Re: [Libguestfs] [PATCH libnbd v3 3/3] copy/copy-nbd-error.sh: Make this test non-stochastic

On 06/29/22 15:36, Richard W.M. Jones wrote: > Because the test previously used error rates of 50%, it could > sometimes "fail to fail". This is noticable if you run the test > repeatedly: > > $ while make -C copy check TESTS=copy-nbd-error.sh >& /tmp/log ; do echo -n . ; done > > This now happens more often because of the larger requests made by the > new multi-threaded loop, resulting in fewer calls to the error filter, > so a greater chance that a series of 50% coin tosses will come up all > heads in the test. > > Fix this by making the test non-stocastic. > > Fixes: commit 8d444b41d09a700c7ee6f9182a649f3f2d325abb > --- > copy/copy-nbd-error.sh | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/copy/copy-nbd-error.sh b/copy/copy-nbd-error.sh > index 0088807f54..01524a890c 100755 > --- a/copy/copy-nbd-error.sh > +++ b/copy/copy-nbd-error.sh > @@ -40,7 +40,7 @@ $VG nbdcopy -- [ nbdkit --exit-with-parent -v --filter=error pattern 5M \ > # Failure to read should be fatal > echo "Testing read failures on non-sparse source" > $VG nbdcopy -- [ nbdkit --exit-with-parent -v --filter=error pattern 5M \ > - error-pread-rate=0.5 ] null: && fail=1 > + error-pread-rate=1 ] null: && fail=1 > > # However, reliable block status on a sparse image can avoid the need to read > echo "Testing read failures on sparse source" > @@ -51,7 +51,7 @@ $VG nbdcopy -- [ nbdkit --exit-with-parent -v --filter=error null 5M \ > echo "Testing write data failures on arbitrary destination" > $VG nbdcopy -- [ nbdkit --exit-with-parent -v pattern 5M ] \ > [ nbdkit --exit-with-parent -v --filter=error --filter=noextents \ > - memory 5M error-pwrite-rate=0.5 ] && fail=1 > + memory 5M error-pwrite-rate=1 ] && fail=1 > > # However, writing zeroes can bypass the need for normal writes > echo "Testing write data failures from sparse source" > Wasn't the original intent of the 50% error rate that the first error manifest usually at a different offset every time? If we change the error rate to 1, the tests will fail upon the first access, which kind of breaks the original intent. I wonder if we could determine a random offset in advance, and make sure that the read or write access fails 100%, but only if the request covers that offset.