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makebuf.c revision 1.13 
      1 /*	$NetBSD: makebuf.c,v 1.13 2003/01/18 11:29:55 thorpej Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1990, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * This code is derived from software contributed to Berkeley by
      8  * Chris Torek.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *	This product includes software developed by the University of
     21  *	California, Berkeley and its contributors.
     22  * 4. Neither the name of the University nor the names of its contributors
     23  *    may be used to endorse or promote products derived from this software
     24  *    without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     36  * SUCH DAMAGE.
     37  */
     38 
     39 #include <sys/cdefs.h>
     40 #if defined(LIBC_SCCS) && !defined(lint)
     41 #if 0
     42 static char sccsid[] = "@(#)makebuf.c	8.1 (Berkeley) 6/4/93";
     43 #else
     44 __RCSID("$NetBSD: makebuf.c,v 1.13 2003/01/18 11:29:55 thorpej Exp $");
     45 #endif
     46 #endif /* LIBC_SCCS and not lint */
     47 
     48 #include "namespace.h"
     49 
     50 #include <sys/types.h>
     51 #include <sys/stat.h>
     52 #include <assert.h>
     53 #include <stdio.h>
     54 #include <stdlib.h>
     55 #include <unistd.h>
     56 #include "reentrant.h"
     57 #include "local.h"
     58 
     59 /*
     60  * Allocate a file buffer, or switch to unbuffered I/O.
     61  * Per the ANSI C standard, ALL tty devices default to line buffered.
     62  *
     63  * As a side effect, we set __SOPT or __SNPT (en/dis-able fseek
     64  * optimisation) right after the fstat() that finds the buffer size.
     65  */
     66 void
     67 __smakebuf(fp)
     68 	FILE *fp;
     69 {
     70 	void *p;
     71 	int flags;
     72 	size_t size;
     73 	int couldbetty;
     74 
     75 	_DIAGASSERT(fp != NULL);
     76 
     77 	if (fp->_flags & __SNBF) {
     78 		fp->_bf._base = fp->_p = fp->_nbuf;
     79 		fp->_bf._size = 1;
     80 		return;
     81 	}
     82 	flags = __swhatbuf(fp, &size, &couldbetty);
     83 	if ((p = malloc(size)) == NULL) {
     84 		fp->_flags |= __SNBF;
     85 		fp->_bf._base = fp->_p = fp->_nbuf;
     86 		fp->_bf._size = 1;
     87 		return;
     88 	}
     89 	__cleanup = _cleanup;
     90 	flags |= __SMBF;
     91 	fp->_bf._base = fp->_p = p;
     92 	fp->_bf._size = size;
     93 	if (couldbetty && isatty(fp->_file))
     94 		flags |= __SLBF;
     95 	fp->_flags |= flags;
     96 }
     97 
     98 /*
     99  * Internal routine to determine `proper' buffering for a file.
    100  */
    101 int
    102 __swhatbuf(fp, bufsize, couldbetty)
    103 	FILE *fp;
    104 	size_t *bufsize;
    105 	int *couldbetty;
    106 {
    107 	struct stat st;
    108 
    109 	_DIAGASSERT(fp != NULL);
    110 	_DIAGASSERT(bufsize != NULL);
    111 	_DIAGASSERT(couldbetty != NULL);
    112 
    113 	if (fp->_file < 0 || fstat(fp->_file, &st) < 0) {
    114 		*couldbetty = 0;
    115 		*bufsize = BUFSIZ;
    116 		return (__SNPT);
    117 	}
    118 
    119 	/* could be a tty iff it is a character device */
    120 	*couldbetty = S_ISCHR(st.st_mode);
    121 	if (st.st_blksize == 0) {
    122 		*bufsize = BUFSIZ;
    123 		return (__SNPT);
    124 	}
    125 
    126 	/*
    127 	 * Optimise fseek() only if it is a regular file.  (The test for
    128 	 * __sseek is mainly paranoia.)  It is safe to set _blksize
    129 	 * unconditionally; it will only be used if __SOPT is also set.
    130 	 */
    131 	*bufsize = st.st_blksize;
    132 	fp->_blksize = st.st_blksize;
    133 	return ((st.st_mode & S_IFMT) == S_IFREG && fp->_seek == __sseek ?
    134 	    __SOPT : __SNPT);
    135 }
    136