Re: [Qemu-devel] [PATCH v2] blkdebug: make the fault injection functionality callable from QMP

[Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>]

At Wed, 27 Aug 2014 06:43:49 -0600,
Eric Blake wrote:
> 
> [1  <text/plain; UTF-8 (quoted-printable)>]
> On 08/26/2014 11:34 PM, Hitoshi Mitake wrote:
> 
> >>> {"execute": "blkdebug-set-rules", "arguments": {"device": "ide0-hd0",
> >>> "rules":[{"event": "write_aio", "type": "inject-error", "immediately":
> >>
> >> Why 'write_aoi'? New QMP commands should prefer dashes (write-aio) if
> >> there is no compelling reason for underscore.
> > 
> > The name of event is defined in the event_names array of
> > block/blkdebug.c, which uses underscore. I think using the original
> > names would be good because the name shouldn't be different from
> > config file notation of blkdebug.
> 
> But it should be fairly easy to code things to accept both spellings
> when parsing the config file, while preferring the dash in QAPI.
> Furthermore, by defining the enum in QAPI instead of in blkdebug.c, you
> get a generated enum that blkdebug.c can reuse, and where you are then
> guaranteed that things stay in sync if new commands are added (by adding
> them to the .json file).
> 
> 
> >>
> >>> +    } else if (!strcmp(type, "inject-error")) {
> >>> +        int _errno, sector;
> >>
> >> The name _errno threw me; is there something better without a leading
> >> underscore that would work better?
> > 
> > I added underscore to the name because errno is already used by
> > errno.h. How about "given_errno"?
> 
> If you use proper .json typing, the generator will automatically rename
> the QMP interface "errno" to the C code "q_errno".  Consistently using
> the type-safe munging already done by the generator, instead of redoing
> a completely different munging on your own, is the preferred solution here.
> 
> 
> >>> +
> >>> +        once = qdict_get_try_bool(dict, "once", 0);
> >>
> >> s/0/bool/ - we use <stdbool.h>, so you should use the named constants
> >> when dealing with bool parameters.
> > 
> > Thanks, I'll fix it in v3.
> 
> Actually, if you use a type-safe qapi definition, you may not even need
> to do raw qdict operations, but can just directly use the C struct that
> gets generated as a result of the qapi.
> 
> 
> > 
> > I also like the detailed specification. But, there are bunch of event
> > names (the event_names array of block/blkdebug.c). In addition, the
> > rule of blkdebug can be extended. So I think defining it in two palces
> > (qapi-schema.json and block/blkdebug.c) is hard to maintain. Parsing
> > qdict in blkdebug.c would be simpler. How do you think?
> 
> No, don't do duplication.  Instead, fix blkdebug.c to USE the enum
> generated by the .json, and you only have to maintain the list in one
> place - the .json file.
> 

OK, I understand your opinion. But it requires amount of change in
existing blkdebug implementation. So I want to hear opinions from the
maintainers. How do you think about this idea (maintaining blkdebug
events in .json format for avoiding duplication), Stefan and Kevin?

Thanks,
Hitoshi