This constructor is useful when you just want to create a BitmapVec
without allocating but don't care how large it is.

Acked-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Reviewed-by: Burak Emir <bqe@google.com>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
 rust/kernel/bitmap.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
index 0705646c6251a49f213a45f1f013cb9eb2ed81de..bbbf0f9e5d9251953584581af57042143447b996 100644
--- a/rust/kernel/bitmap.rs
+++ b/rust/kernel/bitmap.rs
@@ -230,6 +230,16 @@ impl BitmapVec {
     /// The maximum length that uses the inline representation.
     pub const MAX_INLINE_LEN: usize = usize::BITS as usize;
 
+    /// Construct a longest possible inline [`BitmapVec`].
+    #[inline]
+    pub fn new_inline() -> Self {
+        // INVARIANT: `nbits <= NO_ALLOC_MAX_LEN`, so an inline bitmap is the right repr.
+        BitmapVec {
+            repr: BitmapRepr { bitmap: 0 },
+            nbits: BitmapVec::NO_ALLOC_MAX_LEN,
+        }
+    }
+
     /// Constructs a new [`BitmapVec`].
     ///
     /// Fails with [`AllocError`] when the [`BitmapVec`] could not be allocated. This

-- 
2.51.2.1041.gc1ab5b90ca-goog

Hi Alice,

kernel test robot noticed the following build errors:

[auto build test ERROR on 211ddde0823f1442e4ad052a2f30f050145ccada]

url:    https://github.com/intel-lab-lkp/linux/commits/Alice-Ryhl/rust-bitmap-add-MAX_LEN-and-MAX_INLINE_LEN-constants/20251112-205752
base:   211ddde0823f1442e4ad052a2f30f050145ccada
patch link:    https://lore.kernel.org/r/20251112-binder-bitmap-v5-2-8b9d7c7eca82%40google.com
patch subject: [PATCH v5 2/6] rust: bitmap: add BitmapVec::new_inline()
config: x86_64-rhel-9.4-rust (https://download.01.org/0day-ci/archive/20251114/202511140146.shdRx5TZ-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251114/202511140146.shdRx5TZ-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202511140146.shdRx5TZ-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from kernel/sched/rq-offsets.c:5:
   kernel/sched/sched.h:3743:18: warning: variable 'cpumask' set but not used [-Wunused-but-set-variable]
   3743 |         struct cpumask *cpumask;
   |                         ^
   1 warning generated.
>> error[E0599]: no associated item named `NO_ALLOC_MAX_LEN` found for struct `bitmap::BitmapVec` in the current scope
   --> rust/kernel/bitmap.rs:239:31
   |
   154 | pub struct BitmapVec {
   | -------------------- associated item `NO_ALLOC_MAX_LEN` not found for this struct
   ...
   239 |             nbits: BitmapVec::NO_ALLOC_MAX_LEN,
   |                               ^^^^^^^^^^^^^^^^ associated item not found in `BitmapVec`

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

On Wed, Nov 12, 2025 at 12:47:20PM +0000, Alice Ryhl wrote:
> This constructor is useful when you just want to create a BitmapVec
> without allocating but don't care how large it is.
> 
> Acked-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
> Reviewed-by: Burak Emir <bqe@google.com>
> Reviewed-by: Danilo Krummrich <dakr@kernel.org>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/kernel/bitmap.rs | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
> index 0705646c6251a49f213a45f1f013cb9eb2ed81de..bbbf0f9e5d9251953584581af57042143447b996 100644
> --- a/rust/kernel/bitmap.rs
> +++ b/rust/kernel/bitmap.rs
> @@ -230,6 +230,16 @@ impl BitmapVec {
>      /// The maximum length that uses the inline representation.
>      pub const MAX_INLINE_LEN: usize = usize::BITS as usize;
>  
> +    /// Construct a longest possible inline [`BitmapVec`].
> +    #[inline]
> +    pub fn new_inline() -> Self {
> +        // INVARIANT: `nbits <= NO_ALLOC_MAX_LEN`, so an inline bitmap is the right repr.
> +        BitmapVec {
> +            repr: BitmapRepr { bitmap: 0 },
> +            nbits: BitmapVec::NO_ALLOC_MAX_LEN,

This should be MAX_INLINE_LEN, I guess?

> +        }
> +    }
> +
>      /// Constructs a new [`BitmapVec`].
>      ///
>      /// Fails with [`AllocError`] when the [`BitmapVec`] could not be allocated. This
> 
> -- 
> 2.51.2.1041.gc1ab5b90ca-goog