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. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 *
32 * @(#)fseek.c 8.3 (Berkeley) 1/2/94
33 * $FreeBSD: src/lib/libc/stdio/fseek.c,v 1.44 2008/04/17 22:17:54 jhb Exp $
34 */
35
36 #include "namespace.h"
37 #include <sys/param.h>
38 #include <sys/stat.h>
39 #include <errno.h>
40 #include <fcntl.h>
41 #include <limits.h>
42 #include <stdio.h>
43 #include <stdlib.h>
44 #include "un-namespace.h"
45 #include "local.h"
46 #include "libc_private.h"
47
48 #define POS_ERR (-(fpos_t)1)
49
50 int
fseek(FILE * fp,long offset,int whence)51 fseek(FILE *fp, long offset, int whence)
52 {
53 int ret;
54 int serrno = errno;
55
56 /* make sure stdio is set up */
57 if (!__sdidinit)
58 __sinit();
59
60 FLOCKFILE(fp);
61 ret = _fseeko(fp, (off_t)offset, whence, 1);
62 FUNLOCKFILE(fp);
63 if (ret == 0)
64 errno = serrno;
65 return (ret);
66 }
67
68 int
fseeko(FILE * fp,off_t offset,int whence)69 fseeko(FILE *fp, off_t offset, int whence)
70 {
71 int ret;
72 int serrno = errno;
73
74 /* make sure stdio is set up */
75 if (!__sdidinit)
76 __sinit();
77
78 FLOCKFILE(fp);
79 ret = _fseeko(fp, offset, whence, 0);
80 FUNLOCKFILE(fp);
81 if (ret == 0)
82 errno = serrno;
83 return (ret);
84 }
85
86 /*
87 * Seek the given file to the given offset.
88 * `Whence' must be one of the three SEEK_* macros.
89 */
90 int
_fseeko(FILE * fp,off_t offset,int whence,int ltest)91 _fseeko(FILE *fp, off_t offset, int whence, int ltest)
92 {
93 fpos_t (*seekfn)(void *, fpos_t, int);
94 fpos_t target, curoff, ret;
95 size_t n;
96 struct stat st;
97 int havepos;
98
99 /*
100 * Have to be able to seek.
101 */
102 if ((seekfn = fp->_seek) == NULL) {
103 errno = ESPIPE; /* historic practice */
104 return (-1);
105 }
106
107 /*
108 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
109 * After this, whence is either SEEK_SET or SEEK_END.
110 */
111 switch (whence) {
112
113 case SEEK_CUR:
114 /*
115 * In order to seek relative to the current stream offset,
116 * we have to first find the current stream offset via
117 * ftell (see ftell for details).
118 */
119 if (_ftello(fp, &curoff))
120 return (-1);
121 if (curoff < 0) {
122 /* Unspecified position because of ungetc() at 0 */
123 errno = ESPIPE;
124 return (-1);
125 }
126 if (offset > 0 && curoff > OFF_MAX - offset) {
127 errno = EOVERFLOW;
128 return (-1);
129 }
130 offset += curoff;
131 if (offset < 0) {
132 errno = EINVAL;
133 return (-1);
134 }
135 if (ltest && offset > LONG_MAX) {
136 errno = EOVERFLOW;
137 return (-1);
138 }
139 whence = SEEK_SET;
140 havepos = 1;
141 break;
142
143 case SEEK_SET:
144 if (offset < 0) {
145 errno = EINVAL;
146 return (-1);
147 }
148 case SEEK_END:
149 curoff = 0; /* XXX just to keep gcc quiet */
150 havepos = 0;
151 break;
152
153 default:
154 errno = EINVAL;
155 return (-1);
156 }
157
158 /*
159 * Can only optimise if:
160 * reading (and not reading-and-writing);
161 * not unbuffered; and
162 * this is a `regular' Unix file (and hence seekfn==__sseek).
163 * We must check __NBF first, because it is possible to have __NBF
164 * and __SOPT both set.
