[Libguestfs] [libnbd PATCH 0/6] finish wrapping generated C code harder

[Laszlo Ersek]

On 5/10/23 17:25, Eric Blake wrote:
> On Wed, May 10, 2023 at 01:48:08PM +0200, Laszlo Ersek wrote:
>> This is the last wave (wave 5). Line length maxima:
>>
>>   file              before  after
>>   ----------------  ------  -----
>>   lib/states-run.c     102     98
>>   lib/states.c         116     80
>>   lib/states.h         123     86
>>
>> The longest line in "lib/states.h" becomes:
>>
>>> extern int nbd_internal_enter_STATE_NEWSTYLE_OPT_STRUCTURED_REPLY_RECV_REPLY_PAYLOAD (
>>>              struct nbd_handle *h, bool *blocked
>>>            );
>>
>> The one in "lib/states-run.c":
>>
>>>     case STATE_NEWSTYLE_OPT_STRUCTURED_REPLY_RECV_REPLY_PAYLOAD:
>>>       r = nbd_internal_enter_STATE_NEWSTYLE_OPT_STRUCTURED_REPLY_RECV_REPLY_PAYLOAD (h, &blocked);
>>>       break;
>>
>> We couldn't find a "scalable" approach for shortening these (the state
>> machine can be nested indefinitely deeply), so we decided to live with
>> them.
> 
> For public reference, we considered approaches such as shortening
> specific state names:
> 
> s/NEWSTYLE/NEW/
> s/OPT_STRUCTURED_REPLY/OPT_SR/
> s/RECV_REPLY_PAYLOAD/RECV_PAYLOAD/
> 
> but the more names we change, the more places we have to touch, and it
> doesn't alleviate the possibility of future state names being long.
> 
> We also considered a different way of writing state names, by
> introducing a series of glue macros, where you can then wrap macro
> parameters but still generate a long C identifier, something like:
> 
> extern int NBD_GLUE4(nbd_internal_enter_STATE, NEWSTYLE,
>                      OPT_STRUCTURED_REPLY, RECV_REPLY_PAYLOAD) {
> ...
>     case NBD_GLUE4(STATE, NEWSTYLE, OPT_STRUCTURED_REPLY,
>                    RECV_REPLY_PAYLOAD):
> 
> with variations such as writing a variadic macro NBD_GLUE(...) using
> __VA_ARGS__ that then dispatches to the correct NBD_GLUE<n> rather
> than having to be explicit about it at callsites.  But that hurts
> grep'ability when stepping through the state machine in gdb.

Thank you very much for the summary, I didn't have the energy for it :)

Laszlo

> 
>>
>> Thanks
>> Laszlo
>> Laszlo Ersek (6):
>>   state_machine_generator: wrap debug() calls in nbd_internal_run()
>>   generator/utils: add "pr_wrap_c_comment"
>>   state_machine_generator: wrap state comments in lib/states.{h,c}
>>   state_machine_generator: wrap nbd_internal_enter_* prototypes
>>   state_machine_generator: wrap enter_*() calls and prototypes
>>   state_machine_generator: rename, and break up the init. of,
>>     "next_state"
> 
> For those without explicit comments,
> 
> Reviewed-by: Eric Blake <eblake at redhat.com>
>