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/* $OpenBSD: fseek.c,v 1.14 2022/05/14 05:06:32 guenther Exp $ */
/*-
* Copyright (c) 1990, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Chris Torek.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include "local.h"
#define POS_ERR (-(fpos_t)1)
/*
* Seek the given file to the given offset.
* `Whence' must be one of the three SEEK_* macros.
*/
int
fseeko(FILE *fp, off_t offset, int whence)
{
fpos_t (*seekfn)(void *, fpos_t, int);
fpos_t target, curoff;
size_t n;
struct stat st;
int havepos;
/* make sure stdio is set up */
if (!__sdidinit)
__sinit();
/*
* Have to be able to seek.
*/
if ((seekfn = fp->_seek) == NULL) {
errno = ESPIPE; /* historic practice */
return (EOF);
}
/*
* Change any SEEK_CUR to SEEK_SET, and check `whence' argument.
* After this, whence is either SEEK_SET or SEEK_END.
*/
FLOCKFILE(fp);
switch (whence) {
case SEEK_CUR:
/*
* In order to seek relative to the current stream offset,
* we have to first find the current stream offset a la
* ftell (see ftell for details).
*/
__sflush(fp); /* may adjust seek offset on append stream */
if (fp->_flags & __SOFF)
curoff = fp->_offset;
else {
curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
if (curoff == (fpos_t)-1) {
FUNLOCKFILE(fp);
return (EOF);
}
}
if (fp->_flags & __SRD) {
curoff -= fp->_r;
if (HASUB(fp))
curoff -= fp->_ur;
} else if (fp->_flags & __SWR && fp->_p != NULL)
curoff += fp->_p - fp->_bf._base;
offset += curoff;
whence = SEEK_SET;
havepos = 1;
break;
case SEEK_SET:
case SEEK_END:
curoff = 0; /* XXX just to keep gcc quiet */
havepos = 0;
break;
default:
FUNLOCKFILE(fp);
errno = EINVAL;
return (EOF);
}
/*
* Can only optimise if:
* reading (and not reading-and-writing);
* not unbuffered; and
* this is a `regular' Unix file (and hence seekfn==__sseek).
* We must check __NBF first, because it is possible to have __NBF
* and __SOPT both set.
*/
if (fp->_bf._base == NULL)
__smakebuf(fp);
if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
goto dumb;
if ((fp->_flags & __SOPT) == 0) {
if (seekfn != __sseek ||
fp->_file < 0 || fstat(fp->_file, &st) == -1 ||
(st.st_mode & S_IFMT) != S_IFREG) {
fp->_flags |= __SNPT;
goto dumb;
}
fp->_blksize = st.st_blksize;
fp->_flags |= __SOPT;
}
/*
* We are reading; we can try to optimise.
* Figure out where we are going and where we are now.
*/
if (whence == SEEK_SET)
target = offset;
else {
if (fstat(fp->_file, &st) == -1)
goto dumb;
target = st.st_size + offset;
}
if (!havepos) {
if (fp->_flags & __SOFF)
curoff = fp->_offset;
else {
curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
if (curoff == POS_ERR)
goto dumb;
}
curoff -= fp->_r;
if (HASUB(fp))
curoff -= fp->_ur;
}
/*
* Compute the number of bytes in the input buffer (pretending
* that any ungetc() input has been discarded). Adjust current
* offset backwards by this count so that it represents the
* file offset for the first byte in the current input buffer.
*/
if (HASUB(fp)) {
curoff += fp->_r; /* kill off ungetc */
n = fp->_up - fp->_bf._base;
curoff -= n;
n += fp->_ur;
} else {
n = fp->_p - fp->_bf._base;
curoff -= n;
n += fp->_r;
}
/*
* If the target offset is within the current buffer,
* simply adjust the pointers, clear EOF, undo ungetc(),
* and return. (If the buffer was modified, we have to
* skip this; see fgetln.c.)
*/
if ((fp->_flags & __SMOD) == 0 &&
target >= curoff && target < curoff + n) {
int o = target - curoff;
fp->_p = fp->_bf._base + o;
fp->_r = n - o;
if (HASUB(fp))
FREEUB(fp);
fp->_flags &= ~__SEOF;
FUNLOCKFILE(fp);
return (0);
}
/*
* The place we want to get to is not within the current buffer,
* but we can still be kind to the kernel copyout mechanism.
* By aligning the file offset to a block boundary, we can let
* the kernel use the VM hardware to map pages instead of
* copying bytes laboriously. Using a block boundary also
* ensures that we only read one block, rather than two.
*/
curoff = target & ~(fp->_blksize - 1);
if ((*seekfn)(fp->_cookie, curoff, SEEK_SET) == POS_ERR)
goto dumb;
fp->_r = 0;
fp->_p = fp->_bf._base;
if (HASUB(fp))
FREEUB(fp);
fp->_flags &= ~__SEOF;
n = target - curoff;
if (n) {
if (__srefill(fp) || fp->_r < n)
goto dumb;
fp->_p += n;
fp->_r -= n;
}
FUNLOCKFILE(fp);
return (0);
/*
* We get here if we cannot optimise the seek ... just
* do it. Allow the seek function to change fp->_bf._base.
*/
dumb:
if (__sflush(fp) ||
(*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
FUNLOCKFILE(fp);
return (EOF);
}
/* success: clear EOF indicator and discard ungetc() data */
if (HASUB(fp))
FREEUB(fp);
fp->_p = fp->_bf._base;
fp->_r = 0;
/* fp->_w = 0; */ /* unnecessary (I think...) */
fp->_flags &= ~__SEOF;
FUNLOCKFILE(fp);
return (0);
}
DEF_WEAK(fseeko);
int
fseek(FILE *fp, long offset, int whence)
{
return (fseeko(fp, offset, whence));
}
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