[PATCH v14 0/3] rust: replace kernel::str::CStr w/ core::ffi::CStr

[Tamir Duberstein <tamird@gmail.com>]

This picks up from Michal Rostecki's work[0]. Per Michal's guidance I
have omitted Co-authored tags, as the end result is quite different.

This series is intended to be taken through rust-next. The final patch
in the series requires some other subsystems' `Acked-by`s:
- rust/kernel/device.rs: driver-core. Already acked by gregkh.
- rust/kernel/firmware.rs: driver-core. Danilo, could you take a look?
- rust/kernel/seq_file.rs: vfs, I think? missing MAINTAINERS entry.
  Christian Brauner <brauner@kernel.org>, perhaps?
- rust/kernel/sync/*: no clear owner, probably doesn't need any.

This series depends on steps 2a[1] and 2b[2] which both depend on step
1[3].

Link: https://lore.kernel.org/rust-for-linux/20240819153656.28807-2-vadorovsky@protonmail.com/t/#u [0]
Link: https://lore.kernel.org/all/20250709-core-cstr-fanout-1-v1-0-64308e7203fc@gmail.com/ [1]
Link: https://lore.kernel.org/all/20250709-core-cstr-fanout-1-v1-0-fd793b3e58a2@gmail.com/ [2]
Link: https://lore.kernel.org/all/20250704-core-cstr-prepare-v1-0-a91524037783@gmail.com/ [3]
Closes: https://github.com/Rust-for-Linux/linux/issues/1075

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
Changes in v14:
- Break the change into multiple series.
- Move `CStr` reexport to `kernel::ffi`. (Alice Ryhl)
- `pub use core::fmt::{....}` in `kernel/fmt.rs`. (Benno Lossin)
- Avoid unnecessary binding to `first_lit` in `fmt!`. (Benno Lossin)
- Add comment to `identifier`-extracting loop. (Benno Lossin)
- Change `quote_spanned!` formatting. (Benno Lossin)
- Link to v13: https://lore.kernel.org/r/20250701-cstr-core-v13-0-29f7d3eb97a6@gmail.com

Changes in v13:
- Rebase on v6.16-rc4.
- Link to v12: https://lore.kernel.org/r/20250619-cstr-core-v12-0-80c9c7b45900@gmail.com

Changes in v12:
- Introduce `kernel::fmt::Display` to allow implementations on foreign
  types.
- Tidy up doc comment on `str_to_cstr`. (Alice Ryhl).
- Link to v11: https://lore.kernel.org/r/20250530-cstr-core-v11-0-cd9c0cbcb902@gmail.com

Changes in v11:
- Use `quote_spanned!` to avoid `use<'a, T>` and generally reduce manual
  token construction.
- Add a commit to simplify `quote_spanned!`.
- Drop first commit in favor of
  https://lore.kernel.org/rust-for-linux/20240906164448.2268368-1-paddymills@proton.me/.
  (Miguel Ojeda)
- Correctly handle expressions such as `pr_info!("{a}", a = a = a)`.
  (Benno Lossin)
- Avoid dealing with `}}` escapes, which is not needed. (Benno Lossin)
- Revert some unnecessary changes. (Benno Lossin)
- Rename `c_str_avoid_literals!` to `str_to_cstr!`. (Benno Lossin &
  Alice Ryhl).
- Link to v10: https://lore.kernel.org/r/20250524-cstr-core-v10-0-6412a94d9d75@gmail.com

Changes in v10:
- Rebase on cbeaa41dfe26b72639141e87183cb23e00d4b0dd.
- Implement Alice's suggestion to use a proc macro to work around orphan
  rules otherwise preventing `core::ffi::CStr` to be directly printed
  with `{}`.
- Link to v9: https://lore.kernel.org/r/20250317-cstr-core-v9-0-51d6cc522f62@gmail.com

Changes in v9:
- Rebase on rust-next.
- Restore `impl Display for BStr` which exists upstream[1].
- Link: https://doc.rust-lang.org/nightly/std/bstr/struct.ByteStr.html#impl-Display-for-ByteStr [1]
- Link to v8: https://lore.kernel.org/r/20250203-cstr-core-v8-0-cb3f26e78686@gmail.com

