1/*	$NetBSD: fseeko.c,v 1.14 2017/01/10 17:44:28 christos Exp $	*/
2
3/*-
4 * Copyright (c) 1990, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Chris Torek.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#include <sys/cdefs.h>
36#if defined(LIBC_SCCS) && !defined(lint)
37__RCSID("$NetBSD: fseeko.c,v 1.14 2017/01/10 17:44:28 christos Exp $");
38#endif /* LIBC_SCCS and not lint */
39
40#include "namespace.h"
41#include <sys/types.h>
42#include <sys/stat.h>
43
44#include <assert.h>
45#include <errno.h>
46#include <fcntl.h>
47#include <stdio.h>
48#include <stdlib.h>
49#include "reentrant.h"
50#include "local.h"
51
52#ifdef __weak_alias
53__weak_alias(fseeko, _fseeko)
54#endif
55
56#define	POS_ERR	((off_t)-1)
57
58/*
59 * Seek the given file to the given offset.
60 * `Whence' must be one of the three SEEK_* macros.
61 */
62int
63fseeko(FILE *fp, off_t offset, int whence)
64{
65	off_t (*seekfn)(void *, off_t, int);
66	off_t target, curoff;
67	size_t n;
68	struct stat st;
69	int havepos;
70
71	_DIAGASSERT(fp != NULL);
72
73	/* make sure stdio is set up */
74	if (!__sdidinit)
75		__sinit();
76
77	FLOCKFILE(fp);
78
79	/*
80	 * Have to be able to seek.
81	 */
82	if ((seekfn = fp->_seek) == NULL) {
83		errno = ESPIPE;			/* historic practice */
84		FUNLOCKFILE(fp);
85		return -1;
86	}
87
88	/*
89	 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
90	 * After this, whence is either SEEK_SET or SEEK_END.
91	 */
92	switch (whence) {
93
94	case SEEK_CUR:
95		/*
96		 * In order to seek relative to the current stream offset,
97		 * we have to first find the current stream offset a la
98		 * ftell (see ftell for details).
99		 */
100		(void)__sflush(fp); /* may adjust seek offset on append stream */
101		if (fp->_flags & __SOFF)
102			curoff = fp->_offset;
103		else {
104			curoff = (*seekfn)(fp->_cookie, (off_t)0, SEEK_CUR);
105			if (curoff == POS_ERR) {
106				FUNLOCKFILE(fp);
107				return -1;
108			}
109		}
110		if (fp->_flags & __SRD) {
111			curoff -= fp->_r;
112			if (HASUB(fp))
113				curoff -= fp->_ur;
114		} else if (fp->_flags & __SWR && fp->_p != NULL)
115			curoff += fp->_p - fp->_bf._base;
116
117		offset += curoff;
118		if (offset < 0) {
119			errno = EINVAL;
120			FUNLOCKFILE(fp);
121			return -1;
122		}
123		whence = SEEK_SET;
124		havepos = 1;
125		break;
126
127	case SEEK_SET:
128		if (offset < 0) {
129			errno = EINVAL;
130			FUNLOCKFILE(fp);
131			return -1;
132		}
133		/*FALLTHROUGH*/
134	case SEEK_END:
135		curoff = 0;		/* XXX just to keep gcc quiet */
136		havepos = 0;
137		break;
138
139	default:
140		errno = EINVAL;
141		FUNLOCKFILE(fp);
142		return -1;
143	}
144
145	/*
146	 * Can only optimise if:
147	 *	reading (and not reading-and-writing);
148	 *	not unbuffered; and
149	 *	this is a `regular' Unix file (and hence seekfn==__sseek).
150	 * We must check __NBF first, because it is possible to have __NBF
151	 * and __SOPT both set.
152	 */
153	if (fp->_bf._base == NULL)
154		__smakebuf(fp);
155	if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
156		goto dumb;
157	if ((fp->_flags & __SOPT) == 0) {
158		if (seekfn != __sseek ||
159		    __sfileno(fp) == -1 || fstat(__sfileno(fp), &st) ||
160		    !S_ISREG(st.st_mode)) {
161			fp->_flags |= __SNPT;
162			goto dumb;
163		}
164		fp->_blksize = st.st_blksize;
165		fp->_flags |= __SOPT;
166	}
167
168	/*
169	 * We are reading; we can try to optimise.
