linux-ext4 - Re: [PATCH v7 2/9] block: Inline encryption support for blk-mq

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Date:   Mon, 24 Feb 2020 15:34:59 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Satya Tangirala <satyat@...gle.com>
Cc:     Christoph Hellwig <hch@...radead.org>, linux-block@...r.kernel.org,
        linux-scsi@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-ext4@...r.kernel.org,
        Barani Muthukumaran <bmuthuku@....qualcomm.com>,
        Kuohong Wang <kuohong.wang@...iatek.com>,
        Kim Boojin <boojin.kim@...sung.com>
Subject: Re: [PATCH v7 2/9] block: Inline encryption support for blk-mq

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.