Re: [PATCH 2/5] rust: pci: convert IrqVectorRegistration to a lifetime-managed owning type

["Gary Guo" <gary@garyguo.net>]

On Mon Aug 10, 2026 at 11:47 PM BST, Danilo Krummrich wrote:
> Convert IrqVectorRegistration from a devres-managed internal type to a
> lifetime-annotated type that owns the PCI interrupt vector allocation.
> Dropping it frees the vectors.
>
> IrqVector gains a reference to the IrqVectorRegistration it was derived
> from. This reference flows through IrqRequest (via the IrqRequestAnchor
> generic) into irq::Registration, creating a borrow chain that prevents
> the vector allocation from being dropped while any handler is still
> registered.
>
> alloc_irq_vectors() returns IrqVectorRegistration<'_> directly, giving
> drivers explicit control over the allocation lifetime. This is also
> needed by e.g. net and block drivers that re-allocate vectors, e.g.
> during queue reconfiguration or device recovery.
>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  rust/kernel/pci.rs     |   3 +-
>  rust/kernel/pci/irq.rs | 149 ++++++++++++++++++++++-------------------
>  2 files changed, 83 insertions(+), 69 deletions(-)
>
> diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs
> index c6417af2bb17..2757a0cc0f11 100644
> --- a/rust/kernel/pci.rs
> +++ b/rust/kernel/pci.rs
> @@ -51,7 +51,8 @@
>  pub use self::irq::{
>      IrqType,
>      IrqTypes,
> -    IrqVector, //
> +    IrqVector,
> +    IrqVectorRegistration, //
>  };
>  
>  /// An adapter for the registration of PCI drivers.
> diff --git a/rust/kernel/pci/irq.rs b/rust/kernel/pci/irq.rs
> index fea484dcf9cf..38a7d72dcda7 100644
> --- a/rust/kernel/pci/irq.rs
> +++ b/rust/kernel/pci/irq.rs
> @@ -7,17 +7,15 @@
>      bindings,
>      device,
>      device::Bound,
> -    devres,
>      error::to_result,
>      irq::{
>          self,
> -        IrqRequest, //
> +        IrqRequest,
> +        IrqRequestAnchor, //
>      },
> -    prelude::*,
> -    str::CStr,
> -    sync::aref::ARef, //
> +    prelude::*, //
>  };
> -use core::ops::RangeInclusive;
> +use core::num::NonZero;
>  
>  /// IRQ type flags for PCI interrupt allocation.
>  #[derive(Debug, Clone, Copy)]
> @@ -78,6 +76,7 @@ const fn as_raw(self) -> u32 {
>  #[derive(Clone, Copy)]
>  pub struct IrqVector<'a> {
>      dev: &'a Device<Bound>,
> +    reg: &'a IrqVectorRegistration<'a>,
>      index: u32,
>  }
>  
> @@ -86,10 +85,11 @@ impl<'a> IrqVector<'a> {
>      ///
>      /// # Safety
>      ///
> -    /// - `index` must be a valid IRQ vector index for `dev`.
> -    /// - `dev` must point to a [`Device`] that has successfully allocated IRQ vectors.
> -    unsafe fn new(dev: &'a Device<Bound>, index: u32) -> Self {
> -        Self { dev, index }
> +    /// - `index` must be a valid IRQ vector index for `reg`.
> +    /// - `dev` must be the device `reg` was allocated from.
> +    #[inline]
> +    unsafe fn new(dev: &'a Device<Bound>, reg: &'a IrqVectorRegistration<'a>, index: u32) -> Self {
> +        Self { dev, reg, index }
>      }
>  
>      /// Returns the raw vector index.
> @@ -98,75 +98,72 @@ fn index(&self) -> u32 {
>      }
>  }
>  
> -impl<'a> TryInto<IrqRequest<'a>> for IrqVector<'a> {
> +impl IrqRequestAnchor for &IrqVectorRegistration<'_> {}
> +
> +impl<'a> IrqRequest<'a, &'a IrqVectorRegistration<'a>> {
> +    /// Returns the [`IrqVectorRegistration`] this request was derived from.
> +    pub fn vectors(&self) -> &'a IrqVectorRegistration<'a> {
> +        self.anchor()
> +    }
> +}
> +
> +impl<'a> TryInto<IrqRequest<'a, &'a IrqVectorRegistration<'a>>> for IrqVector<'a> {
>      type Error = Error;
>  
> -    fn try_into(self) -> Result<IrqRequest<'a>> {
> -        // SAFETY: `self.as_raw` returns a valid pointer to a `struct pci_dev`.
> +    fn try_into(self) -> Result<IrqRequest<'a, &'a IrqVectorRegistration<'a>>> {
> +        // SAFETY: `self.dev.as_raw()` returns a valid pointer to a `struct pci_dev`.
>          let irq = unsafe { bindings::pci_irq_vector(self.dev.as_raw(), self.index()) };
>          if irq < 0 {
>              return Err(crate::error::Error::from_errno(irq));
>          }
> -        // SAFETY: `irq` is guaranteed to be a valid IRQ number for `&self`.
> -        Ok(unsafe { IrqRequest::new(self.dev.as_ref(), irq as u32) })
> +        // SAFETY: `irq` is guaranteed to be a valid IRQ number for `self.dev`.
> +        Ok(unsafe { IrqRequest::new_anchored(self.dev.as_ref(), irq as u32, self.reg) })

Why is this anchoring thing needed instead apart from the lifetime that already
exists on `IrqRequest`?

Best,
Gary

>      }
>  }
>  
> -/// Represents an IRQ vector allocation for a PCI device.
> +/// An allocation of PCI interrupt vectors for a device.
>  ///
> -/// This type ensures that IRQ vectors are properly allocated and freed by
> -/// tying the allocation to the lifetime of this registration object.
> +/// This type owns the vector allocation; dropping it frees the vectors. IRQ handlers borrow from
> +/// this registration and must be dropped before it is.
>  ///
>  /// # Invariants
>  ///
> -/// The [`Device`] has successfully allocated IRQ vectors.
> -struct IrqVectorRegistration {
> -    dev: ARef<Device>,
> +/// `dev` has an allocation of `count` interrupt vectors.
> +pub struct IrqVectorRegistration<'a> {
> +    dev: &'a Device<Bound>,
> +    count: NonZero<usize>,
>  }