Re: [Libguestfs] [PATCH libnbd] copy/copy-file-to-qcow2-compressed.sh: Skip test for all zeroes disk
On Mon, Aug 07, 2023 at 11:28:42PM +0100, Richard W.M. Jones wrote:
Occasionally this test will choose a random seed which results in an
all-zeroes disk. The test tries to convert this to a compressed qcow2
file, and fails because no compressed clusters are detected in the
resulting file. This happens because qcow2 stores zero clusters with
a special sparse representation, they are never stored compressed, so
a disk with only zeroes in it will never contain compressed clusters.
To fix this, detect an all-zeroes disk and skip.
Skipping a stochastic test on the cases where a random number set up
the corner case is still odd; our testsuite passes, but not always
with the same number of tests. I understand benchmarks wanting to use
stochastic results, but this particular test seems like one where we
aren't buying ourselves any new coverage by using $RANDOM (other than
the fact that we found a corner case where nbdkit's sparse-random can
produce a 1G empty disk), and where a deterministic test better proves
our intent 100% of the time.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization: qemu.org | libguestfs.org