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Date: Sat, 7 Nov 2009 03:44:34 +0000
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] [PATCH 0/4] net-bridge: rootless bridge support for
	qemu
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Mark McLoughlin <markmc@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, Arnd Bergmann <arndbergmann@googlemail.com>, Arnd Bergmann <arnd@arndb.de>, Juan Quintela <quintela@redhat.com>, Dustin Kirkland <kirkland@canonical.com>, qemu-devel@nongnu.org, Michael Tsirkin <mst@redhat.com>, Avi Kivity <avi@redhat.com>

Anthony Liguori wrote:
> Jamie Lokier wrote:
> >Avi Kivity wrote:
> >  
> >>>I know this has been discussed before, but isn't this why there are 
> >>>things like vfork()? 
> >>>      
> >>vfork() doesn't work with threads - it requires that the calling process 
> >>be halted until exec() is called.
> >>    
> >
> >On Linux (NPTL), vfork() is good for this.  It only halts the calling
> >thread.  Other threads continue to run, and when the vfork'd thread
> >called exec*(), it doesn't affect the other threads.  Of course this
> >behaviour isn't portable, but then again, neither is KVM.
> >  
> Yup, see attached program.  Here's the output which confirms this is the 
> case.

Before assuming it, you might want to verify that it's the same on all
kernels which support KVM (including backports) and all versions of
Linux pthreads which might be used.

-- Jamie