Date: Wed, 9 Sep 2009 11:03:03 -0700
From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Arnd Bergmann <arnd@arndb.de>, Nathan Lynch <ntl@pobox.com>,
       linux-kernel@vger.kernel.org,
       Containers <containers@lists.linux-foundation.org>,
       "Eric W. Biederman" <ebiederm@xmission.com>, mingo@elte.hu,
       torvalds@linux-foundation.org, Alexey Dobriyan <adobriyan@gmail.com>,
       Pavel Emelyanov <xemul@openvz.org>
Subject: Re: [RFC][v5][PATCH 8/8]: Define clone_with_pids() syscall
Message-ID: <20090909180303.GA21048@us.ibm.com>
References: <20090907211302.GA5892@us.ibm.com> <20090907211700.GH6685@us.ibm.com> <m3zl95l2oz.fsf@pobox.com> <200909091419.50496.arnd@arndb.de> <4AA7CF1F.3020408@zytor.com>
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H. Peter Anvin [hpa@zytor.com] wrote:
| 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 or C99 below should work. Is it ok to use a data structure that is
not in C89 ? 

BTW, would it work if we defined 

	struct pid_set {
		u64 pids;
		int num_pids;
	}

where ->pids can be still be a pointer ? The data structure would
have the same size on all architectures.

Thanks for the input

Sukadev
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