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1 | /*- |
2 | * Copyright (c) 1990 The Regents of the University of California. | |
3 | * All rights reserved. | |
4 | * | |
5 | * This code is derived from software contributed to Berkeley by | |
6 | * Chris Torek. | |
7 | * | |
8 | * %sccs.include.redist.c% | |
9 | */ | |
10 | ||
2ce81398 | 11 | #if defined(LIBC_SCCS) && !defined(lint) |
cb631443 | 12 | static char sccsid[] = "@(#)fseek.c 5.7 (Berkeley) %G%"; |
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13 | #endif /* LIBC_SCCS and not lint */ |
14 | ||
15 | #include <sys/types.h> | |
411867e7 | 16 | #include <sys/stat.h> |
cb631443 | 17 | #include <fcntl.h> |
411867e7 | 18 | #include <stdio.h> |
cb631443 | 19 | #include <stdlib.h> |
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20 | #include <errno.h> |
21 | #include "local.h" | |
22 | ||
23 | #define POS_ERR (-(fpos_t)1) | |
b8f253e8 | 24 | |
a9e59a21 | 25 | /* |
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26 | * Seek the given file to the given offset. |
27 | * `Whence' must be one of the three SEEK_* macros. | |
a9e59a21 | 28 | */ |
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29 | fseek(fp, offset, whence) |
30 | register FILE *fp; | |
31 | long offset; | |
32 | int whence; | |
33 | { | |
34 | #if __STDC__ | |
d25ccb19 | 35 | register fpos_t (*seekfn)(void *, fpos_t, int); |
411867e7 KB |
36 | #else |
37 | register fpos_t (*seekfn)(); | |
38 | #endif | |
39 | fpos_t target, curoff; | |
40 | size_t n; | |
41 | struct stat st; | |
42 | int havepos; | |
43 | ||
44 | /* make sure stdio is set up */ | |
45 | if (!__sdidinit) | |
46 | __sinit(); | |
a9e59a21 | 47 | |
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48 | /* |
49 | * Have to be able to seek. | |
50 | */ | |
51 | if ((seekfn = fp->_seek) == NULL) { | |
52 | errno = ESPIPE; /* historic practice */ | |
53 | return (EOF); | |
54 | } | |
a9e59a21 | 55 | |
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56 | /* |
57 | * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. | |
58 | * After this, whence is either SEEK_SET or SEEK_END. | |
59 | */ | |
60 | switch (whence) { | |
a9e59a21 | 61 | |
411867e7 KB |
62 | case SEEK_CUR: |
63 | /* | |
64 | * In order to seek relative to the current stream offset, | |
65 | * we have to first find the current stream offset a la | |
66 | * ftell (see ftell for details). | |
67 | */ | |
68 | if (fp->_flags & __SOFF) | |
69 | curoff = fp->_offset; | |
70 | else { | |
71 | curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); | |
72 | if (curoff == -1L) | |
73 | return (EOF); | |
74 | } | |
75 | if (fp->_flags & __SRD) { | |
76 | curoff -= fp->_r; | |
77 | if (HASUB(fp)) | |
78 | curoff -= fp->_ur; | |
79 | } else if (fp->_flags & __SWR && fp->_p != NULL) | |
80 | curoff += fp->_p - fp->_bf._base; | |
81 | ||
82 | offset += curoff; | |
83 | whence = SEEK_SET; | |
84 | havepos = 1; | |
85 | break; | |
86 | ||
87 | case SEEK_SET: | |
88 | case SEEK_END: | |
d25ccb19 | 89 | curoff = 0; /* XXX just to keep gcc quiet */ |
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90 | havepos = 0; |
91 | break; | |
92 | ||
93 | default: | |
94 | errno = EINVAL; | |
95 | return (EOF); | |
96 | } | |
97 | ||
98 | /* | |
99 | * Can only optimise if: | |
100 | * reading (and not reading-and-writing); | |
101 | * not unbuffered; and | |
102 | * this is a `regular' Unix file (and hence seekfn==__sseek). | |
103 | * We must check __NBF first, because it is possible to have __NBF | |
104 | * and __SOPT both set. | |
105 | */ | |
106 | if (fp->_bf._base == NULL) | |
107 | __smakebuf(fp); | |
108 | if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) | |
109 | goto dumb; | |
110 | if ((fp->_flags & __SOPT) == 0) { | |
111 | if (seekfn != __sseek || | |
112 | fp->_file < 0 || fstat(fp->_file, &st) || | |
