min_mbuf_head/tailroom_req in rte_cryptodev_info

[Suanming Mou]

Hi Guys,

Sorry for disturbing you. I have one small question regarding the min_mbuf_head/tailroom_req in rte_cryptodev_info.
I saw you were the people who discussed, reviewed and added that two fields.
IIUC, the two fields provided a hint to the PMD that HW can use(modify) the headroom and tailroom space to improve the performance.
But regarding the space(e.g. headroom) user reserved, should the data offset(sym_op->aead.data.offset) in struct rte_crypto_op also be taken into account?
e.g. if the mbuf in the operation is something like below:
|---headroom--|----op offset---|---payload to process---|---tailroom---|
In that case, what is the headroom mean to HW? Start from real mbuf headroom before op offset or the offset before payload?

Thanks,
Suanming Mou
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