block: add a helper function for dio alignment

This will make it easier to add more complex acceptable alignment
criteria in the future.

Signed-off-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220610195830.3574005-6-kbusch@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/fops.c

@@ -42,6 +42,13 @@ static unsigned int dio_bio_write_op(struct kiocb *iocb)
 	return op;
 }
 
+static bool blkdev_dio_unaligned(struct block_device *bdev, loff_t pos,
+			      struct iov_iter *iter)
+{
+	return ((pos | iov_iter_alignment(iter)) &
+	    (bdev_logical_block_size(bdev) - 1));
+}
+
 #define DIO_INLINE_BIO_VECS 4
 
 static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
@@ -54,8 +61,7 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
 	struct bio bio;
 	ssize_t ret;
 
-	if ((pos | iov_iter_alignment(iter)) &
-	    (bdev_logical_block_size(bdev) - 1))
+	if (blkdev_dio_unaligned(bdev, pos, iter))
 		return -EINVAL;
 
 	if (nr_pages <= DIO_INLINE_BIO_VECS)
@@ -173,8 +179,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	loff_t pos = iocb->ki_pos;
 	int ret = 0;
 
-	if ((pos | iov_iter_alignment(iter)) &
-	    (bdev_logical_block_size(bdev) - 1))
+	if (blkdev_dio_unaligned(bdev, pos, iter))
 		return -EINVAL;
 
 	if (iocb->ki_flags & IOCB_ALLOC_CACHE)
@@ -298,8 +303,7 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
 	loff_t pos = iocb->ki_pos;
 	int ret = 0;
 
-	if ((pos | iov_iter_alignment(iter)) &
-	    (bdev_logical_block_size(bdev) - 1))
+	if (blkdev_dio_unaligned(bdev, pos, iter))
 		return -EINVAL;
 
 	if (iocb->ki_flags & IOCB_ALLOC_CACHE)