Re: [Qemu-devel] [RFC PATCH 0/5] FAULT INJECTION FRAMEWORK

[Stefan Hajnoczi]

On Mon, Jul 01, 2019 at 12:16:44PM +0200, Philippe Mathieu-Daudé wrote:
> On 7/1/19 10:37 AM, Stefan Hajnoczi wrote:
> > On Fri, Jun 28, 2019 at 02:45:29PM +0200, Damien Hedde wrote:
> >> This series adds a python framework aiming to provide some ways to do fault
> >> injection in a running vm. In its current state, it allows to easily 
> >> interact
> >> with memory, change gpios and qom properties.
> >>
> >> The framework consists in a python script based on the qmp existing module
> >> which allows to interact with the vm.
> > 
> > How does this compare to qtest?  There seems to be a lot of overlap
> > between them.
> > 
> > Why is it called "fault injection"?  The commands seem to be
> > general-purpose device testing functions (like qtest and libqos), not
> > functions for testing error code paths as would be expected from a fault
> > injection framework.
> 
> I understand qtest is to test QEMU, while this framework/command is to
> test how the guest react to an hardware faults.

The commands seems to be equivalent to qtest commands, just implemented
as QMP commands.

Damien: Can you explain the use case more and show some example test
cases?

> To use the qtest_mem commands you need to run QEMU with the qtest
> chardev backend, while this series expose a QMP interface.
> 
> To avoid the overlap, a cleaner follow up might be to have qtest wrap
> these QMP commands (mostly like HMP commands do).
> 
> Another note while looking at a glance, qtest uses the 1st cpu address
> space view, this series allow to select a specific cpu.
> 
> It makes sense to me to be able to select address spaces by name (more
> generic, not restricted to a cpu view, since one might want to inject
> fault in a device ram not always mapped to a cpu: dma, emac desc).

The naming issue still stands: none of the commands actually perform
fault injection.  They can be used for other types of testing or even
non-testing purposes.

Fault injection commands would be "make the next watchdog expiry fail",
"return error code X on the next DMA request", "report an AHCI link
failure", etc.

These commands are lower-level.  Therefore, I think "fault injection
framework" is a misnomer and will age poorly if this API is extended in
the future.

Stefan

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