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

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Message-ID: <mwen6fl5yszmk5nh2hbsqtu5pu76ir6rh6jpdfppbczsov7qfz@vivqeew6y7wk>
Date:   Mon, 27 Nov 2023 13:07:32 +0100
From:   Daniel Wagner <dwagner@...e.de>
To:     Keith Busch <kbusch@...nel.org>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Hannes Reinecke <hare@...e.de>
Subject: Re: [RFC v1] nvme: add cse, ds, ms, nsze and nuse to sysfs

On Mon, Nov 27, 2023 at 03:44:11AM -0700, Keith Busch wrote:
> On Mon, Nov 27, 2023 at 11:32:08AM +0100, Daniel Wagner wrote:
> > libnvme is using the sysfs for enumarating the nvme resources. Though
> > there are few missing attritbutes in the sysfs. For these libnvme issues
> > commands during discovering.
> > 
> > As the kernel already knows all these attributes and we would like to
> > avoid libnvme to issue commands all the time, expose these missing
> > attributes.
> 
> The id namespace 'nuse' field can be quite volatile: it can change on
> any write or discard command, so caching it may quickly get out of sync
> with the actual value.

libnvme itself is also cashing this value and exposes it via the
nvme_ns_get_lba_util() getter. I'd say libnvme shouldn't cache it
either. Instead the function should just issue the ns command to report
the current nuse value.

I'll drop the nuse sysfs entry.

Unfortunately, 'nvme list' is using the 'nuse' field for showing the
currently used space. I was hoping to get 'nvme list' working without
issuing any commands.