170	 * Figure out where we are going and where we are now.
171	 */
172	if (whence == SEEK_SET)
173		target = offset;
174	else {
175		if (fstat(__sfileno(fp), &st))
176			goto dumb;
177		target = st.st_size + offset;
178	}
179
180	if (!havepos) {
181		if (fp->_flags & __SOFF)
182			curoff = fp->_offset;
183		else {
184			curoff = (*seekfn)(fp->_cookie, (off_t)0, SEEK_CUR);
185			if (curoff == POS_ERR)
186				goto dumb;
187		}
188		curoff -= fp->_r;
189		if (HASUB(fp))
190			curoff -= fp->_ur;
191	}
192
193	/*
194	 * Compute the number of bytes in the input buffer (pretending
195	 * that any ungetc() input has been discarded).  Adjust current
196	 * offset backwards by this count so that it represents the
197	 * file offset for the first byte in the current input buffer.
198	 */
199	if (HASUB(fp)) {
200		curoff += fp->_r;	/* kill off ungetc */
201		n = fp->_up - fp->_bf._base;
202		curoff -= n;
203		n += fp->_ur;
204	} else {
205		n = fp->_p - fp->_bf._base;
206		curoff -= n;
207		n += fp->_r;
208	}
209
210	/*
211	 * If the target offset is within the current buffer,
212	 * simply adjust the pointers, clear EOF, undo ungetc(),
213	 * and return.  (If the buffer was modified, we have to
214	 * skip this; see fgetln.c.)
215	 */
216	if ((fp->_flags & __SMOD) == 0 &&
217	    target >= curoff && target < curoff + (off_t)n) {
218		int o = (int)(target - curoff);
219
220		fp->_p = fp->_bf._base + o;
221		_DIAGASSERT(__type_fit(int, n - o));
222		fp->_r = (int)(n - o);
223		if (HASUB(fp))
224			FREEUB(fp);
225		fp->_flags &= ~__SEOF;
226		FUNLOCKFILE(fp);
227		return 0;
228	}
229
230	/*
231	 * The place we want to get to is not within the current buffer,
232	 * but we can still be kind to the kernel copyout mechanism.
233	 * By aligning the file offset to a block boundary, we can let
234	 * the kernel use the VM hardware to map pages instead of
235	 * copying bytes laboriously.  Using a block boundary also
236	 * ensures that we only read one block, rather than two.
237	 */
238	curoff = target & ~(fp->_blksize - 1);
239	if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
240		goto dumb;
241	fp->_r = 0;
242 	fp->_p = fp->_bf._base;
243	if (HASUB(fp))
244		FREEUB(fp);
245	fp->_flags &= ~__SEOF;
246	n = (int)(target - curoff);
247	if (n) {
248		if (__srefill(fp) || (size_t)fp->_r < n)
249			goto dumb;
250		fp->_p += n;
251		_DIAGASSERT(__type_fit(int, fp->_r - n));
252		fp->_r -= (int)n;
253	}
254	FUNLOCKFILE(fp);
255	return 0;
256
257	/*
258	 * We get here if we cannot optimise the seek ... just
259	 * do it.  Allow the seek function to change fp->_bf._base.
260	 */
261dumb:
262	if (__sflush(fp) ||
263	    (*seekfn)(fp->_cookie, offset, whence) == POS_ERR) {
264		FUNLOCKFILE(fp);
265		return -1;
266	}
267	/* success: clear EOF indicator and discard ungetc() data */
268	if (HASUB(fp))
269		FREEUB(fp);
270	fp->_p = fp->_bf._base;
271	fp->_r = 0;
272	/* fp->_w = 0; */	/* unnecessary (I think...) */
273	fp->_flags &= ~__SEOF;
274	FUNLOCKFILE(fp);
275	return 0;
276}
277