Re: [Qemu-devel] [PATCH 0/2][RFC] postcopy migration: Linux char device for postcopy

[Isaku Yamahata]

On Thu, Dec 29, 2011 at 03:52:58PM +0200, Avi Kivity wrote:
> On 12/29/2011 03:49 PM, Isaku Yamahata wrote:
> > > 
> > > qemu can have an extra thread that wait4()s the daemon, and relaunch
> > > it.  This extra thread would not be blocked by the page fault.  It can
> > > keep the fd so it isn't lost.
> > > 
> > > The unkillability of process A is a security issue; it could be done on
> > > purpose.  Is it possible to change umem to sleep with
> > > TASK_INTERRUPTIBLE, so it can be killed?
> >
> > The issue is how to solve the page fault, not whether TASK_INTERRUPTIBLE or
> > TASK_UNINTERRUPTIBLE.
> > I can think of several options.
> > - When daemon X is dead, all page faults are served by zero pages.
> > - When daemon X is dead, all page faults are resovled as VM_FAULT_SIGBUS
> > - list/reattach: complications. You don't like it
> > - other?
> 
> Don't resolve the page fault.  It's up to the user/system to make sure
> it happens.  qemu can easily do it by watching for the daemon's death
> and respawning it.
> 
> When the new daemon is started, it can ask the kernel for a list of
> pending requests, and service them.

Great, then we agreed with list/reattach basically.
(Maybe identity scheme needs reconsideration.)
-- 
yamahata