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

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Date:	Wed, 9 Apr 2008 18:07:17 -0700
From:	sukadev@...ibm.com
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andrew Morton <akpm@...l.org>, clg@...ibm.com, 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 [hpa@...or.com] 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.

Maybe I am missing your point. The glibc interface could take a 64bit
parameter, but don't we need to pass 32-bit values into the system call 
on 32 bit systems ?

> 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.

Yes, this was discussed before in the context of Pavel Emelyanov's patch

	http://lkml.org/lkml/2008/1/16/109

along with sys_indirect().  While there was no consensus, it looked like
adding a new system call was better than open ended interfaces.
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