qcow2: Avoid feature name extension on small cluster size
As the feature name table can be quite large (over 9k if all 64 bits of all three feature fields have names; a mere 8 features leaves only 8 bytes for a backing file name in a 512-byte cluster), it is unwise to emit this optional header in images with small cluster sizes. Update iotest 036 to skip running on small cluster sizes; meanwhile, note that iotest 061 never passed on alternative cluster sizes (however, I limited this patch to tests with output affected by adding feature names, rather than auditing for other tests that are not robust to alternative cluster sizes). Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Reviewed-by: Alberto Garcia <berto@igalia.com> Message-Id: <20200324174233.1622067-4-eblake@redhat.com> Signed-off-by: Max Reitz <mreitz@redhat.com>
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@ -2823,8 +2823,15 @@ int qcow2_update_header(BlockDriverState *bs)
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buflen -= ret;
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buflen -= ret;
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}
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}
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/* Feature table */
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/*
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if (s->qcow_version >= 3) {
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* Feature table. A mere 8 feature names occupies 392 bytes, and
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* when coupled with the v3 minimum header of 104 bytes plus the
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* 8-byte end-of-extension marker, that would leave only 8 bytes
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* for a backing file name in an image with 512-byte clusters.
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* Thus, we choose to omit this header for cluster sizes 4k and
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* smaller.
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*/
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if (s->qcow_version >= 3 && s->cluster_size > 4096) {
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static const Qcow2Feature features[] = {
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static const Qcow2Feature features[] = {
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{
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{
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.type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
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.type = QCOW2_FEAT_TYPE_INCOMPATIBLE,
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@ -44,8 +44,10 @@ trap "_cleanup; exit \$status" 0 1 2 3 15
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_supported_fmt qcow2
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_supported_fmt qcow2
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_supported_proto file
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_supported_proto file
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# Only qcow2v3 and later supports feature bits;
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# Only qcow2v3 and later supports feature bits;
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# qcow2.py does not support external data files
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# qcow2.py does not support external data files;
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_unsupported_imgopts 'compat=0.10' data_file
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# this test requires a cluster size large enough for the feature table
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_unsupported_imgopts 'compat=0.10' data_file \
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'cluster_size=\(512\|1024\|2048\|4096\)'
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echo
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echo
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echo === Image with unknown incompatible feature bit ===
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echo === Image with unknown incompatible feature bit ===
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@ -44,8 +44,10 @@ _supported_os Linux
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# Conversion between different compat versions can only really work
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# Conversion between different compat versions can only really work
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# with refcount_bits=16;
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# with refcount_bits=16;
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# we have explicit tests for data_file here, but the whole test does
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# we have explicit tests for data_file here, but the whole test does
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# not work with it
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# not work with it;
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_unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file
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# we have explicit tests for various cluster sizes, the remaining tests
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# require the default 64k cluster
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_unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file cluster_size
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echo
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echo
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echo "=== Testing version downgrade with zero expansion ==="
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echo "=== Testing version downgrade with zero expansion ==="
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