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qcow2: Make distinction between zero cluster types obvious

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Treat plain zero clusters differently from allocated ones, so that
we can simplify the logic of checking whether an offset is present.
Do this by splitting QCOW2_CLUSTER_ZERO into two new enums,
QCOW2_CLUSTER_ZERO_PLAIN and QCOW2_CLUSTER_ZERO_ALLOC.

I tried to arrange the enum so that we could use
'ret <= QCOW2_CLUSTER_ZERO_PLAIN' for all unallocated types, and
'ret >= QCOW2_CLUSTER_ZERO_ALLOC' for allocated types, although
I didn't actually end up taking advantage of the layout.

In many cases, this leads to simpler code, by properly combining
cases (sometimes, both zero types pair together, other times,
plain zero is more like unallocated while allocated zero is more
like normal).

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-id: 20170507000552.20847-7-eblake@redhat.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Eric Blake 2017-05-06 19:05:46 -05:00 • committed by Max Reitz
parent 3ef9521893
commit fdfab37dfe
5 changed files with 63 additions and 83 deletions
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8
block/qcow2.h
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@ -351,9 +351,10 @@ typedef struct QCowL2Meta
typedef enum QCow2ClusterType {
QCOW2_CLUSTER_UNALLOCATED,
QCOW2_CLUSTER_ZERO_PLAIN,
QCOW2_CLUSTER_ZERO_ALLOC,
QCOW2_CLUSTER_NORMAL,
QCOW2_CLUSTER_COMPRESSED,
QCOW2_CLUSTER_ZERO
} QCow2ClusterType;
typedef enum QCow2MetadataOverlap {
@ -448,7 +449,10 @@ static inline QCow2ClusterType qcow2_get_cluster_type(uint64_t l2_entry)
if (l2_entry & QCOW_OFLAG_COMPRESSED) {
return QCOW2_CLUSTER_COMPRESSED;
} else if (l2_entry & QCOW_OFLAG_ZERO) {
return QCOW2_CLUSTER_ZERO;
if (l2_entry & L2E_OFFSET_MASK) {
return QCOW2_CLUSTER_ZERO_ALLOC;
}
return QCOW2_CLUSTER_ZERO_PLAIN;
} else if (!(l2_entry & L2E_OFFSET_MASK)) {
return QCOW2_CLUSTER_UNALLOCATED;
} else {