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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 sccsid[] = "@(#)fseek.c 8.3 (Berkeley) 1/2/94";
39 #endif /* LIBC_SCCS and not lint */
40 #include <sys/cdefs.h>
41 __FBSDID("$FreeBSD: src/lib/libc/stdio/fseek.c,v 1.41 2004/05/22 15:19:41 tjr Exp $");
42
43 #include "namespace.h"
44 #include <sys/types.h>
45 #include <sys/stat.h>
46 #include <errno.h>
47 #include <fcntl.h>
48 #include <limits.h>
49 #include <stdio.h>
50 #include <stdlib.h>
51 #include "un-namespace.h"
52 #include "local.h"
53 #include "libc_private.h"
54
55 #define POS_ERR (-(fpos_t)1)
56
57 int
58 fseek(fp, offset, whence)
59 FILE *fp;
60 long offset;
61 int whence;
62 {
63 int ret;
64 int serrno = errno;
65
66 /* make sure stdio is set up */
67 if (!__sdidinit)
68 __sinit();
69
70 FLOCKFILE(fp);
71 ret = _fseeko(fp, (off_t)offset, whence, 1);
72 FUNLOCKFILE(fp);
73 if (ret == 0)
74 errno = serrno;
75 return (ret);
76 }
77
78 int
79 fseeko(fp, offset, whence)
80 FILE *fp;
81 off_t offset;
82 int whence;
83 {
84 int ret;
85 int serrno = errno;
86
87 /* make sure stdio is set up */
88 if (!__sdidinit)
89 __sinit();
90
91 FLOCKFILE(fp);
92 ret = _fseeko(fp, offset, whence, 0);
93 FUNLOCKFILE(fp);
94 if (ret == 0)
95 errno = serrno;
96 return (ret);
97 }
98
99 /*
100 * Seek the given file to the given offset.
101 * `Whence' must be one of the three SEEK_* macros.
102 */
103 int
104 _fseeko(fp, offset, whence, ltest)
105 FILE *fp;
106 off_t offset;
107 int whence;
108 int ltest;
109 {
110 fpos_t (*seekfn)(void *, fpos_t, int);
111 fpos_t target, curoff, ret;
112 size_t n;
113 struct stat st;
114 int havepos;
115
116 /*
117 * Have to be able to seek.
118 */
119 if ((seekfn = fp->_seek) == NULL) {
120 errno = ESPIPE; /* historic practice */
121 return (-1);
122 }
123
124 /*
125 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
126 * After this, whence is either SEEK_SET or SEEK_END.
127 */
128 switch (whence) {
129
130 case SEEK_CUR:
131 /*
132 * In order to seek relative to the current stream offset,
133 * we have to first find the current stream offset via
134 * ftell (see ftell for details).
135 */
136 if (_ftello(fp, &curoff))
137 return (-1);
138 if (curoff < 0) {
139 /* Unspecified position because of ungetc() at 0 */
140 errno = ESPIPE;
141 return (-1);
142 }
143 if (offset > 0 && curoff > OFF_MAX - offset) {
144 errno = EOVERFLOW;
145 return (-1);
146 }
147 offset += curoff;
148 if (offset < 0) {
149 errno = EINVAL;
150 return (-1);
151 }
152 if (ltest && offset > LONG_MAX) {
153 errno = EOVERFLOW;
154 return (-1);
155 }
156 whence = SEEK_SET;
157 havepos = 1;
158 break;
159
160 case SEEK_SET:
161 if (offset < 0) {
162 errno = EINVAL;
163 return (-1);
164 }
165 case SEEK_END:
166 curoff = 0; /* XXX just to keep gcc quiet */
167 havepos = 0;
168 break;
169
170 default:
171 errno = EINVAL;
172 return (-1);
173 }
174
175 /*
176 * Can only optimise if:
177 * reading (and not reading-and-writing);
178 * not unbuffered; and
179 * this is a `regular' Unix file (and hence seekfn==__sseek).
180 * We must check __NBF first, because it is possible to have __NBF
181 * and __SOPT both set.
