On 5/25/20 1:08 PM, Alberto Garcia wrote:
This patch adds QCow2SubclusterType, which is the subcluster-level
version of QCow2ClusterType. All QCOW2_SUBCLUSTER_* values have the
the same meaning as their QCOW2_CLUSTER_* equivalents (when they
exist). See below for details and caveats.
In images without extended L2 entries clusters are treated as having
exactly one subcluster so it is possible to replace one data type with
the other while keeping the exact same semantics.
With extended L2 entries there are new possible values, and every
subcluster in the same cluster can obviously have a different
QCow2SubclusterType so functions need to be adapted to work on the
subcluster level.
There are several things that have to be taken into account:
a) QCOW2_SUBCLUSTER_COMPRESSED means that the whole cluster is
compressed. We do not support compression at the subcluster
level.
b) There are two different values for unallocated subclusters:
QCOW2_SUBCLUSTER_UNALLOCATED_PLAIN which means that the whole
cluster is unallocated, and QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC
which means that the cluster is allocated but the subcluster is
not. The latter can only happen in images with extended L2
entries.
c) QCOW2_SUBCLUSTER_INVALID is used to detect the cases where an L2
entry has a value that violates the specification. The caller is
responsible for handling these situations.
To prevent compatibility problems with images that have invalid
values but are currently being read by QEMU without causing side
effects, QCOW2_SUBCLUSTER_INVALID is only returned for images
with extended L2 entries.
qcow2_cluster_to_subcluster_type() is added as a separate function
from qcow2_get_subcluster_type(), but this is only temporary and both
will be merged in a subsequent patch.
Signed-off-by: Alberto Garcia <be...@igalia.com>
---
block/qcow2.h | 126 +++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 125 insertions(+), 1 deletion(-)
diff --git a/block/qcow2.h b/block/qcow2.h
index 5c6bf48c7a..27dbcbc502 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -80,6 +80,21 @@
#define QCOW_EXTL2_SUBCLUSTERS_PER_CLUSTER 32
+/* The subcluster X [0..31] is allocated */
+#define QCOW_OFLAG_SUB_ALLOC(X) (1ULL << (X))
+/* The subcluster X [0..31] reads as zeroes */
+#define QCOW_OFLAG_SUB_ZERO(X) (QCOW_OFLAG_SUB_ALLOC(X) << 32)
+/* Subclusters [X, Y) (0 <= X <= Y <= 32) are allocated */
As you are now using a half-open range, should this be:
(0 <= X < Y <= 32)
+#define QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) \
+ (QCOW_OFLAG_SUB_ALLOC(Y) - QCOW_OFLAG_SUB_ALLOC(X))
with <= instead of <, then it is impossible to distinguish between
QCOW_OFLAG_SUB_ALLOC_RANGE(0,0) and QCOW_OFLAG_SUB_ALLOC_RANGE(31,31)
which both resolve to 0. I guess it depends on whether the later uses
of this macro require a non-zero mask ('X < Y') or tolerate the corner
case of no subclusters selected ('X <= Y').
+/* Subclusters [X, Y) (0 <= X <= Y <= 32) read as zeroes */
+#define QCOW_OFLAG_SUB_ZERO_RANGE(X, Y) \
+ (QCOW_OFLAG_SUB_ALLOC_RANGE(X, Y) << 32)
+/* L2 entry bitmap with all allocation bits set */
+#define QCOW_L2_BITMAP_ALL_ALLOC (QCOW_OFLAG_SUB_ALLOC_RANGE(0, 32))
+/* L2 entry bitmap with all "read as zeroes" bits set */
+#define QCOW_L2_BITMAP_ALL_ZEROES (QCOW_OFLAG_SUB_ZERO_RANGE(0, 32))
+
Fixing the comment (if necessary) does not change the code, and the rest
of this patch is fine, so:
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
