[PATCH v10 0/5] rust: replace kernel::str::CStr w/ core::ffi::CStr

Tamir Duberstein
Sat, 24 May 2025 20:33:31 -0000

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.

Link: https://lore.kernel.org/rust-for-linux/20240819153656.28807-2-vadorovsky
at protonmail.com/t/#u [0]
Closes: https://github.com/Rust-for-Linux/linux/issues/1075

Signed-off-by: Tamir Duberstein <tamird at 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 at
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 at
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 at
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 at
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 (5):
      rust: retitle "Example" section as "Examples"
      rust: support formatting of foreign types
      rust: replace `CStr` with `core::ffi::CStr`
      rust: replace `kernel::c_str!` with C-Strings
      rust: remove core::ffi::CStr reexport

 drivers/block/rnull.rs               |   2 +-
 drivers/gpu/drm/drm_panic_qr.rs      |   5 +-
 drivers/gpu/nova-core/driver.rs      |   2 +-
 drivers/gpu/nova-core/firmware.rs    |   2 +-
 drivers/net/phy/ax88796b_rust.rs     |   8 +-
 drivers/net/phy/qt2025.rs            |   6 +-
 rust/kernel/block/mq.rs              |   2 +-
 rust/kernel/device.rs                |   9 +-
 rust/kernel/devres.rs                |   2 +-
 rust/kernel/driver.rs                |   4 +-
 rust/kernel/error.rs                 |  10 +-
 rust/kernel/faux.rs                  |   5 +-
 rust/kernel/firmware.rs              |  16 +-
 rust/kernel/fmt.rs                   |  77 +++++++
 rust/kernel/kunit.rs                 |  21 +-
 rust/kernel/lib.rs                   |   3 +-
 rust/kernel/miscdevice.rs            |   5 +-
 rust/kernel/net/phy.rs               |  12 +-
 rust/kernel/of.rs                    |   5 +-
 rust/kernel/pci.rs                   |   2 +-
 rust/kernel/platform.rs              |   6 +-
 rust/kernel/prelude.rs               |   5 +-
 rust/kernel/print.rs                 |   4 +-
 rust/kernel/seq_file.rs              |   6 +-
 rust/kernel/str.rs                   | 415 ++++++++++-------------------------
 rust/kernel/sync.rs                  |   7 +-
 rust/kernel/sync/condvar.rs          |   4 +-
 rust/kernel/sync/lock.rs             |   4 +-
 rust/kernel/sync/lock/global.rs      |   6 +-
 rust/kernel/sync/poll.rs             |   1 +
 rust/kernel/workqueue.rs             |   1 +
 rust/macros/fmt.rs                   | 118 ++++++++++
 rust/macros/kunit.rs                 |   6 +-
 rust/macros/lib.rs                   |  21 +-
 rust/macros/module.rs                |   2 +-
 samples/rust/rust_driver_faux.rs     |   4 +-
 samples/rust/rust_driver_pci.rs      |   4 +-
 samples/rust/rust_driver_platform.rs |   4 +-
 samples/rust/rust_misc_device.rs     |   3 +-
 scripts/rustdoc_test_gen.rs          |   2 +-
 40 files changed, 426 insertions(+), 395 deletions(-)
---
base-commit: cbeaa41dfe26b72639141e87183cb23e00d4b0dd
change-id: 20250201-cstr-core-d4b9b69120cf

Best regards,
--
Tamir Duberstein <tamird at gmail.com>