Re: [Nbd] NBD wishlist items?

[Mike S. <sn...@gm...>]

On 6/26/07, Paul Clements <pau...@st...> wrote:
> Mike Snitzer wrote:
>
> > How does one do a zero-length read or write?  I've been testing
> > various userspace methods to detect the nbd-client's connection to be
> > hung (TCP timeout).  Using dd is unreliable because the read request
> > is fulfilled from cache if you don't use O_DIRECT.
> >
> > If we could do a zero-length write then this would very easily
> > excercise the nbd connection without any protocol change or O_DIRECT
> > reads.  Can you elaborate on what is needed for reliable zero-length
> > writes?  The 'man 2 write' states:
> > "If count is zero and the file descriptor refers to a regular file, 0
> > may be returned, or an error could be detected.  For a special file,
> > the results are not portable."
>
> I don't know that there is a way to do it from user level. But a minor
> tweak to the driver would allow a user level process or the nbd-client
> itself to do this. And the basic protocol wouldn't change and hopefully
> the server wouldn't have to be modified either -- but that depends on
> how it's implemented.

OK, do you intend to implement this tweak?  I'd be very interested to
give it a go once you have something.

Mike