From:   Asahi Lina <lina@asahilina.net>
Date:   Fri, 24 Feb 2023 16:36:42 +0900
Subject: [PATCH] rust: ioctl: Add ioctl number manipulation functions
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Message-Id: <20230224-rust-ioctl-v1-1-5142d365a934@asahilina.net>
To:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        Arnd Bergmann <arnd@arndb.de>
Cc:     linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org,
        asahi@lists.linux.dev, linux-arch@vger.kernel.org,
        Asahi Lina <lina@asahilina.net>
Precedence: bulk

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@asahilina.net>
---
 rust/bindings/bindings_helper.h |  3 +-
 rust/kernel/ioctl.rs            | 64 +++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |  1 +
 3 files changed, 67 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..6cd8e5738b91
--- /dev/null
+++ b/rust/kernel/ioctl.rs
@@ -0,0 +1,64 @@
+// 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)
+
+/// Build an ioctl number, analogous to the C macro of the same name.
+const fn _IOC(dir: u32, ty: u32, nr: u32, size: usize) -> u32 {
+    core::assert!(dir <= bindings::_IOC_DIRMASK);
+    core::assert!(ty <= bindings::_IOC_TYPEMASK);
+    core::assert!(nr <= bindings::_IOC_NRMASK);
+    core::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.
+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.
+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.
+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.
+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: 83f978b63fa7ad474ca22d7e2772c5988101c9bd
change-id: 20230224-rust-ioctl-a520f3eb3aa8

Thank you,
~~ Lina