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 82348 2001-08-26 10:38:29Z 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 (EOF);
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 (EOF);
138 }
139 if (fp->_flags & __SRD) {
140 curoff -= fp->_r;
141 if (HASUB(fp))
142 curoff -= fp->_ur;
143 } else if (fp->_flags & __SWR && fp->_p != NULL)
144 curoff += fp->_p - fp->_bf._base;
145
146 if (offset > 0 && curoff > OFF_MAX - offset) {
147 errno = EOVERFLOW;
148 return (EOF);
149 }
150 offset += curoff;
151 /* Disallow negative seeks per POSIX */
152 if (offset < 0) {
153 errno = EINVAL;
154 return (EOF);
155 }
156 if (ltest && offset > LONG_MAX) {
157 errno = EOVERFLOW;
158 return (EOF);
159 }
160 whence = SEEK_SET;
161 havepos = 1;
162 break;
163
164 case SEEK_SET:
165 /* Disallow negative seeks per POSIX */
166 if (offset < 0) {
167 errno = EINVAL;
168 return (EOF);
169 }
170 case SEEK_END:
171 curoff = 0; /* XXX just to keep gcc quiet */
172 havepos = 0;
173 break;
174
175 default:
176 errno = EINVAL;
177 return (EOF);
178 }
179
180 /*
181 * Can only optimise if:
182 * reading (and not reading-and-writing);
183 * not unbuffered; and
184 * this is a `regular' Unix file (and hence seekfn==__sseek).
185 * We must check __NBF first, because it is possible to have __NBF

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206 */
207 if (whence == SEEK_SET)
208 target = offset;
209 else {
210 if (_fstat(fp->_file, &st))
211 goto dumb;
212 if (offset > 0 && st.st_size > OFF_MAX - offset) {
213 errno = EOVERFLOW;
214 return (EOF);
215 }
216 target = st.st_size + offset;
217 /* Disallow negative seeks per POSIX */
218 if ((off_t)target < 0) {
219 errno = EINVAL;
220 return (EOF);
221 }
222 if (ltest && (off_t)target > LONG_MAX) {
223 errno = EOVERFLOW;
224 return (EOF);
225 }
226 }
227
228 if (!havepos) {
229 if (fp->_flags & __SOFF)
230 curoff = fp->_offset;
231 else {
232 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
233 if (curoff == POS_ERR)
234 goto dumb;
235 }
236 curoff -= fp->_r;
237 if (HASUB(fp))
238 curoff -= fp->_ur;
239 }
240
241 /*
242 * Compute the number of bytes in the input buffer (pretending
243 * that any ungetc() input has been discarded). Adjust current
244 * offset backwards by this count so that it represents the
245 * file offset for the first byte in the current input buffer.
246 */
247 if (HASUB(fp)) {
248 curoff += fp->_r; /* kill off ungetc */
249 n = fp->_extra->_up - fp->_bf._base;
250 curoff -= n;
251 n += fp->_ur;
252 } else {
253 n = fp->_p - fp->_bf._base;
254 curoff -= n;
255 n += fp->_r;
256 }
257
258 /*
259 * If the target offset is within the current buffer,
260 * simply adjust the pointers, clear EOF, undo ungetc(),
261 * and return. (If the buffer was modified, we have to
262 * skip this; see fgetln.c.)
263 */
264 if ((fp->_flags & __SMOD) == 0 &&
265 target >= curoff && target < curoff + n) {
266 register int o = target - curoff;
267
268 fp->_p = fp->_bf._base + o;
269 fp->_r = n - o;
270 if (HASUB(fp))
271 FREEUB(fp);
272 fp->_flags &= ~__SEOF;
273 return (0);
274 }
275
276 /*
277 * The place we want to get to is not within the current buffer,
278 * but we can still be kind to the kernel copyout mechanism.
279 * By aligning the file offset to a block boundary, we can let
280 * the kernel use the VM hardware to map pages instead of
281 * copying bytes laboriously. Using a block boundary also
282 * ensures that we only read one block, rather than two.
283 */

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300
301 /*
302 * We get here if we cannot optimise the seek ... just
303 * do it. Allow the seek function to change fp->_bf._base.
304 */
305dumb:
306 if (__sflush(fp) ||
307 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR)
308 return (EOF);
309 /* POSIX require long type resulting offset for fseek() */
310 if (ltest && fp->_offset != (long)fp->_offset) {
311 errno = EOVERFLOW;
312 return (EOF);
313 }
314 /* success: clear EOF indicator and discard ungetc() data */
315 if (HASUB(fp))
316 FREEUB(fp);
317 fp->_p = fp->_bf._base;
318 fp->_r = 0;
319 /* fp->_w = 0; */ /* unnecessary (I think...) */
320 fp->_flags &= ~__SEOF;
321 return (0);
322}