xref: /freebsd/lib/libc/stdio/fseek.c (revision 41466b50c1d5bfd1cf6adaae547a579a75d7c04e)
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 #if 0
39 static char sccsid[] = "@(#)fseek.c	8.3 (Berkeley) 1/2/94";
40 #endif
41 static const char rcsid[] =
42   "$FreeBSD$";
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>
51 #include <stdio.h>
52 #include <stdlib.h>
53 #include "un-namespace.h"
54 #include "local.h"
55 #include "libc_private.h"
56 
57 #define	POS_ERR	(-(fpos_t)1)
58 
59 int
60 fseek(fp, offset, whence)
61 	register FILE *fp;
62 	long offset;
63 	int whence;
64 {
65 	int ret;
66 	int serrno = errno;
67 
68 	/* make sure stdio is set up */
69 	if (!__sdidinit)
70 		__sinit();
71 
72 	FLOCKFILE(fp);
73 	ret = _fseeko(fp, (off_t)offset, whence, 1);
74 	FUNLOCKFILE(fp);
75 	if (ret == 0)
76 		errno = serrno;
77 	return (ret);
78 }
79 
80 int
81 fseeko(fp, offset, whence)
82 	FILE *fp;
83 	off_t offset;
84 	int whence;
85 {
86 	int ret;
87 	int serrno = errno;
88 
89 	/* make sure stdio is set up */
90 	if (!__sdidinit)
91 		__sinit();
92 
93 	FLOCKFILE(fp);
94 	ret = _fseeko(fp, offset, whence, 0);
95 	FUNLOCKFILE(fp);
96 	if (ret == 0)
97 		errno = serrno;
98 	return (ret);
99 }
100 
101 /*
102  * Seek the given file to the given offset.
103  * `Whence' must be one of the three SEEK_* macros.
104  */
105 int
106 _fseeko(fp, offset, whence, ltest)
107 	FILE *fp;
108 	off_t offset;
109 	int whence;
110 	int ltest;
111 {
112 	register fpos_t (*seekfn) __P((void *, fpos_t, int));
113 	fpos_t target, curoff, ret;
114 	size_t n;
115 	struct stat st;
116 	int havepos;
117 
118 	/*
119 	 * Have to be able to seek.
120 	 */
121 	if ((seekfn = fp->_seek) == NULL) {
122 		errno = ESPIPE;		/* historic practice */
123 		return (-1);
124 	}
125 
126 	/*
127 	 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
128 	 * After this, whence is either SEEK_SET or SEEK_END.
129 	 */
130 	switch (whence) {
131 
132 	case SEEK_CUR:
133 		/*
134 		 * In order to seek relative to the current stream offset,
135 		 * we have to first find the current stream offset via
136 		 * ftell (see ftell for details).
137 		 */
138 		if (_ftello(fp, &curoff))
139 			return (-1);
140 		if (curoff < 0) {
141 			/* Unspecified position because of ungetc() at 0 */
142 			errno = ESPIPE;
143 			return (-1);
144 		}
145 		if (offset > 0 && curoff > OFF_MAX - offset) {
146 			errno = EOVERFLOW;
147 			return (-1);
148 		}
149 		offset += curoff;
150 		if (offset < 0) {
151 			errno = EINVAL;
152 			return (-1);
153 		}
154 		if (ltest && offset > LONG_MAX) {
155 			errno = EOVERFLOW;
156 			return (-1);
157 		}
158 		whence = SEEK_SET;
159 		havepos = 1;
160 		break;
161 
162 	case SEEK_SET:
163 		if (offset < 0) {
164 			errno = EINVAL;
165 			return (-1);
166 		}
167 	case SEEK_END:
168 		curoff = 0;		/* XXX just to keep gcc quiet */
169 		havepos = 0;
170 		break;
171 
172 	default:
173 		errno = EINVAL;
174 		return (-1);
175 	}
176 
177 	/*
178 	 * Can only optimise if:
179 	 *	reading (and not reading-and-writing);
180 	 *	not unbuffered; and
181 	 *	this is a `regular' Unix file (and hence seekfn==__sseek).
182 	 * We must check __NBF first, because it is possible to have __NBF
183 	 * and __SOPT both set.
