rust: map __kernel_size_t and friends also to usize/isize

Currently bindgen has special logic to recognise `size_t` and `ssize_t`
and map them to Rust `usize` and `isize`. Similarly, `ptrdiff_t` is
mapped to `isize`.

However this falls short for `__kernel_size_t`, `__kernel_ssize_t` and
`__kernel_ptrdiff_t`. To ensure that they are mapped to usize/isize
rather than 32/64 integers depending on platform, blocklist them in
bindgen parameters and manually provide their definition.

Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Link: https://lore.kernel.org/r/20240913213041.395655-3-gary@garyguo.net
[ Formatted comment. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/bindgen_parameters

@@ -1,5 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0
 
+# We want to map these types to `isize`/`usize` manually, instead of
+# define them as `int`/`long` depending on platform bitwidth.
+--blocklist-type __kernel_s?size_t
+--blocklist-type __kernel_ptrdiff_t
+
 --opaque-type xregs_state
 --opaque-type desc_struct
 --opaque-type arch_lbr_state

rust/bindings/lib.rs

@@ -27,6 +27,11 @@
 #[allow(dead_code)]
 #[allow(clippy::undocumented_unsafe_blocks)]
 mod bindings_raw {
+    // Manual definition for blocklisted types.
+    type __kernel_size_t = usize;
+    type __kernel_ssize_t = isize;
+    type __kernel_ptrdiff_t = isize;
+
     // Use glob import here to expose all helpers.
     // Symbols defined within the module will take precedence to the glob import.
     pub use super::bindings_helper::*;

rust/uapi/lib.rs

@@ -25,4 +25,9 @@
     unsafe_op_in_unsafe_fn
 )]
 
+// Manual definition of blocklisted types.
+type __kernel_size_t = usize;
+type __kernel_ssize_t = isize;
+type __kernel_ptrdiff_t = isize;
+
 include!(concat!(env!("OBJTREE"), "/rust/uapi/uapi_generated.rs"));