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[Qemu-devel] [PULL 01/10] virtio-blk: trivial code optimization
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PULL 01/10] virtio-blk: trivial code optimization |
Date: |
Tue, 22 Dec 2015 16:54:11 +0800 |
From: Gonglei <address@hidden>
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 <address@hidden>
Message-id: address@hidden
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
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 b88b726..f72d4b6 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;
}
--
2.5.0
- [Qemu-devel] [PULL 00/10] Block patches, Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 01/10] virtio-blk: trivial code optimization,
Stefan Hajnoczi <=
- [Qemu-devel] [PULL 02/10] block: add BlockLimits.max_iov field, Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 03/10] block-backend: add blk_get_max_iov(), Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 04/10] block: replace IOV_MAX with BlockLimits.max_iov, Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 05/10] block/mirror: replace IOV_MAX with blk_get_max_iov(), Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 06/10] parallels: add format spec, Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 07/10] scripts/gdb: Fix a python exception in mtree.py, Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 08/10] sd: sdhci: Delete over-zealous power check, Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 09/10] sdhci: don't raise a command index error for an unexpected response, Stefan Hajnoczi, 2015/12/22
- [Qemu-devel] [PULL 10/10] sdhci: add optional quirk property to disable card insertion/removal interrupts, Stefan Hajnoczi, 2015/12/22
- Re: [Qemu-devel] [PULL 00/10] Block patches, Peter Maydell, 2015/12/22