Re: [RFC v1] nvme: add cse, ds, ms, nsze and nuse to sysfs

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
Date: Mon, 27 Nov 2023 09:46:43 -0700	[thread overview]
Message-ID: <ZWTH85bmw0cdePXf@kbusch-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20231127163333.GA2273@lst.de>

On Mon, Nov 27, 2023 at 05:33:33PM +0100, Christoph Hellwig wrote:
> On Mon, Nov 27, 2023 at 09:30:14AM -0700, Keith Busch wrote:
> > > > Should this even be an nvme specific attribute? I thought we should have
> > > > blk-integrity.c report its 'tuple_size' attribute instead. That should
> > > > work as long as we're not dealing with extended metadata at least, but
> > > > that's kind of a special format that doesn't have block layer support.
> > > 
> > > Reporting the tuple size is a good idea.  But is that enough for
> > > the existing nvme-cli use case?
> > 
> > nvme-cli currently queries with admin passthrough identify command, so
> > adding a new attribute won't break that. I assume Daniel would have it
> > fallback to that same command for backward compatibilty if a desired
> > sysfs attribute doesn't exist.
> 
> 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;