Re: [Qemu-devel] [PATCH for-2.7 v2 05/17] raw-posix: Implement .bdrv_lockf

[Richard W.M. Jones]

On Tue, Apr 19, 2016 at 02:34:30PM +0100, Daniel P. Berrange wrote:
> Have you ever considered integration with the QEMU NBD server. We
> don't have APIs for enabling it explicitly in libvirt, but it strikes
> me that it could be ideally suited for your needs.
> 
> eg a hypothetical libvirt command to export a disk via NBD:
> 
>    virsh dom-export-disk myguest --readonly vda1  localhost 9000
>    qemu-img create -f qcow2 -b nbd:localhost:9000 tmp-overlay.img
>    ...do stuff...
>    virsh dom-unexport-disk myguest vda1
> 
> Or to make cleanup easier, perhaps there's a way to tell QEMU
> to close its NBD server after it has had 1 client connection.
> 
> With this approach, you wouldn't need to take any lock on the
> underlying real image.

It's been on my todo list for a long time, but this does require
libvirt to be involved, and libvirt is not the default for upstream
libguestfs.  Even with the libvirt backend, there are still uses cases
like:

  virt-df -a /mnt/vms/disk.img -h
  virt-inspector -a /mnt/vms/disk.img | grep some_insecure_software
  for f in /mnt/vms/*; do virt-alignment-scan -a $f; done
and so on.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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