[PATCH] rust: miscdevice: add missing safety comments

[Alice Ryhl <aliceryhl@google.com>]

This fixes the following four warnings:

	warning: unsafe block missing a safety comment
	   --> /home/aliceryhl/rust-for-linux/rust/kernel/miscdevice.rs:168:15
	    |
	168 |             ..unsafe { MaybeUninit::zeroed().assume_init() }
	    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
	    |
	    = help: consider adding a safety comment on the preceding line
	    = help: for further information visit
	      https://rust-lang.github.io/rust-clippy/master/index.html#undocumented_unsafe_blocks
	    = note: requested on the command line with `-W clippy::undocumented-unsafe-blocks`

	warning: unsafe function's docs are missing a `# Safety` section
	   --> /home/aliceryhl/rust-for-linux/rust/kernel/miscdevice.rs:175:1
	    |
	175 | / unsafe extern "C" fn fops_open<T: MiscDevice>(
	176 | |     inode: *mut bindings::inode,
	177 | |     file: *mut bindings::file,
	178 | | ) -> c_int {
	    | |__________^
	    |
	    = help: for further information visit
	      https://rust-lang.github.io/rust-clippy/master/index.html#missing_safety_doc
	    = note: `-W clippy::missing-safety-doc` implied by `-W clippy::all`
	    = help: to override `-W clippy::all` add `#[allow(clippy::missing_safety_doc)]`

	warning: unsafe function's docs are missing a `# Safety` section
	   --> /home/aliceryhl/rust-for-linux/rust/kernel/miscdevice.rs:196:1
	    |
	196 | / unsafe extern "C" fn fops_release<T: MiscDevice>(
	197 | |     _inode: *mut bindings::inode,
	198 | |     file: *mut bindings::file,
	199 | | ) -> c_int {
	    | |__________^
	    |
	    = help: for further information visit
	      https://rust-lang.github.io/rust-clippy/master/index.html#missing_safety_doc

	warning: unsafe function's docs are missing a `# Safety` section
	   --> /home/aliceryhl/rust-for-linux/rust/kernel/miscdevice.rs:210:1
	    |
	210 | / unsafe extern "C" fn fops_ioctl<T: MiscDevice>(
	211 | |     file: *mut bindings::file,
	212 | |     cmd: c_uint,
	213 | |     arg: c_ulong,
	214 | | ) -> c_long {
	    | |___________^
	    |
	    = help: for further information visit
	      https://rust-lang.github.io/rust-clippy/master/index.html#missing_safety_doc

Note that these warnings are currently not enabled in the build, but
rust-next contains a commit that will enable them, so we should fix
them.

Reported-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/kernel/miscdevice.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
index 50885fb511bf..7e2a79b3ae26 100644
--- a/rust/kernel/miscdevice.rs
+++ b/rust/kernel/miscdevice.rs
@@ -165,6 +165,7 @@ impl<T: MiscDevice> VtableHelper<T> {
             } else {
                 None
             },
+            // SAFETY: All zeros is a valid value for `bindings::file_operations`.
             ..unsafe { MaybeUninit::zeroed().assume_init() }
         };
     }
@@ -172,6 +173,10 @@ impl<T: MiscDevice> VtableHelper<T> {
     &VtableHelper::<T>::VTABLE
 }
 
+/// # Safety
+///
+/// `file` and `inode` must be the file and inode for a file that is undergoing initialization.
+/// The file must be associated with a `MiscDeviceRegistration<T>`.
 unsafe extern "C" fn fops_open<T: MiscDevice>(
     inode: *mut bindings::inode,
     file: *mut bindings::file,
@@ -193,6 +198,10 @@ impl<T: MiscDevice> VtableHelper<T> {
     0
 }
 
+/// # Safety
+///
+/// `file` and `inode` must be the file and inode for a file that is being released. The file must
+/// be associated with a `MiscDeviceRegistration<T>`.
 unsafe extern "C" fn fops_release<T: MiscDevice>(
     _inode: *mut bindings::inode,
     file: *mut bindings::file,
@@ -207,6 +216,9 @@ impl<T: MiscDevice> VtableHelper<T> {
     0
 }
 
+/// # Safety
+///
+/// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
 unsafe extern "C" fn fops_ioctl<T: MiscDevice>(
     file: *mut bindings::file,
     cmd: c_uint,
@@ -223,6 +235,9 @@ impl<T: MiscDevice> VtableHelper<T> {
     }
 }
 
+/// # Safety
+///
+/// `file` must be a valid file that is associated with a `MiscDeviceRegistration<T>`.
 #[cfg(CONFIG_COMPAT)]
 unsafe extern "C" fn fops_compat_ioctl<T: MiscDevice>(
     file: *mut bindings::file,

---
base-commit: 4f94fbb8848c4d2bc5260045ed66907b1bf520fd
change-id: 20241022-miscdevice-unsafe-warn-fix-f735035a6511

Best regards,
-- 
Alice Ryhl <aliceryhl@google.com>