zram: refactor zram_bdev_read

Split the partial read into a separate helper.

Link: https://lkml.kernel.org/r/20230411171459.567614-12-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -1416,33 +1416,33 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 	return ret;
 }
 
-static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
-			  u32 index, int offset, struct bio *bio)
+/*
+ * Use a temporary buffer to decompress the page, as the decompressor
+ * always expects a full page for the output.
+ */
+static int zram_bvec_read_partial(struct zram *zram, struct bio_vec *bvec,
+				  u32 index, int offset, struct bio *bio)
 {
+	struct page *page = alloc_page(GFP_NOIO);
 	int ret;
-	struct page *page;
-
-	page = bvec->bv_page;
-	if (is_partial_io(bvec)) {
-		/* Use a temporary buffer to decompress the page */
-		page = alloc_page(GFP_NOIO);
-		if (!page)
-			return -ENOMEM;
-	}
-
-	ret = zram_read_page(zram, page, index, bio, is_partial_io(bvec));
-	if (unlikely(ret))
-		goto out;
 
-	if (is_partial_io(bvec))
+	if (!page)
+		return -ENOMEM;
+	ret = zram_read_page(zram, page, index, bio, true);
+	if (likely(!ret))
 		memcpy_to_bvec(bvec, page_address(page) + offset);
-out:
-	if (is_partial_io(bvec))
-		__free_page(page);
-
+	__free_page(page);
 	return ret;
 }
 
+static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
+			  u32 index, int offset, struct bio *bio)
+{
+	if (is_partial_io(bvec))
+		return zram_bvec_read_partial(zram, bvec, index, offset, bio);
+	return zram_read_page(zram, bvec->bv_page, index, bio, false);
+}
+
 static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
 				u32 index, struct bio *bio)
 {