qcow2: Don't assume 0 is an invalid cluster offset

The cluster allocation code uses 0 as an invalid offset that is used in
case of errors or as "offset not yet determined". With external data
files, a host cluster offset of 0 becomes valid, though.

Define a constant INV_OFFSET (which is not cluster aligned and will
therefore never be a valid offset) that can be used for such purposes.

This removes the additional host_offset == 0 check that commit
ff52aab2df5 introduced; the confusion between an invalid offset and
(erroneous) allocation at offset 0 is removed with this change.

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

1 files changed, 2 insertions, 0 deletions

diff --git a/block/qcow2.h b/block/qcow2.h
index 8fe2d55..e3bf322 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -463,6 +463,8 @@ typedef enum QCow2MetadataOverlap {
 
 #define REFT_OFFSET_MASK 0xfffffffffffffe00ULL
 
+#define INV_OFFSET (-1ULL)
+
 static inline bool has_data_file(BlockDriverState *bs)
 {
     BDRVQcow2State *s = bs->opaque;