[v2,4/4] rust: platform: impl TryFrom<&Device> for &platform::Device

Commit Message

Danilo Krummrich March 20, 2025, 10:27 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]>
Signed-off-by: Danilo Krummrich <[e-mail]>
---
 rust/kernel/platform.rs | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

Comments

Benno Lossin March 20, 2025, 11:44 p.m. UTC | #1

On Thu Mar 20, 2025 at 11:27 PM CET, Danilo Krummrich wrote:
> @@ -234,6 +234,24 @@ 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> {
> +        if dev.bus_type_raw() != 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`.

Same change here as in patch 3. With that:

Reviewed-by: Benno Lossin <[e-mail]>

---
Cheers,
Benno

> +        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 {}
>

Patch

diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs
index e37531bae8e9..c17fc6e7c596 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 +234,24 @@  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> {
+        if dev.bus_type_raw() != 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`.
+        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 {}