Date: Mon, 14 Jun 2010 20:34:15 +1000 From: Lawrence Stewart <lstewart@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org> Subject: Re: svn commit: r209119 - head/sys/sys Message-ID: <4C1605A7.2000202@freebsd.org> In-Reply-To: <20100614085205.GD13238@deviant.kiev.zoral.com.ua> References: <201006130239.o5D2du3m086332@svn.freebsd.org> <20100613101025.GD1320@garage.freebsd.pl> <4C158B71.205@freebsd.org> <20100614085205.GD13238@deviant.kiev.zoral.com.ua>
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On 06/14/10 18:52, Kostik Belousov wrote:
> On Mon, Jun 14, 2010 at 11:52:49AM +1000, Lawrence Stewart wrote:
>> On 06/13/10 20:10, Pawel Jakub Dawidek wrote:
>>> On Sun, Jun 13, 2010 at 02:39:55AM +0000, Lawrence Stewart wrote:
>> [snip]
>>>>
>>>> Modified: head/sys/sys/pcpu.h
>>>> ==============================================================================
>>>> --- head/sys/sys/pcpu.h Sun Jun 13 01:27:29 2010 (r209118)
>>>> +++ head/sys/sys/pcpu.h Sun Jun 13 02:39:55 2010 (r209119)
>>>> @@ -106,6 +106,17 @@ extern uintptr_t dpcpu_off[];
>>>> #define DPCPU_ID_GET(i, n) (*DPCPU_ID_PTR(i, n))
>>>> #define DPCPU_ID_SET(i, n, v) (*DPCPU_ID_PTR(i, n) = v)
>>>>
>>>> +/*
>>>> + * Utility macros.
>>>> + */
>>>> +#define DPCPU_SUM(n, var, sum) \
>>>> +do { \
>>>> + (sum) = 0; \
>>>> + u_int i; \
>>>> + CPU_FOREACH(i) \
>>>> + (sum) += (DPCPU_ID_PTR(i, n))->var; \
>>>> +} while (0)
>>>
>>> I'd suggest first swapping variable declaration and '(sum) = 0;'.
>>> Also using 'i' as a counter in macro can easly lead to name collision.
>>> If you need to do it, I'd suggest '_i' or something.
>>
>> Given that the DPCPU variable name space is flat and variable names have
>> to be unique, perhaps something like the following would address the
>> concerns raised?
>>
>> #define DPCPU_SUM(n, var, sum) \
>> do { \
>> u_int _##n##_i; \
>> (sum) = 0; \
>> CPU_FOREACH(_##n##_i) \
>> (sum) += (DPCPU_ID_PTR(_##n##_i, n))->var; \
>> } while (0)
>
> You do not have to jump through this. Mostly by convention, in our kernel
> sources, names with "_" prefix are reserved for the infrastructure (cannot
> say implementation). I think it is quite safe to use _i for the iteration
> variable.
>
> As an example of this, look at sys/sys/mount.h, implementation of
> VFS_NEEDGIANT, VFS_LOCK_GIANT etc macros. They do use gcc ({}) extension
> to provide function-like macros, but this is irrelevant. Or, look at
> the VFS_ASSERT_GIANT that is exactly like what you need.
Ok cool, thanks for the info and pointers (I didn't know about the ({})
extension or that "_" prefix was definitely reserved). I'm happy to use
_i. Does the following diff against head look suitable to commit?
--- a/sys/sys/pcpu.h Sun Jun 13 02:39:55 2010 +0000
+++ b/sys/sys/pcpu.h Mon Jun 14 20:12:27 2010 +1000
@@ -111,10 +111,10 @@
*/
#define DPCPU_SUM(n, var, sum) \
do { \
+ u_int _i; \
(sum) = 0; \
- u_int i; \
- CPU_FOREACH(i) \
- (sum) += (DPCPU_ID_PTR(i, n))->var; \
+ CPU_FOREACH(_i) \
+ (sum) += (DPCPU_ID_PTR(_i, n))->var; \
} while (0)
/*
Cheers,
Lawrence
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