Re: [PATCH] migration: Add canary to VMSTATE_END_OF_LIST

[Peter Maydell]

On Thu, 13 Jan 2022 at 01:21, Peter Xu <peterx@redhat.com> wrote:
>
> On Wed, Jan 12, 2022 at 10:56:07AM +0000, Peter Maydell wrote:
> > We could have vmstate_register_with_alias_id() iterate through
> > and assert presence of the right terminator (probably only if
> > qtest enabled, or some other suitable condition). Then the
> > existing tests that do the basic "check we can instantiate every
> > device and initialize every board model" would run that code
> > and catch most missing terminator cases, I think.
>
> Agreed.  How about assert it even without qtest?  We do tons of assertion for
> programming errors anyway in QEMU.

I don't inherently object, but in this case to do the assertion
we'd need to do a scan over the fields arrays which we wouldn't
otherwise need to, so the cost of the assert is not simply
the compare-and-branch but also the loop over the array. If
that's not significant in terms of start-up time costs we can
just go ahead and do it (which would be nicer for debugging
and making it really obvious to people writing new devices)
but my remark above was a gesture towards "maybe we need to
not do it for normal startup"..

-- PMM