linux-kernel - Re: [PATCH] Some systems have a dynamic PAGE_SIZE value and do not add a definition for PAGE_SIZE. This value will have to be retrieved using getpagesize() or sysconf().

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Date:	Thu, 07 Aug 2014 17:37:17 +0200
From:	"Thierry Fauck@...ux.vnet.ibm.com" <thierry@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	avagin@...nvz.org, paulmck@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Some systems have a dynamic PAGE_SIZE value and do not
 add a definition for PAGE_SIZE. This value will have to be retrieved using
 getpagesize() or sysconf().

On 08/06/2014 10:06 PM, Andrew Morton wrote:
> On Wed,  6 Aug 2014 13:34:26 +0200 Thierry FAUCK - IBM LTC <thierry@...ux.vnet.ibm.com> wrote:
>
>> --- a/tools/testing/selftests/ptrace/peeksiginfo.c
>> +++ b/tools/testing/selftests/ptrace/peeksiginfo.c
>> @@ -31,6 +31,10 @@ static int sys_ptrace(int request, pid_t pid, void *addr, void *data)
>>  #define TEST_SICODE_PRIV	-1
>>  #define TEST_SICODE_SHARE	-2
>>  
>> +#ifndef PAGE_SIZE
>> +#define PAGE_SIZE sysconf(_SC_PAGESIZE)
>> +#endif
>> +
>>  #define err(fmt, ...)						\
>>  		fprintf(stderr,					\
>>  			"Error (%s:%d): " fmt,			\
> More details, please.  What are "some systems"?
>
Sorry, about that "common description".
A more appropriate one could be : On IBM powerpc where multiple page
size value are supported, current ppc64 and ppc64el distro don't define
the PAGE_SIZE variable in /usr/include as this is a dynamic value
retrieved by the getpagesize() or sysconf() defined in unistd.h. The
PAGE_SIZE variable sounds defined when only one value is supported by
the kernel.
As such, when the PAGE_SIZE definition doesn't exist system should
retrieve the dynamic value.

Is that a better explanation ?

-- 
Thierry Fauck @ linux.vnet.ibm

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