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authorVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>2019-06-04 19:15:04 +0300
committerStefan Hajnoczi <stefanha@redhat.com>2019-08-27 14:52:45 +0100
commitf76889e7b947d896db51be8a4d9c941c2f70365a (patch)
treed233a85f4d166859d08cf38aa556f6297c5f59a6 /util
parentd953169d4840f312d3b9a54952f4a7ccfcb3b311 (diff)
util/iov: improve qemu_iovec_is_zero
We'll need to check a part of qiov soon, so implement it now. Optimization with align down to 4 * sizeof(long) is dropped due to: 1. It is strange: it aligns length of the buffer, but where is a guarantee that buffer pointer is aligned itself? 2. buffer_is_zero() is a better place for optimizations and it has them. Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Acked-by: Stefan Hajnoczi <stefanha@redhat.com> Message-id: 20190604161514.262241-3-vsementsov@virtuozzo.com Message-Id: <20190604161514.262241-3-vsementsov@virtuozzo.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'util')
-rw-r--r--util/iov.c31
1 files changed, 19 insertions, 12 deletions
diff --git a/util/iov.c b/util/iov.c
index 366ff9cdd1..9ac0261853 100644
--- a/util/iov.c
+++ b/util/iov.c
@@ -451,23 +451,30 @@ void qemu_iovec_init_extended(
}
/*
- * Check if the contents of the iovecs are all zero
+ * Check if the contents of subrange of qiov data is all zeroes.
*/
-bool qemu_iovec_is_zero(QEMUIOVector *qiov)
+bool qemu_iovec_is_zero(QEMUIOVector *qiov, size_t offset, size_t bytes)
{
- int i;
- for (i = 0; i < qiov->niov; i++) {
- size_t offs = QEMU_ALIGN_DOWN(qiov->iov[i].iov_len, 4 * sizeof(long));
- uint8_t *ptr = qiov->iov[i].iov_base;
- if (offs && !buffer_is_zero(qiov->iov[i].iov_base, offs)) {
+ struct iovec *iov;
+ size_t current_offset;
+
+ assert(offset + bytes <= qiov->size);
+
+ iov = iov_skip_offset(qiov->iov, offset, &current_offset);
+
+ while (bytes) {
+ uint8_t *base = (uint8_t *)iov->iov_base + current_offset;
+ size_t len = MIN(iov->iov_len - current_offset, bytes);
+
+ if (!buffer_is_zero(base, len)) {
return false;
}
- for (; offs < qiov->iov[i].iov_len; offs++) {
- if (ptr[offs]) {
- return false;
- }
- }
+
+ current_offset = 0;
+ bytes -= len;
+ iov++;
}
+
return true;
}