Re: [PATCH v7 2/9] block: Inline encryption support for blk-mq

[Christoph Hellwig <hch@infradead.org>]

On Fri, Feb 21, 2020 at 04:52:33PM -0800, Satya Tangirala wrote:
> > What is the rationale for this limitation?  Restricting unrelated
> > features from being used together is a pretty bad design pattern and
> > should be avoided where possible.  If it can't it needs to be documented
> > very clearly.
> > 
> My understanding of blk-integrity is that for writes, blk-integrity
> generates some integrity info for a bio and sends it along with the bio,
> and the device on the other end verifies that the data it received to
> write matches up with the integrity info provided with the bio, and
> saves the integrity info along with the data. As for reads, the device
> sends the data along with the saved integrity info and blk-integrity
> verifies that the data received matches up with the integrity info.

Yes, a device supporting inline encryption and integrity will have to
update the guard tag to match the encrypted data as well.  That alone
is a good enough reason to reject the combination for now until it
is fully supported.  It needs to be properly document, and I think
we should also do it at probe time if possible, not when submitting
I/O.