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

[Richard W.M. Jones]

On Fri, Aug 16, 2019 at 12:08:10PM -0500, 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>
> ---
>  plugins/rust/nbdkit-rust-plugin.pod | 10 ++++++++++
>  plugins/rust/src/lib.rs             | 13 +++++++++++++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/plugins/rust/nbdkit-rust-plugin.pod b/plugins/rust/nbdkit-rust-plugin.pod
> index db2a55ee..930829cc 100644
> --- a/plugins/rust/nbdkit-rust-plugin.pod
> +++ b/plugins/rust/nbdkit-rust-plugin.pod
> @@ -90,6 +90,16 @@ thread models, see L<nbdkit-plugin(3)/THREADS>.
> 
>  =back
> 
> +=head2 Missing callbacks
> +
> +=over 4
> +
> +=item Missing: C<can_extents> and C<extents>
> +
> +These are not yet supported.
> +
> +=back
> +
>  =head1 SEE ALSO
> 
>  L<nbdkit(1)>,
> diff --git a/plugins/rust/src/lib.rs b/plugins/rust/src/lib.rs
> index a3dbf43e..25af2fe6 100644
> --- a/plugins/rust/src/lib.rs
> +++ b/plugins/rust/src/lib.rs
> @@ -93,6 +93,15 @@ pub struct Plugin {
>      pub magic_config_key: *const c_char,
> 
>      pub can_multi_conn: Option<extern fn (h: *mut c_void) -> c_int>,
> +
> +    // Slots for extents functions, which needs more integration.
> +    _can_extents: Option<extern fn ()>,
> +    _extents: Option<extern fn ()>,
> +
> +    pub can_cache: Option<extern fn (h: *mut c_void) -> c_int>,
> +    pub cache: Option<extern fn (h: *mut c_void,
> +                                 count: u32, offset: u64,
> +                                 flags: u32) -> c_int>,
>  }
> 
>  pub enum ThreadModel {
> @@ -146,6 +155,10 @@ impl Plugin {
>              zero: None,
>              magic_config_key: std::ptr::null(),
>              can_multi_conn: None,
> +            _can_extents: None,
> +            _extents: None,
> +            can_cache: None,
> +            cache: None,
>          }
>      }
>  }

This one seems straightforward, so ACK.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top