Re: [Qemu-block] [Qemu-devel] [PATCH v6 14/29] libqos: Use explicit QTestState for fw_cfg operations

[Eric Blake]

On 09/05/2017 06:03 AM, Thomas Huth wrote:
> On 05.09.2017 12:12, Thomas Huth wrote:
>> On 01.09.2017 20:03, Eric Blake wrote:
>>> Drop one more client of global_qtest by teaching all fw_cfg test
>>> functionality (invoked through alloc-pc) to pass in an explicit
>>> QTestState, adjusting all callers.  In particular, fw_cfg-test
>>> had to reorder things to create the test state prior to creating
>>> the fw_cfg.
>>>

>>> +++ b/tests/libqos/fw_cfg.h
>>> @@ -15,10 +15,12 @@
>>>
>>>
>>>  typedef struct QFWCFG QFWCFG;
>>> +typedef struct QTestState QTestState;
>>
>> Not sure, but I slightly remember that typedeffing a struct like this in
>> multiple places can cause compiler warnings or errors with certain
>> versions of GCC or clang? So a file that includes both, fw_cfg.h and
>> libqtest.h will then fail to compile?

Yes, older gcc fails to compile (my off-hand recollection is that it was
a bug in the older gcc, and not a standards-compliance issue to
encounter the same typedef twice, but I could be wrong), ergo the fixup
that you later noticed.

>>
>> I think it would be better to change the include order in the .c files
>> instead, so that libqtest.h is always included before fw_cfg.h.
> 
> Ah, well, I just saw that you also sent a fixup patch for this. Anyway,
> I'm not a fan of including header files from other header files, so
> changing the include order in the .c files sounds like the better
> solution to me.

Eww. I like headers to be self-contained.  Other than stuff we get from
osdep.h (which we know is included by EVERY .c file), I prefer that if a
header uses another type, then it guarantees that an idempotent
inclusion of a header that declares that type is also present in the
header file, rather than forcing .c files to know which order to include
things in.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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