linux-kernel - Re: [RFC][v7][PATCH 0/9] Implement clone2() system call

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Date:	Thu, 24 Sep 2009 18:06:42 -0400
From:	Oren Laadan <orenl@...rato.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
CC:	linux-kernel@...r.kernel.org, arnd@...db.de,
	Containers <containers@...ts.linux-foundation.org>,
	Nathan Lynch <nathanl@...tin.ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, hpa@...or.com,
	mingo@...e.hu, torvalds@...ux-foundation.org,
	Alexey Dobriyan <adobriyan@...il.com>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFC][v7][PATCH 0/9] Implement clone2() system call



Sukadev Bhattiprolu wrote:
> Oren Laadan [orenl@...rato.com] wrote:
> | 
> | 
> | Sukadev Bhattiprolu wrote:
> | > Based on these requirements and constraints, we explored a couple of system
> | > call interfaces (in earlier versions of this patchset) and currently define
> | > the system call as:
> | > 
> | > 	struct clone_struct {
> | > 		u64 flags;
> | > 		u64 child_stack;
> | > 		u32 nr_pids;
> | > 		u32 parent_tid;
> | > 		u32 child_tid;
> | 
> | So @parent_tid and @child_tid are pointers to userspace memory and
> | require 'u64' (and it won't hurt to make @reserved1 a 'u64' as well).
> 
> No, as Arnd pointed out, we already pass in a pointer to 'struct clone_struct'
> and the kernel can use that pointer to copy the parent and child tids.

In this form, you place a constraints on where userspace may
place the {parent,child}_tid variable, and require that this
particular clone_struct remain valid memory in the parent until
the child terminates.  This may break existing programs that
use this (threads libraries ?)

Oren.

> 
> | 
> | > 		u32 reserved1;
> | > 		u64 reserved2;
> | > 	};
> | > 
> | 
> | Also, for forward/backward compatibility, explicitly state in the
> | documentation, and enforce in the kernel, that flags which are not
> | defined must not be set, and that reserved{1,2} must remain 0.
> 
> Good idea. Will do.
> 
> Thanks,
> 
> Sukadev
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