From 49cffbc6079c27432b4635d5d03ce14a249d86e2 Mon Sep 17 00:00:00 2001 From: Gonglei Date: Wed, 11 Nov 2015 09:59:26 +0800 Subject: [PATCH] virtio-blk: trivial code optimization 1. avoid possible superflous checking 2. make code more robustness ["make code more robustness" refers to avoiding integer underflows/overflows. --Stefan] Signed-off-by: Gonglei Message-id: 1447207166-12612-1-git-send-email-arei.gonglei@huawei.com Signed-off-by: Stefan Hajnoczi --- hw/block/virtio-blk.c | 28 ++++++++++------------------ 1 file changed, 10 insertions(+), 18 deletions(-) diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c index b88b726be1..f72d4b6069 100644 --- a/hw/block/virtio-blk.c +++ b/hw/block/virtio-blk.c @@ -407,24 +407,16 @@ void virtio_blk_submit_multireq(BlockBackend *blk, MultiReqBuffer *mrb) for (i = 0; i < mrb->num_reqs; i++) { VirtIOBlockReq *req = mrb->reqs[i]; if (num_reqs > 0) { - bool merge = true; - - /* merge would exceed maximum number of IOVs */ - if (niov + req->qiov.niov > IOV_MAX) { - merge = false; - } - - /* merge would exceed maximum transfer length of backend device */ - if (req->qiov.size / BDRV_SECTOR_SIZE + nb_sectors > max_xfer_len) { - merge = false; - } - - /* requests are not sequential */ - if (sector_num + nb_sectors != req->sector_num) { - merge = false; - } - - if (!merge) { + /* + * NOTE: We cannot merge the requests in below situations: + * 1. requests are not sequential + * 2. merge would exceed maximum number of IOVs + * 3. merge would exceed maximum transfer length of backend device + */ + if (sector_num + nb_sectors != req->sector_num || + niov > IOV_MAX - req->qiov.niov || + req->qiov.size / BDRV_SECTOR_SIZE > max_xfer_len || + nb_sectors > max_xfer_len - req->qiov.size / BDRV_SECTOR_SIZE) { submit_requests(blk, mrb, start, num_reqs, niov); num_reqs = 0; } -- 2.39.2