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From: arisawa <karisawa@gmail.com>
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Subject: pipe: bug or feature?
Message-Id: <BFB26C2F-FDF7-4118-B2BD-373750346B2E@gmail.com>
Date: Tue, 28 Mar 2017 10:42:47 +0900
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X-Bullshit: metadata-aware enhancement-scale shader element control 

Hello,

I was playing with an experimental program on pipe and met with a =
problem which I don=E2=80=99t understand.

the program reads a file and writes it back 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 a feature of pipe?

Kenji Arisawa

=3D=3D=3D BEGIN a.c =3D=3D=3D
#include <u.h>
#include <libc.h>

char *argv0;

void
usage(void)
{
	fprint(2,"usage: %s file\n",argv0);
	exits("usage");
}

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");

	if(pipe(pfd) < 0)
		sysfatal("pipe error");
	print("pfd: %d %d\n",pfd[0],pfd[1]);

	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);
	=09
	exits(nil);
}
=3D=3D=3D END a.c =3D=3D=3D