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Re: [PATCH v3 07/22] x86/mtrr: expose functions for pausing caching
- To: Sergii Dmytruk <sergii.dmytruk@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 7 Jul 2025 10:32:58 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, trenchboot-devel@xxxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 07 Jul 2025 08:33:08 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06.07.2025 19:34, Sergii Dmytruk wrote:
> On Wed, Jul 02, 2025 at 04:57:12PM +0200, Jan Beulich wrote:
>>> @@ -440,9 +436,10 @@ static DEFINE_SPINLOCK(set_atomicity_lock);
>>> * has been called.
>>> */
>>>
>>> -static bool prepare_set(void)
>>> +struct mtrr_pausing_state mtrr_pause_caching(void)
>>
>> These becoming non-static without being called from anywhere else isn't
>> going to
>> be liked by Misra. Hence the part of static -> extern may need to be deferred
>> until the new user(s) appear(s).
>
> Sounds like small part needs to be moved into the next patch.
>
>> Furthermore this returning of a struct by value isn't very nice, and looks
>> to be
>> easy to avoid here.
>
> Are you suggesting to use an output parameter instead?
Yes.
> Out of curiosity, what's bad in returning trivial structs by value?
It's generally deemed bad practice from all I know, to a fair degree because of
this then (generally) translating to a hidden function argument. While not
relevant here, this also is a corner case of the respective psABI, which is more
likely to cause interoperability issues.
Jan
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