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Re: [Qemu-devel] [RFC PATCH 0/2] Migration: support working on file:url
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [RFC PATCH 0/2] Migration: support working on file:url |
Date: |
Fri, 22 Jul 2016 09:04:34 +0100 |
User-agent: |
Mutt/1.6.1 (2016-04-27) |
On Thu, Jul 21, 2016 at 06:41:23PM +0100, Dr. David Alan Gilbert wrote:
> * Daniel P. Berrange (address@hidden) wrote:
> > On Thu, Jul 21, 2016 at 01:05:58PM +0800, zhanghailiang wrote:
> > > It is more simple to use file:url to migrate VM into file.
> > > Besides, it will be used in memory snapshot.
> >
> > NB, you can already migrate into a file
> >
> > "exec:/bin/cat > /path/to/file"
> >
> > and likewise
> >
> > qemu -incoming "exec:/bin/cat /path/to/file"
> >
> > This avoids the problem with POSIX I/O on plain files not actually
> > supporting O_NONBLOCK in any sensible manner, which your file:
> > suggestion suffers from.
>
> Hmm that's a shame; I liked this idea as a nice simplification of the
> exec: stuff.
The only way to achieve that would be to spawn a thread in QEMU that
does I/O to the actual file, and then have the migration code do I/O
to/from that thread via a pipe. IOW, the thread would take the role
of cat. What that's worth doing or not I don't know, given that it
is already possible to use exec+cat.
Regards,
Daniel
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