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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17 * must display the following acknowledgement:
18 * This product includes software developed by the University of
19 * California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 * may be used to endorse or promote products derived from this software
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24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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37 #if defined(LIBC_SCCS) && !defined(lint)
39 static char sccsid[] = "@(#)fseek.c 8.3 (Berkeley) 1/2/94";
41 static const char rcsid[] =
42 "$FreeBSD: src/lib/libc/stdio/fseek.c,v 1.9.2.1 2001/03/05 10:56:58 obrien Exp $";
43 #endif /* LIBC_SCCS and not lint */
45 #include <sys/types.h>
52 #include "libc_private.h"
54 #define POS_ERR (-(fpos_t)1)
57 fseek(fp, offset, whence)
62 return (fseeko(fp, offset, whence));
66 * Seek the given file to the given offset.
67 * `Whence' must be one of the three SEEK_* macros.
70 fseeko(fp, offset, whence)
75 register fpos_t (*seekfn) __P((void *, fpos_t, int));
76 fpos_t target, curoff;
81 /* make sure stdio is set up */
87 * Have to be able to seek.
89 if ((seekfn = fp->_seek) == NULL) {
90 errno = ESPIPE; /* historic practice */
96 * Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
97 * After this, whence is either SEEK_SET or SEEK_END.
103 * In order to seek relative to the current stream offset,
104 * we have to first find the current stream offset a la
105 * ftell (see ftell for details).
107 if (fp->_flags & __SOFF)
108 curoff = fp->_offset;
110 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
116 if (fp->_flags & __SRD) {
120 } else if (fp->_flags & __SWR && fp->_p != NULL)
121 curoff += fp->_p - fp->_bf._base;
130 curoff = 0; /* XXX just to keep gcc quiet */
141 * Can only optimise if:
142 * reading (and not reading-and-writing);
143 * not unbuffered; and
144 * this is a `regular' Unix file (and hence seekfn==__sseek).
145 * We must check __NBF first, because it is possible to have __NBF
146 * and __SOPT both set.
148 if (fp->_bf._base == NULL)
150 if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
152 if ((fp->_flags & __SOPT) == 0) {
153 if (seekfn != __sseek ||
154 fp->_file < 0 || fstat(fp->_file, &st) ||
155 (st.st_mode & S_IFMT) != S_IFREG) {
156 fp->_flags |= __SNPT;
159 fp->_blksize = st.st_blksize;
160 fp->_flags |= __SOPT;
164 * We are reading; we can try to optimise.
165 * Figure out where we are going and where we are now.
167 if (whence == SEEK_SET)
170 if (fstat(fp->_file, &st))
172 target = st.st_size + offset;
176 if (fp->_flags & __SOFF)
177 curoff = fp->_offset;
179 curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
180 if (curoff == POS_ERR)
189 * Compute the number of bytes in the input buffer (pretending
190 * that any ungetc() input has been discarded). Adjust current
191 * offset backwards by this count so that it represents the
192 * file offset for the first byte in the current input buffer.
195 curoff += fp->_r; /* kill off ungetc */
196 n = fp->_up - fp->_bf._base;
200 n = fp->_p - fp->_bf._base;
206 * If the target offset is within the current buffer,
207 * simply adjust the pointers, clear EOF, undo ungetc(),
208 * and return. (If the buffer was modified, we have to
209 * skip this; see fgetln.c.)
211 if ((fp->_flags & __SMOD) == 0 &&
212 target >= curoff && target < curoff + n) {
213 register int o = target - curoff;
215 fp->_p = fp->_bf._base + o;
219 fp->_flags &= ~__SEOF;
225 * The place we want to get to is not within the current buffer,
226 * but we can still be kind to the kernel copyout mechanism.
227 * By aligning the file offset to a block boundary, we can let
228 * the kernel use the VM hardware to map pages instead of
229 * copying bytes laboriously. Using a block boundary also
230 * ensures that we only read one block, rather than two.
232 curoff = target & ~(fp->_blksize - 1);
233 if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
236 fp->_p = fp->_bf._base;
239 fp->_flags &= ~__SEOF;
242 if (__srefill(fp) || fp->_r < n)
251 * We get here if we cannot optimise the seek ... just
252 * do it. Allow the seek function to change fp->_bf._base.
256 (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
260 /* success: clear EOF indicator and discard ungetc() data */
263 fp->_p = fp->_bf._base;
265 /* fp->_w = 0; */ /* unnecessary (I think...) */
266 fp->_flags &= ~__SEOF;