On 04.05.2017 05:07, Eric Blake wrote: > We've already improved discards to operate efficiently on the tail > of an unaligned qcow2 image; it's time to make a similar improvement > to write zeroes. The special case is only valid at the tail > cluster of a file, where we must recognize that any sectors beyond > the image end would implicitly read as zero, and therefore should > not penalize our logic for widening a partial cluster into writing > the whole cluster as zero. > > However, note that for now, the special case of end-of-file is only > recognized if there is no backing file, or if the backing file has > the same length; that's because when the backing file is shorter > than the active layer, we don't have code in place to recognize > that reads of a sector unallocated at the top and beyond the backing > end-of-file are implicitly zero. It's not much of a real loss, > because most people don't use images that aren't cluster-aligned, > or where the active layer is a different size than the backing > layer (especially where the difference falls within a single cluster). > > Update test 154 to cover the new scenarios, using two images of > intentionally differing length. > > While at it, fix the test to gracefully skip when run as > ./check -qcow2 -o compat=0.10 154 > since the older format lacks zero clusters already required earlier > in the test. > > Signed-off-by: Eric Blake <ebl...@redhat.com> > > --- > v12: fix testsuite problems, document shortcoming of differing > v11: reserved for blkdebug half of v10 > size of backing file > > v10: rebase to better reporting of preallocated zero clusters > v9: new patch > --- > block/qcow2.c | 7 ++ > tests/qemu-iotests/154 | 160 > ++++++++++++++++++++++++++++++++++++++++++++- > tests/qemu-iotests/154.out | 129 ++++++++++++++++++++++++++++++++++++ > 3 files changed, 294 insertions(+), 2 deletions(-)
[...] > diff --git a/tests/qemu-iotests/154 b/tests/qemu-iotests/154 > index 7ca7219..687b8f3 100755 > --- a/tests/qemu-iotests/154 > +++ b/tests/qemu-iotests/154 [...] > @@ -299,6 +302,159 @@ $QEMU_IO -c "read -P 0 75k 1k" "$TEST_IMG" | > _filter_qemu_io > > $QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map > > +echo > +echo == unaligned image tail cluster, no allocation needed == [...] > +# A preallocated cluster maintains its allocation, whether it stays as > +# data due to a partial write: > +# Convert 128m... | XX XX => ... | XX 00 > +_make_test_img $((size + 1024)) > +$QEMU_IO -c "write -P 1 $((size)) 1024" "$TEST_IMG" | _filter_qemu_io > +$QEMU_IO -c "write -z $((size + 512)) 512" "$TEST_IMG.base" | _filter_qemu_io s/\.base//, I suppose? (You should read your reference output. "Pattern verification failed" is never good. ;-)) With that (and the reference output) fixed: Reviewed-by: Max Reitz <mre...@redhat.com>
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