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Re: [PATCH 11/14] block/qcow2-bitmap: return startus from qcow2_store_pe

From: Markus Armbruster
Subject: Re: [PATCH 11/14] block/qcow2-bitmap: return startus from qcow2_store_persistent_dirty_bitmaps
Date: Fri, 11 Sep 2020 17:22:41 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux)

Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> writes:

> 11.09.2020 14:21, Greg Kurz wrote:
>> On Fri, 11 Sep 2020 13:18:32 +0300
>> Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:
>>> 11.09.2020 12:38, Greg Kurz wrote:
>>>> s/startus/status
>>>> On Wed,  9 Sep 2020 21:59:27 +0300
>>>> Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:
>>>>> It's better to return status together with setting errp. It makes
>>>>> possible to avoid error propagation.
>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>>>> ---
>>>>>    block/qcow2.h        |  2 +-
>>>>>    block/qcow2-bitmap.c | 13 ++++++-------
>>>>>    2 files changed, 7 insertions(+), 8 deletions(-)
>>>>> diff --git a/block/qcow2.h b/block/qcow2.h
>>>>> index e7e662533b..49824be5c6 100644
>>>>> --- a/block/qcow2.h
>>>>> +++ b/block/qcow2.h
>>>>> @@ -972,7 +972,7 @@ bool qcow2_get_bitmap_info_list(BlockDriverState *bs,
>>>>>                                    Qcow2BitmapInfoList **info_list, Error 
>>>>> **errp);
>>>>>    int qcow2_reopen_bitmaps_rw(BlockDriverState *bs, Error **errp);
>>>>>    int qcow2_truncate_bitmaps_check(BlockDriverState *bs, Error **errp);
>>>>> -void qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs,
>>>>> +bool qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs,
>>>>>                                              bool release_stored, Error 
>>>>> **errp);
>>>>>    int qcow2_reopen_bitmaps_ro(BlockDriverState *bs, Error **errp);
>>>>>    bool qcow2_co_can_store_new_dirty_bitmap(BlockDriverState *bs,
>>>>> diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
>>>>> index f58923fce3..5eeff1cb1c 100644
>>>>> --- a/block/qcow2-bitmap.c
>>>>> +++ b/block/qcow2-bitmap.c
>>>>> @@ -1524,9 +1524,10 @@ out:
>>>>>     * readonly to begin with, and whether we opened directly or reopened 
>>>>> to that
>>>>>     * state shouldn't matter for the state we get afterward.
>>>>>     */
>>>>> -void qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs,
>>>>> +bool qcow2_store_persistent_dirty_bitmaps(BlockDriverState *bs,
>>>>>                                              bool release_stored, Error 
>>>>> **errp)
>>>>>    {
>>>>> +    ERRP_GUARD();
>>>> Maybe worth mentioning in the changelog that this ERRP_GUARD() fixes
>>>> an error_prepend(errp, ...) not visible in the patch context.
>>> Ah yes. Actually this is occasional thing I didn't want to include into 
>>> this patch
>>> (and int this part I). So we can just drop it and leave for part II or part 
>>> III,
>>> or add a note into commit message

Either works for me.

>>>> Anyway,
>>>> Reviewed-by: Greg Kurz <groug@kaod.org>
>>> Thanks a lot for reviewing :)
>> Don't mention it :)
>>> Hmm.. With this series I understand the following:
>>> 1. It's no sense in simple applying scripts/coccinelle/errp-guard.cocci to 
>>> the whole code-base, because:
>>>     - it produces a lot of "if (*errp)" in places where it is really simple 
>>> to avoid error propagation at all, like in this series
>>>     - reviewing is the hardest part of the process
>>> So, if we have to review these changes anyway, it's better to invest a bit 
>>> more time into patch creation, and make code correspond to our modern error 
>>> API recommendations.

Yes, going the extra mile is better.

I recommend it for code that is actively maintained.  Making the code
simpler and thus easier to maintain is an investment that'll pay off.

We may have code where it won't pay off.  Do you think a blind
application of errp-guard.cocci might be better than nothing there?

>>> 2. So, the process turns into following steps:
>>>     - apply scripts/coccinelle/errp-guard.cocci
>>>     - look through patches and do obvious refactorings (like this series)
>>>     - keep ERRP_GUARD where necessary (appending info to error, or where 
>>> refactoring of function return status is too invasive and not simple)
>> I've started to follow this process for the spapr code and, indeed,
>> I
>> can come up with better changes by refactoring some code manually.
>> Some of these changes are not that obvious that they could be made
>> by someone who doesn't know the code, so I tend to agree with your
>> arguments in 1.
>> This is also the reason I didn't review patches 10, 13 and 14
>> because
>> they looked like I should understand the corresponding code a bit more.
>>> 3. Obviously, that's too much for me :) Of course, I will invest some time 
>>> into making the series like this one, and reviewing them, but I can't do it 
>>> for weeks and months. (My original —Āunning plan to simply push ~100 
>>> generated commits with my s-o-b and become the greatest contributor failed:)


A lesser craftsman than you would've peddled the generated commits
anyway.  Props!

>> Ha ha :D ... as a consolation prize, maybe we can reach a fair
>> number
>> of r-b by reviewing each other's _simple_ cleanups ;-)
>>> The good thing is that now, with ERRP_GUARD finally merged, we can produce 
>>> parallel series like this, and they will be processed in parallel by 
>>> different maintainers (and Markus will have to merge series for subsystems 
>>> with unavailable maintainers).

If people care enough about [2] to submit patches, I'll feel obliged to
help merging them.

>> This sounds nice. My only concern would be to end up fixing code
>> nobody
>> uses or cares for, so I guess it would be better that active maintainers
>> or supporters give impetus on that.

A bit of weeding on the side is always appreciated, but please don't
feel obliged to sink lots of time into code you don't care about.

>>> So, everybody is welcome to the process [2]. Probably we want to make a 
>>> separate announcement in a list with short recommendations and 
>>> instructions? But who read announcements..
>> I don't :) but the very massive series that were posted on the topic
>> the last few months look like an announcement to me, at least for
>> active maintainers and supporters.
> Aha, I know. Better than announcement is improving checkpatch.

Yes, automated feedback works best.

Relentless pressure from reviewers can also work in the long, long run.
But it's tiresome.

Of course, checkpatch.pl checks only new or changed code.  Any ideas on
how to make people aware of the opportunity to simplify their existing
code?  Obvious: posting more patches simplifying existing code we care
about.  Any other smart ideas?

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