rust: replace kernel::str::CStr w/ core::ffi::CStr

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/[email protected]/t/#u [0]
Closes: Rust-for-Linux#1075

To: Michal Rostecki <[email protected]>
To: Miguel Ojeda <[email protected]>
To: Alex Gaynor <[email protected]>
To: Boqun Feng <[email protected]>
To: Gary Guo <[email protected]>
To: Björn Roy Baron <[email protected]>
To: Benno Lossin <[email protected]>
To: Andreas Hindborg <[email protected]>
To: Alice Ryhl <[email protected]>
To: Trevor Gross <[email protected]>
To: Brendan Higgins <[email protected]>
To: David Gow <[email protected]>
To: Rae Moar <[email protected]>
To: Danilo Krummrich <[email protected]>
To: Maarten Lankhorst <[email protected]>
To: Maxime Ripard <[email protected]>
To: Thomas Zimmermann <[email protected]>
To: David Airlie <[email protected]>
To: Simona Vetter <[email protected]>
To: Greg Kroah-Hartman <[email protected]>
To: "Rafael J. Wysocki" <[email protected]>
To: Luis Chamberlain <[email protected]>
To: Russ Weight <[email protected]>
To: FUJITA Tomonori <[email protected]>
To: Rob Herring <[email protected]>
To: Saravana Kannan <[email protected]>
To: Peter Zijlstra <[email protected]>
To: Ingo Molnar <[email protected]>
To: Will Deacon <[email protected]>
To: Waiman Long <[email protected]>
To: Nathan Chancellor <[email protected]>
To: Nick Desaulniers <[email protected]>
To: Bill Wendling <[email protected]>
To: Justin Stitt <[email protected]>
To: Andrew Lunn <[email protected]>
To: Heiner Kallweit <[email protected]>
To: Russell King <[email protected]>
To: "David S. Miller" <[email protected]>
To: Eric Dumazet <[email protected]>
To: Jakub Kicinski <[email protected]>
To: Paolo Abeni <[email protected]>
To: Bjorn Helgaas <[email protected]>
To: Arnd Bergmann <[email protected]>
To: Jens Axboe <[email protected]>
To: Benno Lossin <[email protected]>
To: Krzysztof Wilczyński <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Tamir Duberstein <[email protected]>
---
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/[email protected]/.
  (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)
- Link to v10: https://lore.kernel.org/r/[email protected]

Changes in v10:
- Rebase on cbeaa41.
- 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/[email protected]

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/[email protected]

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/[email protected]

Changes in v7:
- Rebased on mainline.
- Restore functionality added in commit a321f3a ("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/[email protected]

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`.

--- b4-submit-tracking ---
# This section is used internally by b4 prep for tracking purposes.
{
  "series": {
    "revision": 11,
    "change-id": "20250201-cstr-core-d4b9b69120cf",
    "prefixes": [],
    "from-thread": "[email protected]",
    "history": {
      "v6": [
        "[email protected]"
      ],
      "v7": [
        "[email protected]"
      ],
      "v8": [
        "[email protected]"
      ],
      "v9": [
        "[email protected]"
      ],
      "v10": [
        "[email protected]"
      ]
    }
  }
}

Author: tamird