[PATCH v2 5/5] rust: firmware: implement `Ownable` for Firmware

From: Abdiel Janulgue
Date: Tue Oct 22 2024 - 18:50:47 EST


For consistency, wrap the firmware as an `Owned` smart pointer in the
constructor.

Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
Suggested-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Signed-off-by: Abdiel Janulgue <abdiel.janulgue@xxxxxxxxx>
---
rust/kernel/firmware.rs | 31 ++++++++++++++++++-------------
1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/rust/kernel/firmware.rs b/rust/kernel/firmware.rs
index dee5b4b18aec..6da834b37455 100644
--- a/rust/kernel/firmware.rs
+++ b/rust/kernel/firmware.rs
@@ -4,8 +4,8 @@
//!
//! C header: [`include/linux/firmware.h`](srctree/include/linux/firmware.h)

-use crate::{bindings, device::Device, error::Error, error::Result, str::CStr};
-use core::ptr::NonNull;
+use crate::{bindings, device::Device, error::Error, error::Result, str::CStr,
+ types::{Opaque, Owned, Ownable}};

/// # Invariants
///
@@ -52,10 +52,11 @@ fn request_nowarn() -> Self {
/// # Ok(())
/// # }
/// ```
-pub struct Firmware(NonNull<bindings::firmware>);
+ #[repr(transparent)]
+pub struct Firmware(Opaque<bindings::firmware>);

impl Firmware {
- fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
+ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Owned<Self>> {
let mut fw: *mut bindings::firmware = core::ptr::null_mut();
let pfw: *mut *mut bindings::firmware = &mut fw;

@@ -65,25 +66,26 @@ fn request_internal(name: &CStr, dev: &Device, func: FwFunc) -> Result<Self> {
if ret != 0 {
return Err(Error::from_errno(ret));
}
-
+ // CAST: Self` is a `repr(transparent)` wrapper around `bindings::firmware`.
+ let ptr = fw.cast::<Self>();
// SAFETY: `func` not bailing out with a non-zero error code, guarantees that `fw` is a
// valid pointer to `bindings::firmware`.
- Ok(Firmware(unsafe { NonNull::new_unchecked(fw) }))
+ Ok(unsafe { Owned::to_owned(ptr) })
}

/// Send a firmware request and wait for it. See also `bindings::request_firmware`.
- pub fn request(name: &CStr, dev: &Device) -> Result<Self> {
+ pub fn request(name: &CStr, dev: &Device) -> Result<Owned<Self>> {
Self::request_internal(name, dev, FwFunc::request())
}

/// Send a request for an optional firmware module. See also
/// `bindings::firmware_request_nowarn`.
- pub fn request_nowarn(name: &CStr, dev: &Device) -> Result<Self> {
+ pub fn request_nowarn(name: &CStr, dev: &Device) -> Result<Owned<Self>> {
Self::request_internal(name, dev, FwFunc::request_nowarn())
}

fn as_raw(&self) -> *mut bindings::firmware {
- self.0.as_ptr()
+ self.0.get()
}

/// Returns the size of the requested firmware in bytes.
@@ -101,10 +103,13 @@ pub fn data(&self) -> &[u8] {
}
}

-impl Drop for Firmware {
- fn drop(&mut self) {
- // SAFETY: `self.as_raw()` is valid by the type invariant.
- unsafe { bindings::release_firmware(self.as_raw()) };
+unsafe impl Ownable for Firmware {
+ unsafe fn ptr_drop(ptr: *mut Self) {
+ // SAFETY:
+ // - By the type invariants, we have ownership of the ptr and can free it.
+ // - Per function safety, this is called in Owned::drop(), so `ptr` is a
+ // unique pointer to object, it's safe to release the firmware.
+ unsafe { bindings::release_firmware(ptr.cast()) };
}
}

--
2.43.0