Date: Tue, 10 Jul 2012 18:22:08 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Volodymyr Kostyrko <c.kworr@gmail.com> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, freebsd-standards@freebsd.org Subject: Re: kern/149857: [kqueue] kqueue not reporting EOF under certain circumstances Message-ID: <20120710152208.GF2338@deviant.kiev.zoral.com.ua> In-Reply-To: <4FFC441A.2010500@gmail.com> References: <4FFC1D2D.4020405@gmail.com> <20120710140203.GA2338@deviant.kiev.zoral.com.ua> <4FFC39D9.6080809@gmail.com> <20120710142746.GD2338@deviant.kiev.zoral.com.ua> <4FFC441A.2010500@gmail.com>
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On Tue, Jul 10, 2012 at 06:02:50PM +0300, Volodymyr Kostyrko wrote:
> Konstantin Belousov wrote:
> >>So you mean this is just my false assumption that EOF _should_ occur on
> >>stdin? And it actually occurs only if source is a process which can send
> >>EOF?
> >
> >'Source' cannot be a process. Read filter on pipes can return EV_EOF.
> >Read filter on vnodes (read: regular files) does not return EV_EOF,
> >except in situation that is created by manual intervention of
> >administrator.
>=20
> This keeps me puzzled. How then I can tell that file at stdin is already=
=20
> at EOF? You mean I should treat stdin like normal vnode-backed file?
>=20
> off_t pos =3D 0, endpos;
>=20
> lseek(fileno(stdin), 0, SEEK_END);
> endpos =3D ftell(stdin);
> lseek(fileno(stdin), 0, SEEK_SET);
>=20
> ... and then later check it with:
>=20
> if(endpos !=3D -1) {
> pos +=3D kev.data;
> if(pos >=3D endpos) {
> printf("end reached\n");
> return(0);
> }
> }
>=20
> Is this a correct way to detect EOF? I'm letting besides that I should=20
> also detect vnode changes and update max file size accordingly.
>=20
> >It should have been clear from my previous response.
>=20
> Please excuse me, I'm a bit new to this things...
Why do you use kqueue there at all ? Just read from stdin, and decide
that you hit EOF when read returned 0 bytes.
If insisting on using kqueue, which may be ligitimate if you process
other sources besides stdin, you should first investigate the nature of
the fd 0 using fstat, and then use appropriate code for regular file,
pipe and probably socket (e.g. for the case if code allows to run under
inetd(8)).
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