Re: [Xen-devel] [PATCH v4 --for 4.6 COLOPre 11/25] tools/libxc: support to resume uncooperative HVM guests

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Wen Congyang writes ("Re: [Xen-devel] [PATCH v4 --for 4.6 COLOPre 11/25] 
tools/libxc: support to resume uncooperative HVM guests"):
> Sorry for the late reply.
> BEFORE: HVM resume for slow path does not work. You will get the following
> error message:
> "Cannot resume uncooperative HVM guests"
> 
> Fast resume: the guest status is not changed, so there is no need to 
> disconnect and
> reconnect the backend and frontend pv driver.
> 
> Slow path resume: the guest status is changed, so we must disconnect and 
> reconnect
> the backend and frontend pv driver. When we reconnect the backend and 
> frontend, it
> will take too many time, because xenstore is very slow. That is why it is a 
> slow path.
> 
> In which case the slow path doesn't work? If the guest status is changed, but 
> it is
> also corrupted. I don't know what will happen in this case. I think resuming 
> PV guest
> in such state doesn't work(the behavior is undefined.)

Right.  Thanks, this is nice and clear.  Indeed, the guest will be
corrupted and if we're lucky (!) it will crash.

> [discussion of AFTER]
>
> In my test, it works. I know I cannot say it does work in all cases.
> How to know if it does work in all cases?
>     List all cases, and do a test for all cases.
> But I think it is hard to list all cases...

I certainly don't expect you to list them all and test them.  I'm just
trying to understand what you are saying in the commit message.

So I think you could say something like:

 AFTER: I think it should work in XYZ cases.  I have tested PQR
 (only), but the others are probably good because [explanation].

Or perhaps:

 There may still be problems with situation ABC because of problem
 FOO.  I have not tested this.  But situation ABC is already broken
 and this patch makes it no worse.

Thanks,
Ian.

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