qemu-img: Make unallocated part of backing chain obvious in map

The recently-added NBD context qemu:allocation-depth is able to
distinguish between locally-present data (even when that data is
sparse) [shown as depth 1 over NBD], and data that could not be found
anywhere in the backing chain [shown as depth 0]; and the libnbd
project was recently patched to give the human-readable name "absent"
to an allocation-depth of 0.  But qemu-img map --output=json predates
that addition, and has the unfortunate behavior that all portions of
the backing chain that resolve without finding a hit in any backing
layer report the same depth as the final backing layer.  This makes it
harder to reconstruct a qcow2 backing chain using just 'qemu-img map'
output, especially when using "backing":null to artificially limit a
backing chain, because it is impossible to distinguish between a
QCOW2_CLUSTER_UNALLOCATED (which defers to a [missing] backing file)
and a QCOW2_CLUSTER_ZERO_PLAIN cluster (which would override any
backing file), since both types of clusters otherwise show as
"data":false,"zero":true" (but note that we can distinguish a
QCOW2_CLUSTER_ZERO_ALLOCATED, which would also have an "offset":
listing).

The task of reconstructing a qcow2 chain was made harder in commit
0da9856851 (nbd: server: Report holes for raw images), because prior
to that point, it was possible to abuse NBD's block status command to
see which portions of a qcow2 file resulted in BDRV_BLOCK_ALLOCATED
(showing up as NBD_STATE_ZERO in isolation) vs. missing from the chain
(showing up as NBD_STATE_ZERO|NBD_STATE_HOLE); but now qemu reports
more accurate sparseness information over NBD.

An obvious solution is to make 'qemu-img map --output=json' add an
additional "present":false designation to any cluster lacking an
allocation anywhere in the chain, without any change to the "depth"
parameter to avoid breaking existing clients.  The iotests have
several examples where this distinction demonstrates the additional
accuracy.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210701190655.2131223-3-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
[eblake: fix more iotest fallout]
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 89 insertions, 44 deletions

