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      1 /*	$OpenBSD: makebuf.c,v 1.8 2005/12/28 18:50:22 millert Exp $ */
      2 /*-
      3  * Copyright (c) 1990, 1993
      4  *	The Regents of the University of California.  All rights reserved.
      5  *
      6  * This code is derived from software contributed to Berkeley by
      7  * Chris Torek.
      8  *
      9  * Redistribution and use in source and binary forms, with or without
     10  * modification, are permitted provided that the following conditions
     11  * are met:
     12  * 1. Redistributions of source code must retain the above copyright
     13  *    notice, this list of conditions and the following disclaimer.
     14  * 2. Redistributions in binary form must reproduce the above copyright
     15  *    notice, this list of conditions and the following disclaimer in the
     16  *    documentation and/or other materials provided with the distribution.
     17  * 3. Neither the name of the University nor the names of its contributors
     18  *    may be used to endorse or promote products derived from this software
     19  *    without specific prior written permission.
     20  *
     21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     31  * SUCH DAMAGE.
     32  */
     33 
     34 #include <sys/types.h>
     35 #include <sys/stat.h>
     36 #include <unistd.h>
     37 #include <stdio.h>
     38 #include <stdlib.h>
     39 #include "local.h"
     40 
     41 /*
     42  * Allocate a file buffer, or switch to unbuffered I/O.
     43  * Per the ANSI C standard, ALL tty devices default to line buffered.
     44  *
     45  * As a side effect, we set __SOPT or __SNPT (en/dis-able fseek
     46  * optimisation) right after the fstat() that finds the buffer size.
     47  */
     48 void
     49 __smakebuf(FILE *fp)
     50 {
     51 	void *p;
     52 	int flags;
     53 	size_t size;
     54 	int couldbetty;
     55 
     56 	if (fp->_flags & __SNBF) {
     57 		fp->_bf._base = fp->_p = fp->_nbuf;
     58 		fp->_bf._size = 1;
     59 		return;
     60 	}
     61 	flags = __swhatbuf(fp, &size, &couldbetty);
     62 	if ((p = malloc(size)) == NULL) {
     63 		fp->_flags |= __SNBF;
     64 		fp->_bf._base = fp->_p = fp->_nbuf;
     65 		fp->_bf._size = 1;
     66 		return;
     67 	}
     68 	__atexit_register_cleanup(_cleanup);
     69 	flags |= __SMBF;
     70 	fp->_bf._base = fp->_p = p;
     71 	fp->_bf._size = size;
     72 	if (couldbetty && isatty(fp->_file))
     73 		flags |= __SLBF;
     74 	fp->_flags |= flags;
     75 }
     76 
     77 /*
     78  * Internal routine to determine `proper' buffering for a file.
     79  */
     80 int
     81 __swhatbuf(FILE *fp, size_t *bufsize, int *couldbetty)
     82 {
     83 	struct stat st;
     84 
     85 	if (fp->_file < 0 || fstat(fp->_file, &st) < 0) {
     86 		*couldbetty = 0;
     87 		*bufsize = BUFSIZ;
     88 		return (__SNPT);
     89 	}
     90 
     91 	/* could be a tty iff it is a character device */
     92 	*couldbetty = S_ISCHR(st.st_mode);
     93 	if (st.st_blksize == 0) {
     94 		*bufsize = BUFSIZ;
     95 		return (__SNPT);
     96 	}
     97 
     98 	/*
     99 	 * Optimise fseek() only if it is a regular file.  (The test for
    100 	 * __sseek is mainly paranoia.)  It is safe to set _blksize
    101 	 * unconditionally; it will only be used if __SOPT is also set.
    102 	 */
    103 	*bufsize = st.st_blksize;
    104 	fp->_blksize = st.st_blksize;
    105 	return ((st.st_mode & S_IFMT) == S_IFREG && fp->_seek == __sseek ?
    106 	    __SOPT : __SNPT);
    107 }
    108