Re: [PATCH v2 3/3] common/rc: Check call order of _require_dm_target and _require_scratch*

[Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>]

On Sep 10, 2021 / 10:48, Dave Chinner wrote:
> On Wed, Sep 08, 2021 at 05:37:15PM +0900, Shin'ichiro Kawasaki wrote:
> > When SCRATCH_DEV is not set and the test case does not call
> > _require_scratch* before _require_dm_target, _require_block_device
> > called from _require_dm_target fails to evaluate SCRATCH_DEV and
> > results in the test case failure. This failure reason is not described
> > in the error message and it takes some time to catch.
> 
> You should quote the actual failure message here so we have some
> idea of whether the message that was emitted was appropriate or not
> without having to go know how the test failed...

Sorry about the lack of the infomration. As you found below, the meesage was
"Usage: _require_block_device <dev>".

> 
> > To catch the failure reason easier, check SCRATCH_DEV in
> > _require_dm_target. If SCRATCH_DEV is not set, fail the test case
> > and print message which requests to fix call order of _require_scratch*
> > and _require_dm_target. This improvement follows what _scratch_shutdown
> > does for _require_scratch_shutdown.
> 
> Also, you don't need to describe the change in the commit message -
> the patch does that. The first paragraph is all that is needed here
> as it describes why you want to make the change.

I see. I will write "why" in the commit message, not "what". (In the past, I
was advised to write "what" the patch does, but I think this guide is valid
only when the change is complicated).

> 
> > Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> > ---
> >  common/rc | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/common/rc b/common/rc
> > index dda5da06..cbec8aaa 100644
> > --- a/common/rc
> > +++ b/common/rc
> > @@ -1971,6 +1971,9 @@ _require_dm_target()
> >  
> >  	# require SCRATCH_DEV to be a valid block device with sane BLKFLSBUF
> >  	# behaviour
> > +	if [ -z "$SCRATCH_DEV" ]; then
> > +		_fail "_require_dm_target: call _require_scratch* first in test"
> > +	fi
> >  	_require_block_device $SCRATCH_DEV
> >  	_require_sane_bdev_flush $SCRATCH_DEV
> >  	_require_command "$DMSETUP_PROG" dmsetup
> 
> That's a notrun case, not a fail.
> 
> Also, we report the error that has occurred, not how to resolve the
> problem. That's because we might change behaviour in future and now
> the error message tells people to do something that is
> wrong/non-existent. As such, I think the premise this change is based
> on is not really valid - people running fstests are assumed to have
> a level of knowledge sufficient to trace a failing test and
> determine what went wrong from the error reported. i.e. the error
> message should state what the problem was, not describe a potential
> solution.

Thank you for the comment. These are the points I missed. At least I was
able to catch the cause, so the improvement I suggested is not a big
improvement.

> 
> Also, this is not the place to check if SCRATCH_DEV is set. The
> check for a NULL device should be in _require_block_device(). Oh,
> wait, it already is:
> 
> _require_block_device()
> {
> 	if [ -z "$1" ]; then
> 		echo "Usage: _require_block_device <dev>" 1>&2
> 		exit 1
> 	fi
> ....
> }
> 
> And that's the error message the test emitted that you didn't
> understand, right?

Right :)

> 
> If so, the change here should really be to _require_block_device().
> i.e.
> 
> 	if [ -z "$1" ]; then
> 		_notrun "test requires a block device to be specified"
> 	fi
> 
> A quick scan shows a bunch of similar _requires checks that do
> similar things with poor error messages and 'exit 1' (e.g.
> _require_local_device()). _requires rules should call _notrun if the
> test should not run because of incorrect setup, not 'exit 1'.

Thank you for your thoughts. I walked through _require_* bash functions in
common/, and listed 20 functions below, which call 'exit 1', _fail, or
'return 1' for its argument check failure:

--- list start ---

common/rc

  _require_scratch_size
  _require_scratch_size_nocheck
  _require_command *
  _require_block_device *
  _require_local_device *
  _require_zoned_device *
  _require_non_zoned_device *
  _require_scratch_ext4_feature
  _require_xfs_io_command
  _require_fio
  _require_batched_discard *
  _require_chattr
  _require_fs_sysfs
  _require_scratch_feature

common/btrfs

  _require_btrfs_mkfs_feature
  _require_btrfs_fs_feature

common/xfs

  _require_xfs_db_command
  _require_xfs_spaceman_command

common/encrypt

  _require_encryption_policy_support (checks arguments passed from _require_scratch_encryption)

common/rnameat2

  _require_renameat2

--- list end ---

Many of the functions above check arguments not for incorrect setup, but for
call in test cases with invalid arguments. 6 functions of them with * in the
list check arguments for the incorrect setups, such as DEBUGFS_PROG,
SCRATCH_DEV or SCRATCH_MNT. So I suggest to modify these functions to improve
error messages and call "_notrun". What do you think about this?

-- 
Best Regards,
Shin'ichiro Kawasaki