Re: [PATCH] xen: Put wait.c behind CONFIG_WAIT

[Jason Andryuk <jason.andryuk@xxxxxxx>]

On 2026-02-12 02:38, Jan Beulich wrote:
> On 11.02.2026 18:30, Andrew Cooper wrote:
> > On 11/02/2026 5:01 pm, Jason Andryuk wrote:
> > > wait.c is only used by vm_event.c.  Make CONFIG_VM_EVENT select
> > > CONFIG_WAIT, and use CONFIG_WAIT to control building it.
> > >
> > > Provide stubs of functions called from common code.  entry.S needs an
> > > ifdef to hide the symbol from the assembly.
> > >
> > > Also conditionalize .waitqueue_vcpu in struct vcpu to save space.
> > >
> > > Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> > I'd really rather see the API/ABI changes required to purge wait.c
> > entirely, but I guess this will do in the short term.
> >
> > Two things want further thought.
> >
> > First, because ARM uses per-vCPU stacks not per-pCPU stacks, it doesn't
> > need this infrastructure in the first place, but it looks like it's
> > still compiled in and half wired up.  I suppose you don't notice because
> > you compile out VM_EVENT on ARM too?
> But if we want it compiled out altogether on Arm, ...
>
> > Second CONFIG_WAIT isn't great name because there are many things it
> > could be.  I'd be tempted to just reuse CONFIG_VM_EVENT and go without
> > CONFIG_WAIT.  I do not want to see any new users of wait.c, and it will
> > disappear at some point.
> ... don't we need a separate kconfig control, for it to be selected only
> on x86 (or for it to be dependent on x86, and then imply-ed)? Imo
> CONFIG_WAITQUEUE would be okay, as long as it won't have a prompt. We'd
> then simply want to prevent further select-s / imply-s to appear.
ARM VM_EVENT=y won't link without wait.o.  Undefined references to:
wake_up_nr
prepare_to_wait
finish_wait
destroy_waitqueue_head
init_waitqueue_head

So I think that points to re-using my original patch, but with either 
CONFIG_WAITQUEUE or CONFIG_VM_EVENT.  Since CONFIG_VM_EVENT is the only 
user, and we don't want further uses, I would use that.  But I am open 
to either.
Regards,
Jason