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

[Benno Lossin <benno.lossin@proton.me>]

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
> 
>