[v4,3/3] rust: platform: impl TryFrom<&Device> for &platform::Device

Commit Message

Danilo Krummrich March 21, 2025, 9:47 p.m. UTC

Implement TryFrom<&device::Device> for &Device.

This allows us to get a &platform::Device from a generic &Device in a safe
way; the conversion fails if the device' bus type does not match with
the platform bus type.

Reviewed-by: Alice Ryhl <[e-mail]>
Reviewed-by: Benno Lossin <[e-mail]>
Signed-off-by: Danilo Krummrich <[e-mail]>
---
 rust/kernel/platform.rs | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

Comments

Greg KH March 22, 2025, 3:25 a.m. UTC | #1

On Fri, Mar 21, 2025 at 10:47:55PM +0100, Danilo Krummrich wrote:
> Implement TryFrom<&device::Device> for &Device.
> 
> This allows us to get a &platform::Device from a generic &Device in a safe
> way; the conversion fails if the device' bus type does not match with
> the platform bus type.
> 
> Reviewed-by: Alice Ryhl <[e-mail]>
> Reviewed-by: Benno Lossin <[e-mail]>
> Signed-off-by: Danilo Krummrich <[e-mail]>
> ---
>  rust/kernel/platform.rs | 25 +++++++++++++++++++++++--
>  1 file changed, 23 insertions(+), 2 deletions(-)

Same comment as on the pci one, let's figure out if we really want this
before it gets merged please.

thanks,

greg k-h

Patch

diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
index e37531bae8e9..b39ca2573020 100644
--- a/rust/kernel/platform.rs
+++ b/rust/kernel/platform.rs
@@ -5,7 +5,7 @@ 
 //! C header: [`include/linux/platform_device.h`](srctree/include/linux/platform_device.h)
 
 use crate::{
-    bindings, device, driver,
+    bindings, container_of, device, driver,
     error::{to_result, Result},
     of,
     prelude::*,
@@ -17,7 +17,7 @@ 
 use core::{
     marker::PhantomData,
     ops::Deref,
-    ptr::{addr_of_mut, NonNull},
+    ptr::{addr_of, addr_of_mut, NonNull},
 };
 
 /// An adapter for the registration of platform drivers.
@@ -234,6 +234,27 @@  fn as_ref(&self) -> &device::Device {
     }
 }
 
+impl TryFrom<&device::Device> for &Device {
+    type Error = kernel::error::Error;
+
+    fn try_from(dev: &device::Device) -> Result<Self, Self::Error> {
+        #[allow(unused_unsafe)]
+        // SAFETY: rustc < 1.82 falsely treats this as unsafe, see:
+        // https://blog.rust-lang.org/2024/10/17/Rust-1.82.0.html#safely-addressing-unsafe-statics
+        if dev.bus_type_raw() != unsafe { addr_of!(bindings::platform_bus_type) } {
+            return Err(EINVAL);
+        }
+
+        // SAFETY: We've just verified that the bus type of `dev` equals
+        // `bindings::platform_bus_type`, hence `dev` must be embedded in a valid
+        // `struct platform_device` as guaranteed by the corresponding C code.
+        let pdev = unsafe { container_of!(dev.as_raw(), bindings::platform_device, dev) };
+
+        // SAFETY: `pdev` is a valid pointer to a `struct platform_device`.
+        Ok(unsafe { &*pdev.cast() })
+    }
+}
+
 // SAFETY: A `Device` is always reference-counted and can be released from any thread.
 unsafe impl Send for Device {}