113 | (st.st_mode & S_IFMT) != S_IFREG) { | |
114 | fp->_flags |= __SNPT; | |
115 | goto dumb; | |
d8af6b8b | 116 | } |
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117 | fp->_blksize = st.st_blksize; |
118 | fp->_flags |= __SOPT; | |
119 | } | |
120 | ||
121 | /* | |
122 | * We are reading; we can try to optimise. | |
123 | * Figure out where we are going and where we are now. | |
124 | */ | |
125 | if (whence == SEEK_SET) | |
126 | target = offset; | |
127 | else { | |
128 | if (fstat(fp->_file, &st)) | |
129 | goto dumb; | |
130 | target = st.st_size + offset; | |
a9e59a21 | 131 | } |
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132 | |
133 | if (!havepos) { | |
134 | if (fp->_flags & __SOFF) | |
135 | curoff = fp->_offset; | |
136 | else { | |
137 | curoff = (*seekfn)(fp->_cookie, 0L, SEEK_CUR); | |
138 | if (curoff == POS_ERR) | |
139 | goto dumb; | |
d8af6b8b | 140 | } |
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141 | curoff -= fp->_r; |
142 | if (HASUB(fp)) | |
143 | curoff -= fp->_ur; | |
144 | } | |
145 | ||
146 | /* | |
147 | * Compute the number of bytes in the input buffer (pretending | |
148 | * that any ungetc() input has been discarded). Adjust current | |
149 | * offset backwards by this count so that it represents the | |
150 | * file offset for the first byte in the current input buffer. | |
151 | */ | |
152 | if (HASUB(fp)) { | |
153 | n = fp->_up - fp->_bf._base; | |
154 | curoff -= n; | |
155 | n += fp->_ur; | |
156 | } else { | |
157 | n = fp->_p - fp->_bf._base; | |
158 | curoff -= n; | |
159 | n += fp->_r; | |
160 | } | |
161 | ||
162 | /* | |
163 | * If the target offset is within the current buffer, | |
164 | * simply adjust the pointers, clear EOF, undo ungetc(), | |
165 | * and return. (If the buffer was modified, we have to | |
166 | * skip this; see fgetline.c.) | |
167 | */ | |
168 | if ((fp->_flags & __SMOD) == 0 && | |
169 | target >= curoff && target < curoff + n) { | |
170 | register int o = target - curoff; | |
171 | ||
172 | fp->_p = fp->_bf._base + o; | |
173 | fp->_r = n - o; | |
174 | if (HASUB(fp)) | |
175 | FREEUB(fp); | |
176 | fp->_flags &= ~__SEOF; | |
177 | return (0); | |
178 | } | |
179 | ||
180 | /* | |
181 | * The place we want to get to is not within the current buffer, | |
182 | * but we can still be kind to the kernel copyout mechanism. | |
183 | * By aligning the file offset to a block boundary, we can let | |
184 | * the kernel use the VM hardware to map pages instead of | |
185 | * copying bytes laboriously. Using a block boundary also | |
186 | * ensures that we only read one block, rather than two. | |
187 | */ | |
188 | curoff = target & ~(fp->_blksize - 1); | |
189 | if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) | |
190 | goto dumb; | |
191 | fp->_r = 0; | |
192 | if (HASUB(fp)) | |
193 | FREEUB(fp); | |
194 | fp->_flags &= ~__SEOF; | |
195 | n = target - curoff; | |
196 | if (n) { | |
197 | if (__srefill(fp) || fp->_r < n) | |
198 | goto dumb; | |
199 | fp->_p += n; | |
200 | fp->_r -= n; | |
201 | } | |
202 | return (0); | |
203 | ||
204 | /* | |
205 | * We get here if we cannot optimise the seek ... just | |
206 | * do it. Allow the seek function to change fp->_bf._base. | |
207 | */ | |
208 | dumb: | |
5b2b97c1 | 209 | if (__sflush(fp) || |
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210 | (*seekfn)(fp->_cookie, offset, whence) == POS_ERR) { |
211 | return (EOF); | |
a9e59a21 | 212 | } |
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213 | /* success: clear EOF indicator and discard ungetc() data */ |
214 | if (HASUB(fp)) | |
215 | FREEUB(fp); | |
216 | fp->_p = fp->_bf._base; | |
217 | fp->_r = 0; | |
218 | /* fp->_w = 0; */ /* unnecessary (I think...) */ | |
219 | fp->_flags &= ~__SEOF; | |
220 | return (0); | |
a9e59a21 | 221 | } |