/*	$NetBSD: fseeko.c,v 1.14 2017/01/10 17:44:28 christos 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/cdefs.h>
#include <sys/types.h>
#include <sys/stat.h>

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include "reentrant.h"
#include "local.h"

#define POS_ERR ((off_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) {
  off_t (*seekfn)(void *, off_t, int);
  off_t target, curoff;
  size_t n;
  struct stat st;
  int havepos;

  _DIAGASSERT(fp != NULL);

  /* make sure stdio is set up */
  if (!__sdidinit)
    __sinit();

  FLOCKFILE(fp);

  /*
   * Have to be able to seek.
   */
  if ((seekfn = fp->_seek) == NULL) {
    errno = ESPIPE; /* historic practice */
    FUNLOCKFILE(fp);
    return -1;
  }

  /*
   * 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).
       */
      (void)__sflush(fp); /* may adjust seek offset on append stream */
      if (fp->_flags & __SOFF)
        curoff = fp->_offset;
      else {
        curoff = (*seekfn)(fp->_cookie, (off_t)0, SEEK_CUR);
        if (curoff == POS_ERR) {
          FUNLOCKFILE(fp);
          return -1;
        }
      }
      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;
      if (offset < 0) {
        errno = EINVAL;
        FUNLOCKFILE(fp);
        return -1;
      }
      whence = SEEK_SET;
      havepos = 1;
      break;

    case SEEK_SET:
      if (offset < 0) {
        errno = EINVAL;
        FUNLOCKFILE(fp);
        return -1;
      }
      /*FALLTHROUGH*/
    case SEEK_END:
      curoff = 0; /* XXX just to keep gcc quiet */
      havepos = 0;
      break;

    default:
      errno = EINVAL;
      FUNLOCKFILE(fp);
      return -1;
  }

  /*
   * 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 || __sfileno(fp) == -1 || fstat(__sfileno(fp), &st) ||
        !S_ISREG(st.st_mode)) {
      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(__sfileno(fp), &st))
      goto dumb;
    target = st.st_size + offset;
  }

  if (!havepos) {
    if (fp->_flags & __SOFF)
      curoff = fp->_offset;
    else {
      curoff = (*seekfn)(fp->_cookie, (off_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 + (off_t)n) {
    int o = (int)(target - curoff);

    fp->_p = fp->_bf._base + o;
    _DIAGASSERT(__type_fit(int, n - o));
    fp->_r = (int)(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 = (int)(target - curoff);
  if (n) {
    if (__srefill(fp) || (size_t)fp->_r < n)
      goto dumb;
    fp->_p += n;
    _DIAGASSERT(__type_fit(int, fp->_r - n));
    fp->_r -= (int)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, offset, whence) == POS_ERR) {
    FUNLOCKFILE(fp);
    return -1;
  }
  /* 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;
}
