[PoCv2 00/15] Rust binding for QAPI (qemu-ga only, for now)

[marcandre . lureau]

From: Marc-André Lureau <marcandre.lureau@redhat.com>

Hi,

Among the QEMU developers, there is a desire to use Rust. (see previous
thread from Stefan "Why QEMU should move from C to Rust", the rust-vmm
related projects and other experiments).

Thanks to our QAPI type system and the associate code generator, it is
relatively straightforward to create Rust bindings for the generated C
types (also called sys/ffi binding) and functions. (rust-bindgen could
probably do a similar job, but it would probably bring other issues).
This provides an important internal API already.

Slightly more complicated is to expose a Rust API for those, and provide
convenient conversions C<->Rust. Taking inspiration from glib-rs
binding, I implemented a simplified version of the FromGlib/ToGlib
traits, with simpler ownership model, sufficient for QAPI needs.

The usage is relatively simple:

- from_qemu_none(ptr: *const sys::P) -> T
  Return a Rust type T for a const ffi pointer P.

- from_qemu_full(ptr: *mut sys::P) -> T
  Return a Rust type T for a ffi pointer P, taking ownership.

- T::to_qemu_none() -> Stash<P>
  Returns a borrowed ffi pointer P (using a Stash to destroy "glue"
  storage data, if any).

- T::to_qemu_full() -> P
  Returns a ffi pointer P. (P resources are leaked/passed to C/ffi)

With those traits, it's relatively easy to implement the QMP callbacks. With
enough interest, we could eventually add new commands in Rust, and start
rewriting QGA in Rust, as it is a simple service. See qga/qmp/ for some
examples. QEMU would be the next obvious target.

My biggest pain-point right now is the handling of 'if' conditions. I tried
different approaches, but none of them are satisfying. I am planning to tackle
this next again, along with full QEMU API schema support and hopefully some t=
est
integration.

v2:
 - split the original patch in smaller patches and more digestable form
 - dropped the DBus interface experiment from this series
 - various build-sys improvements, new configure options --with-rust(-target)
 - various attempts at better meson integration, finally satisfied enough wit=
h the
   current solution, which handles getting link flags from Rust sanely.
   (more meson stuff to come to handle config-host/features mapping etc).
 - rebased, QGA QMP now uses unions, added support for it.
 - start a common crate (which re-surfaced issues with foreign types and trai=
ts,
   worked around with a NewPtr wrapper)
 - explicit errors when ifcond are presents (after various unsucessful attemp=
ts,
   I will try to tackle it in v3)
 - mingw cross compilation support
 - some attempts to add it to CI
 - actually implement {get,set}-vcpus
 - vendor the external crates

Marc-Andr=C3=A9 Lureau (15):
  mingw: fix error __USE_MINGW_ANSI_STDIO redefined
  scripts/qapi: teach c_param_type() to return const argument type
  build-sys: add --with-rust{-target} & basic build infrastructure
  build-sys: add a cargo-wrapper script
  qga/rust: build and link an empty static library
  rust: provide a common crate for QEMU
  scripts/qapi: add Rust sys bindings generation
  qga/rust: generate QGA QAPI sys bindings
  scripts/qapi: add generation of Rust bindings for types
  qga/rust: build Rust types
  qga: add qmp! macro helper
  qga: implement get-host-name in Rust
  qga: implement {get,set}-vcpus in Rust
  travis: add Rust
  rust: use vendored-sources

 .cargo/config                |   5 +
 .gitmodules                  |   3 +
 .travis.yml                  |  18 +-
 Cargo.toml                   |   5 +
 configure                    |  26 ++
 include/qemu/osdep.h         |  10 -
 meson.build                  |  29 ++-
 migration/dirtyrate.c        |   3 +-
 qga/Cargo.toml               |  20 ++
 qga/commands-posix.c         | 159 -------------
 qga/commands-win32.c         |  76 ------
 qga/commands.c               |  34 +--
 qga/lib.rs                   |   5 +
 qga/meson.build              |  30 ++-
 qga/qapi.rs                  |   6 +
 qga/qapi_sys.rs              |   5 +
 qga/qmp/hostname.rs          |   9 +
 qga/qmp/mod.rs               |  61 +++++
 qga/qmp/vcpus.rs             | 161 +++++++++++++
 rust/common/Cargo.toml       |  11 +
 rust/common/src/error.rs     | 109 +++++++++
 rust/common/src/lib.rs       |  10 +
 rust/common/src/qemu.rs      |  30 +++
 rust/common/src/sys.rs       |  58 +++++
 rust/common/src/translate.rs | 309 ++++++++++++++++++++++++
 rust/vendored                |   1 +
 scripts/cargo_wrapper.py     | 102 ++++++++
 scripts/qapi-gen.py          |  18 +-
 scripts/qapi/rs.py           | 204 ++++++++++++++++
 scripts/qapi/rs_sys.py       | 254 ++++++++++++++++++++
 scripts/qapi/rs_types.py     | 447 +++++++++++++++++++++++++++++++++++
 scripts/qapi/schema.py       |  14 +-
 tests/test-bitmap.c          |   1 -
 tests/test-qga.c             |   4 +
 util/oslib-posix.c           |  35 ---
 util/oslib-win32.c           |  13 -
 36 files changed, 1962 insertions(+), 323 deletions(-)
 create mode 100644 .cargo/config
 create mode 100644 Cargo.toml
 create mode 100644 qga/Cargo.toml
 create mode 100644 qga/lib.rs
 create mode 100644 qga/qapi.rs
 create mode 100644 qga/qapi_sys.rs
 create mode 100644 qga/qmp/hostname.rs
 create mode 100644 qga/qmp/mod.rs
 create mode 100644 qga/qmp/vcpus.rs
 create mode 100644 rust/common/Cargo.toml
 create mode 100644 rust/common/src/error.rs
 create mode 100644 rust/common/src/lib.rs
 create mode 100644 rust/common/src/qemu.rs
 create mode 100644 rust/common/src/sys.rs
 create mode 100644 rust/common/src/translate.rs
 create mode 160000 rust/vendored
 create mode 100644 scripts/cargo_wrapper.py
 create mode 100644 scripts/qapi/rs.py
 create mode 100644 scripts/qapi/rs_sys.py
 create mode 100644 scripts/qapi/rs_types.py

--=20
2.28.0