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From: Sukadev Bhattiprolu <sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
Subject: Re: [RFC][v3][PATCH 7/7] Define clone_with_pids syscall
Date: Sat, 13 Jun 2009 11:18:38 -0700
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To: Oren Laadan <orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org>
Cc: Containers <containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, "David C. Hansen" <haveblue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
List-Id: containers.vger.kernel.org

| Call clone_with_pids as follows:
| 
| 	pid_t pids[] = { 0, 77, 99 };
| 	struct target_pid_set pid_set;
| 
| 	pid_set.num_pids = sizeof(pids) / sizeof(int);
| 	pid_set.target_pids = &pids;
| 
| 	syscall(__NR_clone_with_pids, flags, stack, NULL, NULL, NULL, &pid_set);


Now that we need to do a copy_from_user() anyway, is it worth collapsing
one or more parameters into a structure ?

	struct clone_with_pid_args {
		u64 flags;
		void *stack;
		void *tls;
		struct target_pid_set *pid_set;
	};

	struct clone_tid_info {
		int *parent_tidptr;
		int *child_tidptr;
	}

	struct clone_with_pid_args cwp_args;
	struct clone_tid_info ctid_inf;

	...

	syscall(__NR_clone_with_pids, &cwp_args, &ctid_info);

One advantage would be that it would make room for 64 bit clone flags, so we
won't need a new flavor of clone_with_pids() when clone_flags is extended.

Sukadev