{"id":2225771,"url":"http://patchwork.ozlabs.org/api/patches/2225771/?format=json","web_url":"http://patchwork.ozlabs.org/project/linux-pci/patch/20260421-io_projection-v2-6-4c251c692ef4@garyguo.net/","project":{"id":28,"url":"http://patchwork.ozlabs.org/api/projects/28/?format=json","name":"Linux PCI development","link_name":"linux-pci","list_id":"linux-pci.vger.kernel.org","list_email":"linux-pci@vger.kernel.org","web_url":null,"scm_url":null,"webscm_url":null,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260421-io_projection-v2-6-4c251c692ef4@garyguo.net>","list_archive_url":null,"date":"2026-04-21T14:56:17","name":"[v2,06/11] rust: io: add view type","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"b22d329fb50e000d4674c927bc10a5928ca840e2","submitter":{"id":76823,"url":"http://patchwork.ozlabs.org/api/people/76823/?format=json","name":"Gary Guo","email":"gary@garyguo.net"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/linux-pci/patch/20260421-io_projection-v2-6-4c251c692ef4@garyguo.net/mbox/","series":[{"id":500833,"url":"http://patchwork.ozlabs.org/api/series/500833/?format=json","web_url":"http://patchwork.ozlabs.org/project/linux-pci/list/?series=500833","date":"2026-04-21T14:56:19","name":"rust: I/O type generalization and projection","version":2,"mbox":"http://patchwork.ozlabs.org/series/500833/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2225771/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2225771/checks/","tags":{},"related":[],"headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linux-pci@vger.kernel.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=garyguo.net header.i=@garyguo.net header.a=rsa-sha256\n header.s=selector1 header.b=IGLO17Mb;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=2600:3c15:e001:75::12fc:5321; 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28f11079-18c8-41d1-7aa9-08de9fb62b5e","X-MS-Exchange-CrossTenant-AuthSource":"LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM","X-MS-Exchange-CrossTenant-AuthAs":"Internal","X-MS-Exchange-CrossTenant-OriginalArrivalTime":"21 Apr 2026 14:56:29.4443\n (UTC)","X-MS-Exchange-CrossTenant-FromEntityHeader":"Hosted","X-MS-Exchange-CrossTenant-Id":"bbc898ad-b10f-4e10-8552-d9377b823d45","X-MS-Exchange-CrossTenant-MailboxType":"HOSTED","X-MS-Exchange-CrossTenant-UserPrincipalName":"\n 1Syz8XJXVkI6KKLCpM9rZmI6lTHNlMxjzta7D73csoPArsab/AkmuOkZk9NFHov1vgmuOBQRP6XHP2OMMxVyug==","X-MS-Exchange-Transport-CrossTenantHeadersStamped":"CWLP265MB5674"},"content":"The view may be created statically via I/O projection using `io_project!()`\nmacro to perform compile-time checks, or created by type-casting an\nexisting view type with `try_cast()` function, where the size and alignment\nchecks are performed at runtime.\n\nReviewed-by: Andreas Hindborg \nSigned-off-by: Gary Guo \n---\n rust/kernel/io.rs | 147 +++++++++++++++++++++++++++++++++++++++++++++++++++++-\n 1 file changed, 146 insertions(+), 1 deletion(-)","diff":"diff --git a/rust/kernel/io.rs b/rust/kernel/io.rs\nindex a13be8c5fd2d..869071d47a13 100644\n--- a/rust/kernel/io.rs\n+++ b/rust/kernel/io.rs\n@@ -7,7 +7,11 @@\n use crate::{\n bindings,\n prelude::*,\n- ptr::KnownSize, //\n+ ptr::KnownSize,\n+ transmute::{\n+ AsBytes,\n+ FromBytes, //\n+ }, //\n };\n \n pub mod mem;\n@@ -297,6 +301,13 @@ pub trait Io {\n /// Type of this I/O region. For untyped I/O regions, [`Region`] type can be used.\n type Type: ?Sized + KnownSize;\n \n+ /// Get a [`View`] covering the entire region.\n+ #[inline]\n+ fn as_view(&self) -> View<'_, Self, Self::Type> {\n+ // SAFETY: This is an empty projection, so it trivially satisfies the invariant.\n+ unsafe { View::new_unchecked(self, self.as_ptr()) }\n+ }\n+\n /// Returns the base pointer of this mapping.