From: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
The dirty bit will make it possible to perform lazy refcount updates,
where the image file is not kept consistent all the time. Upon opening
a dirty image file, it is necessary to perform a consistency check and
repair any incorrect refcounts.
Therefore the dirty bit must be an incompatible feature bit. We don't
want old programs accessing a file with stale refcounts.
Signed-off-by: Stefan Hajnoczi <stefa...@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kw...@redhat.com>
---
docs/specs/qcow2.txt | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletions(-)
diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt
index 87bf785..339cdc1 100644
--- a/docs/specs/qcow2.txt
+++ b/docs/specs/qcow2.txt
@@ -75,7 +75,12 @@ in the description of a field.
Bitmask of incompatible features. An implementation must
fail to open an image if an unknown bit is set.
- Bits 0-63: Reserved (set to 0)
+ Bit 0: Dirty bit. If this bit is set then refcounts
+ may be inconsistent, make sure to scan L1/L2
+ tables to repair refcounts before accessing the
+ image.
+
+ Bits 1-63: Reserved (set to 0)
80 - 87: compatible_features
Bitmask of compatible features. An implementation can
--
1.7.6.5
