Re: [PATCH v5 0/6] rust: reduce pointer casts, enable related lints

[Benno Lossin <benno.lossin@proton.me>]

On Mon Mar 17, 2025 at 3:23 PM CET, Tamir Duberstein wrote:
> This started with a patch that enabled `clippy::ptr_as_ptr`. Benno
> Lossin suggested I also look into `clippy::ptr_cast_constness` and I
> discovered `clippy::as_ptr_cast_mut`. This series now enables all 3
> lints. It also enables `clippy::as_underscore` which ensures other
> pointer casts weren't missed. The first commit reduces the need for
> pointer casts and is shared with another series[1].
>
> The final patch also enables pointer provenance lints and fixes
> violations. See that commit message for details. The build system
> portion of that commit is pretty messy but I couldn't find a better way
> to convincingly ensure that these lints were applied globally.
> Suggestions would be very welcome.

I applied the patches to v6.14-rc7 and did a quick pass with

    rg -nC 3 -t rust ' as ' | bat -l rust

to see if there are any cases left that we could fix and I found a
couple:

* there are several cases of `number as int_type` (like `num as c_int`
  or `my_u32 as usize` etc.) not sure what we can do about these, some
  are probably unavoidable, but since the kernel doesn't support 16 bit
  systems (that is true, right?), we *could* have a `From<u32> for
  usize` impl...
* some instances of `'|' as u32` (samples/rust/rust_misc_device.rs:112).
  There is a `From<char> for u32` impl, so this can just be replaced
  with `.into()` (or maybe by using a byte literal `b'|'`?).
* `shared_ref as *const _` (for example in rust/kernel/uaccess.rs:247,
  rust/kernel/str.rs:32 and rust/kernel/fs/file.rs:367), these we can
  replace with `let ptr: *const ... = shared_ref;`. Don't know if there
  is a clippy lint for this.
* some pointer casts in rust/kernel/list/impl_list_item_mod.rs:{253,254}
  not sure if they can be converted though (maybe they are unsizing the
  pointer?)
  Another pointer cast in rust/kernel/driver.rs:81 (I'm pretty sure this
  one can be replaced by a `.cast()`)

Some clippy lints that we could also enable that share the spirit of
this series:

* `char_lit_as_u8` (maybe that also covers the `'|' as u32` case from
  above?)
* `cast_lossless` (maybe this catches some of the `num as int_type`
  conversions I mentioned above)

I'll leave it up to you what you want to do with this: add it to this
series, make a new one, or let someone else handle it. If you don't want
to handle it, let me know, then I'll create a good-first-issue :)

> ---
> Tamir Duberstein (6):
>       rust: retain pointer mut-ness in `container_of!`
>       rust: enable `clippy::ptr_as_ptr` lint
>       rust: enable `clippy::ptr_cast_constness` lint
>       rust: enable `clippy::as_ptr_cast_mut` lint
>       rust: enable `clippy::as_underscore` lint
>       rust: use strict provenance APIs
>
>  Makefile                               |   4 ++
>  init/Kconfig                           |   3 +
>  rust/bindings/lib.rs                   |   1 +
>  rust/kernel/alloc.rs                   |   2 +-
>  rust/kernel/alloc/allocator_test.rs    |   2 +-
>  rust/kernel/alloc/kvec.rs              |   4 +-
>  rust/kernel/block/mq/operations.rs     |   2 +-
>  rust/kernel/block/mq/request.rs        |   7 +-
>  rust/kernel/device.rs                  |   5 +-
>  rust/kernel/device_id.rs               |   2 +-
>  rust/kernel/devres.rs                  |  19 +++---
>  rust/kernel/error.rs                   |   2 +-
>  rust/kernel/firmware.rs                |   3 +-
>  rust/kernel/fs/file.rs                 |   2 +-
>  rust/kernel/io.rs                      |  16 ++---
>  rust/kernel/kunit.rs                   |  15 ++---
>  rust/kernel/lib.rs                     | 113 ++++++++++++++++++++++++++++++++-
>  rust/kernel/list/impl_list_item_mod.rs |   2 +-
>  rust/kernel/miscdevice.rs              |   2 +-
>  rust/kernel/of.rs                      |   6 +-
>  rust/kernel/pci.rs                     |  15 +++--
>  rust/kernel/platform.rs                |   6 +-
>  rust/kernel/print.rs                   |  11 ++--
>  rust/kernel/rbtree.rs                  |  23 +++----
>  rust/kernel/seq_file.rs                |   3 +-
>  rust/kernel/str.rs                     |  18 ++----
>  rust/kernel/sync/poll.rs               |   2 +-
>  rust/kernel/uaccess.rs                 |  12 ++--
>  rust/kernel/workqueue.rs               |  12 ++--
>  rust/uapi/lib.rs                       |   1 +
>  30 files changed, 218 insertions(+), 97 deletions(-)
> ---
> base-commit: 498f7ee4773f22924f00630136da8575f38954e8

Btw I didn't find this commit anywhere I usually check, where is it
from?

---
Cheers,
Benno

> change-id: 20250307-ptr-as-ptr-21b1867fc4d4