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 * 4. 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
33#if defined(LIBC_SCCS) && !defined(lint)
34static char sccsid[] = "@(#)fseek.c	8.3 (Berkeley) 1/2/94";
35#endif /* LIBC_SCCS and not lint */
36#include <sys/cdefs.h>
37__FBSDID("$FreeBSD: src/lib/libc/stdio/fseek.c,v 1.44 2008/04/17 22:17:54 jhb Exp $");
38
39#include "namespace.h"
40#include <sys/types.h>
41#include <sys/stat.h>
42#include <errno.h>
43#include <fcntl.h>
44#include <limits.h>
45#include <stdio.h>
46#include <stdlib.h>
47#include "un-namespace.h"
48#include "local.h"
49#include "libc_private.h"
50
51#define	POS_ERR	(-(fpos_t)1)
52
53int
54fseek(fp, offset, whence)
55	FILE *fp;
56	long offset;
57	int whence;
58{
59	int ret;
60	int serrno = errno;
61
62	/* make sure stdio is set up */
63	pthread_once(&__sdidinit, __sinit);
64
65	FLOCKFILE(fp);
66	ret = _fseeko(fp, (off_t)offset, whence, 1);
67	FUNLOCKFILE(fp);
68	if (ret == 0)
69		errno = serrno;
70	return (ret);
71}
72
73int
74fseeko(fp, offset, whence)
75	FILE *fp;
76	off_t offset;
77	int whence;
78{
79	int ret;
80	int serrno = errno;
81
82	/* make sure stdio is set up */
83	pthread_once(&__sdidinit, __sinit);
84
85	FLOCKFILE(fp);
86	ret = _fseeko(fp, offset, whence, 0);
87	FUNLOCKFILE(fp);
88	if (ret == 0)
89		errno = serrno;
90	return (ret);
91}
92
93/*
94 * Seek the given file to the given offset.
95 * `Whence' must be one of the three SEEK_* macros.
96 */
97int
98_fseeko(fp, offset, whence, ltest)
99	FILE *fp;
100	off_t offset;
101	int whence;
102	int ltest;
103{
104	fpos_t (*seekfn)(void *, fpos_t, int);
105	fpos_t target, curoff, ret;
106	size_t n;
107	struct stat st;
108	int havepos;
109
110	/*
111	 * Have to be able to seek.
112	 */
113	if ((seekfn = fp->_seek) == NULL) {
114		errno = ESPIPE;		/* historic practice */
115		return (-1);
116	}
117
118	/*
119	 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
120	 * After this, whence is either SEEK_SET or SEEK_END.
121	 */
122	switch (whence) {
123
124	case SEEK_CUR:
125		/*
126		 * In order to seek relative to the current stream offset,
127		 * we have to first find the current stream offset via
128		 * ftell (see ftell for details).
129		 */
130		if (_ftello(fp, &curoff))
131			return (-1);
132		if (curoff < 0) {
133			/* Unspecified position because of ungetc() at 0 */
134			errno = ESPIPE;
135			return (-1);
136		}
137		if (offset > 0 && curoff > OFF_MAX - offset) {
138			errno = EOVERFLOW;
139			return (-1);
140		}
141		offset += curoff;
142		if (offset < 0) {
143			errno = EINVAL;
144			return (-1);
145		}
146		if (ltest && offset > LONG_MAX) {
147			errno = EOVERFLOW;
148			return (-1);
149		}
150		whence = SEEK_SET;
151		havepos = 1;
152		break;
153
154	case SEEK_SET:
155		if (offset < 0) {
156			errno = EINVAL;
157			return (-1);
158		}
159	case SEEK_END:
160		curoff = 0;		/* XXX just to keep gcc quiet */
161		havepos = 0;
162		break;
163
164	default:
165		errno = EINVAL;
166		return (-1);
167	}
168
169	/*
170	 * Can only optimise if:
171	 *	reading (and not reading-and-writing);
172	 *	not unbuffered; and
173	 *	this is a `regular' Unix file (and hence seekfn==__sseek).
174	 * We must check __NBF first, because it is possible to have __NBF
175	 * and __SOPT both set.
