siginfo_t missing member si_band

[Ryan Johnson]

Hi all,

While trying to build python3 for cygwin, I kept encountering the 
following error message:

./Modules/signalmodule.c: In function ‘fill_siginfo’:
./Modules/signalmodule.c:745:60: error: ‘siginfo_t’ has no member named 
‘si_band’
PyStructSequence_SET_ITEM(result, 6, PyLong_FromLong(si->si_band));
^
Include/tupleobject.h:62:75: note: in definition of macro 
‘PyTuple_SET_ITEM’
#define PyTuple_SET_ITEM(op, i, v) (((PyTupleObject *)(op))->ob_item[i] 
= v)
^
./Modules/signalmodule.c:745:5: note: in expansion of macro 
‘PyStructSequence_SET_ITEM’
PyStructSequence_SET_ITEM(result, 6, PyLong_FromLong(si->si_band));

As far as I can tell, siginfo_t::si_band is mandated by POSIX.1-2001, 
and required for proper handling of SIGPOLL. The latter seems to 
correspond to async I/O with poll(2). I'm pretty sure cygwin doesn't 
support async I/O, but shouldn't the struct member at least exist, to 
avoid breaking code that assumes its existence? The alternative is to 
patch python3 locally so its os.sigwaitinfo function no longer touches 
si_band, or to file a bug upstream so that the module's configury tests 
for its existence before using it.

Thoughts?
Ryan


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