[libvirt-users] re-create disk image file

[Eric Blake]

On 11/05/2012 01:52 PM, Joe Linoff wrote:
> Hi Eric:

[please don't top-post on technical lists]

> 
> Thank you for your suggestions. Here is what happened when I tried the
> snapshot. I will try the dd a bit later.
> 
> VERSIONS
> virsh: 0.9.10
> qemu: 2.0.12

Huh?  The current upstream version of qemu is 1.2; I don't recognize the
2.0.12 numbering.

> 
> DOM: webdev
> 
> $ ls -l /proc/13196/fd/9 
> lrwx------. 1 qemu qemu 64 Nov  5 11:57 /proc/13196/fd/9 ->
> /tools/vm/images/webdev.img (deleted)
> 
> $ cp /proc/13196/fd/9 /tools/vm/images/webdev.img
> cp: cannot stat `/proc/13196/fd/9': Stale NFS file handle
> 
> $ virsh snapshot-create-as webdev \
>     --no-metadata \
>     --disk-only \
>     --diskspec
> /tools/vm/images/webdev.img,file=/tools/vm/images/webdev.img1
> error: unsupported configuration: no disk named
> '/tools/vm/images/webdev.img'

What does this say?

virsh domblklist webdev

That is the name of the disk where you are creating the snapshot.  The
--diskspec line needs two pieces of information: a designation for the
current file being snapshotted (either the absolute path you used in
your xml, or the shorthand name like 'vda' - valid names are found by
the domblklist command); and the name of the new file to create the
snapshot as.

The fact that your error message complains about "no disk named
'/tools/vm/images/webdev.img'" says that you probably didn't spell the
file the same as it was named in the XML; seeing the domblklist command
will make it clear what name you should be using instead.

> 
> # Pull the contents into the new file
> virsh blockpull $dom /tmp/guest.img1 --wait --verbose

For the blockpull command, the same usage applies - you name the disk by
its path (but note that you just changed the path as a result of the
snapshot-create-as command; as another domblklist would prove) or by its
device name, such as vda.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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