> On 22 Aug 2025, at 09:14, Andreas Hindborg <a.hindborg@xxxxxxxxxx> wrote:
>
> Allow rust null block devices to be configured and instantiated via
> `configfs`.
>
> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
> ---
> drivers/block/rnull/Kconfig | 2 +-
> drivers/block/rnull/configfs.rs | 207 +++++++++++++++++++++++++++++++++++++++
> drivers/block/rnull/rnull.rs | 59 +++++------
> rust/kernel/block/mq/gen_disk.rs | 2 +-
> 4 files changed, 240 insertions(+), 30 deletions(-)
>
> diff --git a/drivers/block/rnull/Kconfig b/drivers/block/rnull/Kconfig
> index 6dc5aff96bf4..7bc5b376c128 100644
> --- a/drivers/block/rnull/Kconfig
> +++ b/drivers/block/rnull/Kconfig
> @@ -4,7 +4,7 @@
>
> config BLK_DEV_RUST_NULL
> tristate "Rust null block driver (Experimental)"
> - depends on RUST
> + depends on RUST && CONFIGFS_FS
> help
> This is the Rust implementation of the null block driver. Like
> the C version, the driver allows the user to create virutal block
> diff --git a/drivers/block/rnull/configfs.rs b/drivers/block/rnull/configfs.rs
> new file mode 100644
> index 000000000000..46710a1e1af4
> --- /dev/null
> +++ b/drivers/block/rnull/configfs.rs
> @@ -0,0 +1,207 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +use super::{NullBlkDevice, THIS_MODULE};
> +use core::fmt::Write;
> +use kernel::{
> + block::mq::gen_disk::{GenDisk, GenDiskBuilder},
> + c_str,
> + configfs::{self, AttributeOperations},
> + configfs_attrs, new_mutex,
> + page::PAGE_SIZE,
> + prelude::*,
> + str::{kstrtobool_bytes, CString},
> + sync::Mutex,
> +};
> +use pin_init::PinInit;
> +
> +pub(crate) fn subsystem() -> impl PinInit<kernel::configfs::Subsystem<Config>, Error> {
> + let item_type = configfs_attrs! {
> + container: configfs::Subsystem<Config>,
> + data: Config,
> + child: DeviceConfig,
> + attributes: [
> + features: 0,
> + ],
> + };
> +
> + kernel::configfs::Subsystem::new(c_str!("rnull"), item_type, try_pin_init!(Config {}))
> +}
> +
> +#[pin_data]
> +pub(crate) struct Config {}
> +
> +#[vtable]
> +impl AttributeOperations<0> for Config {
> + type Data = Config;
> +
> + fn show(_this: &Config, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
> + let mut writer = kernel::str::Formatter::new(page);
> + writer.write_str("blocksize,size,rotational\n")?;
> + Ok(writer.bytes_written())
> + }
> +}
> +
> +#[vtable]
> +impl configfs::GroupOperations for Config {
> + type Child = DeviceConfig;
> +
> + fn make_group(
> + &self,
> + name: &CStr,
> + ) -> Result<impl PinInit<configfs::Group<DeviceConfig>, Error>> {
> + let item_type = configfs_attrs! {
> + container: configfs::Group<DeviceConfig>,
> + data: DeviceConfig,
> + attributes: [
> + // Named for compatibility with C null_blk
> + power: 0,
> + blocksize: 1,
> + rotational: 2,
> + size: 3,
> + ],
> + };
> +
> + Ok(configfs::Group::new(
> + name.try_into()?,
> + item_type,
> + // TODO: cannot coerce new_mutex!() to impl PinInit<_, Error>, so put mutex inside
> + try_pin_init!( DeviceConfig {
> + data <- new_mutex!(DeviceConfigInner {
> + powered: false,
> + block_size: 4096,
> + rotational: false,
> + disk: None,
> + capacity_mib: 4096,
> + name: name.try_into()?,
> + }),
> + }),
> + ))
> + }
> +}
> +
> +#[pin_data]
> +pub(crate) struct DeviceConfig {
> + #[pin]
> + data: Mutex<DeviceConfigInner>,
> +}
> +
> +#[pin_data]
> +struct DeviceConfigInner {
> + powered: bool,
> + name: CString,
> + block_size: u32,
> + rotational: bool,
> + capacity_mib: u64,
> + disk: Option<GenDisk<NullBlkDevice>>,
> +}
> +
> +#[vtable]
> +impl configfs::AttributeOperations<0> for DeviceConfig {
> + type Data = DeviceConfig;
> +
> + fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
> + let mut writer = kernel::str::Formatter::new(page);
> +
> + if this.data.lock().powered {
> + writer.write_str("1\n")?;
> + } else {
> + writer.write_str("0\n")?;
> + }
> +
> + Ok(writer.bytes_written())
> + }
> +
> + fn store(this: &DeviceConfig, page: &[u8]) -> Result {
> + let power_op = kstrtobool_bytes(page)?;
> + let mut guard = this.data.lock();
> +
> + if !guard.powered && power_op {
> + guard.disk = Some(NullBlkDevice::new(
> + &guard.name,
> + guard.block_size,
> + guard.rotational,
> + guard.capacity_mib,
> + )?);
> + guard.powered = true;
> + } else if guard.powered && !power_op {
