[PATCH 01/80] rust: add definitions for ref-counted inodes and dentries

[Ariel Miculas <amiculas@cisco.com>]

From: Wedson Almeida Filho <wedsonaf@google.com>

This is in preparation for adding support for the implementation of file
systems in Rust.

Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
---
 rust/bindings/bindings_helper.h |  1 +
 rust/helpers.c                  |  7 +++++
 rust/kernel/fs.rs               | 53 +++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |  1 +
 4 files changed, 62 insertions(+)
 create mode 100644 rust/kernel/fs.rs

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 50e7a76d5455..eeb5b7c0528a 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -10,6 +10,7 @@
 #include <linux/refcount.h>
 #include <linux/wait.h>
 #include <linux/sched.h>
+#include <linux/fs.h>
 
 /* `bindgen` gets confused at certain things. */
 const gfp_t BINDINGS_GFP_KERNEL = GFP_KERNEL;
diff --git a/rust/helpers.c b/rust/helpers.c
index 81e80261d597..e00c53c94c43 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -26,6 +26,7 @@
 #include <linux/spinlock.h>
 #include <linux/sched/signal.h>
 #include <linux/wait.h>
+#include <linux/fs_parser.h>
 
 __noreturn void rust_helper_BUG(void)
 {
@@ -128,6 +129,12 @@ void rust_helper_put_task_struct(struct task_struct *t)
 }
 EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
 
+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
diff --git a/rust/kernel/fs.rs b/rust/kernel/fs.rs
new file mode 100644
index 000000000000..157fdb917ad1
--- /dev/null
+++ b/rust/kernel/fs.rs
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! File systems.
+//!
+//! C headers: [`include/linux/fs.h`](../../../../include/linux/fs.h)
+
+use crate::{bindings};
+use crate::types::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()) }
+    }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 85b261209977..486f60912132 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -30,6 +30,7 @@
 #[cfg(not(test))]
 #[cfg(not(testlib))]
 mod allocator;
+pub mod fs;
 mod build_assert;
 pub mod error;
 pub mod init;
-- 
2.40.1