Re: [libvirt-users] Insert/eject USB
On Sat, Mar 04, 2017 at 01:14:39AM -0600, Leroy Tennison wrote:
Is it possible to insert and eject a USB image in kvm/qemu/libvirt or
are
the only dynamically changeable devices cdroms and floppies? I've searched
the web and I'm either not looking for the right terms or it's obscure. I
should mention that I'm not talking about a connecting a physical host USB
drive to a guest image, I want to be able to use a qcow image as the source.
It depends on what kind of USB device you attach. If you attach a USB hard
disk, then to dynamically change the backing store image, you would need to
do USB hotunplug+hotplug to remove the "old" drive & add a "new"
drive. If
you were to attacha USB cdrom, then you have the choice of simply ejecting
the media, but can still also do hotunplug+hotplug.
The context is that I want to be able to revert a VM image back to a prior
state (internal snapshot) when testing but be able to retain some data
without having to go to the effort of transferring it across the network.
I've excluded cdroms as an option because they are read-only (correct me if
I'm wrong on this) and require some effort to (re)build. Floppy drives
appear to be limited to 1.44M which makes sense but is very limiting.
Correct wrt cdroms & floppies.
Network mounts (NFS, Samba, etc.) require a server supporting the
selected
style of filesystem sharing over the network. I'm not sure I want to find
out what happens to filesystem passthrough when a revert is done (unless
someone knows and it's beneficial).
I tried creating a partition associated with the VM but not auto-mounted,
even if I unmounted the partition before reverting its state was rolled
back. I possibly could get exotic here by setting the immutable attribute
after unmounting the partition but, again, I'm hoping for something a little
simpler and more straightforward. If there's a workable option I haven't
considered I'm open to that.
It sounds like you should want to be using qcow2 internals snapshots to
capture memory+disk state, or if you wnt to get more advanced libvirt has
APIs to allow fine grained creation of snapshots in standalone files.
Regards,
Daniel
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