[PATCH v2 1/2] rust: uapi: Add UAPI crate

[Asahi Lina <lina@asahilina.net>]

This crate mirrors the `bindings` crate, but will contain only UAPI
bindings. Unlike the bindings crate, drivers may directly use this crate
if they have to interface with userspace.

Initially, just bind the generic ioctl stuff.

In the future, we would also like to add additional checks to ensure
that all types exposed by this crate satisfy UAPI-safety guarantees
(that is, they are safely castable to/from a "bag of bits").

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Asahi Lina <lina@asahilina.net>
---
 rust/.gitignore         |  1 +
 rust/Makefile           | 18 ++++++++++++++++--
 rust/kernel/lib.rs      |  1 +
 rust/uapi/lib.rs        | 27 +++++++++++++++++++++++++++
 rust/uapi/uapi_helper.h |  9 +++++++++
 5 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/rust/.gitignore b/rust/.gitignore
index 168cb26a31b9..21552992b401 100644
--- a/rust/.gitignore
+++ b/rust/.gitignore
@@ -2,6 +2,7 @@
 
 bindings_generated.rs
 bindings_helpers_generated.rs
+uapi_generated.rs
 exports_*_generated.h
 doc/
 test/
diff --git a/rust/Makefile b/rust/Makefile
index f88d108fbef0..f81fdefec0ab 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -16,6 +16,9 @@ obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o
 always-$(CONFIG_RUST) += exports_alloc_generated.h exports_bindings_generated.h \
     exports_kernel_generated.h
 
+always-$(CONFIG_RUST) += uapi/uapi_generated.rs
+obj-$(CONFIG_RUST) += uapi.o
+
 ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW
 obj-$(CONFIG_RUST) += build_error.o
 else
@@ -288,6 +291,12 @@ $(obj)/bindings/bindings_generated.rs: $(src)/bindings/bindings_helper.h \
     $(src)/bindgen_parameters FORCE
 	$(call if_changed_dep,bindgen)
 
+$(obj)/uapi/uapi_generated.rs: private bindgen_target_flags = \
+    $(shell grep -v '^#\|^$$' $(srctree)/$(src)/bindgen_parameters)
+$(obj)/uapi/uapi_generated.rs: $(src)/uapi/uapi_helper.h \
+    $(src)/bindgen_parameters FORCE
+	$(call if_changed_dep,bindgen)
+
 # See `CFLAGS_REMOVE_helpers.o` above. In addition, Clang on C does not warn
 # with `-Wmissing-declarations` (unlike GCC), so it is not strictly needed here
 # given it is `libclang`; but for consistency, future Clang changes and/or
@@ -388,10 +397,15 @@ $(obj)/bindings.o: $(src)/bindings/lib.rs \
     $(obj)/bindings/bindings_helpers_generated.rs FORCE
 	$(call if_changed_dep,rustc_library)
 
+$(obj)/uapi.o: $(src)/uapi/lib.rs \
+    $(obj)/compiler_builtins.o \
+    $(obj)/uapi/uapi_generated.rs FORCE
+	$(call if_changed_dep,rustc_library)
+
 $(obj)/kernel.o: private rustc_target_flags = --extern alloc \
-    --extern build_error --extern macros --extern bindings
+    --extern build_error --extern macros --extern bindings --extern uapi
 $(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \
-    $(obj)/libmacros.so $(obj)/bindings.o FORCE
+    $(obj)/libmacros.so $(obj)/bindings.o $(obj)/uapi.o FORCE
 	$(call if_changed_dep,rustc_library)
 
 endif # CONFIG_RUST
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 223564f9f0cc..afec0792d982 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -42,6 +42,7 @@ pub mod types;
 #[doc(hidden)]
 pub use bindings;
 pub use macros;
+pub use uapi;
 
 #[doc(hidden)]
 pub use build_error::build_error;
diff --git a/rust/uapi/lib.rs b/rust/uapi/lib.rs
new file mode 100644
index 000000000000..29f69f3a52de
--- /dev/null
+++ b/rust/uapi/lib.rs
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! UAPI Bindings.
+//!
+//! Contains the bindings generated by `bindgen` for UAPI interfaces.
+//!
+//! This crate may be used directly by drivers that need to interact with
+//! userspace APIs.
+
+#![no_std]
+#![feature(core_ffi_c)]
+// See <https://github.com/rust-lang/rust-bindgen/issues/1651>.
+#![cfg_attr(test, allow(deref_nullptr))]
+#![cfg_attr(test, allow(unaligned_references))]
+#![cfg_attr(test, allow(unsafe_op_in_unsafe_fn))]
+#![allow(
+    clippy::all,
+    missing_docs,
+    non_camel_case_types,
+    non_upper_case_globals,
+    non_snake_case,
+    improper_ctypes,
+    unreachable_pub,
+    unsafe_op_in_unsafe_fn
+)]
+
+include!(concat!(env!("OBJTREE"), "/rust/uapi/uapi_generated.rs"));
diff --git a/rust/uapi/uapi_helper.h b/rust/uapi/uapi_helper.h
new file mode 100644
index 000000000000..301f5207f023
--- /dev/null
+++ b/rust/uapi/uapi_helper.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Header that contains the headers for which Rust UAPI bindings
+ * will be automatically generated by `bindgen`.
+ *
+ * Sorted alphabetically.
+ */
+
+#include <uapi/asm-generic/ioctl.h>

-- 
2.40.0