176	 */
177	if (fp->_bf._base == NULL)
178		__smakebuf(fp);
179	if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
180		goto dumb;
181	if ((fp->_flags & __SOPT) == 0) {
182		if (seekfn != __sseek ||
183		    fp->_file < 0 || _fstat(fp->_file, &st) ||
184		    (st.st_mode & S_IFMT) != S_IFREG) {
185			fp->_flags |= __SNPT;
186			goto dumb;
187		}
188		fp->_blksize = st.st_blksize;
189		fp->_flags |= __SOPT;
190	}
191
192	/*
193	 * We are reading; we can try to optimise.
194	 * Figure out where we are going and where we are now.
195	 */
196	if (whence == SEEK_SET)
197		target = offset;
198	else {
199		if (_fstat(fp->_file, &st))
200			goto dumb;
201		if (offset > 0 && st.st_size > OFF_MAX - offset) {
202			errno = EOVERFLOW;
203			return (-1);
204		}
205		target = st.st_size + offset;
206		if ((off_t)target < 0) {
207			errno = EINVAL;
208			return (-1);
209		}
210		if (ltest && (off_t)target > LONG_MAX) {
211			errno = EOVERFLOW;
212			return (-1);
213		}
214	}
215
216	if (!havepos && _ftello(fp, &curoff))
217		goto dumb;
218
219	/*
220	 * (If the buffer was modified, we have to
221	 * skip this; see fgetln.c.)
222	 */
223	if (fp->_flags & __SMOD)
224		goto abspos;
225
226	/*
227	 * Compute the number of bytes in the input buffer (pretending
228	 * that any ungetc() input has been discarded).  Adjust current
229	 * offset backwards by this count so that it represents the
230	 * file offset for the first byte in the current input buffer.
231	 */
232	if (HASUB(fp)) {
233		curoff += fp->_r;	/* kill off ungetc */
234		n = fp->_up - fp->_bf._base;
235		curoff -= n;
236		n += fp->_ur;
237	} else {
238		n = fp->_p - fp->_bf._base;
239		curoff -= n;
240		n += fp->_r;
241	}
242
243	/*
244	 * If the target offset is within the current buffer,
245	 * simply adjust the pointers, clear EOF, undo ungetc(),
246	 * and return.
247	 */
248	if (target >= curoff && target < curoff + n) {
249		size_t o = target - curoff;
250
251		fp->_p = fp->_bf._base + o;
252		fp->_r = n - o;
253		if (HASUB(fp))
254			FREEUB(fp);
255		fp->_flags &= ~__SEOF;
256		memset(&fp->_mbstate, 0, sizeof(mbstate_t));
257		return (0);
258	}
259
260abspos:
261	/*
262	 * The place we want to get to is not within the current buffer,
263	 * but we can still be kind to the kernel copyout mechanism.
264	 * By aligning the file offset to a block boundary, we can let
265	 * the kernel use the VM hardware to map pages instead of
266	 * copying bytes laboriously.  Using a block boundary also
267	 * ensures that we only read one block, rather than two.
268	 */
269	curoff = target & ~(fp->_blksize - 1);
270	if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
271		goto dumb;
272	fp->_r = 0;
273	fp->_p = fp->_bf._base;
274	if (HASUB(fp))
275		FREEUB(fp);
276	n = target - curoff;
277	if (n) {
278		if (__srefill(fp) || fp->_r < n)
279			goto dumb;
280		fp->_p += n;
281		fp->_r -= n;
282	}
283	fp->_flags &= ~__SEOF;
284	memset(&fp->_mbstate, 0, sizeof(mbstate_t));
285	return (0);
286
287	/*
288	 * We get here if we cannot optimise the seek ... just
289	 * do it.  Allow the seek function to change fp->_bf._base.
290	 */
291dumb:
292	if (__sflush(fp) ||
293	    (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
294		return (-1);
295	if (ltest && ret > LONG_MAX) {
296		fp->_flags |= __SERR;
297		errno = EOVERFLOW;
298		return (-1);
299	}
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->_mbstate, 0, sizeof(mbstate_t));
308	return (0);
309}
310