[PATCH] rust: miscdevice: access file in fops

[Alice Ryhl <aliceryhl@xxxxxxxxxx>]

This allows fops to access information about the underlying struct file
for the miscdevice. For example, the Binder driver needs to inspect the
O_NONBLOCK flag inside the fops->ioctl() hook.

Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
---
This could not land with the base miscdevice abstractions due to the
dependency on File.
---
 rust/kernel/miscdevice.rs | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 7e2a79b3ae26..0cb79676c139 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},
+    fs::File,
     prelude::*,
     str::CStr,
     types::{ForeignOwnable, Opaque},
@@ -103,10 +104,10 @@ pub trait MiscDevice {
     /// Called when the misc device is opened.
     ///
     /// The returned pointer will be stored as the private data for the file.
-    fn open() -> Result<Self::Ptr>;
+    fn open(_file: &File) -> Result<Self::Ptr>;
 
     /// Called when the misc device is released.
-    fn release(device: Self::Ptr) {
+    fn release(device: Self::Ptr, _file: &File) {
         drop(device);
     }
 
@@ -117,6 +118,7 @@ fn release(device: Self::Ptr) {
     /// [`kernel::ioctl`]: mod@crate::ioctl
     fn ioctl(
         _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
+        _file: &File,
         _cmd: u32,
         _arg: usize,
     ) -> Result<isize> {
@@ -133,6 +135,7 @@ fn ioctl(
     #[cfg(CONFIG_COMPAT)]
     fn compat_ioctl(
         _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
+        _file: &File,
         _cmd: u32,
         _arg: usize,
     ) -> Result<isize> {
@@ -187,7 +190,10 @@ impl<T: MiscDevice> VtableHelper<T> {
         return ret;
     }
 
-    let ptr = match T::open() {
+    // 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 ptr = match T::open(unsafe { File::from_raw_file(file) }) {
         Ok(ptr) => ptr,
         Err(err) => return err.to_errno(),
     };
@@ -211,7 +217,10 @@ impl<T: MiscDevice> VtableHelper<T> {
     // SAFETY: The release call of a file owns the private data.
     let ptr = unsafe { <T::Ptr as ForeignOwnable>::from_foreign(private) };
 
-    T::release(ptr);
+    // SAFETY:
+    // * The file is valid for the duration of this call.
+    // * There is no active fdget_pos region on the file on this thread.
+    T::release(ptr, unsafe { File::from_raw_file(file) });
 
     0
 }
@@ -229,7 +238,12 @@ impl<T: MiscDevice> VtableHelper<T> {
     // SAFETY: Ioctl calls can borrow the private data of the file.
     let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
 
-    match T::ioctl(device, cmd, arg as usize) {
+    // 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::ioctl(device, file, cmd, arg as usize) {
         Ok(ret) => ret as c_long,
         Err(err) => err.to_errno() as c_long,
     }
@@ -249,7 +263,12 @@ impl<T: MiscDevice> VtableHelper<T> {
     // SAFETY: Ioctl calls can borrow the private data of the file.
     let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
 
-    match T::compat_ioctl(device, cmd, arg as usize) {
+    // 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::compat_ioctl(device, file, cmd, arg as usize) {
         Ok(ret) => ret as c_long,
         Err(err) => err.to_errno() as c_long,
     }

---
base-commit: 40384c840ea1944d7c5a392e8975ed088ecf0b37
change-id: 20241203-miscdevice-file-param-5df7f75861da

Best regards,
-- 
Alice Ryhl <aliceryhl@xxxxxxxxxx>