Re: [PATCHv3 3/8] block: align the bio after building it

On Tue, Aug 19, 2025 at 09:49:17AM -0700, Keith Busch wrote:

+/*
+ * Aligns the bio size to the len_align_mask, releasing any excessive bio vecs
+ * that  __bio_iov_iter_get_pages may have inserted and reverts that length for
+ * the next iteration.
+ */
+static int bio_align(struct bio *bio, struct iov_iter *iter,
+			    unsigned len_align_mask)

I think the name is a bit too generic, as the function is very
specific to the __bio_iov_iter_get_pages-path only releasing of
pages, and also only aligns down.  Maybe name it
bio_iov_iter_align_down or something like that?

+	size_t nbytes = bio->bi_iter.bi_size & len_align_mask;
+
+	if (!nbytes)
+		return 0;
+
+	iov_iter_revert(iter, nbytes);
+	bio->bi_iter.bi_size -= nbytes;
+	while (nbytes) {
+		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
+
+		if (nbytes < bv->bv_len) {
+			bv->bv_len -= nbytes;
+			nbytes = 0;
+		} else {
+			bio_release_page(bio, bv->bv_page);
+			bio->bi_vcnt--;
+			nbytes -= bv->bv_len;
+		}
+	}

Minor nitpicks on the loop:  it could be turned into a do { } while ()
loop, because nbytes is already checked above.  And the condition that
sets nbytes to 0 could just break out of the loo.

+
+	if (!bio->bi_iter.bi_size)
+		return -EFAULT;

And as bi_size doesn't change in the loop, this should probably move
above the loop.