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

[Avi Kivity]

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.

-- 
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