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

[Richard W.M. Jones]

On Fri, Jan 19, 2018 at 05:27:53PM -0600, Eric Blake wrote:
> > +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?

I was leaving this intentionally hazy because I'm not precisely sure
of the rules myself.  I'm going to have a go at caching
[ie. copy-on-read] and copy-on-write filters, which may clarify
things.

I made the other changes you suggested.

Rich.

-- 
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