Re: [Qemu-devel] [PATCH v3 ] doc: Introduce coding style for errors

["Lluís Vilanova" <vilanova@ac.upc.edu>]

Lluís Vilanova writes:

> Thomas Huth writes:
>> On 20.01.2016 15:10, Lluís Vilanova wrote:
>>> Thomas Huth writes:
>>> 
>>>> On 18.01.2016 21:26, Eric Blake wrote:
>>>>> On 01/15/2016 06:54 AM, Lluís Vilanova wrote:
>>>>>> Gives some general guidelines for reporting errors in QEMU.
>>>>>> 
>>>>>> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
>>>>>> ---
>>>>>> HACKING |   36 ++++++++++++++++++++++++++++++++++++
>>>>>> 1 file changed, 36 insertions(+)
>>>> ...
>>>>>> +Functions in this header are used to accumulate error messages in an 'Error'
>>>>>> +object, which can be propagated up the call chain where it is finally reported.
>>>>>> +
>>>>>> +In its simplest form, you can immediately report an error with:
>>>>>> +
>>>>>> +    error_setg(&error_fatal, "Error with %s", "arguments");
>>>>> 
>>>>> This paradigm doesn't appear anywhere in the current code base
>>>>> (hw/ppc/spapr*.c has a few cases of error_setg(&error_abort), but
>>>>> nothing directly passes error_fatal).  It's a bit odd to document
>>>>> something that isn't actually used.
>>> 
>>>> +1 for _not_ documenting this here: IMHO this looks ugly. If we want
>>>> something like this, I think we should introduce a proper
>>>> error_report_fatal() function instead.
>>> 
>>> That's a bit of a chicken and egg problem. My main intention was to provide a
>>> best practices summary on reporting messages/errors, since QEMU's code is really
>>> heterogeneous on that regard. But there seems to be no consensus on some details
>>> of what the proper way should be with the current interfaces.
>>> 
>>> Utility functions for "regular messages", warnings, fatals and aborts would
>>> definitiely be an improvement IMHO, but I dont have time to adapt existing code
>>> to these (and I was told not to add unused utility functions for this).
>>> 
>>> Now, if I were able to add such functions, it'd be something like:
>>> 
>>> // Generate message "as is"; not sure if this should exist.
>>> message_report(fmt, ...)

>> Not sure what this should be good for? We've already got error_report()
>> that generates messages "as is", haven't we?

> Well, it just seemed wrong to me using error_report() to report "regular
> messages" :)


>>> // Generate message with prepended file/line information for the caller.
>>> // Calls exit/abort on the last two.
>>> error_report_{warn,fatal,abort}(fmt, ...)
>>> 
>>> // Same with an added message from strerror.
>>> error_report_{warn,fatal,abort}_errno(fmt, ...)
>>> 
>>> But, should I add these without providing extensive patches that refactor code
>>> to use them?

>> Maybe create a patch that introduces the _fatal and _abort functions
>> (I'd skip the _warn functions for now), and use them in one or two files
>> (e.g. replace the error_setg(&error_abort, ...) in spapr.c). That should
>> not be that much of work, and could be a good base for further discussion?

> I can do that. But then should 'error_fatal' and 'error_abort' be officially
> deprecated in favour of error_report_fatal() and error_report_abort()?

Sorry, I see this is misleading. I mean deprecate directly using
"error_setg(error_fatal)"; you can still decide to pass error_fatal as an error
object to other user functions.


Cheers,
  Lluis