rust: map `long` to `isize` and `char` to `u8`

The following FFI types are replaced compared to `core::ffi`:

1. `char` type is now always mapped to `u8`, since kernel uses
   `-funsigned-char` on the C code. `core::ffi` maps it to platform
   default ABI, which can be either signed or unsigned.

2. `long` is now always mapped to `isize`. It's very common in the
   kernel to use `long` to represent a pointer-sized integer, and in
   fact `intptr_t` is a typedef of `long` in the kernel. Enforce this
   mapping rather than mapping to `i32/i64` depending on platform can
   save us a lot of unnecessary casts.

Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240913213041.395655-5-gary@garyguo.net
[ Moved `uaccess` changes from the next commit, since they were
  irrefutable patterns that Rust >= 1.82.0 warns about. Reworded
  slightly and reformatted a few documentation comments. Rebased on
  top of `rust-next`. Added the removal of two casts to avoid Clippy
  warnings. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index fbd761380384..8f88891fb1d2 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -225,7 +225,7 @@ unsafe extern "C" fn fops_ioctl<T: MiscDevice>(
     // SAFETY: Ioctl calls can borrow the private data of the file.
     let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
 
-    match T::ioctl(device, cmd, arg as usize) {
+    match T::ioctl(device, cmd, arg) {
         Ok(ret) => ret as c_long,
         Err(err) => err.to_errno() as c_long,
     }
@@ -245,7 +245,7 @@ unsafe extern "C" fn fops_compat_ioctl<T: MiscDevice>(
     // SAFETY: Ioctl calls can borrow the private data of the file.
     let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
 
-    match T::compat_ioctl(device, cmd, arg as usize) {
+    match T::compat_ioctl(device, cmd, arg) {
         Ok(ret) => ret as c_long,
         Err(err) => err.to_errno() as c_long,
     }