rust: bindings: rename const binding using sed

Currently, for `const`s that bindgen doesn't recognise, we define a
helper constant with

    const <TYPE> BINDINGS_<NAME> = <NAME>;

in `bindings_helper.h` and then we put

    pub const <NAME>: <TYPE> = BINDINGS_<NAME>;

in `bindings/lib.rs`. This is fine since we currently only have 3
constants that are defined this way, but is going to be more annoying
when more constants are added since every new constant needs to be
defined in two places.

This patch changes the way we define constant helpers to

    const <TYPE> RUST_CONST_HELPER_<NAME> = <NAME>;

and then use `sed` to postprocess Rust code generated by bindgen to
remove the distinct prefix, so users of the `bindings` crate can refer
to the name directly.

Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20231104145700.2495176-1-gary@garyguo.net
[ Reworded for typos. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/Makefile

@@ -337,6 +337,8 @@ quiet_cmd_bindgen = BINDGEN $@
 
 $(obj)/bindings/bindings_generated.rs: private bindgen_target_flags = \
     $(shell grep -Ev '^#|^$$' $(srctree)/$(src)/bindgen_parameters)
+$(obj)/bindings/bindings_generated.rs: private bindgen_target_extra = ; \
+    sed -Ei 's/pub const RUST_CONST_HELPER_([a-zA-Z0-9_]*)/pub const \1/g' $@
 $(obj)/bindings/bindings_generated.rs: $(src)/bindings/bindings_helper.h \
     $(src)/bindgen_parameters FORCE
 	$(call if_changed_dep,bindgen)

rust/bindings/bindings_helper.h

@@ -15,6 +15,6 @@
 #include <linux/workqueue.h>
 
 /* `bindgen` gets confused at certain things. */
-const size_t BINDINGS_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN;
-const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;
-const gfp_t BINDINGS___GFP_ZERO = __GFP_ZERO;
+const size_t RUST_CONST_HELPER_ARCH_SLAB_MINALIGN = ARCH_SLAB_MINALIGN;
+const gfp_t RUST_CONST_HELPER_GFP_KERNEL = GFP_KERNEL;
+const gfp_t RUST_CONST_HELPER___GFP_ZERO = __GFP_ZERO;

rust/bindings/lib.rs

@@ -48,6 +48,3 @@ mod bindings_helper {
 }
 
 pub use bindings_raw::*;
-
-pub const GFP_KERNEL: gfp_t = BINDINGS_GFP_KERNEL;
-pub const __GFP_ZERO: gfp_t = BINDINGS___GFP_ZERO;

rust/kernel/allocator.rs

@@ -21,7 +21,7 @@ unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: bindings::gf
 
     let mut size = layout.size();
 
-    if layout.align() > bindings::BINDINGS_ARCH_SLAB_MINALIGN {
+    if layout.align() > bindings::ARCH_SLAB_MINALIGN {
         // The alignment requirement exceeds the slab guarantee, thus try to enlarge the size
         // to use the "power-of-two" size/alignment guarantee (see comments in `kmalloc()` for
         // more information).