fseek.c - vx32 - Local 9vx git repository for patches.
(HTM) git clone git://r-36.net/vx32
(DIR) Log
(DIR) Files
(DIR) Refs
---
fseek.c (6896B)
---
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)
38 static char rcsid[] = "$OpenBSD: fseek.c,v 1.2 1996/08/19 08:32:46 tholo Exp $";
39 #endif /* LIBC_SCCS and not lint */
40
41 #include <sys/types.h>
42 #include <sys/stat.h>
43 #include <fcntl.h>
44 #include <stdio.h>
45 #include <stdlib.h>
46 #include <errno.h>
47 #include "local.h"
48
49 #define POS_ERR (-(fpos_t)1)
50
51 /*
52 * Seek the given file to the given offset.
53 * `Whence' must be one of the three SEEK_* macros.
54 */
55 int
56 fseek(fp, offset, whence)
57 register FILE *fp;
58 long offset;
59 int whence;
60 {
61 register fpos_t (*seekfn) __P((void *, fpos_t, int));
62 fpos_t target, curoff;
63 size_t n;
64 struct stat st;
65 int havepos;
66
67 /* make sure stdio is set up */
68 if (!__sdidinit)
69 __sinit();
70
71 /*
72 * Have to be able to seek.
73 */
74 if ((seekfn = fp->_seek) == NULL) {
75 errno = ESPIPE; /* historic practice */
76 return (EOF);
77 }
78
79 /*
80 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
81 * After this, whence is either SEEK_SET or SEEK_END.
82 */
83 switch (whence) {
84
85 case SEEK_CUR:
86 /*
87 * In order to seek relative to the current stream offset,
88 * we have to first find the current stream offset a la
89 * ftell (see ftell for details).
90 */
91 __sflush(fp); /* may adjust seek offset on append stream */
92 if (fp->_flags & __SOFF)
93 curoff = fp->_offset;
94 else {
95 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
96 if (curoff == -1L)
97 return (EOF);
98 }
99 if (fp->_flags & __SRD) {
100 curoff -= fp->_r;
101 if (HASUB(fp))
102 curoff -= fp->_ur;
103 } else if (fp->_flags & __SWR && fp->_p != NULL)
104 curoff += fp->_p - fp->_bf._base;
105
106 offset += curoff;
107 whence = SEEK_SET;
108 havepos = 1;
109 break;
110
111 case SEEK_SET:
112 case SEEK_END:
113 curoff = 0; /* XXX just to keep gcc quiet */
114 havepos = 0;
115 break;
116
117 default:
118 errno = EINVAL;
119 return (EOF);
120 }
121
122 /*
123 * Can only optimise if:
124 * reading (and not reading-and-writing);
125 * not unbuffered; and
126 * this is a `regular' Unix file (and hence seekfn==__sseek).
127 * We must check __NBF first, because it is possible to have __NBF
128 * and __SOPT both set.
129 */
130 if (fp->_bf._base == NULL)
131 __smakebuf(fp);
132 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
133 goto dumb;
134 if ((fp->_flags & __SOPT) == 0) {
135 if (seekfn != __sseek ||
136 fp->_file < 0 || fstat(fp->_file, &st) ||
137 (st.st_mode & S_IFMT) != S_IFREG) {
138 fp->_flags |= __SNPT;
139 goto dumb;
140 }
141 fp->_blksize = st.st_blksize;
142 fp->_flags |= __SOPT;
143 }
144
145 /*
146 * We are reading; we can try to optimise.
147 * Figure out where we are going and where we are now.
148 */
149 if (whence == SEEK_SET)
150 target = offset;
151 else {
152 if (fstat(fp->_file, &st))
153 goto dumb;
154 target = st.st_size + offset;
155 }
156
157 if (!havepos) {
158 if (fp->_flags & __SOFF)
159 curoff = fp->_offset;
160 else {
161 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
162 if (curoff == POS_ERR)
163 goto dumb;
164 }
165 curoff -= fp->_r;
166 if (HASUB(fp))
167 curoff -= fp->_ur;
168 }
169
170 /*
171 * Compute the number of bytes in the input buffer (pretending
172 * that any ungetc() input has been discarded). Adjust current
173 * offset backwards by this count so that it represents the
174 * file offset for the first byte in the current input buffer.
175 */
176 if (HASUB(fp)) {
177 curoff += fp->_r; /* kill off ungetc */
178 n = fp->_up - fp->_bf._base;
179 curoff -= n;
180 n += fp->_ur;
181 } else {
182 n = fp->_p - fp->_bf._base;
183 curoff -= n;
184 n += fp->_r;
185 }
186
187 /*
188 * If the target offset is within the current buffer,
189 * simply adjust the pointers, clear EOF, undo ungetc(),
190 * and return. (If the buffer was modified, we have to
191 * skip this; see fgetln.c.)
192 */
193 if ((fp->_flags & __SMOD) == 0 &&
194 target >= curoff && target < curoff + n) {
195 register int o = target - curoff;
196
197 fp->_p = fp->_bf._base + o;
198 fp->_r = n - o;
199 if (HASUB(fp))
200 FREEUB(fp);
201 fp->_flags &= ~__SEOF;
202 return (0);
203 }
204
205 /*
206 * The place we want to get to is not within the current buffer,
207 * but we can still be kind to the kernel copyout mechanism.
208 * By aligning the file offset to a block boundary, we can let
209 * the kernel use the VM hardware to map pages instead of
210 * copying bytes laboriously. Using a block boundary also
211 * ensures that we only read one block, rather than two.
212 */
213 curoff = target & ~(fp->_blksize - 1);
214 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
215 goto dumb;
216 fp->_r = 0;
217 fp->_p = fp->_bf._base;
218 if (HASUB(fp))
219 FREEUB(fp);
220 fp->_flags &= ~__SEOF;
221 n = target - curoff;
222 if (n) {
223 if (__srefill(fp) || fp->_r < n)
224 goto dumb;
225 fp->_p += n;
226 fp->_r -= n;
227 }
228 return (0);
229
230 /*
231 * We get here if we cannot optimise the seek ... just
232 * do it. Allow the seek function to change fp->_bf._base.
233 */
234 dumb:
235 if (__sflush(fp) ||
236 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
237 return (EOF);
238 }
239 /* success: clear EOF indicator and discard ungetc() data */
240 if (HASUB(fp))
241 FREEUB(fp);
242 fp->_p = fp->_bf._base;
243 fp->_r = 0;
244 /* fp->_w = 0; */ /* unnecessary (I think...) */
245 fp->_flags &= ~__SEOF;
246 return (0);
247 }