Re: [PATCH] iomap: follow the alignment requirement for iomap_dio_hole_iter()

[Christoph Hellwig <hch@infradead.org>]

On Thu, Jul 30, 2026 at 10:52:10AM +0930, Qu Wenruo wrote:
> [BUG]
> On the latest development branch, btrfs with 8K block size on 4K page
> sized systems will fail the following fsstress workload:
> 
>  # $fsstress -n 4 -d $mnt -s 1785675805 -v

Please add this to xfstests.

> +/*
> + * File systems that write out of place and always allocate new blocks
> + * need each bio to be block aligned as that's the unit of allocation.
> + */
> +static unsigned int iomap_dio_alignment(const struct iomap_iter *iter,
> +					const struct iomap_dio *dio)
> +{
> +	if (dio->flags & IOMAP_DIO_FSBLOCK_ALIGNED)
> +		return i_blocksize(iter->inode);
> +	return bdev_logical_block_size(iter->iomap.bdev);
> +}

This already exists in the VFS iomap tree (with a slightly different
prototype).

>  static int iomap_dio_hole_iter(struct iomap_iter *iter, struct iomap_dio *dio)
>  {
> -	loff_t length = iov_iter_zero(iomap_length(iter), dio->submit.iter);
> +	loff_t copied = iov_iter_zero(iomap_length(iter), dio->submit.iter);
> +	const unsigned int alignment = iomap_dio_alignment(iter, dio);
> +	const loff_t aligned_copied = round_down(copied, alignment);
>  
> -	dio->size += length;
> -	if (!length)
> +	iov_iter_revert(dio->submit.iter, copied - aligned_copied);
> +	dio->size += aligned_copied;
> +	if (!aligned_copied)
>  		return -EFAULT;
> -	return iomap_iter_advance(iter, length);
> +	return iomap_iter_advance(iter, aligned_copied);
>  }

iomap generall expects extents to be block aligned, how do you end up
with non-aligned reporting here?