static unsigned int check_sharing( struct fd *fd, unsigned int access, unsigned int sharing,
                                   unsigned int open_flags, unsigned int options )
{
    unsigned int existing_sharing = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
    unsigned int existing_access = 0;
    struct list *ptr;

    fd->access = access;
    fd->sharing = sharing;

    LIST_FOR_EACH( ptr, &fd->inode->open )
    {
        struct fd *fd_ptr = LIST_ENTRY( ptr, struct fd, inode_entry );
        if (fd_ptr != fd)
        {
            /* if access mode is 0, sharing mode is ignored */
            if (fd_ptr->access & (FILE_READ_DATA | FILE_WRITE_DATA | DELETE))
                existing_sharing &= fd_ptr->sharing;
            existing_access  |= fd_ptr->access;
        }
    }

    if (((access & FILE_READ_DATA) && !(existing_sharing & FILE_SHARE_READ)) ||
        ((access & FILE_WRITE_DATA) && !(existing_sharing & FILE_SHARE_WRITE)) ||
        ((access & DELETE) && !(existing_sharing & FILE_SHARE_DELETE)))
        return STATUS_SHARING_VIOLATION;
    if (((existing_access & FILE_MAPPING_WRITE) && !(sharing & FILE_SHARE_WRITE)) ||
        ((existing_access & FILE_MAPPING_IMAGE) && (access & FILE_SHARE_WRITE)))
        return STATUS_SHARING_VIOLATION;
    if ((existing_access & FILE_MAPPING_IMAGE) && (options & FILE_DELETE_ON_CLOSE))
        return STATUS_CANNOT_DELETE;
    if ((existing_access & FILE_MAPPING_ACCESS) && (open_flags & O_TRUNC))
        return STATUS_USER_MAPPED_FILE;
    if (!access) return 0;  /* if access mode is 0, sharing mode is ignored (except for mappings) */
    if (((existing_access & FILE_READ_DATA) && !(sharing & FILE_SHARE_READ)) ||
        ((existing_access & FILE_WRITE_DATA) && !(sharing & FILE_SHARE_WRITE)) ||
        ((existing_access & DELETE) && !(sharing & FILE_SHARE_DELETE)))
        return STATUS_SHARING_VIOLATION;
    return 0;
}