Re: [PATCH v10 7/10] xen: implement new foreign copy hypercall

[Frediano Ziglio <freddy77@xxxxxxxxx>]

On Mon, 17 Aug 2026 at 09:04, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 14.08.2026 16:50, Frediano Ziglio wrote:
> > On Fri, 14 Aug 2026 at 15:13, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >> On 14.08.2026 15:47, Frediano Ziglio wrote:
> >>> On Thu, 13 Aug 2026 at 15:22, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >>>> On 13.08.2026 16:03, Frediano Ziglio wrote:
> >>>>> On Thu, 13 Aug 2026 at 10:41, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> >>>>>> On 10.08.2026 12:30, Frediano Ziglio wrote:
> >>>>>>> --- a/xen/common/memory.c
> >>>>>>> +++ b/xen/common/memory.c
> >>>>>>> @@ -1548,6 +1548,141 @@ static int acquire_resource(
> >>>>>>>      return rc;
> >>>>>>>  }
> >>>>>>>
> >>>>>>> +/*
> >>>>>>> + * The "noinline" qualifier avoids the compiler to create a large 
> >>>>>>> function
> >>>>>>> + * consuming quite a lot of stack.
> >>>>>>> + */
> >>>>>>> +static int noinline mem_foreigncopy(
> >>>>>>
> >>>>>> I'm wondering: Is the "mem" prefix really meaningful for a static 
> >>>>>> function in
> >>>>>> a file named memory.c?
> >>>>>>
> >>>>>
> >>>>> Changed
> >>>>>
> >>>>>>> +    XEN_GUEST_HANDLE_PARAM(xen_foreigncopy_t) arg)
> >>>>>>> +{
> >>>>>>> +    struct domain *d, *const currd = current->domain;
> >>>>>>
> >>>>>> With the comment on the new XSM hooks (below) in mind: currd wants to 
> >>>>>> be
> >>>>>> pointer-to-const.
> >>>>>>
> >>>>>
> >>>>> Just rebased on master, all XSM hooks accept no-const pointers to 
> >>>>> domains.
> >>>>> So the suggested change would create warnings.
> >>>>
> >>>> Well, as per below, I pointed you at a particular pending patch, a single
> >>>> hunk of which could be broken out.
> >>>
> >>> Yes, but my changes would have to have casts from const pointers to
> >>> no-const pointers to avoid warnings and the patch you are pointing to
> >>> would have to remove these casts. I find this less clean than having
> >>> one patch using the current code style (that is no-const pointers) and
> >>> another that changes the style entirely.
> >>> But obviously this is just my opinion.
> >>
> >> Such casts would be unacceptable. What instead I have been trying to 
> >> convey:
> >> Your patch wants to gain a dependency on my patch. And if my patch would
> >> take too long to make it in, that one hunk could be broken out into a
> >> separate, easy to get in patch.
> >
> > Okay, then the only choice that's left is the code producing warnings
> > as const pointers are passed to functions requiring no-const pointers.
> > Is this acceptable? Apparently as you are suggesting it it is.
>
> That's not acceptable, the more that due to -Werror this would break the
> build. But that's also not what I said, and I'm having a hard time seeing
> how what I said can be mis-interpreted. What exactly is not clear in "Your
> patch wants to gain a dependency on my patch"?
>
> Btw, I'm about to submit v2 of that XSM series, where I've broken out that
> hunk (for the change to then hopefully go in quickly, allowing you to
> simply re-base rather than carrying a prereq patch).
>
> Jan

Okay, being dependent on
https://lists.xenproject.org/archives/html/xen-devel/2026-08/msg00768.html
would be acceptable.
What was not was being dependent on other large series.
That is more in line to what I proposed multiple times, that is having
a preparation patch for constification and code using const pointer on
my patch.

Frediano