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@oracle.com> (for mm bits)
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/kernel/miscdevice.rs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 7e2a79b3ae26..99e076338f39 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -11,6 +11,7 @@
 use crate::{
     bindings,
     error::{to_result, Error, Result, VTABLE_DEFAULT_ERROR},
+    mm::virt::VmAreaNew,
     prelude::*,
     str::CStr,
     types::{ForeignOwnable, Opaque},
@@ -110,6 +111,11 @@ fn release(device: Self::Ptr) {
         drop(device);
     }
 
+    /// Handle for mmap.
+    fn mmap(_device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>, _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 +162,7 @@ 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 +223,27 @@ 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) };
+
+    match T::mmap(device, 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>`.

-- 
2.47.0.338.g60cca15819-goog