...
> 
> johannes


So, please start by reserving an id.

-- 
MST