linux-kernel - Re: [RFC][v8][PATCH 0/10] Implement clone3() system call

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Date:	Wed, 14 Oct 2009 17:17:39 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Roland McGrath <roland@...hat.com>, linux-kernel@...r.kernel.org,
	Oren Laadan <orenl@...columbia.edu>, serue@...ibm.com,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Andrew Morton <akpm@...l.org>, torvalds@...ux-foundation.org,
	mikew@...gle.com, mingo@...e.hu,
	Nathan Lynch <nathanl@...tin.ibm.com>, arnd@...db.de,
	peterz@...radead.org, Louis.Rilling@...labs.com,
	kosaki.motohiro@...fujitsu.com, randy.dunlap@...cle.com,
	linux-api@...r.kernel.org,
	Containers <containers@...ts.linux-foundation.org>,
	sukadev@...ibm.com
Subject: Re: [RFC][v8][PATCH 0/10] Implement clone3() system call

H. Peter Anvin [hpa@...or.com] wrote:
| On 10/14/2009 03:36 PM, Sukadev Bhattiprolu wrote:
| > H. Peter Anvin [hpa@...or.com] wrote:
| > | 
| > | Overall it seems sane to:
| > | 
| > | a) make it an actual 3-argument call;
| > | b) make the existing flags a u32 forever, and make it a separate
| > |    argument;
| > | c) any new expansion can be via the struct, which may want to have
| > |    an "c3_flags" field first in the structure.
| > 
| > Ok, So will this work ?
| > 
| > 	struct clone_args {
| > 		u32 flags_high;		/* new clone flags (higher bits) */ 
| > 		u32 reserved1;
| > 		u32 nr_pids;
| > 		u32 reserved2;
| > 		u64 child_stack_base;
| > 		u64 child_stack_size;
| > 		u64 parent_tid_ptr;
| > 		u64 child_tid_ptr;
| > 		u64 reserved3;
| > 	};
| > 
| > 	sys_clone3(u32 flags_low, struct clone_args *args, pid_t *pid_list)
| > 
| > Even on 64bit architectures the applications have to use sys_clone3() for
| > the extended features.
| 
| Yes, although I'd just make flags_high a u64.

so we allow 96 bits for flags ?

| The other thing that might be worthwhile is to have a length field on
| the structure; that way we could add new fields at the end if ever
| necessary in the future.

So:
	struct clone_args {
		u64 flags_high;		/* new clone flags (higher bits) */ 
		u64 reserved1;

		u32 nr_pids;
		u32 clone_args_size;

		u64 child_stack_base;
		u64 child_stack_size;

		u64 parent_tid_ptr;
		u64 child_tid_ptr;
	};

	sys_clone3(u32 flags_low, struct clone_args *args, pid_t *pid_list)

BTW, on 64-bit architectures, the flags_low would be 64-bits, but the high-
bits there would be ignored right ?

Not sure if we need a second reserved field now that we add ->clone_args_size.

Thanks,

Sukadev
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