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X-HELO:	calimero.vinschen.de
Date:	Wed, 23 Apr 2014 17:29:40 +0200
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Cygwin's writev() non-standard behavior
Message-ID:	<20140423152940.GM2339@calimero.vinschen.de>
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On Apr 23 16:06, qq qq wrote:
> writev() does not accept count 0 but it should
>=20
> $ cat test.c
> #include <stdio.h>
> #include <errno.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/uio.h>
>=20
> int main()
> {
>  =C2=A0struct iovec vec;
>=20
>  =C2=A0memset(&vec, 0, sizeof(vec));
>  =C2=A0if (writev(1, &vec, 0) < 0)
>  =C2=A0 =C2=A0perror("writev");
>  =C2=A0return 0;
> }
>=20
> Linux:
> $ gcc -Wall test.c
> $ ./a.out
>=20
> Cygwin:
> $ gcc -Wall test.c
> $ ./a.exe
> writev: Invalid argument
>=20
> This behavior is buggy per:
>=20
>  =C2=A0 =C2=A0 =C2=A0 EINVAL ... the vector count count is less than zero=
 or greater than the permitted maximum ...

I applied a patch to CVS.  There's a central function (check_iovec)
checking the validity of the iovec input and this function returns
EINVAL if iovlen is <=3D 0, the total number of bytes otherwise.

However, check_iovec works fine with iovlen 0 and all the callers
(readv/writev/recvmsg/sendmsg) are handling a 0 return from this=20
function, too, so a 0 return is nothing to worry about.

Please given the next snapshot from http://cygwin.com/snapshots/ a try.


Thanks,
Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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