int
vop_read(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
{
    struct buf *bp;
    off_t bytesinfile;
    daddr_t lbn, nextlbn;
    long size, xfersize, blkoffset;
    int error;

    size = block size of file system;

    for (error = 0, bp = NULL; uio->uio_resid > 0; bp = NULL) {
	bytesinfile = size of file - uio->uio_offset;
	if (bytesinfile <= 0)
	    break;

	lbn = uio->uio_offset / size;
	blkoffset = uio->uio_offset - lbn * size;

	xfersize = size - blkoffset;
	if (uio->uio_resid < xfersize)
	    xfersize = uio->uio_resid;
	if (bytesinfile < xfersize)
	    xfersize = bytesinfile;

	error = bread(vp, lbn, size, NOCRED, &bp);
	if (error) {
	    brelse(bp);
	    bp = NULL;
	    break;
	}

	/*
	 * ?????ϥ??顼???????ä????ˤ? 0 ?Ǥʤ? b_resid ?Τ?
	 * ?????ޤ????????Ͼ??? break ?????????????٤??Ǥ???
	 * ???????ʤ??顢û???ɤ߹??ߤ????顼?򵯤????ʤ??ä?
	 * ?????ˤϡ??ְ??ä??ޤ??Ͻ??????????Ƥ??ʤ??ǡ?????
	 * uiomove ???Ԥʤ??ʤ????Ȥ??ݾڤ???????
	 */
	size -= bp->b_resid;
	if (size < xfersize) {
	    if (size == 0)
		break;
	    xfersize = size;
	}

	error = uiomove((char *)bp->b_data + blkoffset, (int)xfersize, uio);
	if (error)
	    break;

	bqrelse(bp);
    }
    if (bp != NULL)
	bqrelse(bp);

    return (error);
}

int
vop_write(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
{
    struct buf *bp;
    off_t bytesinfile;
    daddr_t lbn, nextlbn;
    off_t osize;
    long size, resid, xfersize, blkoffset;
    int flags;
    int error;

    osize = size of file;
    size = block size of file system;
    resid = uio->uio_resid;
    if (ioflag & IO_SYNC)
	flags = B_SYNC;
    else
	flags = 0;

    for (error = 0; uio->uio_resid > 0;) {
	lbn = uio->uio_offset / size;
	blkoffset = uio->uio_offset - lbn * size;

	xfersize = size - blkoffset;
	if (uio->uio_resid < xfersize)
	    xfersize = uio->uio_resid;

	if (uio->uio_offset + xfersize > size of file)
	    vnode_pager_setsize(vp, uio->uio_offset + xfersize);

	if (size > xfersize)
	    flags |= B_CLRBUF;
	else
	    flags &= ~B_CLRBUF;

	error = find_block_in_file(vp, lbn, blkoffset + xfersize,
				   cred, &bp, flags);
	if (error)
	    break;

	if (uio->uio_offset + xfersize > size of file)
	    set size of file to uio->uio_offset + xfersize;

	error = uiomove((char *)bp->b_data + blkoffset, (int) xfersize, uio);
	/* XXX ufs ?Ϥ????ǥ??顼?????å??򤷤Ƥ??ޤ??󡣲???? */

	if (ioflag & IO_VMIO)
	    bp->b_flags |= B_RELBUF; /* ??? */

	if (ioflag & IO_SYNC)
	    bwrite(bp);
	else if (xfersize + blkoffset == size)
	    bawrite(bp);
	else
	    bdwrite(bp);

	if (error || xfersize == 0)
	    break;
    }

    if (error) {
	if (ioflag & IO_UNIT) {
	    /* ?ե????????ڤ??ͤ?????Ū?ʥ롼???????ƤӽФ??? */
	    your_truncate(vp, osize, ioflag & IO_SYNC, cred, uio->uio_td);
	    uio->uio_offset -= resid - uio->uio_resid;
	    uio->uio_resid = resid;
	}
    } else if (resid > uio->uio_resid && (ioflag & IO_SYNC)) {
	struct timeval tv;
	error = VOP_UPDATE(vp, &tv, &tv, 1); /* XXX ?????ϲ??򤷤Ƥ?????? */
    }

    return (error);
}