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

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Date:   Sat, 4 Nov 2017 09:38:45 -0600
From:   Keith Busch <keith.busch@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     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 Sat, Nov 04, 2017 at 09:18:25AM +0100, Christoph Hellwig wrote:
> 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.

That's not quite right. For non-PI metadata formats, we use the
'nop_profile', which gets the metadata buffer allocated so we can safely
use a metadata formatted namespace. There's no in-kernel user of the
allocated payload, but we still need the metadata buffer in order to
use the namespace at all.