linux-kernel - Re: [PATCH 1/3] nvme: do not check for ns on rw path

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Date:   Sat, 4 Nov 2017 09:18:25 +0100
From:   Christoph Hellwig <hch@....de>
To:     Keith Busch <keith.busch@...el.com>
Cc:     Christoph Hellwig <hch@....de>,
        Javier González <jg@...htnvm.io>,
        sagi@...mberg.me, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Javier González <javier@...xlabs.com>
Subject: Re: [PATCH 1/3] nvme: do not check for ns on rw path

On Fri, Nov 03, 2017 at 09:02:04AM -0600, Keith Busch wrote:
> If the namespace has metadata, but the request doesn't have a metadata
> payload attached to it for whatever reason, we can't construct the command
> for that format. We also can't have the controller strip/generate the
> payload with PRACT bit set if it's not a T10 format, so we just fail
> the command.

The only metadata payload a READ or WRITE request can have is a protection
information one.  For a namespace formatted with protection information
bio_integrity_prep as called from blk_mq_make_request will ensure we
always have metadata attached.

If a namespace is formatted with non-PI metadata we will never have
metadata attached to the bio/request and should not even present the
namespace to the kernel.