184 	 */
185 	if (fp->_bf._base == NULL)
186 		__smakebuf(fp);
187 	if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
188 		goto dumb;
189 	if ((fp->_flags & __SOPT) == 0) {
190 		if (seekfn != __sseek ||
191 		    fp->_file < 0 || _fstat(fp->_file, &st) ||
192 		    (st.st_mode & S_IFMT) != S_IFREG) {
193 			fp->_flags |= __SNPT;
194 			goto dumb;
195 		}
196 		fp->_blksize = st.st_blksize;
197 		fp->_flags |= __SOPT;
198 	}
199 
200 	/*
201 	 * We are reading; we can try to optimise.
202 	 * Figure out where we are going and where we are now.
203 	 */
204 	if (whence == SEEK_SET)
205 		target = offset;
206 	else {
207 		if (_fstat(fp->_file, &st))
208 			goto dumb;
209 		if (offset > 0 && st.st_size > OFF_MAX - offset) {
210 			errno = EOVERFLOW;
211 			return (-1);
212 		}
213 		target = st.st_size + offset;
214 		if ((off_t)target < 0) {
215 			errno = EINVAL;
216 			return (-1);
217 		}
218 		if (ltest && (off_t)target > LONG_MAX) {
219 			errno = EOVERFLOW;
220 			return (-1);
221 		}
222 	}
223 
224 	if (!havepos && _ftello(fp, &curoff))
225 		goto dumb;
226 
227 	/*
228 	 * (If the buffer was modified, we have to
229 	 * skip this; see fgetln.c.)
230 	 */
231 	if (fp->_flags & __SMOD)
232 		goto abspos;
233 
234 	/*
235 	 * Compute the number of bytes in the input buffer (pretending
236 	 * that any ungetc() input has been discarded).  Adjust current
237 	 * offset backwards by this count so that it represents the
238 	 * file offset for the first byte in the current input buffer.
239 	 */
240 	if (HASUB(fp)) {
241 		curoff += fp->_r;	/* kill off ungetc */
242 		n = fp->_extra->_up - fp->_bf._base;
243 		curoff -= n;
244 		n += fp->_ur;
245 	} else {
246 		n = fp->_p - fp->_bf._base;
247 		curoff -= n;
248 		n += fp->_r;
249 	}
250 
251 	/*
252 	 * If the target offset is within the current buffer,
253 	 * simply adjust the pointers, clear EOF, undo ungetc(),
254 	 * and return.
255 	 */
256 	if (target >= curoff && target < curoff + n) {
257 		size_t o = target - curoff;
258 
259 		fp->_p = fp->_bf._base + o;
260 		fp->_r = n - o;
261 		if (HASUB(fp))
262 			FREEUB(fp);
263 		fp->_flags &= ~__SEOF;
264 		return (0);
265 	}
266 
267 abspos:
268 	/*
269 	 * The place we want to get to is not within the current buffer,
270 	 * but we can still be kind to the kernel copyout mechanism.
271 	 * By aligning the file offset to a block boundary, we can let
272 	 * the kernel use the VM hardware to map pages instead of
273 	 * copying bytes laboriously.  Using a block boundary also
274 	 * ensures that we only read one block, rather than two.
275 	 */
276 	curoff = target & ~(fp->_blksize - 1);
277 	if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
278 		goto dumb;
279 	fp->_r = 0;
280 	fp->_p = fp->_bf._base;
281 	if (HASUB(fp))
282 		FREEUB(fp);
283 	n = target - curoff;
284 	if (n) {
285 		if (__srefill(fp) || fp->_r < n)
286 			goto dumb;
287 		fp->_p += n;
288 		fp->_r -= n;
289 	}
290 	fp->_flags &= ~__SEOF;
291 	return (0);
292 
293 	/*
294 	 * We get here if we cannot optimise the seek ... just
295 	 * do it.  Allow the seek function to change fp->_bf._base.
296 	 */
297 dumb:
298 	if (__sflush(fp) ||
299 	    (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
300 		return (-1);
301 	/* success: clear EOF indicator and discard ungetc() data */
302 	if (HASUB(fp))
303 		FREEUB(fp);
304 	fp->_p = fp->_bf._base;
305 	fp->_r = 0;
306 	/* fp->_w = 0; */	/* unnecessary (I think...) */
307 	fp->_flags &= ~__SEOF;
308 	if (ltest && ret > LONG_MAX) {
309 		fp->_flags |= __SERR;
310 		errno = EOVERFLOW;
311 		return (-1);
312 	}
313 	return (0);
314 }
315