Re: [Xen-devel] [V10 PATCH 08/23] PVH xen: Introduce PVH guest type and some basic changes.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.08.13 at 01:26, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> On Tue, 6 Aug 2013 13:06:37 +0100
> George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
> 
>> On Tue, Aug 6, 2013 at 12:47 PM, Jan Beulich <JBeulich@xxxxxxxx>
>> wrote:
>> >>>> On 06.08.13 at 13:29, George Dunlap
>> >>>> <George.Dunlap@xxxxxxxxxxxxx> wrote:
>> >> On Wed, Jul 24, 2013 at 2:59 AM, Mukesh Rathor
>> >> <mukesh.rathor@xxxxxxxxxx> wrote:
>> >>> --- a/xen/arch/x86/x86_64/traps.c
>> >>> +++ b/xen/arch/x86/x86_64/traps.c
>> >>> @@ -141,7 +141,7 @@ void show_registers(struct cpu_user_regs
>> >>> *regs) }
>> >>>  }
>> >>>
>> >>> -void vcpu_show_registers(const struct vcpu *v)
>> >>> +void vcpu_show_registers(struct vcpu *v)
>> >>
>> >> Rather than doing this (which could potentially mask a bug in which
>> >> something actually *does* get changed),  wouldn't it make more
>> >> sense to make hvm_kernel_mode (and hvm_get_segment_register) be
>> >> const?
>> >
>> > That's what I suggested first too, but which turned out not to
>> > work: Down the call tree there is a use of v where a pointer to
>> > non-const is required (iirc in VMX specific code).
>> 
>> Then the changelog should say that, preferably the exact function
>> where non-const is needed, so people know why that's necessary without
>> having to do their own looking.
> 
> And the changelog does say it:
> 
> "Note, we drop the const qualifier from vcpu_show_registers() to 
>  accomodate the hvm function call in guest_kernel_mode()."

But I think George really was after you pointing out where down
the call tree the real need for this arises (i.e. why that call tree
can't instead have const-s added).

Jan


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