[RFC PATCH v2 17/30] rust: fs: add empty address space operations

[Wedson Almeida Filho <wedsonaf@gmail.com>]

From: Wedson Almeida Filho <walmeida@microsoft.com>

This is in preparation for allowing modules to implement different
address space callbacks, which will be introduced in subsequent patches.

Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
---
 rust/kernel/fs.rs               |  1 +
 rust/kernel/fs/address_space.rs | 58 +++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 rust/kernel/fs/address_space.rs

diff --git a/rust/kernel/fs.rs b/rust/kernel/fs.rs
index 20fb6107eb4b..f1c1972fabcf 100644
--- a/rust/kernel/fs.rs
+++ b/rust/kernel/fs.rs
@@ -13,6 +13,7 @@
 use macros::{pin_data, pinned_drop};
 use sb::SuperBlock;
 
+pub mod address_space;
 pub mod dentry;
 pub mod file;
 pub mod inode;
diff --git a/rust/kernel/fs/address_space.rs b/rust/kernel/fs/address_space.rs
new file mode 100644
index 000000000000..5b4fcb568f46
--- /dev/null
+++ b/rust/kernel/fs/address_space.rs
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! File system address spaces.
+//!
+//! This module allows Rust code implement address space operations.
+//!
+//! C headers: [`include/linux/fs.h`](srctree/include/linux/fs.h)
+
+use super::FileSystem;
+use crate::bindings;
+use core::marker::PhantomData;
+use macros::vtable;
+
+/// Operations implemented by address spaces.
+#[vtable]
+pub trait Operations {
+    /// File system that these operations are compatible with.
+    type FileSystem: FileSystem + ?Sized;
+}
+
+/// Represents address space operations.
+#[allow(dead_code)]
+pub struct Ops<T: FileSystem + ?Sized>(
+    pub(crate) *const bindings::address_space_operations,
+    pub(crate) PhantomData<T>,
+);
+
+impl<T: FileSystem + ?Sized> Ops<T> {
+    /// Creates the address space operations from a type that implements the [`Operations`] trait.
+    pub const fn new<U: Operations<FileSystem = T> + ?Sized>() -> Self {
+        struct Table<T: Operations + ?Sized>(PhantomData<T>);
+        impl<T: Operations + ?Sized> Table<T> {
+            const TABLE: bindings::address_space_operations = bindings::address_space_operations {
+                writepage: None,
+                read_folio: None,
+                writepages: None,
+                dirty_folio: None,
+                readahead: None,
+                write_begin: None,
+                write_end: None,
+                bmap: None,
+                invalidate_folio: None,
+                release_folio: None,
+                free_folio: None,
+                direct_IO: None,
+                migrate_folio: None,
+                launder_folio: None,
+                is_partially_uptodate: None,
+                is_dirty_writeback: None,
+                error_remove_folio: None,
+                swap_activate: None,
+                swap_deactivate: None,
+                swap_rw: None,
+            };
+        }
+        Self(&Table::<U>::TABLE, PhantomData)
+    }
+}
-- 
2.34.1