block: refactor bio_iov_bvec_set()

Combine bio_iov_bvec_set() and bio_iov_bvec_set_append() and let the
caller to do iov_iter_advance(). Also get rid of __bio_iov_bvec_set(),
which was duplicated in the final binary, and replace a weird
iov_iter_truncate() of a temporal iter copy with min() better reflecting
the intention.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/bcf1ac36fce769a514e19475f3623cd86a1d8b72.1635006010.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bio.c

@@ -1046,36 +1046,27 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
 }
 EXPORT_SYMBOL_GPL(__bio_release_pages);
 
-static void __bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
+static void bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
 {
+	size_t size = iov_iter_count(iter);
+
 	WARN_ON_ONCE(bio->bi_max_vecs);
 
+	if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
+		struct request_queue *q = bdev_get_queue(bio->bi_bdev);
+		size_t max_sectors = queue_max_zone_append_sectors(q);
+
+		size = min(size, max_sectors << SECTOR_SHIFT);
+	}
+
 	bio->bi_vcnt = iter->nr_segs;
 	bio->bi_io_vec = (struct bio_vec *)iter->bvec;
 	bio->bi_iter.bi_bvec_done = iter->iov_offset;
-	bio->bi_iter.bi_size = iter->count;
+	bio->bi_iter.bi_size = size;
 	bio_set_flag(bio, BIO_NO_PAGE_REF);
 	bio_set_flag(bio, BIO_CLONED);
 }
 
-static int bio_iov_bvec_set(struct bio *bio, struct iov_iter *iter)
-{
-	__bio_iov_bvec_set(bio, iter);
-	iov_iter_advance(iter, iter->count);
-	return 0;
-}
-
-static int bio_iov_bvec_set_append(struct bio *bio, struct iov_iter *iter)
-{
-	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
-	struct iov_iter i = *iter;
-
-	iov_iter_truncate(&i, queue_max_zone_append_sectors(q) << 9);
-	__bio_iov_bvec_set(bio, &i);
-	iov_iter_advance(iter, i.count);
-	return 0;
-}
-
 static void bio_put_pages(struct page **pages, size_t size, size_t off)
 {
 	size_t i, nr = DIV_ROUND_UP(size + (off & ~PAGE_MASK), PAGE_SIZE);
@@ -1217,9 +1208,9 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 	int ret = 0;
 
 	if (iov_iter_is_bvec(iter)) {
-		if (bio_op(bio) == REQ_OP_ZONE_APPEND)
-			return bio_iov_bvec_set_append(bio, iter);
-		return bio_iov_bvec_set(bio, iter);
+		bio_iov_bvec_set(bio, iter);
+		iov_iter_advance(iter, bio->bi_iter.bi_size);
+		return 0;
 	}
 
 	do {