e index and is the value returned when the callbacks were initially registered via CRYPTO_get_ex_new_index() and can be used if the same callback handles different types of exdata.</p>

<p>dup_func() is called when a structure is being copied. This is only done for <b>SSL</b>, <b>SSL_SESSION</b>, <b>EC_KEY</b> objects and <b>BIO</b> chains via BIO_dup_chain(). The <b>to</b> and <b>from</b> parameters are pointers to the destination and source <b>CRYPTO_EX_DATA</b> structures, respectively. The <b>from_d</b>