[PATCH v2 2/3] rust: block: add rnull, Rust null_blk implementation

[Andreas Hindborg <nmi@metaspace.dk>]

From: Andreas Hindborg <a.hindborg@samsung.com>

This patch adds an initial version of the Rust null block driver.

Signed-off-by: Andreas Hindborg <a.hindborg@samsung.com>
---
 drivers/block/Kconfig   |  9 +++++
 drivers/block/Makefile  |  3 ++
 drivers/block/rnull.rs  | 86 +++++++++++++++++++++++++++++++++++++++++
 rust/kernel/block/mq.rs |  4 +-
 4 files changed, 101 insertions(+), 1 deletion(-)
 create mode 100644 drivers/block/rnull.rs

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 5b9d4aaebb81..ed209f4f2798 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -354,6 +354,15 @@ config VIRTIO_BLK
 	  This is the virtual block driver for virtio.  It can be used with
           QEMU based VMMs (like KVM or Xen).  Say Y or M.
 
+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. For now it
+	  is only a minimal stub.
+
+	  If unsure, say N.
+
 config BLK_DEV_RBD
 	tristate "Rados block device (RBD)"
 	depends on INET && BLOCK
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index 101612cba303..1105a2d4fdcb 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -9,6 +9,9 @@
 # needed for trace events
 ccflags-y				+= -I$(src)
 
+obj-$(CONFIG_BLK_DEV_RUST_NULL) += rnull_mod.o
+rnull_mod-y := rnull.o
+
 obj-$(CONFIG_MAC_FLOPPY)	+= swim3.o
 obj-$(CONFIG_BLK_DEV_SWIM)	+= swim_mod.o
 obj-$(CONFIG_BLK_DEV_FD)	+= floppy.o
diff --git a/drivers/block/rnull.rs b/drivers/block/rnull.rs
new file mode 100644
index 000000000000..1d6ab6f0f26f
--- /dev/null
+++ b/drivers/block/rnull.rs
@@ -0,0 +1,86 @@
+// 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",
+    author: "Andreas Hindborg",
+    license: "GPL v2",
+}
+
+struct NullBlkModule {
+    _disk: Pin<Box<Mutex<GenDisk<NullBlkDevice, gen_disk::Added>>>>,
+}
+
+fn add_disk(tagset: Arc<TagSet<NullBlkDevice>>) -> Result<GenDisk<NullBlkDevice, gen_disk::Added>> {
+    let block_size: u16 = 4096;
+    if block_size % 512 != 0 || !(512..=4096).contains(&block_size) {
+        return Err(kernel::error::code::EINVAL);
+    }
+
+    let mut disk = gen_disk::try_new(tagset)?;
+    disk.set_name(format_args!("rnullb{}", 0))?;
+    disk.set_capacity_sectors(4096 << 11);
+    disk.set_queue_logical_block_size(block_size.into());
+    disk.set_queue_physical_block_size(block_size.into());
+    disk.set_rotational(false);
+    disk.add()
+}
+
+impl kernel::Module for NullBlkModule {
+    fn init(_module: &'static ThisModule) -> Result<Self> {
+        pr_info!("Rust null_blk loaded\n");
+        let tagset = Arc::pin_init(TagSet::try_new(1, 256, 1), flags::GFP_KERNEL)?;
+        let disk = Box::pin_init(
+            new_mutex!(add_disk(tagset)?, "nullb:disk"),
+            flags::GFP_KERNEL,
+        )?;
+
+        Ok(Self { _disk: 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)
+            .expect("Failed to complete request");
+
+        Ok(())
+    }
+
+    fn commit_rqs() {}
+
+    fn complete(rq: ARef<mq::Request<Self>>) {
+        mq::Request::end_ok(rq)
+            .map_err(|_e| kernel::error::code::EIO)
+            .expect("Failed to complete request")
+    }
+}
diff --git a/rust/kernel/block/mq.rs b/rust/kernel/block/mq.rs
index efbd2588791b..54e032bbdffd 100644
--- a/rust/kernel/block/mq.rs
+++ b/rust/kernel/block/mq.rs
@@ -51,6 +51,7 @@
 //!
 //! ```rust
 //! use kernel::{
+//!     alloc::flags,
 //!     block::mq::*,
 //!     new_mutex,
 //!     prelude::*,
@@ -77,7 +78,8 @@
 //!     }
 //! }
 //!
-//! let tagset: Arc<TagSet<MyBlkDevice>> = Arc::pin_init(TagSet::try_new(1, 256, 1))?;
+//! let tagset: Arc<TagSet<MyBlkDevice>> =
+//!     Arc::pin_init(TagSet::try_new(1, 256, 1), flags::GFP_KERNEL)?;
 //! let mut disk = gen_disk::try_new(tagset)?;
 //! disk.set_name(format_args!("myblk"))?;
 //! disk.set_capacity_sectors(4096);
-- 
2.44.0