block: Add wr_highest_sector blockstat

This adds the wr_highest_sector blockstat which implements what is generally
known as the high watermark. It is the highest offset of a sector written to
the respective BlockDriverState since it has been opened.

The query-blockstat QMP command is extended to add this value to the result,
and also to add the statistics of the underlying protocol in a new "parent"
field. Note that to get the "high watermark" of a qcow2 image, you need to look
into the wr_highest_sector field of the parent (which can be a file, a
host_device, ...). The wr_highest_sector of the qcow2 BlockDriverState itself
is the highest offset on the _virtual_ disk that the guest has written to.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/block_int.h b/block_int.h
index a3afe63..1a7240c 100644
--- a/block_int.h
+++ b/block_int.h
@@ -167,6 +167,7 @@ struct BlockDriverState {
     uint64_t wr_bytes;
     uint64_t rd_ops;
     uint64_t wr_ops;
+    uint64_t wr_highest_sector;
 
     /* Whether the disk can expand beyond total_sectors */
     int growable;