rust: uapi: Add UAPI crate

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").

[ Miguel: added support for the `rustdoc` and `rusttest` targets,
  since otherwise they fail, and we want to keep them working. ]

Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Asahi Lina <lina@asahilina.net>
Link: https://lore.kernel.org/r/20230329-rust-uapi-v2-1-bca5fb4d4a12@asahilina.net
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

5 files changed, 61 insertions, 5 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..04bb52e88331 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
@@ -113,7 +116,7 @@ rustdoc-alloc: $(src)/alloc/lib.rs rustdoc-core rustdoc-compiler_builtins FORCE
 
 rustdoc-kernel: private rustc_target_flags = --extern alloc \
     --extern build_error --extern macros=$(objtree)/$(obj)/libmacros.so \
-    --extern bindings
+    --extern bindings --extern uapi
 rustdoc-kernel: $(src)/kernel/lib.rs rustdoc-core rustdoc-macros \
     rustdoc-compiler_builtins rustdoc-alloc $(obj)/libmacros.so \
     $(obj)/bindings.o FORCE
@@ -141,6 +144,9 @@ rusttestlib-macros: $(src)/macros/lib.rs rusttest-prepare FORCE
 rusttestlib-bindings: $(src)/bindings/lib.rs rusttest-prepare FORCE
 	$(call if_changed,rustc_test_library)
 
+rusttestlib-uapi: $(src)/uapi/lib.rs rusttest-prepare FORCE
+	$(call if_changed,rustc_test_library)
+
 quiet_cmd_rustdoc_test = RUSTDOC T $<
       cmd_rustdoc_test = \
 	OBJTREE=$(abspath $(objtree)) \
@@ -223,9 +229,10 @@ rusttest-macros: $(src)/macros/lib.rs rusttest-prepare FORCE
 	$(call if_changed,rustdoc_test)
 
 rusttest-kernel: private rustc_target_flags = --extern alloc \
-    --extern build_error --extern macros --extern bindings
+    --extern build_error --extern macros --extern bindings --extern uapi
 rusttest-kernel: $(src)/kernel/lib.rs rusttest-prepare \
-    rusttestlib-build_error rusttestlib-macros rusttestlib-bindings FORCE
+    rusttestlib-build_error rusttestlib-macros rusttestlib-bindings \
+    rusttestlib-uapi FORCE
 	$(call if_changed,rustc_test)
 	$(call if_changed,rustc_test_library)
 
@@ -288,6 +295,12 @@ $(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 +401,15 @@ $(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 ee27e10da479..dd3b0d69fdd1 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -50,6 +50,7 @@ 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>