Messages in this thread | | | Subject | Re: [Devel] Re: [PATCH 08/10] Introduce functions to restart a process | From | Greg Kurz <> | Date | Wed, 22 Oct 2008 14:44:15 +0200 |
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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.
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