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

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Date:	Mon, 19 Oct 2009 21:03:15 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Matt Helsley <matthltc@...ibm.com>,
	Oren Laadan <orenl@...rato.com>,
	Daniel Lezcano <daniel.lezcano@...e.fr>,
	randy.dunlap@...cle.com, arnd@...db.de, linux-api@...r.kernel.org,
	Containers <containers@...ts.linux-foundation.org>,
	Nathan Lynch <nathanl@...tin.ibm.com>,
	linux-kernel@...r.kernel.org, Louis.Rilling@...labs.com,
	kosaki.motohiro@...fujitsu.com, hpa@...or.com, mingo@...e.hu,
	torvalds@...ux-foundation.org,
	Alexey Dobriyan <adobriyan@...il.com>, roland@...hat.com,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [RFC][v8][PATCH 0/10] Implement clone3() system call

Eric W. Biederman [ebiederm@...ssion.com] wrote:
| > clone3() seemed to be the leading contender from what I've read so far.
| > Does anyone still object to clone3() after reading the whole thread?
| 
| I object to what clone3() is.  The name is not particularly interesting.
| 
| The sanity checks for assigning pids are missing and there is a todo
| about it.  I am not comfortable with assigning pids to a new process
| in a pid namespace with other processes user space processes executing
| in it.

Could you clarify ? How is the call to alloc_pidmap() from clone3() different
from the call from clone() itself ?

| 
| How we handle a clone extension depends critically on if we want to
| create a processes for restart in user space or kernel space.
| 
| Could some one give me or point me at a strong case for creating the
| processes for restart in user space?

There has been a lot of discussion on this with reference to the
Checkpoint/Restart patchset. See http://lkml.org/lkml/2009/4/13/401
for instance.

| 
| The pid assignment code is currently ugly.  I asked that we just pass
| in the min max pid pids that already exist into the core pid
| assignment function and a constrained min/max that only admits a
| single pid when we are allocating a struct pid for restart.  That was
| not done and now we have a weird abortion with unnecessary special cases.

I did post a version of the patch attemptint to implement that. As
pointed out in:

	http://lkml.org/lkml/2009/8/17/445

we would need more checks in alloc_pidmap() to cover cases like min or max
being invalid or min being greater than max or max being greater than pid_max
etc. Those checks also made the code ugly (imo).

Sukadev
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