Changes in v8:
- Move `{from,as}_char_ptr` back to `CStrExt`. This reduces the diff
  some.
- Restore `from_bytes_with_nul_unchecked_mut`, `to_cstring`.
- Link to v7: https://lore.kernel.org/r/20250202-cstr-core-v7-0-da1802520438@gmail.com

Changes in v7:
- Rebased on mainline.
- Restore functionality added in commit a321f3ad0a5d ("rust: str: add
  {make,to}_{upper,lower}case() to CString").
- Used `diff.algorithm patience` to improve diff readability.
- Link to v6: https://lore.kernel.org/r/20250202-cstr-core-v6-0-8469cd6d29fd@gmail.com

Changes in v6:
- Split the work into several commits for ease of review.
- Restore `{from,as}_char_ptr` to allow building on ARM (see commit
  message).
- Add `CStrExt` to `kernel::prelude`. (Alice Ryhl)
- Remove `CStrExt::from_bytes_with_nul_unchecked_mut` and restore
  `DerefMut for CString`. (Alice Ryhl)
- Rename and hide `kernel::c_str!` to encourage use of C-String
  literals.
- Drop implementation and invocation changes in kunit.rs. (Trevor Gross)
- Drop docs on `Display` impl. (Trevor Gross)
- Rewrite docs in the style of the standard library.
- Restore the `test_cstr_debug` unit tests to demonstrate that the
  implementation has changed.

Changes in v5:
- Keep the `test_cstr_display*` unit tests.

Changes in v4:
- Provide the `CStrExt` trait with `display()` method, which returns a
   `CStrDisplay` wrapper with `Display` implementation. This addresses
   the lack of `Display` implementation for `core::ffi::CStr`.
- Provide `from_bytes_with_nul_unchecked_mut()` method in `CStrExt`,
   which might be useful and is going to prevent manual, unsafe casts.
- Fix a typo (s/preffered/prefered/).

Changes in v3:
- Fix the commit message.
- Remove redundant braces in `use`, when only one item is imported.

Changes in v2:
- Do not remove `c_str` macro. While it's preferred to use C-string
   literals, there are two cases where `c_str` is helpful:
   - When working with macros, which already return a Rust string literal
     (e.g. `stringify!`).
   - When building macros, where we want to take a Rust string literal as an
     argument (for caller's convenience), but still use it as a C-string
     internally.
- Use Rust literals as arguments in macros (`new_mutex`, `new_condvar`,
   `new_mutex`). Use the `c_str` macro to convert these literals to C-string
   literals.
- Use `c_str` in kunit.rs for converting the output of `stringify!` to a
   `CStr`.
- Remove `DerefMut` implementation for `CString`.

---
Tamir Duberstein (3):
      rust: macros: reduce collections in `quote!` macro
      rust: support formatting of foreign types
      rust: replace `CStr` with `core::ffi::CStr`

 rust/ffi.rs                     |   2 +
 rust/kernel/device.rs           |   1 +
 rust/kernel/error.rs            |   2 +
 rust/kernel/firmware.rs         |   9 +-
 rust/kernel/fmt.rs              |  87 ++++++++-
 rust/kernel/prelude.rs          |   7 +-
 rust/kernel/seq_file.rs         |   2 +-
 rust/kernel/str.rs              | 395 +++++++++-------------------------------
 rust/kernel/sync/condvar.rs     |   2 +-
 rust/kernel/sync/lock.rs        |   2 +-
 rust/kernel/sync/lock/global.rs |   2 +-
 rust/macros/fmt.rs              |  94 ++++++++++
 rust/macros/lib.rs              |  19 ++
 rust/macros/quote.rs            | 111 +++++------
 14 files changed, 362 insertions(+), 373 deletions(-)
---
base-commit: 769e324b66b0d92d04f315d0c45a0f72737c7494
change-id: 20250201-cstr-core-d4b9b69120cf
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Best regards,
--  
Tamir Duberstein <tamird@gmail.com>