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

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34 * SUCH DAMAGE.
35 */
36
37#if defined(LIBC_SCCS) && !defined(lint)
38#if 0
39static char sccsid[] = "@(#)fseek.c 8.3 (Berkeley) 1/2/94";
40#endif
41static const char rcsid[] =
42 "$FreeBSD: head/lib/libc/stdio/fseek.c 82588 2001-08-30 19:54:04Z ache $";
43#endif /* LIBC_SCCS and not lint */
44
45#include "namespace.h"
46#include <sys/types.h>
47#include <sys/stat.h>
48#include <errno.h>
49#include <fcntl.h>
50#include <limits.h>

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109 struct stat st;
110 int havepos;
111
112 /*
113 * Have to be able to seek.
114 */
115 if ((seekfn = fp->_seek) == NULL) {
116 errno = ESPIPE; /* historic practice */
117 return (-1);
118 }
119
120 /*
121 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
122 * After this, whence is either SEEK_SET or SEEK_END.
123 */
124 switch (whence) {
125
126 case SEEK_CUR:
127 /*
128 * In order to seek relative to the current stream offset,
129 * we have to first find the current stream offset a la
130 * ftell (see ftell for details).
131 */
132 if (fp->_flags & __SOFF)
133 curoff = fp->_offset;
134 else {
135 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
136 if (curoff == -1)
137 return (-1);
138 }
139 if (fp->_flags & __SRD) {
140 curoff -= fp->_r;
141 if (curoff < 0) {
142 if (HASUB(fp)) {
143 fp->_p -= curoff;
144 fp->_r += curoff;
145 curoff = 0;
146 } else {
147 errno = EBADF;
148 return (-1);
149 }
150 }
151 if (HASUB(fp)) {
152 curoff -= fp->_ur;
153 if (curoff < 0) {
154 errno = EBADF;
155 return (-1);
156 }
157 }
158 } else if ((fp->_flags & __SWR) && fp->_p != NULL) {
159 n = fp->_p - fp->_bf._base;
160 if (curoff > OFF_MAX - n) {
161 errno = EOVERFLOW;
162 return (-1);
163 }
164 curoff += n;
165 }
166 if (offset > 0 && curoff > OFF_MAX - offset) {
167 errno = EOVERFLOW;
168 return (-1);
169 }
170 offset += curoff;
171 if (offset < 0) {
172 errno = EINVAL;
173 return (-1);
174 }
175 if (ltest && offset > LONG_MAX) {
176 errno = EOVERFLOW;
177 return (-1);
178 }
179 whence = SEEK_SET;
180 havepos = 1;
181 break;
182
183 case SEEK_SET:
184 if (offset < 0) {
185 errno = EINVAL;
186 return (-1);
187 }
188 case SEEK_END:
189 curoff = 0; /* XXX just to keep gcc quiet */
190 havepos = 0;
191 break;
192
193 default:
194 errno = EINVAL;
195 return (-1);
196 }
197
198 /*
199 * Can only optimise if:
200 * reading (and not reading-and-writing);
201 * not unbuffered; and
202 * this is a `regular' Unix file (and hence seekfn==__sseek).
203 * We must check __NBF first, because it is possible to have __NBF

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224 */
225 if (whence == SEEK_SET)
226 target = offset;
227 else {
228 if (_fstat(fp->_file, &st))
229 goto dumb;
230 if (offset > 0 && st.st_size > OFF_MAX - offset) {
231 errno = EOVERFLOW;
232 return (-1);
233 }
234 target = st.st_size + offset;
235 if ((off_t)target < 0) {
236 errno = EINVAL;
237 return (-1);
238 }
239 if (ltest && (off_t)target > LONG_MAX) {
240 errno = EOVERFLOW;
241 return (-1);
242 }
243 }
244
245 if (!havepos) {
246 if (fp->_flags & __SOFF)
247 curoff = fp->_offset;
248 else {
249 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
250 if (curoff == POS_ERR)
251 goto dumb;
252 }
253 curoff -= fp->_r;
254 if (curoff < 0) {
255 if (HASUB(fp)) {
256 fp->_p -= curoff;
257 fp->_r += curoff;
258 curoff = 0;
259 } else {
260 errno = EBADF;
261 return (-1);
262 }
263 }
264 if (HASUB(fp)) {
265 curoff -= fp->_ur;
266 if (curoff < 0) {
267 errno = EBADF;
268 return (-1);
269 }
270 }
271 }
272
273 /*
274 * Compute the number of bytes in the input buffer (pretending
275 * that any ungetc() input has been discarded). Adjust current
276 * offset backwards by this count so that it represents the
277 * file offset for the first byte in the current input buffer.
278 */
279 if (HASUB(fp)) {
280 if (curoff > OFF_MAX - fp->_r)
281 goto abspos;
282 curoff += fp->_r; /* kill off ungetc */
283 n = fp->_extra->_up - fp->_bf._base;
284 curoff -= n;
285 n += fp->_ur;
286 } else {
287 n = fp->_p - fp->_bf._base;
288 curoff -= n;
289 n += fp->_r;
290 }
291 /* curoff can be negative at this point. */
292
293 /*
294 * If the target offset is within the current buffer,
295 * simply adjust the pointers, clear EOF, undo ungetc(),
296 * and return. (If the buffer was modified, we have to
297 * skip this; see fgetln.c.)
298 */
299 if ((fp->_flags & __SMOD) == 0 &&
300 target >= curoff &&
301 (curoff <= 0 || curoff <= OFF_MAX - n) &&
302 target < curoff + n) {
303 size_t o = target - curoff;
304
305 fp->_p = fp->_bf._base + o;
306 fp->_r = n - o;
307 if (HASUB(fp))
308 FREEUB(fp);
309 fp->_flags &= ~__SEOF;
310 return (0);
311 }
312
313abspos:
314 /*
315 * The place we want to get to is not within the current buffer,
316 * but we can still be kind to the kernel copyout mechanism.
317 * By aligning the file offset to a block boundary, we can let
318 * the kernel use the VM hardware to map pages instead of
319 * copying bytes laboriously. Using a block boundary also
320 * ensures that we only read one block, rather than two.
321 */

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338
339 /*
340 * We get here if we cannot optimise the seek ... just
341 * do it. Allow the seek function to change fp->_bf._base.
342 */
343dumb:
344 if (__sflush(fp) ||
345 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR)
346 return (-1);
347 if (ltest && fp->_offset > LONG_MAX) {
348 errno = EOVERFLOW;
349 return (-1);
350 }
351 /* success: clear EOF indicator and discard ungetc() data */
352 if (HASUB(fp))
353 FREEUB(fp);
354 fp->_p = fp->_bf._base;
355 fp->_r = 0;
356 /* fp->_w = 0; */ /* unnecessary (I think...) */
357 fp->_flags &= ~__SEOF;
358 return (0);
359}