linux-kernel - [PATCH v11 7/8] rust: miscdevice: add mmap support

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Message-ID: <20241211-vma-v11-7-466640428fc3@google.com>
Date: Wed, 11 Dec 2024 10:37:11 +0000
From: Alice Ryhl <aliceryhl@...gle.com>
To: Miguel Ojeda <ojeda@...nel.org>, Matthew Wilcox <willy@...radead.org>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	John Hubbard <jhubbard@...dia.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Arnd Bergmann <arnd@...db.de>, Christian Brauner <brauner@...nel.org>, Jann Horn <jannh@...gle.com>, 
	Suren Baghdasaryan <surenb@...gle.com>
Cc: Alex Gaynor <alex.gaynor@...il.com>, Boqun Feng <boqun.feng@...il.com>, 
	Gary Guo <gary@...yguo.net>, 
	"Björn Roy Baron" <bjorn3_gh@...tonmail.com>, Benno Lossin <benno.lossin@...ton.me>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, rust-for-linux@...r.kernel.org, 
	Alice Ryhl <aliceryhl@...gle.com>
Subject: [PATCH v11 7/8] rust: miscdevice: add mmap support

Add the ability to write a file_operations->mmap hook in Rust when using
the miscdevice abstraction. The `vma` argument to the `mmap` hook uses
the `VmAreaNew` type from the previous commit; this type provides the
correct set of operations for a file_operations->mmap hook.

Acked-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com> (for mm bits)
Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
---
 rust/kernel/miscdevice.rs | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 7e2a79b3ae26..e5366f9c6d7f 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -11,6 +11,8 @@
 use crate::{
     bindings,
     error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
+    fs::File,
+    mm::virt::VmAreaNew,
     prelude::*,
     str::CStr,
     types::{ForeignOwnable, Opaque},
@@ -110,6 +112,15 @@ fn release(device: Self::Ptr) {
         drop(device);
     }
 
+    /// Handle for mmap.
+    fn mmap(
+        _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
+        _file: &File,
+        _vma: &VmAreaNew,
+    ) -> Result {
+        kernel::build_error!(VTABLE_DEFAULT_ERROR)
+    }
+
     /// Handler for ioctls.
     ///
     /// The `cmd` argument is usually manipulated using the utilties in [`kernel::ioctl`].
@@ -156,6 +167,7 @@ impl<T: MiscDevice> VtableHelper<T> {
         const VTABLE: bindings::file_operations = bindings::file_operations {
             open: Some(fops_open::<T>),
             release: Some(fops_release::<T>),
+            mmap: maybe_fn(T::HAS_MMAP, fops_mmap::<T>),
             unlocked_ioctl: maybe_fn(T::HAS_IOCTL, fops_ioctl::<T>),
             #[cfg(CONFIG_COMPAT)]
             compat_ioctl: if T::HAS_COMPAT_IOCTL {
@@ -216,6 +228,31 @@ impl<T: MiscDevice> VtableHelper<T> {
     0
 }
 
+/// # Safety
+///
+/// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
+/// `vma` must be a vma that is currently being mmap'ed with this file.
+unsafe extern "C" fn fops_mmap<T: MiscDevice>(
+    file: *mut bindings::file,
+    vma: *mut bindings::vm_area_struct,
+) -> c_int {
+    // SAFETY: The mmap call of a file can access the private data.
+    let private = unsafe { (*file).private_data };
+    // SAFETY: Mmap calls can borrow the private data of the file.
+    let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
+    // SAFETY: The caller provides a vma that is undergoing initial VMA setup.
+    let area = unsafe { VmAreaNew::from_raw(vma) };
+    // SAFETY:
+    // * The file is valid for the duration of this call.
+    // * There is no active fdget_pos region on the file on this thread.
+    let file = unsafe { File::from_raw_file(file) };
+
+    match T::mmap(device, file, area) {
+        Ok(()) => 0,
+        Err(err) => err.to_errno() as c_int,
+    }
+}
+
 /// # Safety
 ///
 /// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.

-- 
2.47.1.613.gc27f4b7a9f-goog