int
vop_access(struct vnode *vp, int mode, struct ucred *cred, struct thread *td)
{
    int error;

    /*
     * ?ե????뤬?????åȡ?FIFO???ޤ??ϥե????륷???ƥ???¸?ߤ???
     * ?֥??å????ޤ???ʸ?????ǥХ????Ǥʤ??????ˤϡ??ɤ߹???????
     * ?ե????륷???ƥ??ؤν񤭹??ߤ?ǧ???????ޤ?????
     */
    if (mode & VWRITE) {
	switch (vp->v_type) {
	case VDIR:
	case VLNK:
	case VREG:
	    if (vp->v_mount->mnt_flag & MNT_RDONLY)
		return EROFS;

	    break;
	}
    }

    /* ???ѥӥåȤ????ꤵ???Ƥ????С?ï???񤭹????ޤ????? */
    if ((mode & VWRITE) && vp has immutable bit set)
	return EPERM;

    /* ?????Ǥʤ????С?uid ?? 0 ?ʤ??о??˵??ġ? */
    if (cred->cr_uid == 0)
	return 0;

    mask = 0;

    /* ?????Ǥʤ????С???ͭ?Ԥ?Ĵ?٤ޤ??? */
    if (cred->cr_uid == owner of vp) {
	if (mode & VEXEC)
	    mask |= S_IXUSR;
	if (mode & VREAD)
	    mask |= S_IRUSR;
	if (mode & VWRITE)
	    mask |= S_IWUSR;
	return (((mode of vp) & mask) == mask ? 0 : EACCES);
    }

    /* ?????Ǥʤ????С????롼?פ?Ĵ?٤ޤ??? */
    for (i = 0, gp = cred->cr_groups; i < cred->cr_ngroups; i++, gp++)
	if (group of vp == *gp) {
	    if (mode & VEXEC)
		mask |= S_IXGRP;
	    if (mode & VREAD)
		mask |= S_IRGRP;
	    if (mode & VWRITE)
		mask |= S_IWGRP;
	    return (((mode of vp) & mask) == mask ? 0 : EACCES);
	}

    /* ?????Ǥʤ????С?????¾??Ĵ?٤ޤ??? */
    if (mode & VEXEC)
	mask |= S_IXOTH;
    if (mode & VREAD)
	mask |= S_IROTH;
    if (mode & VWRITE)
	mask |= S_IWOTH;
    return (((mode of vp) & mask) == mask ? 0 : EACCES);
}