Merge pull request raspberrypi#810 from wedsonaf/inode-dentry

rust: add definitions for ref-counted inodes and dentries

Author: wedsonaf

rust/helpers.c

@@ -627,6 +627,12 @@ void rust_helper___INIT_WORK_WITH_KEY(struct work_struct *work,
 }
 EXPORT_SYMBOL_GPL(rust_helper___INIT_WORK_WITH_KEY);
 
+struct dentry *rust_helper_dget(struct dentry *dentry)
+{
+	return dget(dentry);
+}
+EXPORT_SYMBOL_GPL(rust_helper_dget);
+
 /*
  * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
  * as the Rust `usize` type, so we can use it in contexts where Rust

rust/kernel/fs.rs

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! File systems.
+//!
+//! C headers: [`include/linux/fs.h`](../../../../include/linux/fs.h)
+
+use crate::{bindings, AlwaysRefCounted};
+use core::{cell::UnsafeCell, ptr};
+
+/// Wraps the kernel's `struct inode`.
+///
+/// # Invariants
+///
+/// Instances of this type are always ref-counted, that is, a call to `ihold` ensures that the
+/// allocation remains valid at least until the matching call to `iput`.
+#[repr(transparent)]
+pub struct INode(pub(crate) UnsafeCell<bindings::inode>);
+
+// SAFETY: The type invariants guarantee that `INode` is always ref-counted.
+unsafe impl AlwaysRefCounted for INode {
+    fn inc_ref(&self) {
+        // SAFETY: The existence of a shared reference means that the refcount is nonzero.
+        unsafe { bindings::ihold(self.0.get()) };
+    }
+
+    unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
+        // SAFETY: The safety requirements guarantee that the refcount is nonzero.
+        unsafe { bindings::iput(obj.cast().as_ptr()) }
+    }
+}
+
+/// Wraps the kernel's `struct dentry`.
+///
+/// # Invariants
+///
+/// Instances of this type are always ref-counted, that is, a call to `dget` ensures that the
+/// allocation remains valid at least until the matching call to `dput`.
+#[repr(transparent)]
+pub struct DEntry(pub(crate) UnsafeCell<bindings::dentry>);
+
+// SAFETY: The type invariants guarantee that `DEntry` is always ref-counted.
+unsafe impl AlwaysRefCounted for DEntry {
+    fn inc_ref(&self) {
+        // SAFETY: The existence of a shared reference means that the refcount is nonzero.
+        unsafe { bindings::dget(self.0.get()) };
+    }
+
+    unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
+        // SAFETY: The safety requirements guarantee that the refcount is nonzero.
+        unsafe { bindings::dput(obj.cast().as_ptr()) }
+    }
+}

rust/kernel/lib.rs

@@ -51,6 +51,7 @@ pub mod device;
 pub mod driver;
 pub mod error;
 pub mod file;
+pub mod fs;
 pub mod gpio;
 pub mod hwrng;
 pub mod irq;