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Date:   Tue, 28 Nov 2023 12:02:58 -0700
From:   Keith Busch <kbusch@kernel.org>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Daniel Wagner <dwagner@suse.de>, linux-nvme@lists.infradead.org,
        linux-kernel@vger.kernel.org, Sagi Grimberg <sagi@grimberg.me>,
        Hannes Reinecke <hare@suse.de>
Subject: Re: [RFC v1] nvme: add cse, ds, ms, nsze and nuse to sysfs
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On Tue, Nov 28, 2023 at 02:05:08PM +0100, Christoph Hellwig wrote:
> On Mon, Nov 27, 2023 at 09:46:43AM -0700, Keith Busch wrote:
> > > 
> > > Yes.  But does it care about the tuple size, or the actual size of the
> > > metadata field even if is bigger than the PI tuple?
> > 
> > tuple_size is the same value as metadata size regardless of PI usage.
> > See nvme_init_integrity() for how this driver sets it:
> > 
> > 	integrity.tuple_size = ns->ms;
> 
> Yes, for the case where we actually support integrity in the kernel
> for a given device.  But if the device has a metadata size larger than
> the PI size we still support it, and just let the device strip/insert
> the PI.

I'm pretty sure that isn't right. We already support PI regardless of
the metadata size as long as the PI field is in the first 8 bytes.
Strip/insert doesn't even work if metadata is larger than a PI field.
For any metadata case where PI isn't used, the driver requests
allocating an empty buffer for the purpose.

> And if nvme-cli wants to report detailed information about
> the namespace it probably needs to report the actual metadata size
> as the tuple size won't be reported given that we're never initializing
> the kernel PI support.

I don't understand. For any namespace with a metadata size, even if the
namespace format doesn't have PI support, we still register an
"integrity" profile with no-ops to get that unused buffer just so the
block layer can access the format. We alyways set the tuple_size to the
namespace metadata-size so the kernel buffer is correctly sized.

This all works as long as the metadata is separate (not extended) and
kernel has CONFIG_BLK_DEV_INTEGRITY.