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

[Eric Blake]

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.

> 
> 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>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
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