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Re: [Qemu-devel] [PATCH v5 2/4] shutdown: Prepare for use of an enum in

From: Dr. David Alan Gilbert
Subject: Re: [Qemu-devel] [PATCH v5 2/4] shutdown: Prepare for use of an enum in reset/shutdown_request
Date: Fri, 28 Apr 2017 16:27:29 +0100
User-agent: Mutt/1.8.0 (2017-02-23)

* Eric Blake (address@hidden) wrote:
> On 04/28/2017 03:08 AM, Dr. David Alan Gilbert wrote:
> > * Eric Blake (address@hidden) wrote:
> >> We want to track why a guest was shutdown; in particular, being able
> >> to tell the difference between a guest request (such as ACPI request)
> >> and host request (such as SIGINT) will prove useful to libvirt.
> >> Since all requests eventually end up changing shutdown_requested in
> >> vl.c, the logical change is to make that value track the reason,
> >> rather than its current 0/1 contents.
> >>
> >>  ##
> >> +# @ShutdownCause:
> >> +#
> >> +# Enumeration of various causes for shutdown.
> >> +#
> >> +# @host-qmp: Reaction to a QMP command, such as 'quit'
> >> +# @host-signal: Reaction to a signal, such as SIGINT
> >> +# @host-ui: Reaction to a UI event, such as closing the window
> >> +# @host-replay: The host is replaying an earlier shutdown event
> >> +# @host-error: Qemu encountered an error that prevents further use of the 
> >> guest
> >> +# @guest-shutdown: The guest requested a shutdown, such as via ACPI or
> >> +#                  other hardware-specific action
> >> +# @guest-reset: The guest requested a reset, and the command line
> >> +#               response to a reset is to instead trigger a shutdown
> >> +# @guest-panic: The guest panicked, and the command line response to
> >> +#               a panic is to trigger a shutdown
> > 
> > It's a little coarse grained;  is there anyway to pass platform specific 
> > information
> > for debug?  I ask because I spent a while debugging a few bugs with 
> > unexpected
> > resets and had to figure out which of x86's many reset causes triggered it.
> I'm open to any followup patches that add further enum values and
> adjusts the various callers (patch 3 shows how MANY callers use
> qemu_system_shutdown_request).  But I don't think it's necessarily in
> scope for this series - remember, my goal here was merely to distinguish
> between host- and guest-triggered resets (which libvirt and higher
> management tasks want to know)

Yep, that's fine.

> rather than which of multiple reset
> paths was taken (I agree that it is useful during a qemu debug session -
> but that's a different audience).  I also don't consider myself an
> expert in the many ways that x86 can reset - it was easy to blindly
> rewrite qemu_system_shutdown_request() into
> qemu_system_shutdown_request(SHUTDOWN_CAUSE_GUEST_SHUTDOWN) based solely
> on directory, but it would be harder to distinguish which of the
> multiple files should have which finer-grained cause.

Yes, I'm also not an expert on x86 resets - but when I was debugging
I just added a tag in every place it called the reset code.

At a higher level, using your tags, I'm not sure where a reset triggered
by a fault detected by the hypervisor lives - e.g. an x86 triple fault
where the guest screws up so badly that it just gets reset.  Is
that a guest-reset or a guest-panic or what - neither case
was actually asked for by the guest itself.


> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3266
> Virtualization:  qemu.org | libvirt.org

Dr. David Alan Gilbert / address@hidden / Manchester, UK

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