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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) |
d25ccb19 | 12 | static char sccsid[] = "@(#)fseek.c 5.6 (Berkeley) %G%"; |
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13 | #endif /* LIBC_SCCS and not lint */ |
14 | ||
15 | #include <sys/types.h> | |
16 | #include <sys/file.h> | |
17 | #include <sys/stat.h> | |
18 | #include <stdio.h> | |
19 | #include <errno.h> | |
20 | #include "local.h" | |
21 | ||
22 | #define POS_ERR (-(fpos_t)1) | |
b8f253e8 | 23 | |
a9e59a21 | 24 | /* |
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25 | * Seek the given file to the given offset. |
26 | * `Whence' must be one of the three SEEK_* macros. | |
a9e59a21 | 27 | */ |
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28 | fseek(fp, offset, whence) |
29 | register FILE *fp; | |
30 | long offset; | |
31 | int whence; | |
32 | { | |
33 | #if __STDC__ | |
d25ccb19 | 34 | register fpos_t (*seekfn)(void *, fpos_t, int); |
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35 | #else |
36 | register fpos_t (*seekfn)(); | |
37 | #endif | |
38 | fpos_t target, curoff; | |
39 | size_t n; | |
40 | struct stat st; | |
41 | int havepos; | |
42 | ||
43 | /* make sure stdio is set up */ | |
44 | if (!__sdidinit) | |
45 | __sinit(); | |
a9e59a21 | 46 | |
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47 | /* |
48 | * Have to be able to seek. | |
49 | */ | |
50 | if ((seekfn = fp->_seek) == NULL) { | |
51 | errno = ESPIPE; /* historic practice */ | |
52 | return (EOF); | |
53 | } | |
a9e59a21 | 54 | |
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55 | /* |
56 | * Change any SEEK_CUR to SEEK_SET, and check `whence' argument. | |
57 | * After this, whence is either SEEK_SET or SEEK_END. | |
58 | */ | |
59 | switch (whence) { | |
a9e59a21 | 60 | |
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61 | case SEEK_CUR: |
62 | /* | |
63 | * In order to seek relative to the current stream offset, | |
64 | * we have to first find the current stream offset a la | |
65 | * ftell (see ftell for details). | |
66 | */ | |
67 | if (fp->_flags & __SOFF) | |
68 | curoff = fp->_offset; | |
69 | else { | |
70 | curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR); | |
71 | if (curoff == -1L) | |
72 | return (EOF); | |
73 | } | |
74 | if (fp->_flags & __SRD) { | |
75 | curoff -= fp->_r; | |
76 | if (HASUB(fp)) | |
77 | curoff -= fp->_ur; | |
78 | } else if (fp->_flags & __SWR && fp->_p != NULL) | |
79 | curoff += fp->_p - fp->_bf._base; | |
80 | ||
81 | offset += curoff; | |
82 | whence = SEEK_SET; | |
83 | havepos = 1; | |
84 | break; | |
85 | ||
86 | case SEEK_SET: | |
87 | case SEEK_END: | |
d25ccb19 | 88 | curoff = 0; /* XXX just to keep gcc quiet */ |
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89 | havepos = 0; |
90 | break; | |
91 | ||
92 | default: | |
93 | errno = EINVAL; | |
94 | return (EOF); | |
95 | } | |
96 | ||
97 | /* | |
98 | * Can only optimise if: | |
99 | * reading (and not reading-and-writing); | |
100 | * not unbuffered; and | |
101 | * this is a `regular' Unix file (and hence seekfn==__sseek). | |
102 | * We must check __NBF first, because it is possible to have __NBF | |
103 | * and __SOPT both set. | |
104 | */ | |
105 | if (fp->_bf._base == NULL) | |
106 | __smakebuf(fp); | |
107 | if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT)) | |
108 | goto dumb; | |
109 | if ((fp->_flags & __SOPT) == 0) { | |
110 | if (seekfn != __sseek || | |
111 | fp->_file < 0 || fstat(fp->_file, &st) || | |
112 | (st.st_mode & S_IFMT) != S_IFREG) { | |
113 | fp->_flags |= __SNPT; | |
114 | goto dumb; | |
d8af6b8b | 115 | } |
