Re: [RFC PATCH v2 4/8] lib/iov_iter: remove piecewise bvec length checking in iov_iter_aligned_bvec

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2025-07-08 at 12:06 -0400, Mike Snitzer wrote:
> iov_iter_aligned_bvec() is strictly checking alignment of each element
> of the bvec to arrive at whether the bvec is aligned relative to
> dma_alignment and on-disk alignment.  Checking each element
> individually results in disallowing a bvec that in aggregate is
> perfectly aligned relative to the provided @len_mask.
> 
> Relax the on-disk alignment checking such that it is done on the full
> extent described by the bvec but still do piecewise checking of the
> dma_alignment for each bvec's bv_offset.
> 
> This allows for NFS's WRITE payload to be issued using O_DIRECT as
> long as the bvec created with xdr_buf_to_bvec() is composed of pages
> that respect the underlying device's dma_alignment (@addr_mask) and
> the overall contiguous on-disk extent is aligned relative to the
> logical_block_size (@len_mask).
> 
> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
> ---
>  lib/iov_iter.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index bdb37d572e97..b2ae482b8a1d 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -819,13 +819,14 @@ static bool iov_iter_aligned_bvec(const struct iov_iter *i, unsigned addr_mask,
>  	unsigned skip = i->iov_offset;
>  	size_t size = i->count;
>  
> +	if (size & len_mask)
> +		return false;
> +
>  	do {
>  		size_t len = bvec->bv_len;
>  
>  		if (len > size)
>  			len = size;
> -		if (len & len_mask)
> -			return false;
>  		if ((unsigned long)(bvec->bv_offset + skip) & addr_mask)
>  			return false;
>  

cc'ing Keith too since he wrote this helper originally. Should this
also get a:

Fixes: cfa320f72882 ("iov: introduce iov_iter_aligned")

?
-- 
Jeff Layton <jlayton@kernel.org>