Re: [PATCH v3 04/25] error: auto propagated local_err

[Vladimir Sementsov-Ogievskiy]

30.09.2019 19:39, Kevin Wolf wrote:
> Am 30.09.2019 um 18:26 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> 30.09.2019 19:00, Kevin Wolf wrote:
>>> Am 30.09.2019 um 17:19 hat Vladimir Sementsov-Ogievskiy geschrieben:
>>>> 30.09.2019 18:12, Kevin Wolf wrote:
>>>>> Am 24.09.2019 um 22:08 hat Vladimir Sementsov-Ogievskiy geschrieben:
>>>>>> Here is introduced ERRP_FUNCTION_BEGIN macro, to be used at start of
>>>>>> functions with errp parameter.
>>>>>
>>>>> A bit of bike shedding, but FOO_BEGIN suggests to me that a FOO_END will
>>>>> follow. Can we find a different name, especially now that we won't use
>>>>> this macro in every function that uses an errp, so even the "errp
>>>>> function" part isn't really correct any more?
>>>>>
>>>>> How about ERRP_AUTO_PROPAGATE?
>>>>
>>>> I have an idea that with this macro we can (optionally) get the whole call 
>>>> stack
>>>> of the error and print it to log, so it's good to give it more generic 
>>>> name, not
>>>> limited to propagation..
>>>
>>> Hm, what's the context for this feature?
>>>
>>> The obvious one where you want to have a stack trace is &error_abort,
>>> but that one crashes, so you get it automatically. If it's just a normal
>>> error (like a QAPI option contains an invalid value and some function
>>> down the call chain checks it), why would anyone want to know what the
>>> call chain in the QEMU code was?
>>>
>>
>> When I have bug from testers, call stack would be a lot more descriptive, 
>> than just
>> an error message.
>>
>> We may add trace point which will print this information, so with disabled 
>> trace point
>> - no extra output.
> 
> But wouldn't it make much more sense then to optionally add this
> functionality to any trace point? I really don't see how this is related
> specifically to user-visible error messages.

Interesting idea

> 
> However, even if we decide that we want to have this in Error objects,
> wouldn't it make much more sense to use the real C stack trace and save
> it from the innermost error_set() using backtrace() or compiler
> built-ins rather than relying on an error_propagate() chain?
> 
Hmm, I thought about this.. And in concatenation with the fact that we'll have 
macro not
everywhere, backtrace may be better..

On the other hand, backtrace will not show coroutine entries..

OK, anyway, if we will track some additional information in trace-events or in 
macros or
in error_* API functions, it's not bad to track some additional information in 
macro
named ERRP_AUTO_PROPAGATE.

-- 
Best regards,
Vladimir