Re: [Qemu-devel] [PATCH v4 22/47] QEMU_VM_CMD_PACKAGED: Send a packaged chunk of migration stream

[Dr. David Alan Gilbert]

* David Gibson (address@hidden) wrote:
> On Fri, Oct 03, 2014 at 06:47:28PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> > 
> > QEMU_VM_CMD_PACKAGED is a migration command that allows a chunk
> > of migration stream to be sent in one go, and be received by
> > a separate instance of the loadvm loop while not interacting
> > with the migration stream.
> > 
> > This is used by postcopy to load device state (from the package)
> > while loading memory pages from the main stream.
> > 
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> 
> Reviewed-by: David Gibson <address@hidden>
> 
> Though one minor comment:
> 
> [snip]
> > +/* We have a buffer of data to send; we don't want that all to be loaded
> > + * by the command itself, so the command contains just the length of the
> > + * extra buffer that we then send straight after it.
> > + * TODO: Must be a better way to organise that
> 
> I'm not quite understanding what that comment's getting at.

We have these VM Commands; and they are a command type, and a length:
     CMD_whatever
     length: whatever
     data for whatever

This comment is describing that, to make things easier for this code it's
ended up as:

     CMD_PACKAGED
     CMD length: 4    <--- i.e. just enough to hold the next 'length' field
     package length
    ---------------
    The package

Which is a little different, hence i thought it needed the comment.

Dave
 
> 
> -- 
> David Gibson                  | I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au        | minimalist, thank you.  NOT _the_ 
> _other_
>                               | _way_ _around_!
> http://www.ozlabs.org/~dgibson


--
Dr. David Alan Gilbert / address@hidden / Manchester, UK