Re: Modern HMP

["Dr. David Alan Gilbert" <dave@treblig.org>]

* Daniel P. Berrangé (berrange@redhat.com) wrote:
> On Thu, Jan 22, 2026 at 12:47:47PM -0300, Fabiano Rosas wrote:
> > One question I have is what exactly gets (eventually) removed from QEMU
> > and what benefits we expect from it. Is it the entire "manual"
> > interaction that's undesirable? Or just that to maintain HMP there is a
> > certain amount of duplication? Or even the less-than-perfect
> > readline/completion aspects?
> 
> Over time we've been gradually separating our human targetted code from
> our machine targetted code, whether that's command line argument parsing,
> or monitor parsing. Maintaining two ways todo the same thing is always
> going to be a maint burden, and in QEMU it has been especially burdensome
> as they were parallel impls in many cases, rather than one being exclusively
> built on top of the other.
> 
> Even today we still get contributors sending patches which only impl
> HMP code and not QMP code. Separating HMP fully from QMP so that it
> was mandatory to create QMP first gets contributors going down the
> right path, and should reduce the burden on maint.

Having a separate HMP isn't a bad idea - but it does need some idea of
how to make it easy for contributors to add stuff that's just for debug
or for the dev.   For HMP the bar is very low; if it's useful to the
dev, why not (unless it's copying something that's already in the QMP interface
in a different way);  but although the x- stuff in theory lets
you add something via QMP, in practice it's quite hard to get it through
review without a lot of QMP design bikeshedding.

Dave

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