Re: [Qemu-devel] [PATCH 02/14] qerror: add new errors

[Paolo Bonzini]

Il 31/05/2012 17:44, Luiz Capitulino ha scritto:
>> One is "do not shoehorn errors into errno values".  So for QOM invalid 
>> values we
>> have PropertyValueBad, not a generic InvalidArgument value.  We convert 
>> everything
>> to Error rather than returning negative errno values and then returning 
>> generic
>> error codes, because those would be ugly and non-descriptive.  I agree with 
>> that.
>>
>> The other is "when errors come straight from the OS, _do_ use errno values".
>> This is for OpenFileFailed, for the new socket errors and so on.  This is 
>> what
>> I am proposing.
>>
>> These two rules together match what most other programs do.
>>
>>     $ echo | sed p > /dev/full
>>     sed: couldn't flush stdout: No space left on device
>>          ^^^^^^^^^^^^^^                                 error type
>>                         ^^^^^^  ^^^^^^^^^^^^^^^^^^^^^^^ arguments
>>
>> That would become, in JSON:
>>
>>     { 'error': 'FlushFailed',
>>       'file': 'stdout',
>>       'os_error': 'enospc' }
> 
> Actually, I did propose something similar in the past but Anthony objected.

Looks like in the meanwhile we moved closer to this mechanism
(OpenFileFailed, Sock*, etc.), except we have no clear way to identify
_what_ error actually happened rather than _where_.

> We could have optional arguments to NoSpaceLeftOnDevice. Could bloat the 
> error,
> or not (as most error scenarios can be common to each other).

Not as soon as you start reusing the same errors for QOM or similar
scenarios (like PermissionDenied).

Paolo