1 /* $OpenBSD: fseek.c,v 1.11 2012/05/21 22:24:19 matthew Exp $ */
2 /*-
3 * Copyright (c) 1990, 1993
4 * The Regents of the University of California. All rights reserved.
5 *
6 * This code is derived from software contributed to Berkeley by
7 * Chris Torek.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 #include <sys/types.h>
35 #include <sys/stat.h>
36 #include <fcntl.h>
37 #include <stdio.h>
38 #include <stdlib.h>
39 #include <errno.h>
40 #include "local.h"
41
42 #define POS_ERR (-(fpos_t)1)
43
44 /*
45 * Seek the given file to the given offset.
46 * `Whence' must be one of the three SEEK_* macros.
47 */
48 int
fseeko(FILE * fp,off_t offset,int whence)49 fseeko(FILE *fp, off_t offset, int whence)
50 {
51 fpos_t (*seekfn)(void *, fpos_t, int);
52 fpos_t target, curoff;
53 size_t n;
54 struct stat st;
55 int havepos;
56
57 /* make sure stdio is set up */
58 if (!__sdidinit)
59 __sinit();
60
61 /*
62 * Have to be able to seek.
63 */
64 if ((seekfn = fp->_seek) == NULL) {
65 errno = ESPIPE; /* historic practice */
66 return (EOF);
67 }
68
69 /*
70 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
71 * After this, whence is either SEEK_SET or SEEK_END.
72 */
73 FLOCKFILE(fp);
74 switch (whence) {
75
76 case SEEK_CUR:
77 /*
78 * In order to seek relative to the current stream offset,
79 * we have to first find the current stream offset a la
80 * ftell (see ftell for details).
81 */
82 __sflush(fp); /* may adjust seek offset on append stream */
83 if (fp->_flags & __SOFF)
84 curoff = fp->_offset;
85 else {
86 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
87 if (curoff == (fpos_t)-1) {
88 FUNLOCKFILE(fp);
89 return (EOF);
90 }
91 }
92 if (fp->_flags & __SRD) {
93 curoff -= fp->_r;
94 if (HASUB(fp))
95 curoff -= fp->_ur;
96 } else if (fp->_flags & __SWR && fp->_p != NULL)
97 curoff += fp->_p - fp->_bf._base;
98
99 offset += curoff;
100 whence = SEEK_SET;
101 havepos = 1;
102 break;
103
104 case SEEK_SET:
105 case SEEK_END:
106 curoff = 0; /* XXX just to keep gcc quiet */
107 havepos = 0;
108 break;
109
110 default:
111 FUNLOCKFILE(fp);
112 errno = EINVAL;
113 return (EOF);
114 }
115
116 /*
117 * Can only optimise if:
118 * reading (and not reading-and-writing);
119 * not unbuffered; and
120 * this is a `regular' Unix file (and hence seekfn==__sseek).
121 * We must check __NBF first, because it is possible to have __NBF
122 * and __SOPT both set.
123 */
124 if (fp->_bf._base == NULL)
125 __smakebuf(fp);
126 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
127 goto dumb;
128 if ((fp->_flags & __SOPT) == 0) {
129 if (seekfn != __sseek ||
130 fp->_file < 0 || fstat(fp->_file, &st) ||
131 (st.st_mode & S_IFMT) != S_IFREG) {
132 fp->_flags |= __SNPT;
133 goto dumb;
134 }
135 fp->_blksize = st.st_blksize;
136 fp->_flags |= __SOPT;
137 }
138
139 /*
140 * We are reading; we can try to optimise.
141 * Figure out where we are going and where we are now.
142 */
143 if (whence == SEEK_SET)
144 target = offset;
145 else {
146 if (fstat(fp->_file, &st))
147 goto dumb;
148 target = st.st_size + offset;
149 }
150
151 if (!havepos) {
152 if (fp->_flags & __SOFF)
153 curoff = fp->_offset;
154 else {
155 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
156 if (curoff == POS_ERR)
157 goto dumb;
158 }
159 curoff -= fp->_r;
160 if (HASUB(fp))
161 curoff -= fp->_ur;
162 }
163
164 /*
165 * Compute the number of bytes in the input buffer (pretending
166 * that any ungetc() input has been discarded). Adjust current
167 * offset backwards by this count so that it represents the
168 * file offset for the first byte in the current input buffer.
169 */
170 if (HASUB(fp)) {
171 curoff += fp->_r; /* kill off ungetc */
172 n = fp->_up - fp->_bf._base;
173 curoff -= n;
174 n += fp->_ur;
175 } else {
176 n = fp->_p - fp->_bf._base;
177 curoff -= n;
178 n += fp->_r;
179 }
180
181 /*
182 * If the target offset is within the current buffer,
183 * simply adjust the pointers, clear EOF, undo ungetc(),
184 * and return. (If the buffer was modified, we have to
185 * skip this; see fgetln.c.)
186 */
187 if ((fp->_flags & __SMOD) == 0 &&
188 target >= curoff && target < curoff + n) {
189 int o = target - curoff;
190
191 fp->_p = fp->_bf._base + o;
192 fp->_r = n - o;
193 if (HASUB(fp))
194 FREEUB(fp);
195 fp->_flags &= ~__SEOF;
196 FUNLOCKFILE(fp);
197 return (0);
198 }
199
200 /*
201 * The place we want to get to is not within the current buffer,
202 * but we can still be kind to the kernel copyout mechanism.
203 * By aligning the file offset to a block boundary, we can let
204 * the kernel use the VM hardware to map pages instead of
205 * copying bytes laboriously. Using a block boundary also
206 * ensures that we only read one block, rather than two.
207 */
208 curoff = target & ~(fp->_blksize - 1);
209 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
210 goto dumb;
211 fp->_r = 0;
212 fp->_p = fp->_bf._base;
213 if (HASUB(fp))
214 FREEUB(fp);
215 fp->_flags &= ~__SEOF;
216 n = target - curoff;
217 if (n) {
218 if (__srefill(fp) || fp->_r < n)
219 goto dumb;
220 fp->_p += n;
221 fp->_r -= n;
222 }
223 FUNLOCKFILE(fp);
224 return (0);
225
226 /*
227 * We get here if we cannot optimise the seek ... just
228 * do it. Allow the seek function to change fp->_bf._base.
229 */
230 dumb:
231 if (__sflush(fp) ||
232 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
233 FUNLOCKFILE(fp);
234 return (EOF);
235 }
236 /* success: clear EOF indicator and discard ungetc() data */
237 if (HASUB(fp))
238 FREEUB(fp);
239 fp->_p = fp->_bf._base;
240 fp->_r = 0;
241 /* fp->_w = 0; */ /* unnecessary (I think...) */
242 fp->_flags &= ~__SEOF;
243 FUNLOCKFILE(fp);
244 return (0);
245 }
246
247 int
fseek(FILE * fp,long offset,int whence)248 fseek(FILE *fp, long offset, int whence)
249 {
250 return (fseeko(fp, offset, whence));
251 }
252