Re: [PATCH 0/3] rust_binder: Update bitmaps to use kernel::impl_flags!

[Alice Ryhl]

On Thu, Jul 16, 2026 at 01:02:33PM +0000, Jahnavi MN via B4 Relay wrote:
> In the current Rust Binder driver, internal state variables (thread
> looper states, deferred work, and transaction configurations) are
> represented as raw integers and manipulated using manual bitwise
> operations.
> 
> This approach lacks type safety. Because the compiler treats all
> integers identically, it is possible to pass a thread looper flag
> into a function expecting a transaction flag without triggering
> compile-time warnings. These cross-contamination errors compile
> cleanly but can cause runtime bugs or undefined behavior.
> 
> This patch series resolves this issue by migrating these raw integer
> bitmaps (`defer_work`, `looper_flags`, `flags`) to strongly-typed
> bitmasks using the `kernel::impl_flags!` macro. Functions now accept
> specific, distinct types rather than generic integers, preventing
> flags from being mixed up. This transition also replaces manual
> bitwise arithmetic with readable, safe methods.
> 
> Based on top of:
> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
> 
> Signed-off-by: Jahnavi MN <jahnavimn@xxxxxxxxxx>

Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>

It would be nice if our impl_flags! macro could allow us to omit the
right-hand-side that's saying `= bit_u8(i)` here:

    /// Represents a single deferred work category.
    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
    pub enum DeferWork {
        Flush = bit_u8(0),
        Release = bit_u8(1),
    }

After all, if we don't care what values the bits take, the macro could
just assign them for us.

Alice