Re: [PATCH 00/11] Rust device model patches and misc cleanups

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/24/24 16:02, Manos Pitsidianakis wrote:
> Hello everyone, the pathological corrosion of QEMU code continues.
> This series expands the device model harness work performed in the
> initial Rust work from the previous month. In particular:

Wow, there's a lot of stuff here!

The very good news is that it's basically all the code that is needed to 
get CI running, after which we can start with the fun stuff.  At the 
same time, "the fun stuff" is also the one that risks introducing 
technical debt, so we need to switch to quality-over-quantity mode and 
have a serious design discussion about it.  I'll do that later as a 
reply to the patches.

>    Code and functionality duplication is not fun, and pl011 was mostly
>    done as a proof of concept for a Rust device because of its small
>    complexity. As of this moment we have not decided on a policy for how
>    to handle these things and it is not in **scope for this patch series
>    anyway**.

That's fine.

Looking at the currently posted series, it seems that we have three main 
themes:

1) small scale cleanups: duplicated and useless code, improved testing. 
These are in 
https://lore.kernel.org/qemu-devel/20241021163538.136941-1-pbonzini@redhat.com/T/ 
and they have been reviewed already.  But these two:

>        Revert "rust: add PL011 device model"
>        rust: add PL011 device model

... should definitely be moved on top to clean up the authorship in "git 
blame" and other similar tools.  Sorry about that.

2) allow using older rustc/bindgen, extend CI to cover it.  This is 
https://lore.kernel.org/qemu-devel/20241022100956.196657-1-pbonzini@redhat.com/T/ 
which still needs review.  These five:

>        rust: add support for migration in device models
>        rust/pl011: move CLK_NAME static to function scope
>        rust/pl011: add TYPE_PL011_LUMINARY device
>        rust/pl011: remove commented out C code
>        rust/pl011: Use correct masks for IBRD and FBRD

(minus the usage of #[derive()] should be included in that series, so 
that qtests pass.  It's not a huge amount of work and I can extract it, 
of course with proper attribution/authorship.

The rest are future work:

>        rust/qemu-api-macros: introduce Device proc macro

This is useful as a starting point but it has the limit of being very 
device-specific.  This is of course okay with properties and vmstate, 
but in my opinion the implementation of class_init should be as generic 
as possible, and not too specialized for methods in Object or Device.

As I said above, we first need to agree on the design.

>        rust/pl011: move pub callback decl to local scope

This depends a lot on how we go implementing bindings to chardev.  For 
example if the callbacks turn out to be a trait, it would have to be 
undone.  Possibly the C callback wrappers would move to 
rust/qemu-api/chardev.  For now I'd leave it aside.

>        rust/qemu-api: add log module
>        rust/pl011: log guest/unimp errors

This also needs design discussion.  Do we want the API to be the same as 
C, i.e. keep the qemu_* prefix?  Do we want wrapper macros that include 
the format!() call?

You also have "pub enum LogMask" to work around the fact that log masks 
are preprocessor macros.  Is that okay, or do we want to modify C code 
to make the bindings nicer?  I for example would prefer the latter and 
then declaring LogMask as a bitfield in bindgen.

Thanks,

Paolo

> 
>   rust/wrapper.h                                |   1 +
>   rust/hw/char/pl011/src/device.rs              | 419 +++++++++++++++++---------
>   rust/hw/char/pl011/src/device_class.rs        |  70 -----
>   rust/hw/char/pl011/src/lib.rs                 |   2 +-
>   rust/qemu-api-macros/src/device.rs            | 370 +++++++++++++++++++++++
>   rust/qemu-api-macros/src/lib.rs               |  46 +--
>   rust/qemu-api-macros/src/object.rs            | 107 +++++++
>   rust/qemu-api-macros/src/symbols.rs           |  57 ++++
>   rust/qemu-api-macros/src/utilities.rs         | 152 ++++++++++
>   rust/qemu-api-macros/src/vmstate.rs           | 113 +++++++
>   rust/qemu-api/meson.build                     |   5 +-
>   rust/qemu-api/src/definitions.rs              |  97 ------
>   rust/qemu-api/src/device_class.rs             | 128 --------
>   rust/qemu-api/src/lib.rs                      |  10 +-
>   rust/qemu-api/src/log.rs                      | 140 +++++++++
>   rust/qemu-api/src/objects.rs                  |  90 ++++++
>   rust/qemu-api/src/tests.rs                    |  49 ---
>   rust/qemu-api/src/vmstate.rs                  | 403 +++++++++++++++++++++++++
>   subprojects/packagefiles/syn-2-rs/meson.build |   1 +
>   19 files changed, 1726 insertions(+), 534 deletions(-)
> ---
> base-commit: 55522f72149fbf95ee3b057f1419da0cad46d0dd
> change-id: 20241024-rust-round-2-69fa10c9a0c9
> 
> --
> γαῖα πυρί μιχθήτω
> 
> 
>