linux-kernel - [PATCH v1 19/28] rust: str: add `c

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Message-Id: <20221110164152.26136-20-ojeda@kernel.org>
Date:   Thu, 10 Nov 2022 17:41:31 +0100
From:   Miguel Ojeda <ojeda@...nel.org>
To:     Miguel Ojeda <ojeda@...nel.org>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>
Cc:     rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev
Subject: [PATCH v1 19/28] rust: str: add `c_str!` macro

From: Gary Guo <gary@...yguo.net>

Add `c_str!`, which is a convenience macro that creates a new `CStr`
from a string literal.

It is designed to be similar to a `str` in usage, and it is usable
in const contexts, for instance:

    const X: &CStr = c_str!("Example");

Co-developed-by: Alex Gaynor <alex.gaynor@...il.com>
Signed-off-by: Alex Gaynor <alex.gaynor@...il.com>
Signed-off-by: Gary Guo <gary@...yguo.net>
[Reworded, adapted for upstream and applied latest changes]
Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
---
 rust/kernel/str.rs | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
index 3ed685cb5a3c..3fb73b888dce 100644
--- a/rust/kernel/str.rs
+++ b/rust/kernel/str.rs
@@ -128,6 +128,18 @@ impl CStr {
         Ok(unsafe { Self::from_bytes_with_nul_unchecked(bytes) })
     }
 
+    /// Creates a [`CStr`] from a `[u8]`, panic if input is not valid.
+    ///
+    /// This function is only meant to be used by `c_str!` macro, so
+    /// crates using `c_str!` macro don't have to enable `const_panic` feature.
+    #[doc(hidden)]
+    pub const fn from_bytes_with_nul_unwrap(bytes: &[u8]) -> &Self {
+        match Self::from_bytes_with_nul(bytes) {
+            Ok(v) => v,
+            Err(_) => panic!("string contains interior NUL"),
+        }
+    }
+
     /// Creates a [`CStr`] from a `[u8]` without performing any additional
     /// checks.
     ///
@@ -321,6 +333,26 @@ where
     }
 }
 
+/// Creates a new [`CStr`] from a string literal.
+///
+/// The string literal should not contain any `NUL` bytes.
+///
+/// # Examples
+///
+/// ```
+/// # use kernel::c_str;
+/// # use kernel::str::CStr;
+/// const MY_CSTR: &CStr = c_str!("My awesome CStr!");
+/// ```
+#[macro_export]
+macro_rules! c_str {
+    ($str:expr) => {{
+        const S: &str = concat!($str, "\0");
+        const C: &$crate::str::CStr = $crate::str::CStr::from_bytes_with_nul_unwrap(S.as_bytes());
+        C
+    }};
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
-- 
2.38.1