Re: [PATCH] btrfs/029: fix wrong usage of name filter

[Eryu Guan <eguan@redhat.com>]

On Thu, Aug 31, 2017 at 08:53:09AM +0900, Misono, Tomohiro wrote:
> On 2017/08/30 20:09, Eryu Guan wrote:
> > On Wed, Aug 30, 2017 at 04:38:16PM +0900, Misono, Tomohiro wrote:
> >> btrfs/029 uses _filter_testdirs() to filter the name of $TEST_DIR and
> >> $SCRATCH_MNT directory.
> >>
> >> In this function, it calls both _filter_test_dir and _filter_scratch
> >> concatenapted by pipe. Therefore if $TEST_DIR is a prefix of
> >> $SCRATCH_MNT, this filter function gives wrong filtered name for
> >> $SCRATCH_MNT and the test fails.
> > 
> > Sorry, I'm a bit confused, how could $TEST_DIR be a prefix of
> > $SCRATCH_MNT? Won't that fail the test at setup time?
> 
> I used "/mnt" for $TEST_DIR and "/mnt_scratch" for $SCRATCH_MNT and hit
> this problem because "/mnt_scratch" is filtered to "$TEST_DIR_scrach"
> instead of "$SCRATCH_MNT".
> 
> I think these are valid directory names and other btrfs tests run correctly
> with these names.

Ah, yes, that's possible and a valid (though not usual) test setup. The
filter becomes complex when one string is prefix of another string, we
have similar problems when filtering TEST_DIR vs TEST_DEV and
SCRATCH_MNT vs SCRATCH_DEV in _filter_test_dir and _filter_scratch.

But the fix only works around btrfs/029, but there're other places we
use the two filters together, like in _filter_quota, TEST_DIR filter
results would be wrong if SCRATCH_MNT is a prefix of TEST_DIR, because
in _filter_quota it calls _filter_scratch first.

I think one solution is that we filter the longer string first, e.g.
move _filter_testdirs to common/filter and update it to something like:

# filter both test and scratch mount points and devices, but always
# filter the longer string if the other string is a substring of the
# first one.
_filter_testdirs()
{
	if echo "$TEST_DIR" | grep -q "$SCRATCH_MNT"; then
		_filter_test_dir | _filter_scratch
	else
		_filter_scratch | _filter_test_dir
	fi
}

And use this new helper when needed. I found 4 places that need update,
they're btrfs/029, generic/409, generic/410, generic/411 and
_filter_quota().

Thanks,
Eryu