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

[Corneliu ZUZU <czuzu@bitdefender.com>]

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On 2/26/2016 2:31 PM, Jan Beulich wrote:
>>>> On 26.02.16 at 13:20, <czuzu@bitdefender.com> 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@bitdefender.com> 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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