182 */
183 if (fp->_bf._base == NULL)
184 __smakebuf(fp);
185 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
186 goto dumb;
187 if ((fp->_flags & __SOPT) == 0) {
188 if (seekfn != __sseek ||
189 fp->_file < 0 || _fstat(fp->_file, &st) ||
190 (st.st_mode & S_IFMT) != S_IFREG) {
191 fp->_flags |= __SNPT;
192 goto dumb;
193 }
194 fp->_blksize = st.st_blksize;
195 fp->_flags |= __SOPT;
196 }
197
198 /*
199 * We are reading; we can try to optimise.
200 * Figure out where we are going and where we are now.
201 */
202 if (whence == SEEK_SET)
203 target = offset;
204 else {
205 if (_fstat(fp->_file, &st))
206 goto dumb;
207 if (offset > 0 && st.st_size > OFF_MAX - offset) {
208 errno = EOVERFLOW;
209 return (-1);
210 }
211 target = st.st_size + offset;
212 if ((off_t)target < 0) {
213 errno = EINVAL;
214 return (-1);
215 }
216 if (ltest && (off_t)target > LONG_MAX) {
217 errno = EOVERFLOW;
218 return (-1);
219 }
220 }
221
222 if (!havepos && _ftello(fp, &curoff))
223 goto dumb;
224
225 /*
226 * (If the buffer was modified, we have to
227 * skip this; see fgetln.c.)
228 */
229 if (fp->_flags & __SMOD)
230 goto abspos;
231
232 /*
233 * Compute the number of bytes in the input buffer (pretending
234 * that any ungetc() input has been discarded). Adjust current
235 * offset backwards by this count so that it represents the
236 * file offset for the first byte in the current input buffer.
237 */
238 if (HASUB(fp)) {
239 curoff += fp->_r; /* kill off ungetc */
240 n = fp->_extra->_up - fp->_bf._base;
241 curoff -= n;
242 n += fp->_ur;
243 } else {
244 n = fp->_p - fp->_bf._base;
245 curoff -= n;
246 n += fp->_r;
247 }
248
249 /*
250 * If the target offset is within the current buffer,
251 * simply adjust the pointers, clear EOF, undo ungetc(),
252 * and return.
253 */
254 if (target >= curoff && target < curoff + n) {
255 size_t o = target - curoff;
256
257 fp->_p = fp->_bf._base + o;
258 fp->_r = n - o;
259 if (HASUB(fp))
260 FREEUB(fp);
261 fp->_flags &= ~__SEOF;
262 memset(&fp->_extra->mbstate, 0, sizeof(mbstate_t));
263 return (0);
264 }
265
266 abspos:
267 /*
268 * The place we want to get to is not within the current buffer,
269 * but we can still be kind to the kernel copyout mechanism.
270 * By aligning the file offset to a block boundary, we can let
271 * the kernel use the VM hardware to map pages instead of
272 * copying bytes laboriously. Using a block boundary also
273 * ensures that we only read one block, rather than two.
274 */
275 curoff = target & ~(fp->_blksize - 1);
276 if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
277 goto dumb;
278 fp->_r = 0;
279 fp->_p = fp->_bf._base;
280 if (HASUB(fp))
281 FREEUB(fp);
282 n = target - curoff;
283 if (n) {
284 if (__srefill(fp) || fp->_r < n)
285 goto dumb;
286 fp->_p += n;
287 fp->_r -= n;
288 }
289 fp->_flags &= ~__SEOF;
290 return (0);
291
292 /*
293 * We get here if we cannot optimise the seek ... just
294 * do it. Allow the seek function to change fp->_bf._base.
295 */
296 dumb:
297 if (__sflush(fp) ||
298 (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
299 return (-1);
300 /* success: clear EOF indicator and discard ungetc() data */
301 if (HASUB(fp))
302 FREEUB(fp);
303 fp->_p = fp->_bf._base;
304 fp->_r = 0;
305 /* fp->_w = 0; */ /* unnecessary (I think...) */
306 fp->_flags &= ~__SEOF;
307 memset(&fp->_extra->mbstate, 0, sizeof(mbstate_t));
308 if (ltest && ret > LONG_MAX) {
309 fp->_flags |= __SERR;
310 errno = EOVERFLOW;
311 return (-1);
312 }
313 return (0);
314 }