[Libguestfs] Re: [nbdkit PATCH] server: Add --no-meta-contexts option

On Wed, Feb 21, 2024 at 07:12:28PM +0000, Richard W.M. Jones wrote: > > +++ b/docs/nbdkit-protocol.pod > > +as sparse reads or meta contexts for obtaining block status. By > > +default, nbdkit advertises as many features as it can support (in some > > +cases, this can be limited by what callbacks the plugin handles), even > > +if the client does not negotiate to use all advertised features. > > > > Nbdkit also includes some options that are useful mainly when > > performing integration tests, for proving whether clients have sane > > fallback behavior when dealing various older servers permitted by the > > -NBD protocol. Use the I<--no-sr> flag to force the newstyle protocol > > -to decline any client request for structured replies. Use the > > -I<--mask-handshake> parameter to mask off particular global features > > -which are advertised during new-style handshake (defaulting to all > > -supported bits set). Clearing bit 0 (the low order bit) limits a > > -client to using just C<NBD_OPT_EXPORT_NAME> (and is incompatible with > > -TLS or structured replies); clearing bit 1 causes the handshake to > > -send more padding bytes in response to C<NBD_OPT_EXPORT_NAME>. Other > > -bits in the mask will only have an effect if the NBD protocol is > > +NBD protocol. The following options intentionally disable optional > > +parts of the NBD protocol, with successively larger impacts: > > + > > +Use the I<--no-meta-contexts> flag to force the newstyle protocol to > > If you wanted you could do this: > > NBD protocol. The following options intentionally disable optional > parts of the NBD protocol, with successively larger impacts: > > =over 4 > > =item I<--no-meta-contexts> > > Force the newstyle protocol to [...] > > =item I<--no-sr> > > [...] > > =item I<--mask-handshake> > > [...] > > =back Yeah, that does look nicer. I amended along those lines,... > > Looks alright, so: > > Reviewed-by: Richard W.M. Jones <rjones(a)redhat.com&gt; ...then pushed the result as commit 3e401181 Would it also be worth a quick followup to add a --no-structured-replies alias for --no-sr, and/or to document the --no-mc alias silently added here?

Down the road, it would be nice to teach nbdkit to do extended headers (since qemu and libnbd already support it); at that time, it would also make sense to add --no-eh / --no-extended-headers options with comparable semantics.