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

Benno Lossin
2024-05-29T18:18:44Z

On 29.05.24 15:00, Andreas Hindborg wrote:
> Benno Lossin <benno.lossin@proton.me> writes:
>
>> 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?
>
> Would you embed it inside the `init` function? To what end? I don't
> think that would read well.

I just found it strange that you have this extracted into its own
function, since I just expected it to be present in the init function.
Does this look really that bad?:

impl kernel::Module for NullBlkModule {
fn init(_module: &'static ThisModule) -> Result<Self> {
pr_info!("Rust null_blk loaded\n");
let block_size: u16 = 4096;
if block_size % 512 != 0 ||
!(512..=4096).contains(&block_size) {
return Err(kernel::error::code::EINVAL);
}

let disk = {
let tagset = 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!("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()
};
let disk = Box::pin_init(
new_mutex!(disk, "nullb:disk"),
flags::GFP_KERNEL,
)?;

Ok(Self { _disk: disk })
}
}

>>> + 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?
>
> Yes, it should never happen. If it happens, something is seriously
> broken and panic is adequate.
>
> Other drivers might want to retry later or something, but in this case
> it should just work.

In that case, I think the error message should reflect that and not just
be a generic "failed to complete request" error.

>>> +
>>> + 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?
>
> Yes, re my other email. It is a callback that cannot be triggered for
> now. I will move it to a later patch where it belongs.
>
>>
>>> + 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).
>
> Yes, thank you for spotting that. I thought I checked that this was
> building, so this is strange to me. Maybe I failed to build the
> doctests between the two patches. It is weird that kernel robot did not
> pick this up. Maybe it is not building doctests?

Hmm, that is strange...

---
Cheers,
Benno