[Libguestfs] [nbdkit PATCH 3/4] server: Implement list_exports.

[Richard W.M. Jones]

On Mon, Aug 03, 2020 at 09:31:17AM -0500, Eric Blake wrote:
> On 7/31/20 5:22 PM, Eric Blake wrote:
> >From: "Richard W.M. Jones" <rjones at redhat.com>
> >
> >See also:
> >https://www.redhat.com/archives/libguestfs/2020-July/msg00090.html
> >Message-Id: <20200722124201.1823468-2-rjones at redhat.com>
> >
> >For now, this implementation is only for plugins; adding filter
> >support will come later (and probably requires further edits, for the
> >ability for any filter to open up an independent connection to the
> >plugin without being handed next_ops on entry).
> >---
> 
> >@@ -652,6 +661,46 @@ Returning C<0> will allow the connection to continue.  If there is an
> >  error or you want to deny the connection, call C<nbdkit_error> with an
> >  error message and return C<-1>.
> >
> >+=head2 C<.list_exports>
> >+
> >+ int list_exports (int readonly, int default_only,
> >+                   struct nbdkit_exports *exports);
> 
> I'm trying to figure out a situation where knowing whether we are
> running under 'nbdkit -r' (and thus all exports will be read-only)
> will affect the list advertised by the plugin.  But then again, we
> _do_ pass the readonly flag to both .preconnect and .open, which are
> bookends around this call.  That said, now's the time to decide
> whether to keep it or to simplify the interface by dropping it,
> before we bake in a stable release with the API.

A local file which is not writable might be an example of an export
that should only be listed when readonly == 1.  But ...

Unfortunately we only have the -r flag.  What would be actually useful
information is whether the client wants to connect readonly (ie. it
will be sending NBD_FLAG_READ_ONLY) but as that is per-export
information we don't know that yet.

But I'd say we should probably stick with keeping this flag, along
with a stronger disclaimer in the documentation that it might not be
as useful as it appears.

Rich.

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