rust: sync: add `Arc` for ref-counted allocations

This is a basic implementation of `Arc` backed by C's `refcount_t`. It
allows Rust code to idiomatically allocate memory that is ref-counted.

Cc: Will Deacon <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Mark Rutland <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Reviewed-by: Vincenzo Palazzo <[email protected]>
Acked-by: Boqun Feng <[email protected]>
Signed-off-by: Miguel Ojeda <[email protected]>

1 files changed, 19 insertions, 0 deletions

diff --git a/rust/helpers.c b/rust/helpers.c
index b4f15eee2ffd..09a4d93f9d62 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -20,6 +20,7 @@
 
 #include <linux/bug.h>
 #include <linux/build_bug.h>
+#include <linux/refcount.h>
 
 __noreturn void rust_helper_BUG(void)
 {
@@ -27,6 +28,24 @@ __noreturn void rust_helper_BUG(void)
 }
 EXPORT_SYMBOL_GPL(rust_helper_BUG);
 
+refcount_t rust_helper_REFCOUNT_INIT(int n)
+{
+	return (refcount_t)REFCOUNT_INIT(n);
+}
+EXPORT_SYMBOL_GPL(rust_helper_REFCOUNT_INIT);
+
+void rust_helper_refcount_inc(refcount_t *r)
+{
+	refcount_inc(r);
+}
+EXPORT_SYMBOL_GPL(rust_helper_refcount_inc);
+
+bool rust_helper_refcount_dec_and_test(refcount_t *r)
+{
+	return refcount_dec_and_test(r);
+}
+EXPORT_SYMBOL_GPL(rust_helper_refcount_dec_and_test);
+
 /*
  * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
  * as the Rust `usize` type, so we can use it in contexts where Rust