From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752829AbZHMH7o (ORCPT ); Thu, 13 Aug 2009 03:59:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752449AbZHMH7o (ORCPT ); Thu, 13 Aug 2009 03:59:44 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:33676 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752324AbZHMH7n (ORCPT ); Thu, 13 Aug 2009 03:59:43 -0400 Date: Thu, 13 Aug 2009 01:00:49 -0700 From: Sukadev Bhattiprolu To: "Eric W. Biederman" Cc: linux-kernel@vger.kernel.org, Oren Laadan , serue@us.ibm.com, Alexey Dobriyan , Pavel Emelyanov , Andrew Morton , torvalds@linux-foundation.org, mikew@google.com, mingo@elte.hu, hpa@zytor.com, Containers , sukadev@us.ibm.com, Oleg Nesterov Subject: Re: [RFC][v4][PATCH 0/7] clone_with_pids() system call Message-ID: <20090813080049.GA16639@us.ibm.com> References: <20090807061103.GA19343@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: Linux 2.0.32 on an i486 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Eric W. Biederman [ebiederm@xmission.com] wrote: | Sukadev Bhattiprolu writes: | | > === NEW CLONE() SYSTEM CALL: | > | > To support application checkpoint/restart, a task must have the same pid it | > had when it was checkpointed. When containers are nested, the tasks within | > the containers exist in multiple pid namespaces and hence have multiple pids | > to specify during restart. | > | > This patchset implements a new system call, clone_with_pids() that lets a | > process specify the pids of the child process. | > | > Patches 1 through 5 are helpers and we believe they are needed for application | > restart, regardless of the kernel implementation of application restart. | | I'm not very impressed. | | - static int alloc_pidmap(struct pid_namespace *pid_ns) | + static int alloc_pidmap(struct pid_namespace *pid_ns, int pid_max, int last_pid) | | Do that. | | That is pass in pid_max and last_pid, and you don't have to do weird | things in alloc_pidmap, and no set_pidmap is needed. But last_pid is from the pid_ns. Do you mean to have alloc_pidmap() take a pid_min and pid_max and when choosing a specific pid, have pid_min == pid_max == target_pid ? | | No changes to copy_process are needed it already takes a struct pid | argument. I see your point about passing in both 'struct pid*' and target_pids[]. But in the common case the struct pid passed into copy_process() is NULL - allocating pid in do_fork() would significantly alter the existing control flow - no ? alloc_pid() assumes any new pid namespace has been created - in copy_namespaces(). Moving the alloc_pid() to do_fork() would require parsing clone_flags in do_fork() and pulling pid namespace code out of copy_namespaces(). | | I haven't been following closely what is gained by having a clone_with_pids | syscall? When restarting an application from a checkpoint, the application must get the same pid it had at the time of checkpoint. clone_with_pids() would be used during restart so the child can be created with a specific set of pids. | | As for new namespaces that don't need to happen at process creation time | (which is just about anything that is left) we can create a new syscall that | unshares just that one. | Ok. If all new namespaces can be handled with a variant of unshare(), we can decouple clone_with_pids() from the clone-flags issue. | | Eric