\n ///\n /// This is a pointer to capture metadata. The specific meaning of the pointer depends on\n@@ -912,3 +923,137 @@ pub fn relaxed(&self) -> &RelaxedMmio {\n readq_relaxed,\n writeq_relaxed\n );\n+\n+/// A view into an I/O region.\n+///\n+/// # Invariants\n+///\n+/// - `ptr` is aligned for `T`\n+/// - `ptr` has same provenance as `io.as_ptr()`\n+/// - `ptr.byte_offset_from(io.as_ptr())` is between 0 to\n+/// `KnownSize::size(io.as_ptr()) - KnownSize::size(ptr)`.\n+///\n+/// These invariants are trivially satisfied if the pointer is created via pointer projection.\n+pub struct View<'a, IO: ?Sized, T: ?Sized> {\n+ io: &'a IO,\n+ ptr: *mut T,\n+}\n+\n+impl<'a, IO: ?Sized, T: ?Sized> View<'a, IO, T> {\n+ // For `io_project!` macro use only.\n+ #[doc(hidden)]\n+ #[inline]\n+ pub fn as_view(&self) -> Self {\n+ *self\n+ }\n+\n+ /// Create a view of a provided I/O region.\n+ ///\n+ /// # Safety\n+ ///\n+ /// `ptr` must satisfy the invariants of the view type.\n+ #[inline]\n+ pub unsafe fn new_unchecked(io: &'a IO, ptr: *mut T) -> Self {\n+ // INVARIANT: Per function safety requirement.\n+ Self { io, ptr }\n+ }\n+\n+ /// Obtain the underlying I/O region.\n+ #[inline]\n+ pub fn io(self) -> &'a IO {\n+ self.io\n+ }\n+\n+ /// Obtain a pointer to the subview.\n+ ///\n+ /// The interpretation of the pointer depends on the underlying I/O region.\n+ #[inline]\n+ pub fn as_ptr(self) -> *mut T {\n+ self.ptr\n+ }\n+}\n+\n+impl Clone for View<'_, IO, T> {\n+ #[inline]\n+ fn clone(&self) -> Self {\n+ *self\n+ }\n+}\n+\n+impl Copy for View<'_, IO, T> {}\n+\n+impl<'a, IO: ?Sized, T: ?Sized> View<'a, IO, T> {\n+ /// Try to convert this view into a different typed I/O view.\n+ ///\n+ /// The target type must be of same or smaller size to current type, and the current view must\n+ /// be properly aligned for the target type.\n+ #[inline]\n+ pub fn try_cast(self) -> Result>\n+ where\n+ T: KnownSize + FromBytes + AsBytes,\n+ U: FromBytes + AsBytes,\n+ {\n+ if size_of::() > KnownSize::size(self.ptr) {\n+ return Err(EINVAL);\n+ }\n+\n+ if self.ptr.addr() % align_of::() != 0 {\n+ return Err(EINVAL);\n+ }\n+\n+ // INVARIANT: We have checked bounds and alignment.\n+ Ok(View {\n+ io: self.io,\n+ ptr: self.ptr.cast(),\n+ })\n+ }\n+}\n+\n+/// Project an I/O type to a subview of it.\n+///\n+/// The syntax is of form `io_project!(io, proj)` where `io` is an expression to a type that\n+/// implements [`Io`] and `proj` is a [projection specification](kernel::ptr::project!).\n+///\n+/// In addition to projecting from [`Io`], you may also project from a [`View`] of an [`Io`].\n+///\n+/// # Examples\n+///\n+/// ```\n+/// use kernel::io::{\n+/// io_project,\n+/// Mmio,\n+/// View,\n+/// };\n+/// struct MyStruct { field: u32, }\n+///\n+/// // SAFETY: All bit patterns are acceptable values for `MyStruct`.\n+/// unsafe impl kernel::transmute::FromBytes for MyStruct{};\n+/// // SAFETY: Instances of `MyStruct` have no uninitialized portions.\n+/// unsafe impl kernel::transmute::AsBytes for MyStruct{};\n+///\n+/// # fn test(mmio: &Mmio<[MyStruct]>) -> Result {\n+/// // let mmio: Mmio<[MyStruct]>;\n+/// let field: View<'_, _, u32> = io_project!(mmio, [try: 1].field);\n+/// let whole: View<'_, _, MyStruct> = io_project!(mmio, [try: 2]);\n+/// let nested: View<'_, Mmio<_>, u32> = io_project!(whole, .field);\n+/// # Ok::<(), Error>(()) }\n+#[macro_export]\n+#[doc(hidden)]\n+macro_rules! io_project {\n+ ($io:expr, $($proj:tt)*) => {{\n+ // Bring `as_view` to scope.\n+ use $crate::io::Io as _;\n+\n+ // Convert IO to view for unified handling.\n+ // This also takes advantage to deref coercion.\n+ let view: $crate::io::View<'_, _, _> = $io.as_view();\n+ let ptr = $crate::ptr::project!(\n+ mut view.as_ptr(), $($proj)*\n+ );\n+ // SAFETY: projection of a projection is still a valid projection.\n+ unsafe { $crate::io::View::new_unchecked(view.io(), ptr) }\n+ }};\n+}\n+\n+#[doc(inline)]\n+pub use crate::io_project;\n","prefixes":["v2","06/11"]}