[Libguestfs] [nbdkit PATCH 1/2] rust: Implement can_cache

[Richard W.M. Jones]

On Fri, Aug 16, 2019 at 01:05:58PM -0500, Eric Blake wrote:
> On 8/16/19 1:01 PM, Eric Blake wrote:
> > On 8/16/19 12:08 PM, Eric Blake wrote:
> >> Implementing extents requires some coordination for the Rust code to
> >> call back into libnbdkit; I'm not familiar with Rust enough to do
> >> that. But with placeholders for those slots, implementing
> >> can_cache/cache is trivial.  This improves the situation mentioned in
> >> commit 031fae85.
> >>
> >> Signed-off-by: Eric Blake <eblake at redhat.com>
> >> ---
> 
> > And of course, if you want to actually implement extents, and figure out
> > how to expose C-based nbdkit functions to be called by Rust code, be my
> > guest (for .zero, we need nbdkit_set_error(), for extents, we need
> > nbdkit_add_extent(), and then we have several other utility functions
> > like nbdkit_realpath() that could be useful).
> 
> Also, we are lacking a tests/*rust* usage; it would be nice if 'make
> check' covered a Rust plugin (more than just running 'nbdkit
> plugins/rust/target/release/examples/libramdisk.so').

We certainly do need tests for the Rust plugin.  Actually placing them
in tests/ might be difficult because Rust assumes a build environment
(called cargo) and that requires a bunch of files.

Since we already have cargo files it's probably better to put the
tests for this plugin next to the plugin.  Unfortunately an additional
complication is that we probably can't use the tests facility of cargo
because we need to go through building a shared library and running it
under the nbdkit wrapper.  Perhaps we can add them as further examples
and wire up 'make check' to run them?  It's not especially elegant but
here we are.

Rich.

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