Re: [Qemu-devel] [libvirt] [PATCH v2] Add support for fd: protocol

[Eric Blake <eblake@redhat.com>]

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On 06/14/2011 03:39 PM, Corey Bryant wrote:
>> Incremental support is fine by me, but we'll need it sooner or later.
> 
> Qemu currently opens the specified copy-on-write file, finds a backing
> file name in the opened file's header, opens that backing file, and
> repeats.
> 
> So it seems that either a backingN= would be needed or a way to map a
> file descriptor to the file name in the header.
> 
> I think the latter is along the lines of what was discussed here with
> -blockdev:
> http://lists.gnu.org/archive/html/qemu-devel/2011-05/msg02417.html
> 
> Repeating the syntax specified in that thread, you'd have:
> 
> -blockdev id=foo-base,path=fd:4,format=raw
> -blockdev id=foo,path=fd:3,format=qcow2,backing_file=foo-base
> 
> where id is the file name.  This chains the backing files on the command
> line.

I like it.  It scales as deep as we want by adding as many additional
-blockdev entries prior to the -drive that uses the nested -blockdevs.

-- 
Eric Blake   eblake@redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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