Re: [Qemu-devel] [PATCH 1/3] nbd: Only try to send flush/discard commands if connected to the NBD server

[Nicholas Thomas <nick@bytemark.co.uk>]

On Tue, 2012-10-23 at 12:33 +0200, Kevin Wolf wrote:
> Am 22.10.2012 13:09, schrieb nick@bytemark.co.uk:
> > 
> > This is unlikely to come up now, but is a necessary prerequisite for reconnection
> > behaviour.
> > 
> > Signed-off-by: Nick Thomas <nick@bytemark.co.uk>
> > ---
> >  block/nbd.c |   13 +++++++++++--
> >  1 files changed, 11 insertions(+), 2 deletions(-)
> 
> What's the real requirement here? Silently ignoring a flush and
> returning success for it feels wrong. Why is it correct?
> 
> Kevin

I just needed to avoid socket operations while s->sock == -1, and
extending the existing case of "can't do the command, so pretend I did
it" to "can't do the command right now, so pretend..." seemed like an
easy way out. 

In the Bytemark case, the NBD server always opens the file O_SYNC, so
nbd_co_flush could check in_flight == 0 and return 0/1 based on that;
but I'd be surprised if that's true for all NBD servers. Should we be
returning 1 here for both "not supported" and "can't do it right now",
instead? 


/Nick