From:	"Mark E." <snowball3 AT bigfoot DOT com>
To:	djgpp-workers AT delorie DOT com
Date:	Fri, 23 Mar 2001 00:37:10 -0500
MIME-Version:	1.0
Subject:	Re: pipe() emulation
Message-ID:	<3ABA9AB6.9970.50AA59@localhost>
X-mailer:	Pegasus Mail for Win32 (v3.12c)
Reply-To:	djgpp-workers AT delorie DOT com

After looking over the POSIX docs for pipe, I took out the code that moved up 
the handles since it goes against at least two sentences in the draft 
standard. I also added docs. To make the emulation more complete, I could 
even add code to prevent lseek from working with files opened with pipe since 
POSIX explicitly forbids that.

Index: pipe.c
===================================================================
RCS file: /cvs/djgpp/djgpp/src/libc/posix/unistd/pipe.c,v
retrieving revision 1.1
diff -c -p -r1.1 pipe.c
*** pipe.c	1995/04/01 23:49:02	1.1
--- pipe.c	2001/03/23 05:32:46
***************
*** 1,10 ****
  /* Copyright (C) 1995 DJ Delorie, see COPYING.DJ for details */
  #include <unistd.h>
! #include <errno.h>
  
  int
! pipe(int _fildes[2])
  {
!   errno = EACCES;
!   return -1;
  }
--- 1,34 ----
+ /* Copyright (C) 2001 DJ Delorie, see COPYING.DJ for details */
  /* Copyright (C) 1995 DJ Delorie, see COPYING.DJ for details */
  #include <unistd.h>
! #include <stdlib.h>
! #include <fcntl.h>
! #include <stdio.h>
! #include <sys/stat.h>
  
+ /* Emulate a pipe using a temporary file.  */
  int
! pipe(int fildes[2])
  {
!   int ifd, ofd;
!   char temp_name[FILENAME_MAX + 1];
!   char *tname;
! 
!   tname = tmpnam(temp_name);
!   if (tname == NULL)
!     return -1;
!     
!   ofd = open(tname, O_WRONLY | O_CREAT | O_TRUNC | O_APPEND | O_TEMPORARY,
!              S_IWUSR);
!   if (ofd < 0)
!     return -1;
!     
!   ifd = open(tname, O_RDONLY | O_TEMPORARY);
!   if (ifd < 0)
!     return -1;
! 
!   fildes[0] = ifd;
!   fildes[1] = ofd;
!     
!   return 0;
  }
Index: pipe.txh
===================================================================
RCS file: /cvs/djgpp/djgpp/src/libc/posix/unistd/pipe.txh,v
retrieving revision 1.2
diff -c -p -r1.2 pipe.txh
*** pipe.txh	1998/09/27 15:22:26	1.2
--- pipe.txh	2001/03/23 05:32:56
*************** int pipe(int fildes[2]);
*** 9,17 ****
  
  @subheading Description
  
! This function is provided only to assist in porting from Unix.  It
! always returns an error condition. 
  
  
  @subheading Portability
  
--- 9,27 ----
  
  @subheading Description
  
! This function creates a pipe and places a file descriptor for the read end
! of the pipe in @var{fildes[0]}, and another for the write end in
! @var{fildes[1]}.  Data written to @var{fildes[1]} will be read from
! @var{fildes[0]} in a first-in first-out (FIFO) basis.
  
+ Note that DOS doesn't support pipes so they are emulated with temporary
+ files.  This function should only be used in porting Unix and POSIX 
programs
+ that use it.
+ 
+ @subheading Return Value
+ 
+ Zero for success, otherwise -1 is returned and @var{errno} is set to 
indicate
+ the error.
  
  @subheading Portability
  

- Raw text -