Re: [Libguestfs] [PATCH nbdkit filters-v3 3/7] Introduce filters.

> +This is called when a new client connection is opened and can be used > +to allocate any per-connection data structures needed by the filter. > +The handle (which is not the same as the plugin handle) is passed back > +to other filter callbacks and could be freed in the C<.close> > +callback. > + > +Note that the handle is completely opaque to nbdkit, but it must not > +be NULL. > + > +If there is an error, C<.open> should call C<nbdkit_error> with an > +error message and return C<NULL>. No documentation about setting the underlying layers read-only (useful in a copy-on-write or copy-on-read filter)? Also, is it possible to write a filter that is read-only to the client, but must be able to write to the plugin?