Re: [Qemu-devel] chardev's and fd's in monitors

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Daniel P. Berrange (berrange@redhat.com) wrote:
> On Tue, Oct 18, 2016 at 02:08:14PM +0200, Markus Armbruster wrote:
> > "Daniel P. Berrange" <berrange@redhat.com> writes:
> > 
> > > On Wed, Oct 12, 2016 at 08:15:02PM +0100, Dr. David Alan Gilbert wrote:
> > >> Hi,
> > >>   I had a look at a couple of readline like libraries;
> > >> editline and linenoise.  A difficulty with using them is that
> > >> they both want fd's or FILE*'s; editline takes either but
> > >> from a brief look I think it's expecting to extract the fd.
> > >> That makes them tricky to integrate into qemu, where
> > >> the chardev's hide a whole bunch of non-fd things; in particular
> > >> tls, mux, ringbuffers etc.
> > >> 
> > >> If we could get away with just a FILE* then we could use fopencookie,
> > >> but that's GNU only.
> > >> 
> > >> Is there any sane way of shepherding all chardev's into having an
> > >> fd?
> > >
> > > The entire chardev abstraction model exists precisely because we cannot
> > > make all chardevs look like a single fd. Even those which are fd based
> > > may have separate FDs for input and output.
> > >
> > > IMHO the only viable approach would be to enhance linenoise/editline to
> > > not assume use of fd* or FILE * abstractions.
> > 
> > The real thing (GNU readline) has hooks rl_getc_function,
> > rl_input_available_hook, rl_redisplay_function and so forth, which might
> > do the trick.  Unfortunately, we're stuck with cheap copies due to our
> > foolish acceptance of GPLv2-only contributions.
> 
> I'm wondering if improving read line facilities in HMP is really important
> enough for us to bother dealing with the problems, as opposed to just
> staying with our current impl ?

It's worth us understanding it, but not worth us putting infrastructure in for.
If we can find a way to do it sanely on top of what we've got I think it's worth
it.

Dave

> Regards,
> Daniel
> -- 
> |: http://berrange.com      -o-    http://www.flickr.com/photos/dberrange/ :|
> |: http://libvirt.org              -o-             http://virt-manager.org :|
> |: http://entangle-photo.org       -o-    http://search.cpan.org/~danberr/ :|
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK