Re: [PATCH] configfs: rust: add an API for adding default groups from C

[Alice Ryhl <aliceryhl@google.com>]

On Sun, Feb 15, 2026 at 09:33:47PM +0100, Andreas Hindborg wrote:
> Some C subsystems provide a feature to add configfs default groups to the
> configfs hierarchy of other drivers or subsystems. Rust abstractions for
> these subsystems will want a way to add these default groups via the
> configfs Rust API. So add infrastructure to make this possible.
> 
> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
> ---
>  drivers/block/rnull/configfs.rs |  1 +
>  rust/helpers/configfs.c         | 16 ++++++++++++++++
>  rust/helpers/helpers.c          |  1 +
>  rust/kernel/configfs.rs         | 33 ++++++++++++++++++++++++++++++++-
>  samples/rust/rust_configfs.rs   |  8 +++++++-
>  5 files changed, 57 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/rnull/configfs.rs b/drivers/block/rnull/configfs.rs
> index 6713a6d92391d..ea38b27a9011c 100644
> --- a/drivers/block/rnull/configfs.rs
> +++ b/drivers/block/rnull/configfs.rs
> @@ -78,6 +78,7 @@ fn make_group(
>                      name: name.try_into()?,
>                  }),
>              }),
> +            core::iter::empty(),
>          ))
>      }
>  }
> diff --git a/rust/helpers/configfs.c b/rust/helpers/configfs.c
> new file mode 100644
> index 0000000000000..7cec8ffcb093d
> --- /dev/null
> +++ b/rust/helpers/configfs.c
> @@ -0,0 +1,16 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/configfs.h>
> +
> +__rust_helper void
> +rust_helper_configfs_add_default_group(struct config_group *new_group,
> +				       struct config_group *group)
> +{
> +	configfs_add_default_group(new_group, group);
> +}
> +
> +__rust_helper void
> +__rust_helper_configfs_remove_default_groups(struct config_group *group)

Only the annotation has the two __ prefix, not the symbol name.

> +#[pinned_drop]
> +impl<Data> PinnedDrop for Group<Data> {
> +    fn drop(self: Pin<&mut Self>) {
> +        // SAFETY: We have exclusive access to `self` and we know the default groups are alive
> +        // because we reference them through `self.default_groups`.
> +        unsafe { bindings::configfs_remove_default_groups(self.group.get()) };

Why isn't this here already?

> +    }
>  }
>  
>  impl<Data> Group<Data> {
> @@ -259,7 +269,13 @@ pub fn new(
>          name: CString,
>          item_type: &'static ItemType<Group<Data>, Data>,
>          data: impl PinInit<Data, Error>,
> +        default_groups: impl IntoIterator<Item = Arc<dyn CDefaultGroup>>,

Honestly, I'd just take a KVec here.

>      ) -> impl PinInit<Self, Error> {
> +        let mut dg = KVec::new();
> +        for group in default_groups {
> +            dg.push(group, GFP_KERNEL).unwrap();
> +        }
> +
>          try_pin_init!(Self {
>              group <- pin_init::init_zeroed().chain(|v: &mut Opaque<bindings::config_group>| {
>                  let place = v.get();
> @@ -268,13 +284,28 @@ pub fn new(
>                  unsafe {
>                      bindings::config_group_init_type_name(place, name.cast(), item_type.as_ptr())
>                  };
> +
> +                for default_group in &dg {
> +                    // SAFETY: We keep the default groups alive until `Self` is dropped.
> +                    unsafe { bindings::configfs_add_default_group(default_group.group_ptr(), place) }
> +                }

Do these not need to be removed in drop?

Alice