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Re: [PATCH v5 02/11] pci: add option for net failover


From: Jens Freimann
Subject: Re: [PATCH v5 02/11] pci: add option for net failover
Date: Wed, 23 Oct 2019 22:31:37 +0200
User-agent: NeoMutt/20180716-1376-5d6ed1

On Wed, Oct 23, 2019 at 02:02:11PM -0600, Alex Williamson wrote:
On Wed, 23 Oct 2019 21:30:35 +0200
Jens Freimann <address@hidden> wrote:

On Wed, Oct 23, 2019 at 12:06:48PM -0600, Alex Williamson wrote:
>On Wed, 23 Oct 2019 10:27:02 +0200
>Jens Freimann <address@hidden> wrote:
[...]
>Are there also multi-function considerations that
>should be prevented or documented?  For example, if a user tries to
>configure both the primary and failover NICs in the same slot, I assume
>bad things will happen.

  I would have expected that this is already checked in pci code, but
it is not. I tried it and when I put both devices into the same slot
they are both unplugged from the guest during boot but nothing else
happens. I don't know what triggers that unplug of the devices.

I'm not aware of any other problems regarding multi-function, which
doesn't mean there aren't any.

Hmm, was the hidden device at function #0?  The guest won't find any
functions if function #0 isn't present, but I don't know what would
trigger the hotplug.  The angle I'm thinking is that we only have slot
level granularity for hotplug, so any sort of automatic hotplug of a
slot should probably think about bystander devices within the slot.

Yes that would be a problem, but isn't it the same in the non-failover case
where a user configures it wrong? The slot where the device is plugged is not
chosen automatically it's configured by the user, no? I might be mixing 
something
up here.  I have no idea yet how to check if a slot is already populated, but
I'll think about it.
Thanks!

regards,
Jens



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