rust: devres: add DevresLt for ForLt-aware device resource access

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Devres<T> stores resources as T and returns &'a T from access(). For
lifetime-parameterized types like Bar<'a, SIZE> that are transmuted to
'static for storage, this exposes the synthetic 'static lifetime to
callers -- any method on the stored type that returns a reference with
its lifetime parameter would yield a &'static reference, which is
unsound.

Add DevresLt<F: ForLt>, a thin wrapper around Devres<F::Of<'static>>
that shortens the stored 'static lifetime to the caller's borrow
lifetime in all access methods.

DevresLt::new() is unsafe because the caller must guarantee that the
data remains valid for the device's full bound scope; the internal
transmute from F::Of<'a> to F::Of<'static> would otherwise allow
use-after-free.

Two access patterns are provided:

- CovariantForLt types get direct-reference accessors (access,
  try_access) that return shortened references via
  CovariantForLt::cast_ref.

- Plain ForLt types use closure-based accessors (access_with,
  try_access_with) whose universally quantified lifetime prevents
  callers from smuggling in concrete short-lived references.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260626183630.2585057-6-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

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Danilo Krummrich 2026-06-26 20:36:12 +02:00

parent 6763c8876d

commit b85f672a3e

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rust/kernel/devres.rs

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