[RFC PATCH v2 3/4] rust: miscdevice: add uring_cmd() for MiscDevice trait

[Sidong Yang <sidong.yang@furiosa.ai>]

This patch adds uring_cmd() function for MiscDevice trait and its
callback implementation. It uses IoUringCmd that io_uring_cmd rust
abstraction.

Signed-off-by: Sidong Yang <sidong.yang@furiosa.ai>
---
 rust/kernel/miscdevice.rs | 41 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 288f40e79906..54be866ea7ff 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,
+    io_uring::IoUringCmd,
     mm::virt::VmaNew,
     prelude::*,
     seq_file::SeqFile,
@@ -175,6 +176,19 @@ fn show_fdinfo(
     ) {
         build_error!(VTABLE_DEFAULT_ERROR)
     }
+
+    /// Handler for uring_cmd.
+    ///
+    /// This function is invoked when userspace process submits the uring_cmd op
+    /// on io_uring submission queue. The `io_uring_cmd` would be used for get
+    /// arguments cmd_op, sqe, cmd_data.
+    fn uring_cmd(
+        _device: <Self::Ptr as ForeignOwnable>::Borrowed<'_>,
+        _io_uring_cmd: Pin<&mut IoUringCmd>,
+        _issue_flags: u32,
+    ) -> Result<i32> {
+        build_error!(VTABLE_DEFAULT_ERROR)
+    }
 }
 
 /// A vtable for the file operations of a Rust miscdevice.
@@ -332,6 +346,28 @@ impl<T: MiscDevice> MiscdeviceVTable<T> {
         T::show_fdinfo(device, m, file);
     }
 
+    /// # Safety
+    ///
+    /// `ioucmd` is not null and points to a valid `bindings::io_uring_cmd`.
+    unsafe extern "C" fn uring_cmd(
+        ioucmd: *mut bindings::io_uring_cmd,
+        issue_flags: ffi::c_uint,
+    ) -> ffi::c_int {
+        // SAFETY: The file is valid for the duration of this call.
+        let ioucmd = unsafe { IoUringCmd::from_raw(ioucmd) };
+        let file = ioucmd.file();
+
+        // SAFETY: The file is valid for the duration of this call.
+        let private = unsafe { (*file.as_ptr()).private_data }.cast();
+        // SAFETY: uring_cmd calls can borrow the private data of the file.
+        let device = unsafe { <T::Ptr as ForeignOwnable>::borrow(private) };
+
+        match T::uring_cmd(device, ioucmd, issue_flags) {
+            Ok(ret) => ret as ffi::c_int,
+            Err(err) => err.to_errno() as ffi::c_int,
+        }
+    }
+
     const VTABLE: bindings::file_operations = bindings::file_operations {
         open: Some(Self::open),
         release: Some(Self::release),
@@ -354,6 +390,11 @@ impl<T: MiscDevice> MiscdeviceVTable<T> {
         } else {
             None
         },
+        uring_cmd: if T::HAS_URING_CMD {
+            Some(Self::uring_cmd)
+        } else {
+            None
+        },
         // SAFETY: All zeros is a valid value for `bindings::file_operations`.
         ..unsafe { MaybeUninit::zeroed().assume_init() }
     };
-- 
2.43.0