From mboxrd@z Thu Jan  1 00:00:00 1970
Content-Type: text/plain; charset=utf-8
Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2104\))
From: arisawa <karisawa@gmail.com>
In-Reply-To: <CAJSxfmKMhyh=R-9FVCkzQ1V9yoGQK2H6B1TT_jTBb5T72zdtGg@mail.gmail.com>
Date: Sun,  2 Apr 2017 17:01:38 +0900
Content-Transfer-Encoding: quoted-printable
Message-Id: <112F60CB-D7E4-412E-9B48-BF5C38050AFA@gmail.com>
References: <57E90700-85A0-47F4-9156-DE732859A74C@gmail.com>
	<CAJSxfmKMhyh=R-9FVCkzQ1V9yoGQK2H6B1TT_jTBb5T72zdtGg@mail.gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: Re: [9fans] pipe: bug or feature?
Topicbox-Message-UUID: b9102c82-ead9-11e9-9d60-3106f5b1d025

thanks,

that is my fault.
it should be
	while((n =3D read(fd,buf0,sizeof(buf0)-1)) > 0){
and
	while((n =3D read(pfd[0],buf,sizeof(buf)-1)) > 0){

> 2017/04/02 16:34=E3=80=81Skip Tavakkolian <skip.tavakkolian@gmail.com> =
=E3=81=AE=E3=83=A1=E3=83=BC=E3=83=AB=EF=BC=9A
>=20
> this is either a bug in devpipe or the documentation is misleading. =
the man page seems to say that the pair of fd's returned by pipe(2) are =
symmetrical, but it matters which fd of the pair is used for writing.  =
if you switch around pfd[0] and pfd[1], it works as you'd expect.
>=20
> On Fri, Mar 31, 2017 at 5:29 PM arisawa <karisawa@gmail.com> wrote:
> Hello,
>=20
> I was playing with an experimental code on pipe and met with a problem =
which I don=E2=80=99t understand.
>=20
> the program reads a file and writes it to one end of pipe and then =
reads it from another end of pipe.
> the buffer for writing pipe is named buf0, and for reading pipe is =
named buf.
> and I found the program does not finish unless sizeof(buf) > =
sizeof(buf0).
> is this a bug or feature of pipe?
>=20
> Kenji Arisawa
>=20
> =3D=3D=3D BEGIN a.c =3D=3D=3D
> #include <u.h>
> #include <libc.h>
>=20
> char *argv0;
>=20
> void
> usage(void)
> {
>         fprint(2,"usage: %s file\n",argv0);
>         exits("usage");
> }
>=20
> void
> main(int argc, char *argv[])
> {
>         int fd,pfd[2];
>         char buf[256];
>         char buf0[256];
>         /* need to be sizeof(buf) > sizeof(buf0)
>          * but this condition is very curious to me */
>         int n;
>         char *file;
>         argv0 =3D argv[0];
>         argc--;argv++;
>         USED(argc);
>         if(argv[0] =3D=3D nil)
>                 usage();
>         file =3D argv[0];
>         fd =3D open(file,OREAD);
>         if(fd < 0)
>                 sysfatal("no such file");
>=20
>         if(pipe(pfd) < 0)
>                 sysfatal("pipe error");
>         print("pfd: %d %d\n",pfd[0],pfd[1]);
>=20
>         while((n =3D read(fd,buf0,sizeof(buf0))) > 0){
>                 print("read: %d %s\n",n,file);
>                 n =3D write(pfd[1],buf0,n);
>                 print("write: %d\n",n);
>         }
>         close(pfd[1]);
>         while((n =3D read(pfd[0],buf,sizeof(buf))) > 0){
>                 buf[n] =3D 0;
>                 print("%d %s\n",n,buf);
>         }
>         print("%d\n",n);
>=20
>         exits(nil);
> }
> =3D=3D=3D END a.c =3D=3D=3D