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116 | fp->_blksize = st.st_blksize; |
117 | fp->_flags |= __SOPT; | |
118 | } | |
119 | ||
120 | /* | |
121 | * We are reading; we can try to optimise. | |
122 | * Figure out where we are going and where we are now. | |
123 | */ | |
124 | if (whence == SEEK_SET) | |
125 | target = offset; | |
126 | else { | |
127 | if (fstat(fp->_file, &st)) | |
128 | goto dumb; | |
129 | target = st.st_size + offset; | |
a9e59a21 | 130 | } |
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131 | |
132 | if (!havepos) { | |
133 | if (fp->_flags & __SOFF) | |
134 | curoff = fp->_offset; | |
135 | else { | |
136 | curoff = (*seekfn)(fp->_cookie, 0L, SEEK_CUR); | |
137 | if (curoff == POS_ERR) | |
138 | goto dumb; | |
d8af6b8b | 139 | } |
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140 | curoff -= fp->_r; |
141 | if (HASUB(fp)) | |
142 | curoff -= fp->_ur; | |
143 | } | |
144 | ||
145 | /* | |
146 | * Compute the number of bytes in the input buffer (pretending | |
147 | * that any ungetc() input has been discarded). Adjust current | |
148 | * offset backwards by this count so that it represents the | |
149 | * file offset for the first byte in the current input buffer. | |
150 | */ | |
151 | if (HASUB(fp)) { | |
152 | n = fp->_up - fp->_bf._base; | |
153 | curoff -= n; | |
154 | n += fp->_ur; | |
155 | } else { | |
156 | n = fp->_p - fp->_bf._base; | |
157 | curoff -= n; | |
158 | n += fp->_r; | |
159 | } | |
160 | ||
161 | /* | |
162 | * If the target offset is within the current buffer, | |
163 | * simply adjust the pointers, clear EOF, undo ungetc(), | |
164 | * and return. (If the buffer was modified, we have to | |
165 | * skip this; see fgetline.c.) | |
166 | */ | |
167 | if ((fp->_flags & __SMOD) == 0 && | |
168 | target >= curoff && target < curoff + n) { | |
169 | register int o = target - curoff; | |
170 | ||
171 | fp->_p = fp->_bf._base + o; | |
172 | fp->_r = n - o; | |
173 | if (HASUB(fp)) | |
174 | FREEUB(fp); | |
175 | fp->_flags &= ~__SEOF; | |
176 | return (0); | |
177 | } | |
178 | ||
179 | /* | |
180 | * The place we want to get to is not within the current buffer, | |
181 | * but we can still be kind to the kernel copyout mechanism. | |
182 | * By aligning the file offset to a block boundary, we can let | |
183 | * the kernel use the VM hardware to map pages instead of | |
184 | * copying bytes laboriously. Using a block boundary also | |
185 | * ensures that we only read one block, rather than two. | |
186 | */ | |
187 | curoff = target & ~(fp->_blksize - 1); | |
188 | if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR) | |
189 | goto dumb; | |
190 | fp->_r = 0; | |
191 | if (HASUB(fp)) | |
192 | FREEUB(fp); | |
193 | fp->_flags &= ~__SEOF; | |
194 | n = target - curoff; | |
195 | if (n) { | |
196 | if (__srefill(fp) || fp->_r < n) | |
197 | goto dumb; | |
198 | fp->_p += n; | |
199 | fp->_r -= n; | |
200 | } | |
201 | return (0); | |
202 | ||
203 | /* | |
204 | * We get here if we cannot optimise the seek ... just | |
205 | * do it. Allow the seek function to change fp->_bf._base. | |
206 | */ | |
207 | dumb: | |
5b2b97c1 | 208 | if (__sflush(fp) || |
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209 | (*seekfn)(fp->_cookie, offset, whence) == POS_ERR) { |
210 | return (EOF); | |
a9e59a21 | 211 | } |
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212 | /* success: clear EOF indicator and discard ungetc() data */ |
213 | if (HASUB(fp)) | |
214 | FREEUB(fp); | |
215 | fp->_p = fp->_bf._base; | |
216 | fp->_r = 0; | |
217 | /* fp->_w = 0; */ /* unnecessary (I think...) */ | |
218 | fp->_flags &= ~__SEOF; | |
219 | return (0); | |
a9e59a21 | 220 | } |