qcow2: Reduce number of I/O requests

If the first part of a write request is allocated, but the second isn't
and it can be allocated so that the resulting area is contiguous, handle
it at once. This is a common case for sequential writes.

After this patch, alloc_cluster_offset() only checks if the clusters are
already allocated or how many new clusters can be allocated contigouosly.
The actual cluster allocation is split off into a new function
do_alloc_cluster_offset().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/block/qcow2.h b/block/qcow2.h
index 5129e3eab9..e4ac366cfc 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -155,6 +155,7 @@ typedef struct QCowL2Meta
 {
     uint64_t offset;
     uint64_t cluster_offset;
+    uint64_t alloc_offset;
     int n_start;
     int nb_available;
     int nb_clusters;