[PATCH v12 0/5] rust: replace kernel::str::CStr w/ core::ffi::CStr

Tamir Duberstein
2025-06-19T15:06:31Z

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@protonmail.com/t/#u [0]
Closes: https://github.com/Rust-for-Linux/linux/issues/1075

Signed-off-by: Tamir Duberstein <tamird@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 (5):
rust: macros: reduce collections in `quote!` macro
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 | 4 +-
drivers/cpufreq/rcpufreq_dt.rs | 5 +-
drivers/gpu/drm/drm_panic_qr.rs | 5 +-
drivers/gpu/drm/nova/driver.rs | 10 +-
drivers/gpu/nova-core/driver.rs | 6 +-
drivers/gpu/nova-core/firmware.rs | 2 +-
drivers/gpu/nova-core/gpu.rs | 4 +-
drivers/gpu/nova-core/nova_core.rs | 2 +-
drivers/net/phy/ax88796b_rust.rs | 8 +-
drivers/net/phy/qt2025.rs | 6 +-
rust/kernel/auxiliary.rs | 6 +-
rust/kernel/block/mq.rs | 2 +-
rust/kernel/clk.rs | 9 +-
rust/kernel/configfs.rs | 14 +-
rust/kernel/cpufreq.rs | 6 +-
rust/kernel/device.rs | 9 +-
rust/kernel/devres.rs | 2 +-
rust/kernel/driver.rs | 4 +-
rust/kernel/drm/device.rs | 4 +-
rust/kernel/drm/driver.rs | 3 +-
rust/kernel/drm/ioctl.rs | 2 +-
rust/kernel/error.rs | 10 +-
rust/kernel/faux.rs | 5 +-
rust/kernel/firmware.rs | 16 +-
rust/kernel/fmt.rs | 89 +++++++
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 | 444 ++++++++++------------------------
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 | 9 +-
rust/macros/fmt.rs | 99 ++++++++
rust/macros/kunit.rs | 10 +-
rust/macros/lib.rs | 19 ++
rust/macros/module.rs | 2 +-
rust/macros/quote.rs | 111 ++++-----
samples/rust/rust_configfs.rs | 9 +-
samples/rust/rust_driver_auxiliary.rs | 7 +-
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 | 6 +-
54 files changed, 540 insertions(+), 515 deletions(-)
---
base-commit: e04c78d86a9699d136910cfc0bdcf01087e3267e
change-id: 20250201-cstr-core-d4b9b69120cf

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