On 4/5/26 23:32, Luan Haickel Araujo wrote:
> Encapsulate find_next_bit and find_next_zero_bit calls into helpers
> to verify if a range of subblocks is entirely plugged or unplugged.
>
> This improves readability as requested by the TODO comments in the
> source code.
>
> Validation confirms the change is binary-neutral on ARM64, with the
> generated instructions remaining identical.
>
> Suggested-by: David Hildenbrand <[email protected]>
>
> Signed-off-by: Luan Haickel Araujo <[email protected]>
> ---
> Hi David,
>
Hi!
> This is my first patch contribution to the Linux kernel, following up on
> your TODO notes in virtio_mem.c.
>
> As part of my learning process (LFX 103), I verified the change in a
> QEMU (KVM) environment with test_bitmap. I also compared the generated
> assembly on ARM64 and it remains identical, confirming the helpers are
> binary-neutral as expected.
>
> I noticed these helpers could also be useful in include/linux/bitmap.h in
> the future. If you think it makes sense to move them there, I'd be happy
> to work on that in a next step.
Right, the TODO really indicated that core code should provide such
helpers, not virtio-mem itself. There is no real benefit in having these
local helpers.
>
> Looking forward to your feedback.
>
> Luan.
> drivers/virtio/virtio_mem.c | 24 ++++++++++++++++++------
> 1 file changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
> index 48051e9e98ab..e94e30af3a5d 100644
> --- a/drivers/virtio/virtio_mem.c
> +++ b/drivers/virtio/virtio_mem.c
> @@ -538,6 +538,22 @@ static void virtio_mem_sbm_set_sb_unplugged(struct
> virtio_mem *vm,
> __bitmap_clear(vm->sbm.sb_states, bit, count);
> }
>
> +static inline bool bitmap_test_range_all_set(const unsigned long *map,
> + unsigned int start, unsigned int
> nbits)
> +{
> + unsigned int next_zero_bit = find_next_zero_bit(map, start + nbits,
> start);
> +
> + return next_zero_bit >= start + nbits;
> +}
> +
> +static inline bool bitmap_test_range_all_zero(const unsigned long *map,
> + unsigned int start, unsigned int
> nbits)
> +{
> + unsigned int next_set_bit = find_next_bit(map, start + nbits, start);
> +
> + return next_set_bit >= start + nbits;
> +}
If you look closely, fs/btrfs/misc.h provides these functions. So they
should probably be factored out into common code.
Then, virtio-mem could just naturally reuse them.
But, I wonder whether we want to call them
bitmap_test_set()
bitmap_test_clear()
Given that they have the exact same interface as
bitmap_set/bitmap_clear, consuming a range.
--
Cheers,
David
