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

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Date:   Mon, 27 Nov 2023 15:18:57 +0100
From:   Christoph Hellwig <hch@....de>
To:     Daniel Wagner <dwagner@...e.de>
Cc:     linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Keith Busch <kbusch@...nel.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 11:32:08AM +0100, Daniel Wagner wrote:
> Also getting a pointer to the nvme_ns data structure is a bit strange
> (dev_to_nvme_ns).
> This stip is necessary as many of the ns attributes are in
> nvme_ns. Shouldn't these per path values not all be the same and thus couldn't
> these be in nvme_ns_head? Anyway, just not sure who to deal with this. So any
> pointers highly welcomed!

Yes, they probably should be in the ns_head.

> +		list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
> +			down_read(&ctrl->namespaces_rwsem);
> +			list_for_each_entry(ns, &ctrl->namespaces, list) {
> +				ret = ns;
> +				break;
> +			}
> +			up_read(&ctrl->namespaces_rwsem);
> +		}
> +		return ret;
> +	}

.. I also don't think this would even be safe as-is as we dont hold
a reference to the ns after dropping the lock.

> +static ssize_t csi_show(struct device *dev, struct device_attribute *attr,
> +		char *buf)
> +{
> +	return sysfs_emit(buf, "%d\n", dev_to_ns_head(dev)->ids.csi);
> +}
> +static DEVICE_ATTR_RO(csi);
> +
> +static ssize_t lba_ds_show(struct device *dev, struct device_attribute *attr,
> +		char *buf)
> +{
> +	struct nvme_ns *ns = dev_to_nvme_ns(dev);
> +
> +	return sysfs_emit(buf, "%d\n", ns->lba_shift);

lba_ds is a bit of an odd name.  And I also don't think we even need
this, because it really is just a weird enconding for the logical block
size already exposed by the block layer.

> +static ssize_t lba_ms_show(struct device *dev, struct device_attribute *attr,
> +		char *buf)
> +{
> +	struct nvme_ns *ns = dev_to_nvme_ns(dev);
> +
> +	return sysfs_emit(buf, "%d\n", ns->ms);
> +}
> +static DEVICE_ATTR_RO(lba_ms);

I'd probably spell out metadata_size, or probably even better
metadata_bytes to match the unit postfixes elsewhere in the block code.

> +
> +static ssize_t nsze_show(struct device *dev, struct device_attribute *attr,
> +		char *buf)
> +{
> +	struct nvme_ns *ns = dev_to_nvme_ns(dev);
> +
> +	return sysfs_emit(buf, "%llu\n", ns->nsze);
> +}
> +static DEVICE_ATTR_RO(nsze);

This is just the normal size of the block device we already export.