Re: [Xen-devel] [PATCH v2] arm/monitor vm-events: Implement guest-request support

[Corneliu ZUZU <czuzu@xxxxxxxxxxxxxxx>]

On 2/26/2016 2:31 PM, Jan Beulich wrote:

On 26.02.16 at 13:20, <czuzu@xxxxxxxxxxxxxxx> wrote:

On 2/26/2016 2:14 PM, Razvan Cojocaru wrote:

On 02/26/2016 02:05 PM, Corneliu ZUZU wrote:

On 2/26/2016 1:56 PM, Jan Beulich wrote:

On 26.02.16 at 12:07, <czuzu@xxxxxxxxxxxxxxx> wrote:

--- a/xen/include/asm-x86/altp2m.h
+++ b/xen/include/asm-x86/altp2m.h
@@ -15,8 +15,8 @@
    * this program; If not, see <http://www.gnu.org/licenses/>.
    */
   -#ifndef _X86_ALTP2M_H
-#define _X86_ALTP2M_H
+#ifndef __ASM_X86_ALTP2M_H
+#define __ASM_X86_ALTP2M_H

Unrelated change? (No need to undo, but please don't mix such
into patches especially when they are quite large already anyway.)

Noted.

@@ -33,5 +33,9 @@ void altp2m_vcpu_initialise(struct vcpu *v);
   void altp2m_vcpu_destroy(struct vcpu *v);
   void altp2m_vcpu_reset(struct vcpu *v);
   -#endif /* _X86_ALTP2M_H */
+static inline uint16_t altp2m_vcpu_idx(struct vcpu *v)

const

'const', as in:

+static inline const uint16_t altp2m_vcpu_idx(struct vcpu *v)

Since there's no functional difference between returning const uint6_t
and plain uint16_t, I assume that Jan meant "const struct vcpu *v".

I thought the functional difference would be when calling:

uint16_t idx = altp2m_vcpu_idx(v); // => can subsequently modify idx
const uint16_t idx = altp2m_vcpu_idx(v); // => cannot subsequently 
modify idx (unless const is casted to non-const)

That's correct, but for this the return type of the function doesn't
matter. In fact I'd expect the compiler to warn about a meaningless
modifier placed on a function return type.

Jan

I find having

static inline const uint16_t altp2m_vcpu_idx(struct vcpu *v)

and subsequently writing

uint16_t idx = altp2m_vcpu_idx(v);

instead of

const uint16_t idx = altp2m_vcpu_idx(v);

without the compiler throwing at least a warning counter-intuitive.

Reminds me of something Linus said in an email: "it would be *stupid* for a C compiler to do anything but what we assume it does".

Noted, will change to 'const struct vcpu *v'.

Corneliu.

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