linux-kernel - Re: [RFC][v5][PATCH 8/8]: Define clone_with

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Date:	Wed, 09 Sep 2009 08:51:59 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Nathan Lynch <ntl@...ox.com>,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Containers <containers@...ts.linux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, mingo@...e.hu,
	torvalds@...ux-foundation.org,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFC][v5][PATCH 8/8]: Define clone_with_pids() syscall

On 09/09/2009 05:19 AM, Arnd Bergmann wrote:
> 
> This is a complex problem. The structure above would need a conversion
> for the pointer size that you can avoid by using a u64, but that introduces
> another problem:
> 
> 2. use a single pointer, with variable length data structures:
> 
> struct pid_set {
> 	int num_pids;
> 	pid_t pids[0];
> };
> 
> Since pid_t is always an int, you have no problem with padding or
> incompatible types, but rely on a data structure definition that
> is not in C89 (not sure about C99).
> 

C90 has these data structures, but you have to give the array a nonzero
length:

struct pid_set {
	int num_pids;
	pid_t pids[1];
};

In C99, this is spelt:

struct pid_set {
	int num_pids;
	pid_t pids[];
};

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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