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Date:	Thu, 25 Apr 2019 19:08:47 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: bug: cygwin-devel v3.0.2-1 socket.h does not #define MSG_EOR per the POSIX standard
Message-ID:	<20190425170847.GH30041@calimero.vinschen.de>
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On Apr 24 15:50, Eric Blake wrote:
> On 4/24/19 3:36 PM, Hans-Bernhard Br=C3=B6ker wrote:
> > Am 24.04.2019 um 19:54 schrieb Eliot Moss:
> >> On 4/24/2019 12:43 PM, Corinna Vinschen wrote:
> >=20
> >>> Since MSG_EOR isn't implemented in the underlying transport layer,
> >>> there's no way to implement it in userspace.=C2=A0 That's why it's not
> >>> defined in Cygwin's headers.=C2=A0 If you have an idea how to impleme=
nt
> >>> this in plain userspace, feel free to provide patches.
> >>
> >> I don't have a direct interest in this issue, but I do have a wonderin=
g.
> >> If Cygwin fails to define an error code -- even if the error cannot
> >> actually happen under Cygwin -- isn't that a problem when trying to
> >> compile imported software?=C2=A0=20
> >=20
>=20
> Well, MSG_EOR is not an error, but we can certainly do better than not
> defining it at all. My suggestion for the least-cost implementation:
>=20
> - add a define for MSG_EOR to a non-zero value that is bitwise distinct
> from other required MSG_ values
> - return EOPNOTSUPP on attempts to use the flag in
> send()/sendmsg()/sendto() (POSIX permits that failure for protocols that
> don't support it - and none of Cygwin's protocols support it)
> - optionally, document that MSG_EOR will never be set in the results
> returned by recvmsg() (POSIX says it will only be set on protocols that
> support it - and none of Cygwin's protocols support it)
>=20
> This will at least let software compile that attempts to use it, and
> hopefully that software is robust to the fact that send() may reject the
> flag and that recvmsg() cannot reliably report use of that flag.

Interesting.  I really thought it's better that a programm does not
compile, rather than it compiles and misbehaves from the POV of the
developer.

I added the MSG_EOR definition and send(2) and friends return EOPNOTSUPP
now.  I uploaded a snapshot to https://cygwin.com/snapshots/ with this
change.


Corinna

--=20
Corinna Vinschen
Cygwin Maintainer

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