Libguestfs - Aug 2021 - [PATCH virt-v2v] v2v: -o rhv-upload: Enable multi-conn

On Mon, Aug 02, 2021 at 08:41:20AM +0100, Richard W.M. Jones
wrote:
> ---
>  v2v/rhv-upload-plugin.py | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/v2v/rhv-upload-plugin.py b/v2v/rhv-upload-plugin.py
> index a3d578176..51e9b33f7 100644
> --- a/v2v/rhv-upload-plugin.py
> +++ b/v2v/rhv-upload-plugin.py
> @@ -169,6 +169,10 @@ def open(readonly):
>      }
>  
>  
> +def can_multi_conn(h):
> +    return True
Should this be h['can_flush'] instead of True?

Are we guaranteed that imageio guarantees a consistent image across
all other http connections when a flush is received on a single http
connection?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

On Tue, Aug 03, 2021 at 02:20:01PM -0500, Eric Blake
wrote:
> On Mon, Aug 02, 2021 at 08:41:20AM +0100, Richard W.M. Jones wrote:
> > ---
> >  v2v/rhv-upload-plugin.py | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/v2v/rhv-upload-plugin.py b/v2v/rhv-upload-plugin.py
> > index a3d578176..51e9b33f7 100644
> > --- a/v2v/rhv-upload-plugin.py
> > +++ b/v2v/rhv-upload-plugin.py
> > @@ -169,6 +169,10 @@ def open(readonly):
> >      }
> >  
> >  
> > +def can_multi_conn(h):
> > +    return True
> 
> Should this be h['can_flush'] instead of True?
In the later version this is different(-ly bad):

https://listman.redhat.com/archives/libguestfs/2021-August/msg00022.html
> Are we guaranteed that imageio guarantees a consistent image across
> all other http connections when a flush is received on a single http
> connection?
That's a question for Nir (CC'd).

However it's likely true anyway since even in the the current
implementation it flushes all HTTP connections inside the nbdkit
plugin:

https://github.com/libguestfs/virt-v2v/blob/0d6d15ebdcad4a4df54f397cbc1b46fcdaf3f16a/v2v/rhv-upload-plugin.py#L342

and I didn't change this behaviour in the proposed patches.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
http://libguestfs.org/virt-v2v

On Tue, Aug 3, 2021 at 10:26 PM Eric Blake <eblake at redhat.com>
wrote:
>
> On Mon, Aug 02, 2021 at 08:41:20AM +0100, Richard W.M. Jones wrote:
> > ---
> >  v2v/rhv-upload-plugin.py | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/v2v/rhv-upload-plugin.py b/v2v/rhv-upload-plugin.py
> > index a3d578176..51e9b33f7 100644
> > --- a/v2v/rhv-upload-plugin.py
> > +++ b/v2v/rhv-upload-plugin.py
> > @@ -169,6 +169,10 @@ def open(readonly):
> >      }
> >
> >
> > +def can_multi_conn(h):
> > +    return True
>
> Should this be h['can_flush'] instead of True?
>
> Are we guaranteed that imageio guarantees a consistent image across
> all other http connections when a flush is received on a single http
> connection?
imageio keeps multiple connections to qemu-nbd, and pass all requests
to qemu-nbd. No caching is done in imageio.

But we don't do any synchronization, so we may have one flush command
in the middle of a write/write_zeros commands.

Does qemu-nbd wait until the write/wirte_zeros commands complete
before flushing?