| Message ID | 20200131174436.2961874-4-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Improve qcow2 all-zero detection | expand |
31.01.2020 20:44, Eric Blake wrote: > 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>
On Fri 31 Jan 2020 06:44:22 PM CET, Eric Blake wrote: > 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: Alberto Garcia <berto@igalia.com> Berto
diff --git a/block/qcow2.c b/block/qcow2.c index d3e7709ac2b4..6ea06dbdf48a 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2819,8 +2819,15 @@ int qcow2_update_header(BlockDriverState *bs) buflen -= ret; } - /* Feature table */ - if (s->qcow_version >= 3) { + /* + * Feature table. A mere 8 feature names occupies 392 bytes, and + * when coupled with the v3 minimum header of 104 bytes plus the + * 8-byte end-of-extension marker, that would leave only 8 bytes + * for a backing file name in an image with 512-byte clusters. + * Thus, we choose to omit this header for cluster sizes 4k and + * smaller. + */ + if (s->qcow_version >= 3 && s->cluster_size > 4096) { static const Qcow2Feature features[] = { { .type = QCOW2_FEAT_TYPE_INCOMPATIBLE, diff --git a/tests/qemu-iotests/036 b/tests/qemu-iotests/036 index 512598421c20..cf522de7a1aa 100755 --- a/tests/qemu-iotests/036 +++ b/tests/qemu-iotests/036 @@ -44,8 +44,10 @@ trap "_cleanup; exit \$status" 0 1 2 3 15 _supported_fmt qcow2 _supported_proto file # Only qcow2v3 and later supports feature bits; -# qcow2.py does not support external data files -_unsupported_imgopts 'compat=0.10' data_file +# qcow2.py does not support external data files; +# this test requires a cluster size large enough for the feature table +_unsupported_imgopts 'compat=0.10' data_file \ + 'cluster_size=\(512\|1024\|2048\|4096\)' echo echo === Image with unknown incompatible feature bit === diff --git a/tests/qemu-iotests/061 b/tests/qemu-iotests/061 index 36b040491fef..ce285d308408 100755 --- a/tests/qemu-iotests/061 +++ b/tests/qemu-iotests/061 @@ -44,8 +44,10 @@ _supported_os Linux # Conversion between different compat versions can only really work # with refcount_bits=16; # we have explicit tests for data_file here, but the whole test does -# not work with it -_unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file +# not work with it; +# we have explicit tests for various cluster sizes, the remaining tests +# require the default 64k cluster +_unsupported_imgopts 'refcount_bits=\([^1]\|.\([^6]\|$\)\)' data_file cluster_size echo echo "=== Testing version downgrade with zero expansion ==="
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> --- block/qcow2.c | 11 +++++++++-- tests/qemu-iotests/036 | 6 ++++-- tests/qemu-iotests/061 | 6 ++++-- 3 files changed, 17 insertions(+), 6 deletions(-)