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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 <arei.gonglei@huawei.com>
Message-id: 1447207166-12612-1-git-send-email-arei.gonglei@huawei.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Gonglei 2015-11-11 09:59:26 +08:00 committed by Stefan Hajnoczi
parent c688084506
commit 49cffbc607
1 changed files with 10 additions and 18 deletions
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28
hw/block/virtio-blk.c
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@ -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;
}