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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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(FILE *fp, long offset, int whence)
59 /* make sure stdio is set up */
64 ret = _fseeko(fp, (off_t)offset, whence, 1);
72 fseeko(FILE *fp, off_t offset, int whence)
77 /* make sure stdio is set up */
82 ret = _fseeko(fp, offset, whence, 0);
90 * Seek the given file to the given offset.
91 * `Whence' must be one of the three SEEK_* macros.
94 _fseeko(FILE *fp, off_t offset, int whence, int ltest)
96 fpos_t (*seekfn)(void *, fpos_t, int);
97 fpos_t target, curoff, ret;
103 * Have to be able to seek.
105 if ((seekfn = fp->_seek) == NULL) {
106 errno = ESPIPE; /* historic practice */
111 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
112 * After this, whence is either SEEK_SET or SEEK_END.
118 * In order to seek relative to the current stream offset,
119 * we have to first find the current stream offset via
120 * ftell (see ftell for details).
122 if (_ftello(fp, &curoff))
125 /* Unspecified position because of ungetc() at 0 */
129 if (offset > 0 && curoff > OFF_MAX - offset) {
138 if (ltest && offset > LONG_MAX) {
152 curoff = 0; /* XXX just to keep gcc quiet */
162 * Can only optimise if:
163 * reading (and not reading-and-writing);
164 * not unbuffered; and
165 * this is a `regular' Unix file (and hence seekfn==__sseek).
166 * We must check __NBF first, because it is possible to have __NBF
167 * and __SOPT both set.
169 if (fp->_bf._base == NULL)
171 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
173 if ((fp->_flags & __SOPT) == 0) {
174 if (seekfn != __sseek ||
175 fp->_file < 0 || _fstat(fp->_file, &st) ||
176 (st.st_mode & S_IFMT) != S_IFREG) {
177 fp->_flags |= __SNPT;
180 fp->_blksize = st.st_blksize;
181 fp->_flags |= __SOPT;
185 * We are reading; we can try to optimise.
186 * Figure out where we are going and where we are now.
188 if (whence == SEEK_SET)
191 if (_fstat(fp->_file, &st))
193 if (offset > 0 && st.st_size > OFF_MAX - offset) {
197 target = st.st_size + offset;
198 if ((off_t)target < 0) {
202 if (ltest && (off_t)target > LONG_MAX) {
208 if (!havepos && _ftello(fp, &curoff))
212 * (If the buffer was modified, we have to
213 * skip this; see fgetln.c.)
215 if (fp->_flags & __SMOD)
219 * Compute the number of bytes in the input buffer (pretending
220 * that any ungetc() input has been discarded). Adjust current
221 * offset backwards by this count so that it represents the
222 * file offset for the first byte in the current input buffer.
225 curoff += fp->_r; /* kill off ungetc */
226 n = fp->_up - fp->_bf._base;
230 n = fp->_p - fp->_bf._base;
236 * If the target offset is within the current buffer,
237 * simply adjust the pointers, clear EOF, undo ungetc(),
240 if (target >= curoff && target < curoff + n) {
241 size_t o = target - curoff;
243 fp->_p = fp->_bf._base + o;
247 fp->_flags &= ~__SEOF;
248 memset(&fp->_mbstate, 0, sizeof(mbstate_t));
254 * The place we want to get to is not within the current buffer,
255 * but we can still be kind to the kernel copyout mechanism.
256 * By aligning the file offset to a block boundary, we can let
257 * the kernel use the VM hardware to map pages instead of
258 * copying bytes laboriously. Using a block boundary also
259 * ensures that we only read one block, rather than two.
261 curoff = target & ~(fp->_blksize - 1);
262 if (_sseek(fp, curoff, SEEK_SET) == POS_ERR)
265 fp->_p = fp->_bf._base;
270 if (__srefill(fp) || fp->_r < n)
275 fp->_flags &= ~__SEOF;
276 memset(&fp->_mbstate, 0, sizeof(mbstate_t));
280 * We get here if we cannot optimise the seek ... just
281 * do it. Allow the seek function to change fp->_bf._base.
285 (ret = _sseek(fp, (fpos_t)offset, whence)) == POS_ERR)
287 if (ltest && ret > LONG_MAX) {
288 fp->_flags |= __SERR;
292 /* success: clear EOF indicator and discard ungetc() data */
295 fp->_p = fp->_bf._base;
297 /* fp->_w = 0; */ /* unnecessary (I think...) */
298 fp->_flags &= ~__SEOF;
299 memset(&fp->_mbstate, 0, sizeof(mbstate_t));