Callback at XFRM ESP tunnel creation

My goal is to run some code before actual packets begin running in the IPSec tunnel. For this, I am thinking of running a callback at the time of an XFRM ESP tunnel creation, where tunnel IPs and the SPI will be known. Is there a standard way of achieving this? If I'm not mistaken, registering for any event that has xfrm_state available should be enough, for instance, xfrm_add_sa, esp_init_state. 

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