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block: Fix harmless off-by-one in bdrv_aligned_preadv()

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If the amount of data to read ends exactly on the total size
of the bs, then we were wasting time creating a local qiov
to read the data in preparation for what would normally be
appending zeroes beyond the end, even though this corner case
has nothing further to do.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Eric Blake 2016-06-23 16:37:07 -06:00 committed by Kevin Wolf
parent a604fa2ba5
commit 82524274ea
1 changed files with 1 additions and 1 deletions
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block/io.c
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@ -1036,7 +1036,7 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
}
max_bytes = ROUND_UP(MAX(0, total_bytes - offset), align);
if (bytes < max_bytes) {
if (bytes <= max_bytes) {
ret = bdrv_driver_preadv(bs, offset, bytes, qiov, 0);
} else if (max_bytes > 0) {
QEMUIOVector local_qiov;