250 lines
6.7 KiB
C
250 lines
6.7 KiB
C
/*-
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* Copyright (c) 1990 The Regents of the University of California.
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* All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Chris Torek.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#if defined(LIBC_SCCS) && !defined(lint)
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/*static char *sccsid = "from: @(#)fseek.c 5.7 (Berkeley) 2/24/91";*/
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static char *rcsid = "$Id: fseek.c,v 1.6 1994/01/04 05:38:13 cgd Exp $";
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#endif /* LIBC_SCCS and not lint */
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <errno.h>
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#include "local.h"
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#define POS_ERR (-(fpos_t)1)
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/*
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* Seek the given file to the given offset.
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* `Whence' must be one of the three SEEK_* macros.
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*/
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fseek(fp, offset, whence)
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register FILE *fp;
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long offset;
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int whence;
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{
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#if __STDC__
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register fpos_t (*seekfn)(void *, fpos_t, int);
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#else
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register fpos_t (*seekfn)();
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#endif
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fpos_t target, curoff;
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size_t n;
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struct stat st;
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int havepos;
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/* make sure stdio is set up */
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if (!__sdidinit)
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__sinit();
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/*
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* Have to be able to seek.
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*/
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if ((seekfn = fp->_seek) == NULL) {
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errno = ESPIPE; /* historic practice */
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return (EOF);
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}
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/*
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* Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
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* After this, whence is either SEEK_SET or SEEK_END.
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*/
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switch (whence) {
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case SEEK_CUR:
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/*
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* In order to seek relative to the current stream offset,
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* we have to first find the current stream offset a la
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* ftell (see ftell for details).
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*/
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if (fp->_flags & __SOFF)
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curoff = fp->_offset;
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else {
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curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
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if (curoff == -1L)
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return (EOF);
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}
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if (fp->_flags & __SRD) {
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curoff -= fp->_r;
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if (HASUB(fp))
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curoff -= fp->_ur;
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} else if (fp->_flags & __SWR && fp->_p != NULL)
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curoff += fp->_p - fp->_bf._base;
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offset += curoff;
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whence = SEEK_SET;
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havepos = 1;
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break;
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case SEEK_SET:
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case SEEK_END:
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curoff = 0; /* XXX just to keep gcc quiet */
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havepos = 0;
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break;
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default:
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errno = EINVAL;
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return (EOF);
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}
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/*
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* Can only optimise if:
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* reading (and not reading-and-writing);
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* not unbuffered; and
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* this is a `regular' Unix file (and hence seekfn==__sseek).
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* We must check __NBF first, because it is possible to have __NBF
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* and __SOPT both set.
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*/
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if (fp->_bf._base == NULL)
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__smakebuf(fp);
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if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
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goto dumb;
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if ((fp->_flags & __SOPT) == 0) {
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if (seekfn != __sseek ||
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fp->_file < 0 || fstat(fp->_file, &st) ||
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(st.st_mode & S_IFMT) != S_IFREG) {
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fp->_flags |= __SNPT;
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goto dumb;
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}
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fp->_blksize = st.st_blksize;
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fp->_flags |= __SOPT;
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}
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/*
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* We are reading; we can try to optimise.
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* Figure out where we are going and where we are now.
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*/
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if (whence == SEEK_SET)
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target = offset;
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else {
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if (fstat(fp->_file, &st))
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goto dumb;
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target = st.st_size + offset;
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}
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if (!havepos) {
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if (fp->_flags & __SOFF)
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curoff = fp->_offset;
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else {
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curoff = (*seekfn)(fp->_cookie, 0L, SEEK_CUR);
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if (curoff == POS_ERR)
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goto dumb;
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}
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curoff -= fp->_r;
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if (HASUB(fp))
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curoff -= fp->_ur;
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}
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/*
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* Compute the number of bytes in the input buffer (pretending
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* that any ungetc() input has been discarded). Adjust current
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* offset backwards by this count so that it represents the
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* file offset for the first byte in the current input buffer.
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*/
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if (HASUB(fp)) {
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n = fp->_up - fp->_bf._base;
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curoff -= n;
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n += fp->_ur;
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} else {
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n = fp->_p - fp->_bf._base;
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curoff -= n;
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n += fp->_r;
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}
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/*
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* If the target offset is within the current buffer,
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* simply adjust the pointers, clear EOF, undo ungetc(),
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* and return. (If the buffer was modified, we have to
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* skip this; see fgetln.c.)
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*/
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if ((fp->_flags & __SMOD) == 0 &&
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target >= curoff && target < curoff + n) {
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register int o = target - curoff;
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fp->_p = fp->_bf._base + o;
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fp->_r = n - o;
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if (HASUB(fp))
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FREEUB(fp);
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fp->_flags &= ~__SEOF;
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return (0);
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}
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/*
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* The place we want to get to is not within the current buffer,
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* but we can still be kind to the kernel copyout mechanism.
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* By aligning the file offset to a block boundary, we can let
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* the kernel use the VM hardware to map pages instead of
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* copying bytes laboriously. Using a block boundary also
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* ensures that we only read one block, rather than two.
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*/
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curoff = target & ~(fp->_blksize - 1);
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if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
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goto dumb;
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fp->_r = 0;
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fp->_p = fp->_bf._base;
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if (HASUB(fp))
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FREEUB(fp);
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fp->_flags &= ~__SEOF;
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n = target - curoff;
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if (n) {
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if (__srefill(fp) || fp->_r < n)
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goto dumb;
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fp->_p += n;
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fp->_r -= n;
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}
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return (0);
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/*
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* We get here if we cannot optimise the seek ... just
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* do it. Allow the seek function to change fp->_bf._base.
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*/
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dumb:
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if (__sflush(fp) ||
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(*seekfn)(fp->_cookie, offset, whence) == POS_ERR) {
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return (EOF);
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}
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/* success: clear EOF indicator and discard ungetc() data */
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if (HASUB(fp))
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FREEUB(fp);
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fp->_p = fp->_bf._base;
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fp->_r = 0;
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/* fp->_w = 0; */ /* unnecessary (I think...) */
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fp->_flags &= ~__SEOF;
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return (0);
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}
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