ublk: cleanup ublk_copy_user_pages

Clean up ublk_copy_user_pages() by using iov_iter_get_pages2, and code
gets simplified a lot and becomes much more readable than before.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230519065030.351216-4-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -412,49 +412,39 @@ static const struct block_device_operations ub_fops = {
 
 #define UBLK_MAX_PIN_PAGES	32
 
-struct ublk_map_data {
-	const struct request *rq;
-	unsigned long	ubuf;
-	unsigned int	len;
-};
-
 struct ublk_io_iter {
 	struct page *pages[UBLK_MAX_PIN_PAGES];
-	unsigned pg_off;	/* offset in the 1st page in pages */
-	int nr_pages;		/* how many page pointers in pages */
 	struct bio *bio;
 	struct bvec_iter iter;
 };
 
-static inline unsigned ublk_copy_io_pages(struct ublk_io_iter *data,
-		unsigned max_bytes, bool to_vm)
+/* return how many pages are copied */
+static void ublk_copy_io_pages(struct ublk_io_iter *data,
+		size_t total, size_t pg_off, int dir)
 {
-	const unsigned total = min_t(unsigned, max_bytes,
-			PAGE_SIZE - data->pg_off +
-			((data->nr_pages - 1) << PAGE_SHIFT));
 	unsigned done = 0;
 	unsigned pg_idx = 0;
 
 	while (done < total) {
 		struct bio_vec bv = bio_iter_iovec(data->bio, data->iter);
-		const unsigned int bytes = min3(bv.bv_len, total - done,
-				(unsigned)(PAGE_SIZE - data->pg_off));
+		unsigned int bytes = min3(bv.bv_len, (unsigned)total - done,
+				(unsigned)(PAGE_SIZE - pg_off));
 		void *bv_buf = bvec_kmap_local(&bv);
 		void *pg_buf = kmap_local_page(data->pages[pg_idx]);
 
-		if (to_vm)
-			memcpy(pg_buf + data->pg_off, bv_buf, bytes);
+		if (dir == ITER_DEST)
+			memcpy(pg_buf + pg_off, bv_buf, bytes);
 		else
-			memcpy(bv_buf, pg_buf + data->pg_off, bytes);
+			memcpy(bv_buf, pg_buf + pg_off, bytes);
 
 		kunmap_local(pg_buf);
 		kunmap_local(bv_buf);
 
 		/* advance page array */
-		data->pg_off += bytes;
-		if (data->pg_off == PAGE_SIZE) {
+		pg_off += bytes;
+		if (pg_off == PAGE_SIZE) {
 			pg_idx += 1;
-			data->pg_off = 0;
+			pg_off = 0;
 		}
 
 		done += bytes;
@@ -468,41 +458,40 @@ static inline unsigned ublk_copy_io_pages(struct ublk_io_iter *data,
 			data->iter = data->bio->bi_iter;
 		}
 	}
-
-	return done;
 }
 
-static int ublk_copy_user_pages(struct ublk_map_data *data, bool to_vm)
+/*
+ * Copy data between request pages and io_iter, and 'offset'
+ * is the start point of linear offset of request.
+ */
+static size_t ublk_copy_user_pages(const struct request *req,
+		struct iov_iter *uiter, int dir)
 {
-	const unsigned int gup_flags = to_vm ? FOLL_WRITE : 0;
-	const unsigned long start_vm = data->ubuf;
-	unsigned int done = 0;
 	struct ublk_io_iter iter = {
-		.pg_off	= start_vm & (PAGE_SIZE - 1),
-		.bio	= data->rq->bio,
-		.iter	= data->rq->bio->bi_iter,
+		.bio	= req->bio,
+		.iter	= req->bio->bi_iter,
 	};
-	const unsigned int nr_pages = round_up(data->len +
-			(start_vm & (PAGE_SIZE - 1)), PAGE_SIZE) >> PAGE_SHIFT;
-
-	while (done < nr_pages) {
-		const unsigned to_pin = min_t(unsigned, UBLK_MAX_PIN_PAGES,
-				nr_pages - done);
-		unsigned i, len;
-
-		iter.nr_pages = get_user_pages_fast(start_vm +
-				(done << PAGE_SHIFT), to_pin, gup_flags,
-				iter.pages);
-		if (iter.nr_pages <= 0)
-			return done == 0 ? iter.nr_pages : done;
-		len = ublk_copy_io_pages(&iter, data->len, to_vm);
-		for (i = 0; i < iter.nr_pages; i++) {
-			if (to_vm)
+	size_t done = 0;
+
+	while (iov_iter_count(uiter) && iter.bio) {
+		unsigned nr_pages;
+		size_t len, off;
+		int i;
+
+		len = iov_iter_get_pages2(uiter, iter.pages,
+				iov_iter_count(uiter),
+				UBLK_MAX_PIN_PAGES, &off);
+		if (len <= 0)
+			return done;
+
+		ublk_copy_io_pages(&iter, len, off, dir);
+		nr_pages = DIV_ROUND_UP(len + off, PAGE_SIZE);
+		for (i = 0; i < nr_pages; i++) {
+			if (dir == ITER_DEST)
 				set_page_dirty(iter.pages[i]);
 			put_page(iter.pages[i]);
 		}
-		data->len -= len;
-		done += iter.nr_pages;
+		done += len;
 	}
 
 	return done;
@@ -529,15 +518,14 @@ static int ublk_map_io(const struct ublk_queue *ubq, const struct request *req,
 	 * context is pretty fast, see ublk_pin_user_pages
 	 */
 	if (ublk_need_map_req(req)) {
-		struct ublk_map_data data = {
-			.rq	=	req,
-			.ubuf	=	io->addr,
-			.len	=	rq_bytes,
-		};
+		struct iov_iter iter;
+		struct iovec iov;
+		const int dir = ITER_DEST;
 
-		ublk_copy_user_pages(&data, true);
+		import_single_range(dir, u64_to_user_ptr(io->addr), rq_bytes,
+				&iov, &iter);
 
-		return rq_bytes - data.len;
+		return ublk_copy_user_pages(req, &iter, dir);
 	}
 	return rq_bytes;
 }
@@ -549,17 +537,15 @@ static int ublk_unmap_io(const struct ublk_queue *ubq,
 	const unsigned int rq_bytes = blk_rq_bytes(req);
 
 	if (ublk_need_unmap_req(req)) {
-		struct ublk_map_data data = {
-			.rq	=	req,
-			.ubuf	=	io->addr,
-			.len	=	io->res,
-		};
+		struct iov_iter iter;
+		struct iovec iov;
+		const int dir = ITER_SOURCE;
 
 		WARN_ON_ONCE(io->res > rq_bytes);
 
-		ublk_copy_user_pages(&data, false);
-
-		return io->res - data.len;
+		import_single_range(dir, u64_to_user_ptr(io->addr), io->res,
+				&iov, &iter);
+		return ublk_copy_user_pages(req, &iter, dir);
 	}
 	return rq_bytes;
 }