Re: [PATCH v3 2/2] 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>
---
 include/linux/tracepoint.h      | 18 +++++++++++++++-
 include/trace/define_trace.h    |  7 ++++++
 rust/bindings/bindings_helper.h |  1 +
 rust/kernel/lib.rs              |  1 +
 rust/kernel/tracepoint.rs       | 47 +++++++++++++++++++++++++++++++++++++++++
 5 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 689b6d71590e..d82af4d77c9f 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h

@@ -238,6 +238,20 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
 #define __DECLARE_TRACE_RCU(name, proto, args, cond)
 #endif

+/*
+ * Declare an exported function that Rust code can call to trigger this
+ * tracepoint. This function does not include the static branch; that is done
+ * in Rust to avoid a function call when the tracepoint is disabled.
+ */
+#define DEFINE_RUST_DO_TRACE(name, proto, args)
+#define DEFINE_RUST_DO_TRACE_REAL(name, proto, args)                   \
+       notrace void rust_do_trace_##name(proto)                        \
+       {                                                               \
+               __DO_TRACE(name,                                        \
+                       TP_ARGS(args),                                  \
+                       cpu_online(raw_smp_processor_id()), 0);         \
+       }
+
 /*
  * Make sure the alignment of the structure in the __tracepoints section will
  * not add unwanted padding between the beginning of the section and the

@@ -253,6 +267,7 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
        extern int __traceiter_##name(data_proto);                      \
        DECLARE_STATIC_CALL(tp_func_##name, __traceiter_##name);        \
        extern struct tracepoint __tracepoint_##name;                   \
+       extern void rust_do_trace_##name(proto);                        \
        static inline void trace_##name(proto)                          \
        {                                                               \
                if (static_key_false(&__tracepoint_##name.key))         \

@@ -337,7 +352,8 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
        void __probestub_##_name(void *__data, proto)                   \
        {                                                               \
        }                                                               \
-       DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);
+       DEFINE_STATIC_CALL(tp_func_##_name, __traceiter_##_name);       \
+       DEFINE_RUST_DO_TRACE(_name, TP_PROTO(proto), TP_ARGS(args))

 #define DEFINE_TRACE(name, proto, args)                \
        DEFINE_TRACE_FN(name, NULL, NULL, PARAMS(proto), PARAMS(args));

diff --git a/include/trace/define_trace.h b/include/trace/define_trace.h
index 00723935dcc7..b47cc036acba 100644
--- a/include/trace/define_trace.h
+++ b/include/trace/define_trace.h

@@ -72,6 +72,13 @@
 #define DECLARE_TRACE(name, proto, args)       \
        DEFINE_TRACE(name, PARAMS(proto), PARAMS(args))

+/* If requested, create helpers for calling these tracepoints from Rust. */
+#ifdef CREATE_RUST_TRACE_POINTS
+#undef DEFINE_RUST_DO_TRACE
+#define DEFINE_RUST_DO_TRACE(name, proto, args)        \
+       DEFINE_RUST_DO_TRACE_REAL(name, PARAMS(proto), PARAMS(args))
+#endif
+
 #undef TRACE_INCLUDE
 #undef __TRACE_INCLUDE

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h