rnull: move driver to separate directory

The rust null block driver is about to gain some additional modules. Rather
than pollute the current directory, move the driver to a subdirectory.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250902-rnull-up-v6-16-v7-12-b5212cc89b98@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

3 files changed, 96 insertions, 0 deletions

diff --git a/drivers/block/rnull/Kconfig b/drivers/block/rnull/Kconfig
new file mode 100644
index 000000000000..6dc5aff96bf4
--- /dev/null
+++ b/drivers/block/rnull/Kconfig
@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Rust null block device driver configuration
+
+config BLK_DEV_RUST_NULL
+	tristate "Rust null block driver (Experimental)"
+	depends on RUST
+	help
+	  This is the Rust implementation of the null block driver. Like
+	  the C version, the driver allows the user to create virutal block
+	  devices that can be configured via various configuration options.
+
+	  If unsure, say N.
diff --git a/drivers/block/rnull/Makefile b/drivers/block/rnull/Makefile
new file mode 100644
index 000000000000..11cfa5e615dc
--- /dev/null
+++ b/drivers/block/rnull/Makefile
@@ -0,0 +1,3 @@
+
+obj-$(CONFIG_BLK_DEV_RUST_NULL) += rnull_mod.o
+rnull_mod-y := rnull.o
diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
new file mode 100644
index 000000000000..d07e76ae2c13
--- /dev/null
+++ b/drivers/block/rnull/rnull.rs
@@ -0,0 +1,80 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! This is a Rust implementation of the C null block driver.
+//!
+//! Supported features:
+//!
+//! - blk-mq interface
+//! - direct completion
+//! - block size 4k
+//!
+//! The driver is not configurable.
+
+use kernel::{
+    alloc::flags,
+    block::mq::{
+        self,
+        gen_disk::{self, GenDisk},
+        Operations, TagSet,
+    },
+    error::Result,
+    new_mutex, pr_info,
+    prelude::*,
+    sync::{Arc, Mutex},
+    types::ARef,
+};
+
+module! {
+    type: NullBlkModule,
+    name: "rnull_mod",
+    authors: ["Andreas Hindborg"],
+    description: "Rust implementation of the C null block driver",
+    license: "GPL v2",
+}
+
+#[pin_data]
+struct NullBlkModule {
+    #[pin]
+    _disk: Mutex<GenDisk<NullBlkDevice>>,
+}
+
+impl kernel::InPlaceModule for NullBlkModule {
+    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
+        pr_info!("Rust null_blk loaded\n");
+
+        // Use a immediately-called closure as a stable `try` block
+        let disk = /* try */ (|| {
+            let tagset = Arc::pin_init(TagSet::new(1, 256, 1), flags::GFP_KERNEL)?;
+
+            gen_disk::GenDiskBuilder::new()
+                .capacity_sectors(4096 << 11)
+                .logical_block_size(4096)?
+                .physical_block_size(4096)?
+                .rotational(false)
+                .build(format_args!("rnullb{}", 0), tagset)
+        })();
+
+        try_pin_init!(Self {
+            _disk <- new_mutex!(disk?, "nullb:disk"),
+        })
+    }
+}
+
+struct NullBlkDevice;
+
+#[vtable]
+impl Operations for NullBlkDevice {
+    #[inline(always)]
+    fn queue_rq(rq: ARef<mq::Request<Self>>, _is_last: bool) -> Result {
+        mq::Request::end_ok(rq)
+            .map_err(|_e| kernel::error::code::EIO)
+            // We take no refcounts on the request, so we expect to be able to
+            // end the request. The request reference must be unique at this
+            // point, and so `end_ok` cannot fail.
+            .expect("Fatal error - expected to be able to end request");
+
+        Ok(())
+    }
+
+    fn commit_rqs() {}
+}