rust: kernel: use core::ffi::CStr method names

Prepare for `core::ffi::CStr` taking the place of `kernel::str::CStr` by
avoiding methods that only exist on the latter.

Also avoid `Deref<Target=BStr> for CStr` as that impl doesn't exist on
`core::ffi::CStr`.

Link: Rust-for-Linux#1075
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250704-core-cstr-prepare-v1-6-a91524037783@gmail.com
[ Reworded title. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: tamird

rust/kernel/error.rs

@@ -188,7 +188,7 @@ impl fmt::Debug for Error {
             Some(name) => f
                 .debug_tuple(
                     // SAFETY: These strings are ASCII-only.
-                    unsafe { core::str::from_utf8_unchecked(name) },
+                    unsafe { core::str::from_utf8_unchecked(name.to_bytes()) },
                 )
                 .finish(),
         }

rust/kernel/str.rs

@@ -57,11 +57,11 @@ impl fmt::Display for BStr {
     /// # use kernel::{prelude::fmt, b_str, str::{BStr, CString}};
     /// let ascii = b_str!("Hello, BStr!");
     /// let s = CString::try_from_fmt(fmt!("{ascii}"))?;
-    /// assert_eq!(s.as_bytes(), "Hello, BStr!".as_bytes());
+    /// assert_eq!(s.to_bytes(), "Hello, BStr!".as_bytes());
     ///
     /// let non_ascii = b_str!("🦀");
     /// let s = CString::try_from_fmt(fmt!("{non_ascii}"))?;
-    /// assert_eq!(s.as_bytes(), "\\xf0\\x9f\\xa6\\x80".as_bytes());
+    /// assert_eq!(s.to_bytes(), "\\xf0\\x9f\\xa6\\x80".as_bytes());
     /// # Ok::<(), kernel::error::Error>(())
     /// ```
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -89,11 +89,11 @@ impl fmt::Debug for BStr {
     /// // Embedded double quotes are escaped.
     /// let ascii = b_str!("Hello, \"BStr\"!");
     /// let s = CString::try_from_fmt(fmt!("{ascii:?}"))?;
-    /// assert_eq!(s.as_bytes(), "\"Hello, \\\"BStr\\\"!\"".as_bytes());
+    /// assert_eq!(s.to_bytes(), "\"Hello, \\\"BStr\\\"!\"".as_bytes());
     ///
     /// let non_ascii = b_str!("😺");
     /// let s = CString::try_from_fmt(fmt!("{non_ascii:?}"))?;
-    /// assert_eq!(s.as_bytes(), "\"\\xf0\\x9f\\x98\\xba\"".as_bytes());
+    /// assert_eq!(s.to_bytes(), "\"\\xf0\\x9f\\x98\\xba\"".as_bytes());
     /// # Ok::<(), kernel::error::Error>(())
     /// ```
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -465,15 +465,15 @@ impl fmt::Display for CStr {
     /// # use kernel::str::CString;
     /// let penguin = c_str!("🐧");
     /// let s = CString::try_from_fmt(fmt!("{penguin}"))?;
-    /// assert_eq!(s.as_bytes_with_nul(), "\\xf0\\x9f\\x90\\xa7\0".as_bytes());
+    /// assert_eq!(s.to_bytes_with_nul(), "\\xf0\\x9f\\x90\\xa7\0".as_bytes());
     ///
     /// let ascii = c_str!("so \"cool\"");
     /// let s = CString::try_from_fmt(fmt!("{ascii}"))?;
-    /// assert_eq!(s.as_bytes_with_nul(), "so \"cool\"\0".as_bytes());
+    /// assert_eq!(s.to_bytes_with_nul(), "so \"cool\"\0".as_bytes());
     /// # Ok::<(), kernel::error::Error>(())
     /// ```
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        for &c in self.as_bytes() {
+        for &c in self.to_bytes() {
             if (0x20..0x7f).contains(&c) {
                 // Printable character.
                 f.write_char(c as char)?;
@@ -874,11 +874,11 @@ impl fmt::Write for Formatter {
 /// use kernel::{str::CString, prelude::fmt};
 ///
 /// let s = CString::try_from_fmt(fmt!("{}{}{}", "abc", 10, 20))?;
-/// assert_eq!(s.as_bytes_with_nul(), "abc1020\0".as_bytes());
+/// assert_eq!(s.to_bytes_with_nul(), "abc1020\0".as_bytes());
 ///
 /// let tmp = "testing";
 /// let s = CString::try_from_fmt(fmt!("{tmp}{}", 123))?;
-/// assert_eq!(s.as_bytes_with_nul(), "testing123\0".as_bytes());
+/// assert_eq!(s.to_bytes_with_nul(), "testing123\0".as_bytes());
 ///
 /// // This fails because it has an embedded `NUL` byte.
 /// let s = CString::try_from_fmt(fmt!("a\0b{}", 123));
@@ -948,7 +948,7 @@ impl<'a> TryFrom<&'a CStr> for CString {
     fn try_from(cstr: &'a CStr) -> Result<CString, AllocError> {
         let mut buf = KVec::new();
 
-        buf.extend_from_slice(cstr.as_bytes_with_nul(), GFP_KERNEL)?;
+        buf.extend_from_slice(cstr.to_bytes_with_nul(), GFP_KERNEL)?;
 
         // INVARIANT: The `CStr` and `CString` types have the same invariants for
         // the string data, and we copied it over without changes.