sysdeps/posix/stdio_init.c

   1 /* Copyright (C) 1991, 1992, 1993, 1995, 1997 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <stdio.h>
  20 #include <sys/types.h>
  21 #include <sys/stat.h>
  22 #include <unistd.h>
  23
  24 /* Initialize STREAM as necessary.
  25    This may change I/O functions, give a buffer, etc.
  26    If no buffer is allocated, but the bufsize is set,
  27    the bufsize will be used to allocate the buffer.  */
  28 void
  29 __stdio_init_stream (FILE *stream)
  30 {
  31   const int fd = (int) stream->__cookie;
  32   struct stat statb;
  33
  34   if (stream->__buffer != NULL || stream->__userbuf)
  35     /* If's unbuffered by request, we can't do anything useful.  */
  36     return;
  37
  38   /* Find out what sort of file this is.  */
  39   if (__fstat (fd, &statb) < 0)
  40       return;
  41
  42   if (S_ISCHR (statb.st_mode))
  43     {
  44       /* It's a character device.
  45          Make it line-buffered if it's a terminal.  */
  46       if (__isatty (fd))
  47         {
  48           stream->__linebuf = 1;
  49
  50           /* Unix terminal devices have the bad habit of claiming to be
  51              seekable.  On systems I have tried, seeking on a terminal
  52              device seems to set its file position as specified, such that
  53              a later tell says the same thing.  This is in no way related
  54              to actual seekability--the ability to seek back and read old
  55              data.  Unix terminal devices will let you "seek back", and
  56              then read more new data from the terminal.  I can think of
  57              nothing to do about this lossage except to preemptively disable
  58              seeking on terminal devices.  */
  59
  60           stream->__io_funcs.__seek = NULL; /* Seeks get ESPIPE.  */
  61         }
  62     }
  63
  64 #ifdef  _STATBUF_ST_BLKSIZE
  65   /* Use the block-size field to determine
  66      the system's optimal buffering size.  */
  67   stream->__bufsize = statb.st_blksize;
  68 #endif
  69 }