Re: [PATCH 3/3] rust: add tracepoint support

Make it possible to have Rust code call into tracepoints defined by C
code. It is still required that the tracepoint is declared in a C
header, and that this header is included in the input to bindgen.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/bindings/bindings_helper.h |  1 +
 rust/bindings/lib.rs            | 15 +++++++
 rust/helpers.c                  | 24 +++++++++++
 rust/kernel/lib.rs              |  1 +
 rust/kernel/tracepoint.rs       | 92 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 133 insertions(+)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index ddb5644d4fd9..d442f9ccfc2c 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h

@@ -15,6 +15,7 @@
 #include <linux/refcount.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/tracepoint.h>
 #include <linux/wait.h>
 #include <linux/workqueue.h>
 

diff --git a/rust/bindings/lib.rs b/rust/bindings/lib.rs
index 40ddaee50d8b..48856761d682 100644
--- a/rust/bindings/lib.rs
+++ b/rust/bindings/lib.rs

@@ -48,3 +48,18 @@ mod bindings_helper {
 }
 
 pub use bindings_raw::*;
+
+/// Rust version of the C macro `rcu_dereference_raw`.
+///
+/// The rust helper only works with void pointers, but this wrapper method makes it work with any
+/// pointer type using pointer casts.
+///
+/// # Safety
+///
+/// This method has the same safety requirements as the C macro of the same name.
+#[inline(always)]
+pub unsafe fn rcu_dereference_raw<T>(p: *const *mut T) -> *mut T {
+    // SAFETY: This helper calls into the C macro, so the caller promises to uphold the safety
+    // requirements.
+    unsafe { __rcu_dereference_raw(p as *mut *mut _) as *mut T }
+}

diff --git a/rust/helpers.c b/rust/helpers.c
index 2c37a0f5d7a8..0560cc2a512a 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c

@@ -165,6 +165,30 @@ rust_helper_krealloc(const void *objp, size_t new_size, gfp_t flags)
 }
 EXPORT_SYMBOL_GPL(rust_helper_krealloc);
 
+void rust_helper_preempt_enable_notrace(void)
+{
+	preempt_enable_notrace();
+}
+EXPORT_SYMBOL_GPL(rust_helper_preempt_enable_notrace);
+
+void rust_helper_preempt_disable_notrace(void)
+{
+	preempt_disable_notrace();
+}
+EXPORT_SYMBOL_GPL(rust_helper_preempt_disable_notrace);

+bool rust_helper_current_cpu_online(void)
+{
+	return cpu_online(raw_smp_processor_id());
+}
+EXPORT_SYMBOL_GPL(rust_helper_current_cpu_online);
+
+void *rust_helper___rcu_dereference_raw(void **p)
+{
+	return rcu_dereference_raw(p);
+}
+EXPORT_SYMBOL_GPL(rust_helper___rcu_dereference_raw);