Re: [Qemu-devel] [PATCH 0/2] ipmi: Allow UUID to be set for a BMC

[Corey Minyard]

On 11/8/18 5:22 PM, David Gibson wrote:
> On Thu, Nov 08, 2018 at 08:19:42AM -0600, address@hidden wrote:
> > The code was using the qemu UUID for the BMC.  But that's really
> > not a good method.  In general, you don't want the GUID to change
> > when you migrate, and you want the GUID to be the same between
> > invocations of qemu (if you have a GUID).
> Hrm.  Generally the qemu UUID should remain the same across a
> migration too, and I think that will be the case if using libvirt.
> Maybe not if running qemu by hand and not specifying the uuid on the
> command line.
>
> I don't really have an objection to allowing the BMC's id to be
> explicitly controlled, but the rationale above seems a bit
> disingenuous.


I'm not sure about migration.  I suppose it could be migrated, but I
would consider the BMC part of the hardware that needs to be the
same on both sides.  It's a fuzzy line, I suppose.  The qemu UUID
is migrated, so I suppose that's not an issue.

Controlling it explicitly is important for some testing I do, and might
be for other people at some point in time, if you are trying to
emulate something specific.  And when re-invoking qemu, you
might want to keep it the same to avoid confusing software.

The big question for you is the lack of a GUID if it's not supplied.
With this change, the get GUID command will return a "command
not supported" error if the GUID is not supplied.

Thanks,

-corey

> > Plus, if you have multiple BMCs, they need to have different
> > GUIDs or the host code cannot tell them apart.  I'm not sure
> > anyone really uses multiple BMCs, but I do a lot of testing
> > with that scenario.
> >
> > This change lets the user set the GUID on the command line, and
> > if the GUID is not set return an error for the GUID fetch command.
> > This maps better to how IPMI should work.
> >
> > This change relies on the UUID being set to all zeros to know that
> > it is not set.  This is not optimal, perhaps, but an all zero
> > UUID isn't valid (it's the Nil UUID), so it should be ok.