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
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9 * modification, are permitted provided that the following conditions
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12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
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16 * 4. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
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20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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33 #if defined(LIBC_SCCS) && !defined(lint)
34 static char sccsid[] = "@(#)fseek.c 8.3 (Berkeley) 1/2/94";
35 #endif /* LIBC_SCCS and not lint */
36 #include <sys/cdefs.h>
37 __FBSDID("$FreeBSD$");
39 #include "namespace.h"
40 #include <sys/types.h>
47 #include "un-namespace.h"
49 #include "libc_private.h"
51 #define POS_ERR (-(fpos_t)1)
54 fseek(fp, offset, whence)
62 /* make sure stdio is set up */
67 ret = _fseeko(fp, (off_t)offset, whence, 1);
75 fseeko(fp, offset, whence)
83 /* make sure stdio is set up */
88 ret = _fseeko(fp, offset, whence, 0);
96 * Seek the given file to the given offset.
97 * `Whence' must be one of the three SEEK_* macros.
100 _fseeko(fp, offset, whence, ltest)
106 fpos_t (*seekfn)(void *, fpos_t, int);
107 fpos_t target, curoff, ret;
113 * Have to be able to seek.
115 if ((seekfn = fp->_seek) == NULL) {
116 errno = ESPIPE; /* historic practice */
121 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
122 * After this, whence is either SEEK_SET or SEEK_END.
128 * In order to seek relative to the current stream offset,
129 * we have to first find the current stream offset via
130 * ftell (see ftell for details).
132 if (_ftello(fp, &curoff))
135 /* Unspecified position because of ungetc() at 0 */
139 if (offset > 0 && curoff > OFF_MAX - offset) {
148 if (ltest && offset > LONG_MAX) {
162 curoff = 0; /* XXX just to keep gcc quiet */
172 * Can only optimise if:
173 * reading (and not reading-and-writing);
174 * not unbuffered; and
175 * this is a `regular' Unix file (and hence seekfn==__sseek).
176 * We must check __NBF first, because it is possible to have __NBF
177 * and __SOPT both set.
179 if (fp->_bf._base == NULL)
181 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
183 if ((fp->_flags & __SOPT) == 0) {
184 if (seekfn != __sseek ||
185 fp->_file < 0 || _fstat(fp->_file, &st) ||
186 (st.st_mode & S_IFMT) != S_IFREG) {
187 fp->_flags |= __SNPT;
190 fp->_blksize = st.st_blksize;
191 fp->_flags |= __SOPT;
195 * We are reading; we can try to optimise.
196 * Figure out where we are going and where we are now.
198 if (whence == SEEK_SET)
201 if (_fstat(fp->_file, &st))
203 if (offset > 0 && st.st_size > OFF_MAX - offset) {
207 target = st.st_size + offset;
208 if ((off_t)target < 0) {
212 if (ltest && (off_t)target > LONG_MAX) {
218 if (!havepos && _ftello(fp, &curoff))
222 * (If the buffer was modified, we have to
223 * skip this; see fgetln.c.)
225 if (fp->_flags & __SMOD)
229 * Compute the number of bytes in the input buffer (pretending
230 * that any ungetc() input has been discarded). Adjust current
231 * offset backwards by this count so that it represents the
232 * file offset for the first byte in the current input buffer.
235 curoff += fp->_r; /* kill off ungetc */
236 n = fp->_up - fp->_bf._base;
240 n = fp->_p - fp->_bf._base;
246 * If the target offset is within the current buffer,
247 * simply adjust the pointers, clear EOF, undo ungetc(),
250 if (target >= curoff && target < curoff + n) {
251 size_t o = target - curoff;
253 fp->_p = fp->_bf._base + o;
257 fp->_flags &= ~__SEOF;
258 memset(&fp->_mbstate, 0, sizeof(mbstate_t));
264 * The place we want to get to is not within the current buffer,
265 * but we can still be kind to the kernel copyout mechanism.
266 * By aligning the file offset to a block boundary, we can let
267 * the kernel use the VM hardware to map pages instead of
268 * copying bytes laboriously. Using a block boundary also
269 * ensures that we only read one block, rather than two.
271 curoff = target & ~(fp->_blksize - 1);
272 if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
275 fp->_p = fp->_bf._base;
280 if (__srefill(fp) || fp->_r < n)
285 fp->_flags &= ~__SEOF;
286 memset(&fp->_mbstate, 0, sizeof(mbstate_t));
290 * We get here if we cannot optimise the seek ... just
291 * do it. Allow the seek function to change fp->_bf._base.
295 (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
297 if (ltest && ret > LONG_MAX) {
298 fp->_flags |= __SERR;
302 /* success: clear EOF indicator and discard ungetc() data */
305 fp->_p = fp->_bf._base;
307 /* fp->_w = 0; */ /* unnecessary (I think...) */
308 fp->_flags &= ~__SEOF;
309 memset(&fp->_mbstate, 0, sizeof(mbstate_t));