good catch! the behavior makes sense now. On Sun, Apr 2, 2017 at 5:34 AM Antons Suspans <[email protected]> wrote:
> This was writing a \0 just past end of buf[], into memory alloted for > pfd[0]. > See the explanation by Alex in the 9front list: > /n/9front.org/lists/9front/1490668028.00 > > On Sun, Apr 02, 2017 at 07:34:52AM +0000, Skip Tavakkolian wrote: > > 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. > > > > On Fri, Mar 31, 2017 at 5:29 PM arisawa <[email protected]> wrote: > > > > Hello, > > > > I was playing with an experimental code on pipe and met with a problem > which > > I don’t understand. > > > > 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? > > > > Kenji Arisawa > > > > === BEGIN a.c === > > #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 = argv[0]; > > argc--;argv++; > > USED(argc); > > if(argv[0] == nil) > > usage(); > > file = argv[0]; > > fd = 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 = read(fd,buf0,sizeof(buf0))) > 0){ > > print("read: %d %s\n",n,file); > > n = write(pfd[1],buf0,n); > > print("write: %d\n",n); > > } > > close(pfd[1]); > > while((n = read(pfd[0],buf,sizeof(buf))) > 0){ > > buf[n] = 0; > > print("%d %s\n",n,buf); > > } > > print("%d\n",n); > > > > exits(nil); > > } > > === END a.c === > > > >