diff --git a/tests/qemu-iotests/179.out b/tests/qemu-iotests/179.out
index 1f76800..7cf22cd 100644
--- a/tests/qemu-iotests/179.out
+++ b/tests/qemu-iotests/179.out
@@ -13,7 +13,11 @@ wrote 2097152/2097152 bytes at offset 6291456
 2 MiB (0x200000) bytes not allocated at offset 4 MiB (0x400000)
 2 MiB (0x200000) bytes     allocated at offset 6 MiB (0x600000)
 56 MiB (0x3800000) bytes not allocated at offset 8 MiB (0x800000)
-[{ "start": 0, "length": 67108864, "depth": 0, "zero": true, "data": false}]
+[{ "start": 0, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 2097152, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 4194304, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 6291456, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 8388608, "length": 58720256, "depth": 0, "present": false, "zero": true, "data": false}]
 wrote 2097150/2097150 bytes at offset 10485761
 2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2097150/2097150 bytes at offset 14680065
@@ -27,7 +31,15 @@ wrote 2097150/2097150 bytes at offset 14680065
 2 MiB (0x200000) bytes not allocated at offset 12 MiB (0xc00000)
 2 MiB (0x200000) bytes     allocated at offset 14 MiB (0xe00000)
 48 MiB (0x3000000) bytes not allocated at offset 16 MiB (0x1000000)
-[{ "start": 0, "length": 67108864, "depth": 0, "zero": true, "data": false}]
+[{ "start": 0, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 2097152, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 4194304, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 6291456, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 8388608, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 10485760, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 12582912, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 14680064, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 16777216, "length": 50331648, "depth": 0, "present": false, "zero": true, "data": false}]
 wrote 14680064/14680064 bytes at offset 18874368
 14 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2097152/2097152 bytes at offset 20971520
@@ -45,13 +57,21 @@ wrote 6291456/6291456 bytes at offset 25165824
 2 MiB (0x200000) bytes not allocated at offset 16 MiB (0x1000000)
 14 MiB (0xe00000) bytes     allocated at offset 18 MiB (0x1200000)
 32 MiB (0x2000000) bytes not allocated at offset 32 MiB (0x2000000)
-[{ "start": 0, "length": 18874368, "depth": 0, "zero": true, "data": false},
-{ "start": 18874368, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 20971520, "length": 2097152, "depth": 0, "zero": true, "data": false},
-{ "start": 23068672, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 25165824, "length": 6291456, "depth": 0, "zero": true, "data": false, "offset": OFFSET},
-{ "start": 31457280, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 33554432, "length": 33554432, "depth": 0, "zero": true, "data": false}]
+[{ "start": 0, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 2097152, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 4194304, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 6291456, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 8388608, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 10485760, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 12582912, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 14680064, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 16777216, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 18874368, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 20971520, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 23068672, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 25165824, "length": 6291456, "depth": 0, "present": true, "zero": true, "data": false, "offset": OFFSET},
+{ "start": 31457280, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 33554432, "length": 33554432, "depth": 0, "present": false, "zero": true, "data": false}]
 wrote 2097152/2097152 bytes at offset 27262976
 2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2097152/2097152 bytes at offset 29360128
@@ -67,15 +87,23 @@ wrote 2097152/2097152 bytes at offset 29360128
 2 MiB (0x200000) bytes not allocated at offset 16 MiB (0x1000000)
 14 MiB (0xe00000) bytes     allocated at offset 18 MiB (0x1200000)
 32 MiB (0x2000000) bytes not allocated at offset 32 MiB (0x2000000)
-[{ "start": 0, "length": 18874368, "depth": 0, "zero": true, "data": false},
-{ "start": 18874368, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 20971520, "length": 2097152, "depth": 0, "zero": true, "data": false},
-{ "start": 23068672, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 25165824, "length": 2097152, "depth": 0, "zero": true, "data": false, "offset": OFFSET},
-{ "start": 27262976, "length": 2097152, "depth": 0, "zero": true, "data": false},
-{ "start": 29360128, "length": 2097152, "depth": 0, "zero": true, "data": false, "offset": OFFSET},
-{ "start": 31457280, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 33554432, "length": 33554432, "depth": 0, "zero": true, "data": false}]
+[{ "start": 0, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 2097152, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 4194304, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 6291456, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 8388608, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 10485760, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 12582912, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 14680064, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 16777216, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 18874368, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 20971520, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 23068672, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 25165824, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false, "offset": OFFSET},
+{ "start": 27262976, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 29360128, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false, "offset": OFFSET},
+{ "start": 31457280, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 33554432, "length": 33554432, "depth": 0, "present": false, "zero": true, "data": false}]
 wrote 8388608/8388608 bytes at offset 33554432
 8 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2097152/2097152 bytes at offset 35651584
@@ -93,15 +121,24 @@ wrote 2097152/2097152 bytes at offset 37748736
 2 MiB (0x200000) bytes not allocated at offset 16 MiB (0x1000000)
 22 MiB (0x1600000) bytes     allocated at offset 18 MiB (0x1200000)
 24 MiB (0x1800000) bytes not allocated at offset 40 MiB (0x2800000)
-[{ "start": 0, "length": 18874368, "depth": 0, "zero": true, "data": false},
-{ "start": 18874368, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 20971520, "length": 2097152, "depth": 0, "zero": true, "data": false},
-{ "start": 23068672, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 25165824, "length": 2097152, "depth": 0, "zero": true, "data": false, "offset": OFFSET},
-{ "start": 27262976, "length": 2097152, "depth": 0, "zero": true, "data": false},
-{ "start": 29360128, "length": 2097152, "depth": 0, "zero": true, "data": false, "offset": OFFSET},
-{ "start": 31457280, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 33554432, "length": 33554432, "depth": 0, "zero": true, "data": false}]
+[{ "start": 0, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 2097152, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 4194304, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 6291456, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 8388608, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 10485760, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 12582912, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 14680064, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 16777216, "length": 2097152, "depth": 0, "present": false, "zero": true, "data": false},
+{ "start": 18874368, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 20971520, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 23068672, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 25165824, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false, "offset": OFFSET},
+{ "start": 27262976, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 29360128, "length": 2097152, "depth": 0, "present": true, "zero": true, "data": false, "offset": OFFSET},
+{ "start": 31457280, "length": 2097152, "depth": 0, "present": true, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 33554432, "length": 8388608, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 41943040, "length": 25165824, "depth": 0, "present": false, "zero": true, "data": false}]
 wrote 8388608/8388608 bytes at offset 41943040
 8 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 8388608/8388608 bytes at offset 50331648
@@ -125,23 +162,31 @@ wrote 2097152/2097152 bytes at offset 62914560
 4 MiB (0x400000) bytes not allocated at offset 54 MiB (0x3600000)
 4 MiB (0x400000) bytes     allocated at offset 58 MiB (0x3a00000)
 2 MiB (0x200000) bytes not allocated at offset 62 MiB (0x3e00000)
-[{ "start": 0, "length": 18874368, "depth": 1, "zero": true, "data": false},
-{ "start": 18874368, "length": 2097152, "depth": 1, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 20971520, "length": 2097152, "depth": 1, "zero": true, "data": false},
-{ "start": 23068672, "length": 2097152, "depth": 1, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 25165824, "length": 2097152, "depth": 1, "zero": true, "data": false, "offset": OFFSET},
-{ "start": 27262976, "length": 2097152, "depth": 1, "zero": true, "data": false},
-{ "start": 29360128, "length": 2097152, "depth": 1, "zero": true, "data": false, "offset": OFFSET},
-{ "start": 31457280, "length": 2097152, "depth": 1, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 33554432, "length": 10485760, "depth": 1, "zero": true, "data": false},
-{ "start": 44040192, "length": 4194304, "depth": 0, "zero": true, "data": false},
-{ "start": 48234496, "length": 2097152, "depth": 1, "zero": true, "data": false},
-{ "start": 50331648, "length": 2097152, "depth": 1, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 52428800, "length": 4194304, "depth": 0, "zero": true, "data": false},
-{ "start": 56623104, "length": 2097152, "depth": 1, "zero": false, "data": true, "offset": OFFSET},
-{ "start": 58720256, "length": 2097152, "depth": 1, "zero": true, "data": false},
-{ "start": 60817408, "length": 4194304, "depth": 0, "zero": true, "data": false},
-{ "start": 65011712, "length": 2097152, "depth": 1, "zero": true, "data": false}]
+[{ "start": 0, "length": 2097152, "depth": 1, "present": false, "zero": true, "data": false},
+{ "start": 2097152, "length": 2097152, "depth": 1, "present": true, "zero": true, "data": false},
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+{ "start": 8388608, "length": 2097152, "depth": 1, "present": false, "zero": true, "data": false},
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+{ "start": 20971520, "length": 2097152, "depth": 1, "present": true, "zero": true, "data": false},
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+{ "start": 44040192, "length": 4194304, "depth": 0, "present": true, "zero": true, "data": false},
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+{ "start": 52428800, "length": 4194304, "depth": 0, "present": true, "zero": true, "data": false},
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+{ "start": 60817408, "length": 4194304, "depth": 0, "present": true, "zero": true, "data": false},
+{ "start": 65011712, "length": 2097152, "depth": 1, "present": false, "zero": true, "data": false}]
 No errors were found on the image.
 No errors were found on the image.