text: /*	$OpenBSD: makebuf.c,v 1.10 2019/06/28 13:32:42 deraadt Exp $ */
  /*-
   * Copyright (c) 1990, 1993
   *	The Regents of the University of California.  All rights reserved.
   *
   * This code is derived from software contributed to Berkeley by
   * Chris Torek.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   */
  
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <unistd.h>
  #include <stdio.h>
  #include <stdlib.h>
  #include "local.h"
  
  /*
   * Allocate a file buffer, or switch to unbuffered I/O.
   * Per the ANSI C standard, ALL tty devices default to line buffered.
   *
   * As a side effect, we set __SOPT or __SNPT (en/dis-able fseek
   * optimisation) right after the fstat() that finds the buffer size.
   */
  void
  __smakebuf(FILE *fp)
  {
  	void *p;
  	int flags;
  	size_t size;
  	int couldbetty;
  
  	if (fp->_flags & __SNBF) {
  		fp->_bf._base = fp->_p = fp->_nbuf;
  		fp->_bf._size = 1;
  		return;
  	}
  	flags = __swhatbuf(fp, &size, &couldbetty);
  	if ((p = malloc(size)) == NULL) {
  		fp->_flags |= __SNBF;
  		fp->_bf._base = fp->_p = fp->_nbuf;
  		fp->_bf._size = 1;
  		return;
  	}
  	flags |= __SMBF;
  	fp->_bf._base = fp->_p = p;
  	fp->_bf._size = size;
  	if (couldbetty && isatty(fp->_file))
  		flags |= __SLBF;
  	fp->_flags |= flags;
  }
  
  /*
   * Internal routine to determine `proper' buffering for a file.
   */
  int
  __swhatbuf(FILE *fp, size_t *bufsize, int *couldbetty)
  {
  	struct stat st;
  
  	if (fp->_file < 0 || fstat(fp->_file, &st) == -1) {
  		*couldbetty = 0;
  		*bufsize = BUFSIZ;
  		return (__SNPT);
  	}
  
  	/* could be a tty iff it is a character device */
  	*couldbetty = S_ISCHR(st.st_mode);
  	if (st.st_blksize == 0) {
  		*bufsize = BUFSIZ;
  		return (__SNPT);
  	}
  
  	/*
  	 * Optimise fseek() only if it is a regular file.  (The test for
  	 * __sseek is mainly paranoia.)  It is safe to set _blksize
  	 * unconditionally; it will only be used if __SOPT is also set.
  	 */
  	*bufsize = st.st_blksize;
  	fp->_blksize = st.st_blksize;
  	return ((st.st_mode & S_IFMT) == S_IFREG && fp->_seek == __sseek ?
  	    __SOPT : __SNPT);
  }
  