> + drop(guard.disk.take());
> + guard.powered = false;
> + }
> +
> + Ok(())
> + }
> +}
> +
> +#[vtable]
> +impl configfs::AttributeOperations<1> for DeviceConfig {
> + type Data = DeviceConfig;
> +
> + fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
> + let mut writer = kernel::str::Formatter::new(page);
> + writer.write_fmt(fmt!("{}\n", this.data.lock().block_size))?;
> + Ok(writer.bytes_written())
> + }
> +
> + fn store(this: &DeviceConfig, page: &[u8]) -> Result {
> + if this.data.lock().powered {
> + return Err(EBUSY);
> + }
> +
> + let text = core::str::from_utf8(page)?.trim();
> + let value = text.parse::<u32>().map_err(|_| EINVAL)?;
> +
> + GenDiskBuilder::validate_block_size(value)?;
> + this.data.lock().block_size = value;
> + Ok(())
> + }
> +}
> +
> +#[vtable]
> +impl configfs::AttributeOperations<2> for DeviceConfig {
> + type Data = DeviceConfig;
> +
> + fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
> + let mut writer = kernel::str::Formatter::new(page);
> +
> + if this.data.lock().rotational {
> + writer.write_str("1\n")?;
> + } else {
> + writer.write_str("0\n")?;
> + }
> +
> + Ok(writer.bytes_written())
> + }
> +
> + fn store(this: &DeviceConfig, page: &[u8]) -> Result {
> + if this.data.lock().powered {
> + return Err(EBUSY);
> + }
> +
> + this.data.lock().rotational = kstrtobool_bytes(page)?;
> +
> + Ok(())
> + }
> +}
> +
> +#[vtable]
> +impl configfs::AttributeOperations<3> for DeviceConfig {
> + type Data = DeviceConfig;
> +
> + fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
> + let mut writer = kernel::str::Formatter::new(page);
> + writer.write_fmt(fmt!("{}\n", this.data.lock().capacity_mib))?;
> + Ok(writer.bytes_written())
> + }
> +
> + fn store(this: &DeviceConfig, page: &[u8]) -> Result {
> + if this.data.lock().powered {
> + return Err(EBUSY);
> + }
> +
> + let text = core::str::from_utf8(page)?.trim();
> + let value = text.parse::<u64>().map_err(|_| EINVAL)?;
> +
> + this.data.lock().capacity_mib = value;
> + Ok(())
> + }
> +}
> diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
> index d07e76ae2c13..8690ff5f974f 100644
> --- a/drivers/block/rnull/rnull.rs
> +++ b/drivers/block/rnull/rnull.rs
> @@ -1,28 +1,25 @@
> // 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.
> +
> +mod configfs;
>
> use kernel::{
> - alloc::flags,
> - block::mq::{
> + block::{
> self,
> - gen_disk::{self, GenDisk},
> - Operations, TagSet,
> + mq::{
> + self,
> + gen_disk::{self, GenDisk},
> + Operations, TagSet,
> + },
> },
> error::Result,
> - new_mutex, pr_info,
> + pr_info,
> prelude::*,
> - sync::{Arc, Mutex},
> + sync::Arc,
> types::ARef,
> };
> +use pin_init::PinInit;
>
> module! {
> type: NullBlkModule,
> @@ -35,33 +32,39 @@
> #[pin_data]
> struct NullBlkModule {
> #[pin]
> - _disk: Mutex<GenDisk<NullBlkDevice>>,
> + configfs_subsystem: kernel::configfs::Subsystem<configfs::Config>,
> }
>
> 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"),
> + configfs_subsystem <- configfs::subsystem(),
> })
> }
> }
>
> struct NullBlkDevice;
>
> +impl NullBlkDevice {
> + fn new(
> + name: &CStr,
> + block_size: u32,
> + rotational: bool,
> + capacity_mib: u64,
> + ) -> Result<GenDisk<Self>> {
> + let tagset = Arc::pin_init(TagSet::new(1, 256, 1), GFP_KERNEL)?;
> +
> + gen_disk::GenDiskBuilder::new()
> + .capacity_sectors(capacity_mib << (20 - block::SECTOR_SHIFT))
> + .logical_block_size(block_size)?
> + .physical_block_size(block_size)?
> + .rotational(rotational)
> + .build(fmt!("{}", name.to_str()?), tagset)
> + }
> +}
> +
> #[vtable]
> impl Operations for NullBlkDevice {
> #[inline(always)]
> diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
> index 20f1d46c774d..6b1b846874db 100644
> --- a/rust/kernel/block/mq/gen_disk.rs
> +++ b/rust/kernel/block/mq/gen_disk.rs
> @@ -51,7 +51,7 @@ pub fn rotational(mut self, rotational: bool) -> Self {
>
> /// Validate block size by verifying that it is between 512 and `PAGE_SIZE`,
> /// and that it is a power of two.
> - fn validate_block_size(size: u32) -> Result {
> + pub fn validate_block_size(size: u32) -> Result {
> if !(512..=bindings::PAGE_SIZE as u32).contains(&size) || !size.is_power_of_two() {
> Err(error::code::EINVAL)
> } else {
>
> --
> 2.47.2
>
>
>
Reviewed-by: Daniel Almeida <daniel.almeida@xxxxxxxxxxxxx>
