svn commit: r209119 - head/sys/sys

[Lawrence Stewart]

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