makebuf.c revision 1573 
1/*-
2 * Copyright (c) 1990, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Chris Torek.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#if defined(LIBC_SCCS) && !defined(lint)
38static char sccsid[] = "@(#)makebuf.c	8.1 (Berkeley) 6/4/93";
39#endif /* LIBC_SCCS and not lint */
40
41#include <sys/types.h>
42#include <sys/stat.h>
43#include <unistd.h>
44#include <stdio.h>
45#include <stdlib.h>
46#include "local.h"
47
48/*
49 * Allocate a file buffer, or switch to unbuffered I/O.
50 * Per the ANSI C standard, ALL tty devices default to line buffered.
51 *
52 * As a side effect, we set __SOPT or __SNPT (en/dis-able fseek
53 * optimisation) right after the fstat() that finds the buffer size.
54 */
55void
56__smakebuf(fp)
57	register FILE *fp;
58{
59	register void *p;
60	register int flags;
61	size_t size;
62	int couldbetty;
63
64	if (fp->_flags & __SNBF) {
65		fp->_bf._base = fp->_p = fp->_nbuf;
66		fp->_bf._size = 1;
67		return;
68	}
69	flags = __swhatbuf(fp, &size, &couldbetty);
70	if ((p = malloc(size)) == NULL) {
71		fp->_flags |= __SNBF;
72		fp->_bf._base = fp->_p = fp->_nbuf;
73		fp->_bf._size = 1;
74		return;
75	}
76	__cleanup = _cleanup;
77	flags |= __SMBF;
78	fp->_bf._base = fp->_p = p;
79	fp->_bf._size = size;
80	if (couldbetty && isatty(fp->_file))
81		flags |= __SLBF;
82	fp->_flags |= flags;
83}
84
85/*
86 * Internal routine to determine `proper' buffering for a file.
87 */
88int
89__swhatbuf(fp, bufsize, couldbetty)
90	register FILE *fp;
91	size_t *bufsize;
92	int *couldbetty;
93{
94	struct stat st;
95
96	if (fp->_file < 0 || fstat(fp->_file, &st) < 0) {
97		*couldbetty = 0;
98		*bufsize = BUFSIZ;
99		return (__SNPT);
100	}
101
102	/* could be a tty iff it is a character device */
103	*couldbetty = (st.st_mode & S_IFMT) == S_IFCHR;
104	if (st.st_blksize <= 0) {
105		*bufsize = BUFSIZ;
106		return (__SNPT);
107	}
108
109	/*
110	 * Optimise fseek() only if it is a regular file.  (The test for
111	 * __sseek is mainly paranoia.)  It is safe to set _blksize
112	 * unconditionally; it will only be used if __SOPT is also set.
113	 */
114	*bufsize = st.st_blksize;
115	fp->_blksize = st.st_blksize;
116	return ((st.st_mode & S_IFMT) == S_IFREG && fp->_seek == __sseek ?
117	    __SOPT : __SNPT);
118}
119