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Danilo Krummrich <dakr@kernel.org> says: The ForLt trait currently guarantees covariance, which allows safe lifetime shortening via cast_ref(). However, some types (e.g. those containing Mutex<&'bound T>) are invariant over their lifetime parameter and cannot safely use cast_ref(). This series splits ForLt into two traits: - ForLt: base trait for all lifetime-parameterized types, providing only the Of<'a> GAT. - CovariantForLt: unsafe subtrait that guarantees covariance, providing a safe cast_ref() method. For invariant types, a closure-based API (registration_data_with()) is added to the auxiliary subsystem. The closure's HRTB prevents the caller from choosing a concrete lifetime, which would be unsound for invariant types. On top of that, this series adds DevresLt<F: ForLt>, a thin wrapper around Devres<F::Of<'static>> that shortens the stored 'static lifetime back to the caller's borrow scope. DevresLt provides both closure-based access (access_with/try_access_with for ForLt types) and direct reference access (access/try_access for CovariantForLt types). Also implement ForLt and CovariantForLt for Bar, IoMem and ExclusiveIoMem, and update their into_devres() methods to return DevresLt. Provide convenience type aliases DevresBar, DevresIoMem and DevresExclusiveIoMem. Link: https://patch.msgid.link/20260626183630.2585057-1-dakr@kernel.org Signed-off-by: Danilo Krummrich <dakr@kernel.org>