differ depending on how buffers are overlapped.
This patch introduces logic to honor overlap relationships when cloning
I/O vectors.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
---
block/blkverify.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 60 insertions(+), 2 deletions(-)
@@ -166,17 +166,75 @@ static ssize_t blkverify_iovec_compare(QEMUIOVector *a, QEMUIOVector *b)
return -1;
}
+typedef struct {
+ int src_index;
+ struct iovec *src_iov;
+ void *dest_base;
+} IOVectorSortElem;
+
+static int sortelem_cmp_src_base(const void *a, const void *b)
+{
+ const IOVectorSortElem *elem_a = a;
+ const IOVectorSortElem *elem_b = b;
+
+ /* Don't overflow */
+ if (elem_a->src_iov->iov_base < elem_b->src_iov->iov_base) {
+ return -1;
+ } else if (elem_a->src_iov->iov_base > elem_b->src_iov->iov_base) {
+ return 1;
+ } else {
+ return 0;
+ }
+}
+
+static int sortelem_cmp_src_index(const void *a, const void *b)
+{
+ const IOVectorSortElem *elem_a = a;
+ const IOVectorSortElem *elem_b = b;
+
+ return elem_a->src_index - elem_b->src_index;
+}
+
/**
* Copy contents of I/O vector
+ *
+ * The relative relationships of overlapping iovecs are preserved. This is
+ * necessary to ensure identical semantics in the cloned I/O vector.
*/
static void blkverify_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src,
void *buf)
{
+ IOVectorSortElem sortelems[src->niov];
+ void *last_end;
int i;
+ /* Sort by source iovecs by base address */
+ for (i = 0; i < src->niov; i++) {
+ sortelems[i].src_index = i;
+ sortelems[i].src_iov = &src->iov[i];
+ }
+ qsort(sortelems, src->niov, sizeof(sortelems[0]), sortelem_cmp_src_base);
+
+ /* Allocate buffer space taking into account overlapping iovecs */
+ last_end = NULL;
+ for (i = 0; i < src->niov; i++) {
+ struct iovec *cur = sortelems[i].src_iov;
+ ptrdiff_t rewind = 0;
+
+ /* Detect overlap */
+ if (last_end && last_end > cur->iov_base) {
+ rewind = last_end - cur->iov_base;
+ }
+
+ sortelems[i].dest_base = buf - rewind;
+ buf += cur->iov_len - MIN(rewind, cur->iov_len);
+ last_end = MAX(cur->iov_base + cur->iov_len, last_end);
+ }
+
+ /* Sort by source iovec index and build destination iovec */
+ qsort(sortelems, src->niov, sizeof(sortelems[0]), sortelem_cmp_src_index);
for (i = 0; i < src->niov; i++) {
- qemu_iovec_add(dest, buf, src->iov[i].iov_len);
- buf += src->iov[i].iov_len;
+ qemu_iovec_add(dest, sortelems[i].dest_base, src->iov[i].iov_len);
}
}