I mentioned this already to Danilo via alternate channels, but to clarify - this patch -is- actually needed, as we make use of `AsRef<Device<Bound>>` in the kunit test for SGTable
On Thu, 2026-06-04 at 15:25 +0200, Danilo Krummrich wrote:
On Wed Jun 3, 2026 at 9:42 PM CEST, Lyude Paul wrote:
When writing up some rust code that used faux devices for unit testing, I noticed that we never actually added the Bound device context to faux::Registration's AsRefdevice::Device implementation. This being said: the Registration object itself is proof that a driver is bound to the device - so this should be safe.
Yes, it should be, but the reasons are non-trivial and should be part of the safety comment below.
- faux_match() always returns 1, and probe runs synchronously (PROBE_FORCE_SYNCHRONOUS)
- suppress_bind_attrs = true on faux_driver prevents userspace- triggered unbind via sysfs
- mem::forget(Registration) is not a problem; if the Registration is leaked, the faux device stays bound forever
Signed-off-by: Lyude Paul lyude@redhat.com
I can pick this through the driver-core tree already, as it seems this it not needed by this series. Feel free to resend as individual patch for thus purpose.
rust/kernel/faux.rs | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/rust/kernel/faux.rs b/rust/kernel/faux.rs index 43b4974f48cd2..e0856b2964a2c 100644 --- a/rust/kernel/faux.rs +++ b/rust/kernel/faux.rs @@ -25,7 +25,8 @@ /// /// # Invariants /// -/// `self.0` always holds a valid pointer to an initialized and registered [`struct faux_device`]. +/// - `self.0` always holds a valid pointer to an initialized and registered [`struct faux_device`]. +/// - This object is proof that the object described by this `Registration` is bound to a device. /// /// [`struct faux_device`]: srctree/include/linux/device/faux.h pub struct Registration(NonNullbindings::faux_device); @@ -59,8 +60,8 @@ fn as_raw(&self) -> *mut bindings::faux_device { } } -impl AsRefdevice::Device for Registration { - fn as_ref(&self) -> &device::Device { +impl AsRef<device::Devicedevice::Bound> for Registration { + fn as_ref(&self) -> &device::Devicedevice::Bound { // SAFETY: The underlying `device` in `faux_device` is guaranteed by the C API to be // a valid initialized `device`. unsafe { device::Device::from_raw(addr_of_mut!((*self.as_raw()).dev)) } -- 2.54.0