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

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Date:	Wed, 09 Apr 2008 17:00:25 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	sukadev@...ibm.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

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.

	-hpa
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