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

[Mike Snitzer <snitzer@kernel.org>]

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;
 
-- 
2.44.0