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| author | Eric Blake <eblake@redhat.com> | 2020-03-24 12:42:32 -0500 |
|---|---|---|
| committer | Max Reitz <mreitz@redhat.com> | 2020-03-26 14:44:33 +0100 |
| commit | e7be13ad3ff593608a118bfb69553037bd221563 (patch) | |
| tree | dc2b8da191a1c4ee29500d769ec7ee773603c5b6 /block | |
| parent | bb40ebce2cb0bd4bf37968074d43d5a864fb6dee (diff) | |
| download | qemu-e7be13ad3ff593608a118bfb69553037bd221563.zip qemu-e7be13ad3ff593608a118bfb69553037bd221563.tar.gz qemu-e7be13ad3ff593608a118bfb69553037bd221563.tar.bz2 | |
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>
Diffstat (limited to 'block')
| -rw-r--r-- | block/qcow2.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/block/qcow2.c b/block/qcow2.c index b74cbeb..2bb536b 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2823,8 +2823,15 @@ 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, |