Re: [PATCH v5 09/13] hw/cxl/events: Add qmp interfaces to add/release dynamic capacity extents

[Ira Weiny]

Markus Armbruster wrote:
> fan <nifan.cxl@gmail.com> writes:
> 
> > On Wed, Apr 24, 2024 at 03:09:52PM +0200, Markus Armbruster wrote:
> >> nifan.cxl@gmail.com writes:
> >> 
> >> > From: Fan Ni <fan.ni@samsung.com>
> >> >
> >> > Since fabric manager emulation is not supported yet, the change 
> >> > implements
> >> > the functions to add/release dynamic capacity extents as QMP interfaces.
> >> 
> >> Will fabric manager emulation obsolete these commands?
> >
> > If in the future, fabric manager emulation supports commands for dynamic 
> > capacity
> > extent add/release, it is possible we do not need the commands.
> > But it seems not to happen soon, we need the qmp commands for the
> > end-to-end test with kernel DCD support.
> 
> I asked because if the commands are temporary testing aids, they should
> probably be declared unstable.  Even if they are permanent testing aids,
> unstable might be the right choice.  This is for the CXL maintainers to
> decide.
> 
> What does "unstable" mean?  docs/devel/qapi-code-gen.rst: "Interfaces so
> marked may be withdrawn or changed incompatibly in future releases."
> 
> Management applications need stable interfaces.  Libvirt developers
> generally refuse to touch anything in QMP that's declared unstable.
> 
> Human users and their ad hoc scripts appreciate stability, but they
> don't need it nearly as much as management applications do.
> 
> A stability promise increases the maintenance burden.  By how much is
> unclear.  In other words, by promising stability, the maintainers take
> on risk.  Are the CXL maintainers happy to accept the risk here?
> 

Ah...  All great points.

Outside of CXL development I don't think there is a strong need for them
to be stable.  I would like to see more than ad hoc scripts use them
though.  So I don't think they are going to be changed without some
thought though.

Ira

[snip]