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Date: Tue, 04 Mar 2008 11:09:44 +0800
From: David Xu <davidxu@FreeBSD.org>
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To: Jeff Roberson <jroberson@chesapeake.net>
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Cc: cvs-src@FreeBSD.org, Jeff Roberson <jeff@FreeBSD.org>,
	src-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/kern init_sysent.c syscalls.c
 systrace_args.c src/sys/sys syscall.h syscall.mk sysproto.h
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Jeff Roberson wrote:
> 
> On Tue, 4 Mar 2008, David Xu wrote:
> 
>> Jeff Roberson wrote:
>>
>>>> One question is how I can determine the size of cpuset the kernel is
>>>> using ?
>>>
>>> I wrote it to tolerate user masks that were much larger than the 
>>> kernel mask.  I set the default CPU_SETSIZE in userspace to 128 and 
>>> in kernel it's MAXCPU.  So in practice an application shouldn't have 
>>> to redefine CPU_SETSIZE.  If your set is too small the kernel will 
>>> return ERANGE however.  Unfortunately, if your set is larger than the 
>>> kernel's CPU_MAXSIZE it'll also return ERANGE.  Maybe I should use 
>>> different errnos for those cases.
>>>
>>
>> From my point, userland has to write some urgly code to guess what
>> kernel code wants, it is rather frustrate.
> 
> You can use sysctl kern.smp.maxcpus to get the precise size.
> 

if kern.smp.maxcpus is a stable ABI, I may use it, can it be guaranteed?
I saw following code in kern_cpuset.c, obviously, maxcpus is not
respected.

if (uap->cpusetsize < CPU_SETSIZE || uap->cpusetsize > CPU_MAXSIZE)
     return (ERANGE);