165 */
166 if (fp->_bf._base == NULL)
167 __smakebuf(fp);
168 if (fp->pub._flags & (__SWR | __SRW | __SNBF | __SNPT))
169 goto dumb;
170 if ((fp->pub._flags & __SOPT) == 0) {
171 if (seekfn != __sseek ||
172 fp->pub._fileno < 0 || _fstat(fp->pub._fileno, &st) ||
173 (st.st_mode & S_IFMT) != S_IFREG) {
174 fp->pub._flags |= __SNPT;
175 goto dumb;
176 }
177 fp->_blksize = st.st_blksize;
178 fp->pub._flags |= __SOPT;
179 }
180
181 /*
182 * We are reading; we can try to optimise.
183 * Figure out where we are going and where we are now.
184 */
185 if (whence == SEEK_SET)
186 target = offset;
187 else {
188 if (_fstat(fp->pub._fileno, &st))
189 goto dumb;
190 if (offset > 0 && st.st_size > OFF_MAX - offset) {
191 errno = EOVERFLOW;
192 return (-1);
193 }
194 target = st.st_size + offset;
195 if ((off_t)target < 0) {
196 errno = EINVAL;
197 return (-1);
198 }
199 if (ltest && (off_t)target > LONG_MAX) {
200 errno = EOVERFLOW;
201 return (-1);
202 }
203 }
204
205 if (!havepos && _ftello(fp, &curoff))
206 goto dumb;
207
208 /*
209 * (If the buffer was modified, we have to
210 * skip this; see fgetln.c.)
211 */
212 if (fp->pub._flags & __SMOD)
213 goto abspos;
214
215 /*
216 * Compute the number of bytes in the input buffer (pretending
217 * that any ungetc() input has been discarded). Adjust current
218 * offset backwards by this count so that it represents the
219 * file offset for the first byte in the current input buffer.
220 */
221 if (HASUB(fp)) {
222 curoff += fp->pub._r; /* kill off ungetc */
223 n = fp->_up - fp->_bf._base;
224 curoff -= n;
225 n += fp->_ur;
226 } else {
227 n = fp->pub._p - fp->_bf._base;
228 curoff -= n;
229 n += fp->pub._r;
230 }
231
232 /*
233 * If the target offset is within the current buffer,
234 * simply adjust the pointers, clear EOF, undo ungetc(),
235 * and return.
236 */
237 if (target >= curoff && target < curoff + n) {
238 size_t o = target - curoff;
239
240 fp->pub._p = fp->_bf._base + o;
241 fp->pub._r = n - o;
242 if (HASUB(fp))
243 FREEUB(fp);
244 fp->pub._flags &= ~__SEOF;
245 memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
246 return (0);
247 }
248
249 abspos:
250 /*
251 * The place we want to get to is not within the current buffer,
252 * but we can still be kind to the kernel copyout mechanism.
253 * By aligning the file offset to a block boundary, we can let
254 * the kernel use the VM hardware to map pages instead of
255 * copying bytes laboriously. Using a block boundary also
256 * ensures that we only read one block, rather than two.
257 */
258 curoff = rounddown2(target, fp->_blksize);
259 if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
260 goto dumb;
261 fp->pub._r = 0;
262 fp->pub._p = fp->_bf._base;
263 if (HASUB(fp))
264 FREEUB(fp);
265 n = target - curoff;
266 if (n) {
267 if (__srefill(fp) || fp->pub._r < n)
268 goto dumb;
269 fp->pub._p += n;
270 fp->pub._r -= n;
271 }
272 fp->pub._flags &= ~__SEOF;
273 memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
274 return (0);
275
276 /*
277 * We get here if we cannot optimise the seek ... just
278 * do it. Allow the seek function to change fp->_bf._base.
279 */
280 dumb:
281 if (__sflush(fp) ||
282 (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
283 return (-1);
284 if (ltest && ret > LONG_MAX) {
285 fp->pub._flags |= __SERR;
286 errno = EOVERFLOW;
287 return (-1);
288 }
289 /* success: clear EOF indicator and discard ungetc() data */
290 if (HASUB(fp))
291 FREEUB(fp);
292 fp->pub._p = fp->_bf._base;
293 fp->pub._r = 0;
294 /* fp->pub._w = 0; */ /* unnecessary (I think...) */
295 fp->pub._flags &= ~__SEOF;
296 memset(WCIO_GET(fp), 0, sizeof(struct wchar_io_data));
297 return (0);
298 }
299