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

Benno Lossin
2024-05-28T13:28:00Z

On 21.05.24 16:03, Andreas Hindborg wrote:
> 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>> {

Any reason that this is its own function and not in the
`NullBlkModule::init` function?

> + 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");

This error would only happen if `rq` is not the only ARef to that
request, right?

> +
> + Ok(())
> + }
> +
> + fn commit_rqs() {}
> +
> + fn complete(rq: ARef<mq::Request<Self>>) {

Am I correct in thinking that this function is never actually called,
since all requests that are queued are immediately ended?

> + 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)?;

This change should probably be in the patch before (seems like an
artifact from rebasing).

---
Cheers,
Benno

> //! let mut disk = gen_disk::try_new(tagset)?;
> //! disk.set_name(format_args!("myblk"))?;
> //! disk.set_capacity_sectors(4096);
> --
> 2.44.0
>
>