Re: [PATCH]: Add a "migrate_incoming" monitor option

[Chris Lalancette <clalance@redhat.com>]

Daniel P. Berrange wrote:
> An accept trick only handles the TCP case though. I know this was Chris'
> example that we're currently using, but we intend to switch to passing 
> an open file descriptor instead, and proxying the data via a secure 
> channel instead of the plain tcp, or builtin SSH tunnelling. 
> 
> With an open FD we'll need another way - I guess just registering a
> event on POLLIN might do the trick. It seems to me that just having
> an explicit migrate incoming monitor command would be simpler than having
> to code different triggers to implement 'nowait' for each transport
> we have.

I just finished a patch to do the "nowait" for tcp as suggested by Anthony, and
it was actually far less code then I feared.  It just needed a little
re-factoring of the migrate_incoming_tcp() function.  I'll be posting that in a
couple of minutes.  Given how this code worked out, doing a "nowait" for the fd
style is really no big deal.

Both ways (explicit monitor command and "nowait") seem to have their benefits;
the monitor command has the benefit of being more flexible, while the nowait has
the benefit of being similar to already existing Qemu commands.  My preference
is for the monitor command since it seems a little more natural for a management
tool, but the nowait is clearly an option as well.

I'll also post a cleanup patch with Dan's suggestion for the monitor patch, so
both implementations will be available.

Chris Lalancette