Subversion Repositories shark

Rev

Rev 2 | Details | Compare with Previous | Last modification | View Log | RSS feed

Rev Author Line No. Line
2 pj 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
                "$\Id: fseek.c,v 1.4 1996/06/22 10:33:22 jraynard Exp $";
43
#endif /* LIBC_SCCS and not lint */
44
 
45
#include <sys/types.h>
46
#include <sys/stat.h>
47
#include <fcntl.h>
48
#include <stdio.h>
49
#include <stdlib.h>
50
#include <errno.h>
51
#include "local.h"
52
#ifdef _THREAD_SAFE
53
#include <pthread.h>
54
#include "pthread_private.h"
55
#endif
56
 
57
#define POS_ERR (-(fpos_t)1)
58
 
59
/*
60
 * Seek the given file to the given offset.
61
 * `Whence' must be one of the three SEEK_* macros.
62
 */
63
int
64
fseek(fp, offset, whence)
65
        register FILE *fp;
66
        long offset;
67
        int whence;
68
{
69
        register fpos_t (*seekfn) __P((void *, fpos_t, int));
70
        fpos_t target, curoff;
71
        size_t n;
72
        struct stat st;
73
        int havepos;
74
 
75
        /* make sure stdio is set up */
76
        if (!__sdidinit)
77
                __sinit();
78
 
79
#ifdef _THREAD_SAFE
80
        _thread_flockfile(fp,__FILE__,__LINE__);
81
#endif
82
        /*
83
         * Have to be able to seek.
84
         */
85
        if ((seekfn = fp->_seek) == NULL) {
86
                errno = ESPIPE;                 /* historic practice */
87
                return (EOF);
88
        }
89
 
90
        /*
91
         * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
92
         * After this, whence is either SEEK_SET or SEEK_END.
93
         */
94
        switch (whence) {
95
 
96
        case SEEK_CUR:
97
                /*
98
                 * In order to seek relative to the current stream offset,
99
                 * we have to first find the current stream offset a la
100
                 * ftell (see ftell for details).
101
                 */
102
                if (fp->_flags & __SOFF)
103
                        curoff = fp->_offset;
104
                else {
105
                        curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
106
                        if (curoff == -1) {
107
#ifdef _THREAD_SAFE
108
                                _thread_funlockfile(fp);
109
#endif
110
                                return (EOF);
111
                        }
112
                }
113
                if (fp->_flags & __SRD) {
114
                        curoff -= fp->_r;
115
                        if (HASUB(fp))
116
                                curoff -= fp->_ur;
117
                } else if (fp->_flags & __SWR && fp->_p != NULL)
118
                        curoff += fp->_p - fp->_bf._base;
119
 
120
                offset += curoff;
121
                whence = SEEK_SET;
122
                havepos = 1;
123
                break;
124
 
125
        case SEEK_SET:
126
        case SEEK_END:
127
                curoff = 0;             /* XXX just to keep gcc quiet */
128
                havepos = 0;
129
                break;
130
 
131
        default:
132
                errno = EINVAL;
133
#ifdef _THREAD_SAFE
134
                _thread_funlockfile(fp);
135
#endif
136
                return (EOF);
137
        }
138
 
139
        /*
140
         * Can only optimise if:
141
         *      reading (and not reading-and-writing);
142
         *      not unbuffered; and
143
         *      this is a `regular' Unix file (and hence seekfn==__sseek).
144
         * We must check __NBF first, because it is possible to have __NBF
145
         * and __SOPT both set.
146
         */
147
        if (fp->_bf._base == NULL)
148
                __smakebuf(fp);
149
        if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
150
                goto dumb;
151
        if ((fp->_flags & __SOPT) == 0) {
152
                if (seekfn != __sseek ||
153
                    fp->_file < 0 || fstat(fp->_file, &st) ||
154
                    (st.st_mode & S_IFMT) != S_IFREG) {
155
                        fp->_flags |= __SNPT;
156
                        goto dumb;
157
                }
158
                fp->_blksize = st.st_blksize;
159
                fp->_flags |= __SOPT;
160
        }
161
 
162
        /*
163
         * We are reading; we can try to optimise.
164
         * Figure out where we are going and where we are now.
165
         */
166
        if (whence == SEEK_SET)
167
                target = offset;
168
        else {
169
                if (fstat(fp->_file, &st))
170
                        goto dumb;
171
                target = st.st_size + offset;
172
        }
173
 
174
        if (!havepos) {
175
                if (fp->_flags & __SOFF)
176
                        curoff = fp->_offset;
177
                else {
178
                        curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
179
                        if (curoff == POS_ERR)
180
                                goto dumb;
181
                }
182
                curoff -= fp->_r;
183
                if (HASUB(fp))
184
                        curoff -= fp->_ur;
185
        }
186
 
187
        /*
188
         * Compute the number of bytes in the input buffer (pretending
189
         * that any ungetc() input has been discarded).  Adjust current
190
         * offset backwards by this count so that it represents the
191
         * file offset for the first byte in the current input buffer.
192
         */
193
        if (HASUB(fp)) {
194
                curoff += fp->_r;       /* kill off ungetc */
195
                n = fp->_up - fp->_bf._base;
196
                curoff -= n;
197
                n += fp->_ur;
198
        } else {
199
                n = fp->_p - fp->_bf._base;
200
                curoff -= n;
201
                n += fp->_r;
202
        }
203
 
204
        /*
205
         * If the target offset is within the current buffer,
206
         * simply adjust the pointers, clear EOF, undo ungetc(),
207
         * and return.  (If the buffer was modified, we have to
208
         * skip this; see fgetln.c.)
209
         */
210
        if ((fp->_flags & __SMOD) == 0 &&
211
            target >= curoff && target < curoff + n) {
212
                register int o = target - curoff;
213
 
214
                fp->_p = fp->_bf._base + o;
215
                fp->_r = n - o;
216
                if (HASUB(fp))
217
                        FREEUB(fp);
218
                fp->_flags &= ~__SEOF;
219
#ifdef _THREAD_SAFE
220
                _thread_funlockfile(fp);
221
#endif
222
                return (0);
223
        }
224
 
225
        /*
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.
232
         */
233
        curoff = target & ~(fp->_blksize - 1);
234
        if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
235
                goto dumb;
236
        fp->_r = 0;
237
        fp->_p = fp->_bf._base;
238
        if (HASUB(fp))
239
                FREEUB(fp);
240
        fp->_flags &= ~__SEOF;
241
        n = target - curoff;
242
        if (n) {
243
                if (__srefill(fp) || fp->_r < n)
244
                        goto dumb;
245
                fp->_p += n;
246
                fp->_r -= n;
247
        }
248
#ifdef _THREAD_SAFE
249
        _thread_funlockfile(fp);
250
#endif
251
        return (0);
252
 
253
        /*
254
         * We get here if we cannot optimise the seek ... just
255
         * do it.  Allow the seek function to change fp->_bf._base.
256
         */
257
dumb:
258
        if (__sflush(fp) ||
259
            (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
260
#ifdef _THREAD_SAFE
261
                _thread_funlockfile(fp);
262
#endif
263
                return (EOF);
264
        }
265
        /* success: clear EOF indicator and discard ungetc() data */
266
        if (HASUB(fp))
267
                FREEUB(fp);
268
        fp->_p = fp->_bf._base;
269
        fp->_r = 0;
270
        /* fp->_w = 0; */       /* unnecessary (I think...) */
271
        fp->_flags &= ~__SEOF;
272
#ifdef _THREAD_SAFE
273
        _thread_funlockfile(fp);
274
#endif
275
        return (0);
276
}