linux-kernel - Re: [PATCH 0/3] clone64() and unshare64() system calls

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Date:	Thu, 10 Apr 2008 08:48:50 +0200
From:	Cedric Le Goater <clg@...ibm.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	sukadev@...ibm.com, Andrew Morton <akpm@...l.org>,
	serue@...ibm.com, "David C. Hansen" <haveblue@...ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] clone64() and unshare64() system calls

H. Peter Anvin wrote:
> sukadev@...ibm.com wrote:
>> This is a resend of the patch set Cedric had sent earlier. I ported
>> the patch set to 2.6.25-rc8-mm1 and tested on x86 and x86_64.
>> ---
>>
>> We have run out of the 32 bits in clone_flags !
>>
>> This patchset introduces 2 new system calls which support 64bit
>> clone-flags.
>>
>>      long sys_clone64(unsigned long flags_high, unsigned long flags_low,
>>         unsigned long newsp);
>>
>>      long sys_unshare64(unsigned long flags_high, unsigned long
>> flags_low);
>>
>> The current version of clone64() does not support CLONE_PARENT_SETTID
>> and CLONE_CHILD_CLEARTID because we would exceed the 6 registers limit
>> of some arches. It's possible to get around this limitation but we
>> might not
>> need it as we already have clone()
>>
> 
> I really dislike this interface.
> 
> If you're going to make it a 64-bit pass it in as a 64-bit number,
> instead of breaking it into two numbers.  Better yet, IMO, would be to
> pass a pointer to a structure like:
> 
> struct shared {
>     unsigned long nwords;
>     unsigned long flags[];
> };
> 
> ... which can be expanded indefinitely.

ok.

What about the copy_from_user() overhead ? is this something we care 
about for a clone like syscall ?

If not, this would certainly make our life simpler to extend clone flags.
I'm ready to implement anything if someone would just tell me in which
direction.

Thanks !

C. 
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