linux-kernel - [PATCH v3] rust: ioctl: Add ioctl number manipulation functions

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Message-Id: <20230224-rust-ioctl-v3-1-3c5f7a6954b5@asahilina.net>
Date:   Thu, 23 Mar 2023 21:33:54 +0900
From:   Asahi Lina <lina@...hilina.net>
To:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
        asahi@...ts.linux.dev, linux-arch@...r.kernel.org,
        Asahi Lina <lina@...hilina.net>
Subject: [PATCH v3] rust: ioctl: Add ioctl number manipulation functions

Add simple 1:1 wrappers of the C ioctl number manipulation functions.
Since these are macros we cannot bindgen them directly, and since they
should be usable in const context we cannot use helper wrappers, so
we'll have to reimplement them in Rust. Thankfully, the C headers do
declare defines for the relevant bitfield positions, so we don't need
to duplicate that.

Signed-off-by: Asahi Lina <lina@...hilina.net>
---
Changes in v3:
- Actually made the change intended in v2.
- Link to v2: https://lore.kernel.org/r/20230224-rust-ioctl-v2-1-5325e76a92df@asahilina.net

Changes in v2:
- Changed from assert!() to build_assert!() (static_assert!() can't work
  here)
- Link to v1: https://lore.kernel.org/r/20230224-rust-ioctl-v1-1-5142d365a934@asahilina.net
---
 rust/bindings/bindings_helper.h |  3 +-
 rust/kernel/ioctl.rs            | 71 +++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |  1 +
 3 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 75d85bd6c592..aef60f300be0 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -6,8 +6,9 @@
  * Sorted alphabetically.
  */
 
-#include <linux/slab.h>
+#include <linux/ioctl.h>
 #include <linux/refcount.h>
+#include <linux/slab.h>
 
 /* `bindgen` gets confused at certain things. */
 const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;
diff --git a/rust/kernel/ioctl.rs b/rust/kernel/ioctl.rs
new file mode 100644
index 000000000000..b2076113b6a8
--- /dev/null
+++ b/rust/kernel/ioctl.rs
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+#![allow(non_snake_case)]
+
+//! ioctl() number definitions
+//!
+//! C header: [`include/asm-generic/ioctl.h`](../../../../include/asm-generic/ioctl.h)
+
+use crate::build_assert;
+
+/// Build an ioctl number, analogous to the C macro of the same name.
+#[inline(always)]
+const fn _IOC(dir: u32, ty: u32, nr: u32, size: usize) -> u32 {
+    build_assert!(dir <= bindings::_IOC_DIRMASK);
+    build_assert!(ty <= bindings::_IOC_TYPEMASK);
+    build_assert!(nr <= bindings::_IOC_NRMASK);
+    build_assert!(size <= (bindings::_IOC_SIZEMASK as usize));
+
+    (dir << bindings::_IOC_DIRSHIFT)
+        | (ty << bindings::_IOC_TYPESHIFT)
+        | (nr << bindings::_IOC_NRSHIFT)
+        | ((size as u32) << bindings::_IOC_SIZESHIFT)
+}
+
+/// Build an ioctl number for an argumentless ioctl.
+#[inline(always)]
+pub const fn _IO(ty: u32, nr: u32) -> u32 {
+    _IOC(bindings::_IOC_NONE, ty, nr, 0)
+}
+
+/// Build an ioctl number for an read-only ioctl.
+#[inline(always)]
+pub const fn _IOR<T>(ty: u32, nr: u32) -> u32 {
+    _IOC(bindings::_IOC_READ, ty, nr, core::mem::size_of::<T>())
+}
+
+/// Build an ioctl number for an write-only ioctl.
+#[inline(always)]
+pub const fn _IOW<T>(ty: u32, nr: u32) -> u32 {
+    _IOC(bindings::_IOC_WRITE, ty, nr, core::mem::size_of::<T>())
+}
+
+/// Build an ioctl number for a read-write ioctl.
+#[inline(always)]
+pub const fn _IOWR<T>(ty: u32, nr: u32) -> u32 {
+    _IOC(
+        bindings::_IOC_READ | bindings::_IOC_WRITE,
+        ty,
+        nr,
+        core::mem::size_of::<T>(),
+    )
+}
+
+/// Get the ioctl direction from an ioctl number.
+pub const fn _IOC_DIR(nr: u32) -> u32 {
+    (nr >> bindings::_IOC_DIRSHIFT) & bindings::_IOC_DIRMASK
+}
+
+/// Get the ioctl type from an ioctl number.
+pub const fn _IOC_TYPE(nr: u32) -> u32 {
+    (nr >> bindings::_IOC_TYPESHIFT) & bindings::_IOC_TYPEMASK
+}
+
+/// Get the ioctl number from an ioctl number.
+pub const fn _IOC_NR(nr: u32) -> u32 {
+    (nr >> bindings::_IOC_NRSHIFT) & bindings::_IOC_NRMASK
+}
+
+/// Get the ioctl size from an ioctl number.
+pub const fn _IOC_SIZE(nr: u32) -> usize {
+    ((nr >> bindings::_IOC_SIZESHIFT) & bindings::_IOC_SIZEMASK) as usize
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 223564f9f0cc..7610b18ee642 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -30,6 +30,7 @@ compile_error!("Missing kernel configuration for conditional compilation");
 mod allocator;
 mod build_assert;
 pub mod error;
+pub mod ioctl;
 pub mod prelude;
 pub mod print;
 mod static_assert;

---
base-commit: fe15c26ee26efa11741a7b632e9f23b01aca4cc6
change-id: 20230224-rust-ioctl-a520f3eb3aa8

Thank you,
~~ Lina