Subversion Repositories shark

/*-
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.
 */

#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)fseek.c     8.3 (Berkeley) 1/2/94";
#endif
static const char rcsid[] =
                "$\Id: fseek.c,v 1.4 1996/06/22 10:33:22 jraynard Exp $";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include "local.h"
#ifdef _THREAD_SAFE
#include <pthread.h>
#include "pthread_private.h"
#endif

#define POS_ERR (-(fpos_t)1)

/*
 * Seek the given file to the given offset.
 * `Whence' must be one of the three SEEK_* macros.
 */
int
fseek(fp, offset, whence)
        register FILE *fp;
        long offset;
        int whence;
{
        register fpos_t (*seekfn) __P((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();

#ifdef _THREAD_SAFE
        _thread_flockfile(fp,__FILE__,__LINE__);
#endif
        /*
         * 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.
         */
        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).
                 */
                if (fp->_flags & __SOFF)
                        curoff = fp->_offset;
                else {
                        curoff = (*seekfn)(fp->_cookie, (fpos_t)0, SEEK_CUR);
                        if (curoff == -1) {
#ifdef _THREAD_SAFE
                                _thread_funlockfile(fp);
#endif
                                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:
                errno = EINVAL;
#ifdef _THREAD_SAFE
                _thread_funlockfile(fp);
#endif
                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) ||
                    (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))
                        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) {
                register int o = target - curoff;

                fp->_p = fp->_bf._base + o;
                fp->_r = n - o;
                if (HASUB(fp))
                        FREEUB(fp);
                fp->_flags &= ~__SEOF;
#ifdef _THREAD_SAFE
                _thread_funlockfile(fp);
#endif
                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;
        }
#ifdef _THREAD_SAFE
        _thread_funlockfile(fp);
#endif
        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) {
#ifdef _THREAD_SAFE
                _thread_funlockfile(fp);
#endif
                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;
#ifdef _THREAD_SAFE
        _thread_funlockfile(fp);
#endif
        return (0);
}