[libvirt] virsh save produces "unknown migration protocol: stdio"

Daniel P. Berrange berrange at redhat.com
Mon Dec 15 15:10:18 UTC 2008

On Mon, Dec 15, 2008 at 02:51:56PM +0000, Richard W.M. Jones wrote:
> I just want to forward this comment on from #virt so that we don't
> lose it.  It appears to be an incompatibility between libvirt 0.5.0
> and recent KVM.
>   <knowinters> Hi, I'm using libvirt 0.5.0 with kvm-79, when I do virsh
>   save kvm replies with "unknown migration protocol: stdio". A state
>   file is created, but it's only 4K and when restored the vm boots from
>   scratch instead of starting where it was when i saved. I googled but
>   couldn't find a resolution. Is this a known issue?
>   <knowinters> nm i think i see what's happening.. it
>   <knowinters> 's using the exec: migration method to call dd to move
>   the state from stdio to a file
>   <knowinters> exec: isn't in kvm-79 i don't think, but i see it in git
>   so ill try that

Suport for the 'stdio' protocol was dropped when migration stuff was 
merged upto QEMU :-( We should never implemented this in libvirt until
it was in QEMU in the first place - we always get screwed when this
kind of stuff eventually gets un-forked() into the main codebase.

danpb_ltop: aliguori: any idea what happened to '-incoming stdio' 
            migration support.... seems to have disappeared
  aliguori: danpb_ltop, no particular reason, just requires a patch
  aliguori: danpb_ltop, what are you using it for?
danpb_ltop: libvirt was using it to restore from a saved state image
  aliguori: danpb_ltop, maybe higher level commands would be better than
            playing tricks with migration?
  aliguori: danpb_ltop, i'm happen to take a suspend command that uses 
            live migration to save to an image or something like that
danpb_ltop: aliguori: i don't particularly mind - we used to have higher 
            level commands, but they got removed in 0.9.0 :-(
danpb_ltop: ok, i'll try and get someone to send a patch for this

So another item for the KVM todo list. Implement a 'suspend filename'
command in the monitor, and a '-restore filename' command line argument.
Or re-add the '-incoming stdio' command line support

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