rust: adapt `alloc` crate to the kernel

This customizes the subset of the Rust standard library `alloc` that
was just imported as-is, mainly by:

  - Adding SPDX license identifiers.

  - Skipping modules (e.g. `rc` and `sync`) via new `cfg`s.

  - Adding fallible (`try_*`) versions of existing infallible methods
    (i.e. returning a `Result` instead of panicking).

    Since the standard library requires stable/unstable attributes,
    these additions are annotated with:

        #[stable(feature = "kernel", since = "1.0.0")]

    Using "kernel" as the feature allows to have the additions
    clearly marked. The "1.0.0" version is just a placeholder.

    (At the moment, only one is needed, but in the future more
    fallible methods will be added).

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
Co-developed-by: Wedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Co-developed-by: Matthew Bakhtiari <dev@mtbk.me>
Signed-off-by: Matthew Bakhtiari <dev@mtbk.me>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/rust/alloc/raw_vec.rs b/rust/alloc/raw_vec.rs
index 4be5f6cf9ca5..daf5f2da7168 100644
--- a/rust/alloc/raw_vec.rs
+++ b/rust/alloc/raw_vec.rs
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 #![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")]
 
 use core::alloc::LayoutError;
@@ -307,6 +309,12 @@ impl<T, A: Allocator> RawVec<T, A> {
         }
     }
 
+    /// The same as `reserve_for_push`, but returns on errors instead of panicking or aborting.
+    #[inline(never)]
+    pub fn try_reserve_for_push(&mut self, len: usize) -> Result<(), TryReserveError> {
+        self.grow_amortized(len, 1)
+    }
+
     /// Ensures that the buffer contains at least enough space to hold `len +
     /// additional` elements. If it doesn't already, will reallocate the
     /// minimum possible amount of memory necessary. Generally this will be
@@ -421,6 +429,7 @@ impl<T, A: Allocator> RawVec<T, A> {
         Ok(())
     }
 
+    #[allow(dead_code)]
     fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
         assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity");