Commit 68aabb29 authored by Alice Ryhl's avatar Alice Ryhl Committed by Greg Kroah-Hartman
Browse files

rust: redefine `bindings::compat_ptr_ioctl` in Rust 



There is currently an inconsistency between C and Rust, which is that
when Rust requires cfg(CONFIG_COMPAT) on compat_ioctl when using the
compat_ptr_ioctl symbol because '#define compat_ptr_ioctl NULL' does not
get translated to anything by bindgen.

But it's not *just* a matter of translating the '#define' into Rust when
CONFIG_COMPAT=n. This is because when CONFIG_COMPAT=y, the type of
compat_ptr_ioctl is a non-nullable function pointer, and to seamlessly
use it regardless of the config, we need a nullable function pointer.

I think it's important to do something about this; I've seen the mistake
of accidentally forgetting '#[cfg(CONFIG_COMPAT)]' when compat_ptr_ioctl
is used multiple times now.

This explicitly declares 'bindings::compat_ptr_ioctl' as an Option that
is always defined but might be None. This matches C, but isn't ideal:
it modifies the bindings crate. But I'm not sure if there's a better way
to do it. If we just redefine in kernel/, then people may still use the
one in bindings::, since that is where you would normally find it. I am
open to suggestions.

Signed-off-by: default avatarAlice Ryhl <aliceryhl@google.com>
Reviewed-by: default avatarGary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260105-redefine-compat_ptr_ioctl-v1-1-25edb3d91acc@google.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent b0e930a6

drivers/android/binder/rust_binder_main.rs

+1 −2
Original line number Diff line number Diff line
@@ -322,8 +322,7 @@ unsafe impl<T> Sync for AssertSync<T> {} 
        owner: THIS_MODULE.as_ptr(),

        poll: Some(rust_binder_poll),

        unlocked_ioctl: Some(rust_binder_ioctl),

        #[cfg(CONFIG_COMPAT)]

        compat_ioctl: Some(bindings::compat_ptr_ioctl),

        compat_ioctl: bindings::compat_ptr_ioctl,

        mmap: Some(rust_binder_mmap),

        open: Some(rust_binder_open),

        release: Some(rust_binder_release),

rust/bindings/lib.rs

+13 −0
Original line number Diff line number Diff line
@@ -67,3 +67,16 @@ mod bindings_helper { 
}



pub use bindings_raw::*;



pub const compat_ptr_ioctl: Option<

    unsafe extern "C" fn(*mut file, ffi::c_uint, ffi::c_ulong) -> ffi::c_long,

> = {

    #[cfg(CONFIG_COMPAT)]

    {

        Some(bindings_raw::compat_ptr_ioctl)

    }

    #[cfg(not(CONFIG_COMPAT))]

    {

        None

    }

};

rust/kernel/miscdevice.rs

+1 −1
Original line number Diff line number Diff line
@@ -410,7 +410,7 @@ impl<T: MiscDevice> MiscdeviceVTable<T> { 
        compat_ioctl: if T::HAS_COMPAT_IOCTL {

            Some(Self::compat_ioctl)

        } else if T::HAS_IOCTL {

            Some(bindings::compat_ptr_ioctl)

            bindings::compat_ptr_ioctl

        } else {

            None

        },