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

On 07/08/13 00:26, Mukesh Rathor 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>
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
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()."

I said *exact function*. guest_kernel_mode() doesn't need it non-const; it needs it because of a function that it calls. That in turn doesn't need it non-const either -- it needs it because of the next one down. Who *actually* needs vcpu to be non-const, way down at the bottom? That's what I need to know to understand why we can't just change each of those functions to const all the way down.


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