2 * Copyright (c) 1990, 1993
3 * The Regents of the University of California. All rights reserved.
5 * This code is derived from software contributed to Berkeley by
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
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.
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
36 * @(#)fseek.c 8.3 (Berkeley) 1/2/94
37 * $FreeBSD: src/lib/libc/stdio/fseek.c,v 1.9.2.1 2001/03/05 10:56:58 obrien Exp $
38 * $DragonFly: src/lib/libc/stdio/fseek.c,v 1.7 2005/05/09 12:43:40 davidxu Exp $
41 #include "namespace.h"
42 #include <sys/types.h>
48 #include "un-namespace.h"
50 #include "libc_private.h"
52 #define POS_ERR (-(fpos_t)1)
55 fseek(FILE *fp, long offset, int whence)
57 return (fseeko(fp, offset, whence));
61 fseeko(fp, offset, whence)
68 /* make sure stdio is set up */
73 ret = _fseeko(fp, offset, whence);
79 * Seek the given file to the given offset.
80 * `Whence' must be one of the three SEEK_* macros.
83 _fseeko(FILE *fp, off_t offset, int whence)
85 fpos_t (*seekfn) (void *, fpos_t, int);
86 fpos_t target, curoff;
92 * Have to be able to seek.
94 if ((seekfn = fp->_seek) == NULL) {
95 errno = ESPIPE; /* historic practice */
100 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
101 * After this, whence is either SEEK_SET or SEEK_END.
107 * In order to seek relative to the current stream offset,
108 * we have to first find the current stream offset a la
109 * ftell (see ftell for details).
111 if (fp->_flags & __SOFF)
112 curoff = fp->_offset;
114 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
119 if (fp->_flags & __SRD) {
123 } else if (fp->_flags & __SWR && fp->_p != NULL)
124 curoff += fp->_p - fp->_bf._base;
133 curoff = 0; /* XXX just to keep gcc quiet */
143 * Can only optimise if:
144 * reading (and not reading-and-writing);
145 * not unbuffered; and
146 * this is a `regular' Unix file (and hence seekfn==__sseek).
147 * We must check __NBF first, because it is possible to have __NBF
148 * and __SOPT both set.
150 if (fp->_bf._base == NULL)
152 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
154 if ((fp->_flags & __SOPT) == 0) {
155 if (seekfn != __sseek ||
156 fp->_file < 0 || _fstat(fp->_file, &st) ||
157 (st.st_mode & S_IFMT) != S_IFREG) {
158 fp->_flags |= __SNPT;
161 fp->_blksize = st.st_blksize;
162 fp->_flags |= __SOPT;
166 * We are reading; we can try to optimise.
167 * Figure out where we are going and where we are now.
169 if (whence == SEEK_SET)
172 if (_fstat(fp->_file, &st))
174 target = st.st_size + offset;
178 if (fp->_flags & __SOFF)
179 curoff = fp->_offset;
181 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
182 if (curoff == POS_ERR)
191 * Compute the number of bytes in the input buffer (pretending
192 * that any ungetc() input has been discarded). Adjust current
193 * offset backwards by this count so that it represents the
194 * file offset for the first byte in the current input buffer.
197 curoff += fp->_r; /* kill off ungetc */
198 n = fp->_extra->_up - fp->_bf._base;
202 n = fp->_p - fp->_bf._base;
208 * If the target offset is within the current buffer,
209 * simply adjust the pointers, clear EOF, undo ungetc(),
210 * and return. (If the buffer was modified, we have to
211 * skip this; see fgetln.c.)
213 if ((fp->_flags & __SMOD) == 0 &&
214 target >= curoff && target < curoff + n) {
215 int o = target - curoff;
217 fp->_p = fp->_bf._base + o;
221 fp->_flags &= ~__SEOF;
226 * The place we want to get to is not within the current buffer,
227 * but we can still be kind to the kernel copyout mechanism.
228 * By aligning the file offset to a block boundary, we can let
229 * the kernel use the VM hardware to map pages instead of
230 * copying bytes laboriously. Using a block boundary also
231 * ensures that we only read one block, rather than two.
233 curoff = target & ~(fp->_blksize - 1);
234 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
237 fp->_p = fp->_bf._base;
240 fp->_flags &= ~__SEOF;
243 if (__srefill(fp) || fp->_r < n)
251 * We get here if we cannot optimise the seek ... just
252 * do it. Allow the seek function to change fp->_bf._base.
256 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
259 /* success: clear EOF indicator and discard ungetc() data */
262 fp->_p = fp->_bf._base;
264 /* fp->_w = 0; */ /* unnecessary (I think...) */
265 fp->_flags &= ~__SEOF;