util: add qemu_iovec_is_zero

Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 22 insertions, 0 deletions

diff --git a/include/qemu-common.h b/include/qemu-common.h
index 3f3fd60f5b..66ceceb2ad 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -318,6 +318,7 @@ void qemu_iovec_concat(QEMUIOVector *dst,
 void qemu_iovec_concat_iov(QEMUIOVector *dst,
                            struct iovec *src_iov, unsigned int src_cnt,
                            size_t soffset, size_t sbytes);
+bool qemu_iovec_is_zero(QEMUIOVector *qiov);
 void qemu_iovec_destroy(QEMUIOVector *qiov);
 void qemu_iovec_reset(QEMUIOVector *qiov);
 size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,
diff --git a/util/iov.c b/util/iov.c
index 6569b5aae1..49f88388f8 100644
--- a/util/iov.c
+++ b/util/iov.c
@@ -335,6 +335,27 @@ void qemu_iovec_concat(QEMUIOVector *dst,
     qemu_iovec_concat_iov(dst, src->iov, src->niov, soffset, sbytes);
 }
 
+/*
+ * Check if the contents of the iovecs are all zero
+ */
+bool qemu_iovec_is_zero(QEMUIOVector *qiov)
+{
+    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)) {
+            return false;
+        }
+        for (; offs < qiov->iov[i].iov_len; offs++) {
+            if (ptr[offs]) {
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
 void qemu_iovec_destroy(QEMUIOVector *qiov)
 {
     assert(qiov->nalloc != -1);