[v16,7/9] rust: miscdevice: add mmap support

Commit Message

Alice Ryhl April 8, 2025, 9:22 a.m. UTC

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 `VmaNew` type from the previous commit; this type provides the
correct set of operations for a file_operations->mmap hook.

Acked-by: Greg Kroah-Hartman <[e-mail]>
Acked-by: Lorenzo Stoakes <[e-mail]>
Acked-by: Liam R. Howlett <[e-mail]>
Reviewed-by: Andreas Hindborg <[e-mail]>
Reviewed-by: Gary Guo <[e-mail]>
Signed-off-by: Alice Ryhl <[e-mail]>
---
 rust/kernel/miscdevice.rs | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

Patch

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index fa9ecc42602a477328a25b5d357db90b59dc72ae..9d9771247c3865761c4387467de3f1d1a82691b7 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -14,6 +14,7 @@ 
     error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
     ffi::{c_int, c_long, c_uint, c_ulong},
     fs::File,
+    mm::virt::VmaNew,
     prelude::*,
     seq_file::SeqFile,
     str::CStr,
@@ -119,6 +120,22 @@  fn release(device: Self::Ptr, _file: &File) {
         drop(device);
     }
 
+    /// Handle for mmap.
+    ///
+    /// This function is invoked when a user space process invokes the `mmap` system call on
+    /// `file`. The function is a callback that is part of the VMA initializer. The kernel will do
+    /// initial setup of the VMA before calling this function. The function can then interact with
+    /// the VMA initialization by calling methods of `vma`. If the function does not return an
+    /// error, the kernel will complete initialization of the VMA according to the properties of
+    /// `vma`.
+    fn mmap(
+        _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
+        _file: &File,
+        _vma: &VmaNew,
+    ) -> Result {
+        build_error!(VTABLE_DEFAULT_ERROR)
+    }
+
     /// Handler for ioctls.
     ///
     /// The `cmd` argument is usually manipulated using the utilties in [`kernel::ioctl`].
@@ -223,6 +240,33 @@  impl<T: MiscDevice> MiscdeviceVTable<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 mmap(
+        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: This is a Rust Miscdevice, so we call `into_foreign` in `open` and
+        // `from_foreign` in `release`, and `fops_mmap` is guaranteed to be called between those
+        // two operations.
+        let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
+        // SAFETY: The caller provides a vma that is undergoing initial VMA setup.
+        let area = unsafe { VmaNew::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(),
+        }
+    }
+
     /// # Safety
     ///
     /// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
@@ -291,6 +335,7 @@  impl<T: MiscDevice> MiscdeviceVTable<T> {
     const VTABLE: bindings::file_operations = bindings::file_operations {
         open: Some(Self::open),
         release: Some(Self::release),
+        mmap: if T::HAS_MMAP { Some(Self::mmap) } else { None },
         unlocked_ioctl: if T::HAS_IOCTL {
             Some(Self::ioctl)
         } else {