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Date: Mon, 3 Mar 2008 16:42:45 -1000 (HST)
From: Jeff Roberson <jroberson@chesapeake.net>
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To: David Xu <davidxu@FreeBSD.org>
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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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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.

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