try:
    from flash_attn.flash_attn_interface import flash_attn_varlen_func
except ImportError:
    flash_attn_varlen_func = None

def flash_attn2(
    q,
    k,
    v,
    cu_seqlens_q=None,
    cu_seqlens_kv=None,
    max_seqlen_q=None,
    max_seqlen_kv=None
):
    x = flash_attn_varlen_func(
        q,
        k,
        v,
        cu_seqlens_q,
        cu_seqlens_kv,
        max_seqlen_q,
        max_seqlen_kv,
    ).reshape(max_seqlen_q, -1)
    return x