Re: [Nbd] Question about the expected behaviour of nbd-server for async ops

[Wouter Verhelst <w@...112...>]

On Sun, May 29, 2011 at 08:50:38AM +0200, Wouter Verhelst wrote:
> > Handles can be reused only once the command in question is completed.
> > 
> > You may process commands out of order, and reply out of order,
> > save that
> > a) all write commands *completed* before you process a REQ_FLUSH
> >    must be written to non-volatile storage prior to completing
> >    that REQ_FLUSH (though apparently you should, if possible, make
> >    this true for all write commands *received*, which is a stronger
> >    condition) [Ignore this if you don't set SEND_REQ_FLUSH]
> 
> We already implement that stronger condition, because writes are handled
> in the way they are received. It shouldn't be too hard to implement when
> disordered handling of requests is done, either: stop handling incoming
> requests when you receive a flush request; flag all outstanding requests
> so you know when the flush can be done (after which you can start
> handling incoming requests again); and handle the flush when all flagged
> requests have been handled.

Better yet: don't stop handling and loop over them to flag, which will
take time; instead, just create a new queue of requests to handle, and
only handle the FLUSH request once the old queue is empty.

-- 
The volume of a pizza of thickness a and radius z can be described by
the following formula:

pi zz a