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Date: Tue, 15 Oct 2013 18:36:45 -0400
From: Christopher Faylor <cgf-use-the-mailinglist-please@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: siginfo_t missing member si_band
Message-ID: <20131015223645.GB7490@ednor.casa.cgf.cx>
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References: <525D55B3.3050002@cs.utoronto.ca> <20131015194242.GA2368@ednor.casa.cgf.cx> <525DB015.1010707@cs.utoronto.ca>
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User-Agent: Mutt/1.5.20 (2009-06-14)

On Tue, Oct 15, 2013 at 05:13:57PM -0400, Ryan Johnson wrote:
>On 15/10/2013 3:42 PM, Christopher Faylor wrote:
>> On Tue, Oct 15, 2013 at 10:48:19AM -0400, Ryan Johnson wrote:
>>> 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?
>> Sure.  I question the utility of lying in a structure about the
>> availability of an unimplemented feature.  If something is specifically
>> expecting the structure member to exist it seems like it would be
>> expecting it to do something.
>So that would be a vote for filing a bug upstream with python's FFI 
>interface to signal handling? Fair enough.

I guess so.  In a project that wasn't requestware or wishware it would
be a spur for someone to submit code to Cygwin to implement SIGPOLL and
it's accompanying siginfo_t handling.  Unfortunately, Cygwin seems to
be mainly requestware these days.

cgf

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