Re: [libgpiod][PATCH 3/3] bindings: rust: mark all owning types as `Send`

["Erik Schilling" <erik.schilling@xxxxxxxxxx>]

On Fri Sep 29, 2023 at 2:45 PM CEST, Bartosz Golaszewski wrote:
> On Fri, Sep 29, 2023 at 12:58 PM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> >
> > On 28-09-23, 16:37, Erik Schilling wrote:
> > > The thread-safety rules of libgpiod allow individual object instances to
> > > be used from different threads. So far, this was not actually possible
> > > with the Rust bindings. Not being `Send` disallowed the user to transfer
> > > the ownership to different threads.
> > >
> > > Rust also has a `Sync` marker. That one would even allow sending
> > > references of objects to other threads. Since we wrap a lot of C
> > > functions with `fn foo(&self)` signatures, that would not be safe.
> > > libgpiod does not allow concurrent API calls to the same object instance
> > > - which Rust would allow for read-only references. Thus, we do not
> > > define that one.
> > >
> > > Chip was already modeled correctly.
> > >
> > > line::Info is not marked as Send since it may either be owning or non-
> > > owning. That problem is fixed as part of a separate pull request [1].
> > >
> > > [1] https://lore.kernel.org/r/20230927-rust-line-info-soundness-v1-0-990dce6f18ab@xxxxxxxxxx
> > >
> > > Link: https://lore.kernel.org/r/CVHO091CC80Y.3KUOSLSOBVL0T@ablu-work
> > > Signed-off-by: Erik Schilling <erik.schilling@xxxxxxxxxx>
> > > ---
> > >  bindings/rust/libgpiod/src/edge_event.rs     | 4 ++++
> > >  bindings/rust/libgpiod/src/event_buffer.rs   | 8 ++++++++
> > >  bindings/rust/libgpiod/src/info_event.rs     | 4 ++++
> > >  bindings/rust/libgpiod/src/line_config.rs    | 4 ++++
> > >  bindings/rust/libgpiod/src/line_request.rs   | 4 ++++
> > >  bindings/rust/libgpiod/src/line_settings.rs  | 4 ++++
> > >  bindings/rust/libgpiod/src/request_config.rs | 4 ++++
> > >  7 files changed, 32 insertions(+)
> >
> > Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> >
>
> Thanks, do you have any comments about the other patches in this series?

Hm. The others are not Rust-related and mostly try to document our
discussion about thread-safety of the C lib. It would probably be good
if you could double-check that I summarized everything correctly.

- Erik