Re: [Qemu-devel] [RFC] HACKING: Document 'struct' keyword usage

[Thomas Huth]

On 01/08/2019 21.23, Paolo Bonzini wrote:
> On 01/08/19 20:50, Eduardo Habkost wrote:
>> On Wed, Jul 31, 2019 at 10:35:31AM +0200, Thomas Huth wrote:
>>> On 30/07/2019 23.07, Eduardo Habkost wrote:
>>>> Sometimes we use the 'struct' keyword to help us reduce
>>>> dependencies between header files.  Document that practice.
>>>>
>>>> Signed-off-by: Eduardo Habkost <address@hidden>
>>>> ---
>>>> I wonder if this is too terse?  Should we give examples?
>>>> ---
>>>>  HACKING | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/HACKING b/HACKING
>>>> index 0fc3e0fc04..112685bdaf 100644
>>>> --- a/HACKING
>>>> +++ b/HACKING
>>>> @@ -101,6 +101,8 @@ it points to, or it is aliased to another pointer that 
>>>> is.
>>>>  
>>>>  2.3. Typedefs
>>>>  Typedefs are used to eliminate the redundant 'struct' keyword.
>>>> +However, the 'struct' keyword may be sometimes used in header
>>>> +files to avoid unnecessary dependencies between headers.
>>>
>>> See also the discussion earlier this year:
>>>
>>> https://www.mail-archive.com/address@hidden/msg586180.html
>>
>> Nice, it adds even more information than this patch.
>>
>> For reference, this is the patch at the URL above:
>>
>> -Typedefs are used to eliminate the redundant 'struct' keyword.
>> +Typedefs can be used to eliminate the redundant 'struct' keyword. This is
>> +especially helpful for common types that are used all over the place. Since
>> +certain C compilers choke on duplicated typedefs, you should avoid them and
>> +declare a typedef only in one header file. For common types, you can use
>> +"include/qemu/typedefs.h" for example. Note that it is also perfectly fine 
>> to
>> +use forward struct definitions without typedefs for references in headers
>> +to avoid the problem with duplicated typedefs.
>>
>> I don't agree with the first two sentences, and I agree with what Paolo said
>> here:
>>   https://www.mail-archive.com/address@hidden/msg586214.html
>>
>> ("I agree 100% with the wording after 'Since'.  However, I think the first
>> part should be made stronger, not weaker.")
>>
>> Paolo sent the following proposal:
>>
>> | Typedefs are use to eliminate the redundant 'struct' keyword, since type

s/use/used/

>> | names have a different style than other identifiers ("CamelCase" versus
>> | "snake_case").  Each struct should have a CamelCase name and a
>> | corresponding typedef.
>> | 
>> | Since certain C compilers choke on duplicated typedefs, you should avoid
>> | them and declare a typedef only in one header file.  For common types,
>> | you can use "include/qemu/typedefs.h" for example.  However, as a metter

s/metter/matter/

>> | of convenience it is also perfectly fine to use forward struct
>> | definitions instead of typedefs in headers and function prototypes; this
>> | avoids problems with duplicated typedefs and reduces the need to include
>> | headers from other headers.

With the typos fixed:

Reviewed-by: Thomas Huth <address@hidden>