From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755832AbYJVMo3 (ORCPT ); Wed, 22 Oct 2008 08:44:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752451AbYJVMoV (ORCPT ); Wed, 22 Oct 2008 08:44:21 -0400 Received: from mtagate1.de.ibm.com ([195.212.17.161]:33741 "EHLO mtagate1.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752267AbYJVMoU (ORCPT ); Wed, 22 Oct 2008 08:44:20 -0400 Subject: Re: [Devel] Re: [PATCH 08/10] Introduce functions to restart a process From: Greg Kurz To: Louis.Rilling@kerlabs.com Cc: Andrey Mirkin , containers@lists.linux-foundation.org, Cedric Le Goater , linux-kernel@vger.kernel.org, Pavel Emelyanov In-Reply-To: <20081022104448.GX15171@hawkmoon.kerlabs.com> References: <1224285098-573-1-git-send-email-major@openvz.org> <1224285098-573-9-git-send-email-major@openvz.org> <48FC4E0C.7050008@fr.ibm.com> <200810221249.55600.major@openvz.org> <20081022092502.GW15171@hawkmoon.kerlabs.com> <1224669979.4210.15.camel@localhost.localdomain> <20081022104448.GX15171@hawkmoon.kerlabs.com> Content-Type: text/plain Date: Wed, 22 Oct 2008 14:44:15 +0200 Message-Id: <1224679455.4210.24.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 (2.22.3.1-1.fc9) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2008-10-22 at 12:44 +0200, Louis Rilling wrote: > On Wed, Oct 22, 2008 at 12:06:19PM +0200, Greg Kurz wrote: > > On Wed, 2008-10-22 at 11:25 +0200, Louis Rilling wrote: > > > Do you checkpoint uninterruptible syscalls as well? If only interruptible > > > syscalls are checkpointed, I'd say that either this syscall uses ERESTARTSYS or > > > ERESTART_RESTARTBLOCK, and then signal handling code already does the trick, or > > > this syscall does not restart itself when interrupted, and well, this is life, > > > userspace just sees -EINTR, which is allowed by the syscall spec. > > > Actually this is how we checkpoint/migrate tasks in interruptible syscalls in > > > Kerrighed and this works. > > > > > > Louis > > > > > > > I don't know Kerrighed internals but I understand you perform checkpoint > > with a signal handler. Right ? > > Right. This is an kernel-internal-only signal, so all signals remain available > for userspace. > > > This approach has a huge benefit: the > > signal handling code do all the arch dependant stuff to save registers > > in user memory. > > Hm, I'm not sure to understand what you mean here. We just rely on arch code > that jumps to signal handling to correctly setup struct pt_regs, which is then > passed to the checkpoint code. So yes, userspace registers are mostly saved by > existing arch code. But in x86-64 for instance, segment registers still need to > be saved by the checkpoint code (a bit like copy_thread() does), and I don't > know arch-independent functions doing this. > You're right, some segment registers need to be saved on x86 also... I should have written 'most of' in my previous mail. -- Gregory Kurz gkurz@fr.ibm.com Software Engineer @ IBM/Meiosys http://www.ibm.com Tel +33 (0)534 638 479 Fax +33 (0)561 400 420 "Anarchy is about taking complete responsibility for yourself." Alan Moore.