linux-kernel - Re: [PATCH 2/5] nvme: register ns_id attributes as default sysfs groups

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Date:   Tue, 14 Aug 2018 17:39:20 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Bart Van Assche <Bart.VanAssche@....com>,
        "axboe@...nel.dk" <axboe@...nel.dk>
Cc:     "hch@....de" <hch@....de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "keith.busch@...el.com" <keith.busch@...el.com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "hare@...e.com" <hare@...e.com>,
        "sagi@...mberg.me" <sagi@...mberg.me>
Subject: Re: [PATCH 2/5] nvme: register ns_id attributes as default sysfs
 groups

On 08/14/2018 05:20 PM, Bart Van Assche wrote:
> On Tue, 2018-08-14 at 09:33 +0200, Hannes Reinecke wrote:
>> +const struct attribute_group *nvme_ns_id_attr_groups[] = {
>> +	&nvme_ns_id_attr_group,
>> +	NULL, /* Will be filled in by lightnvm if present */
>> +	NULL,
>> +};
> [ ... ]
>> -void nvme_nvm_unregister_sysfs(struct nvme_ns *ns)
>> -{
>> -	struct nvm_dev *ndev = ns->ndev;
>> -	struct nvm_geo *geo = &ndev->geo;
>> +		return;
>>  
>>  	switch (geo->major_ver_id) {
>>  	case 1:
>> -		sysfs_remove_group(&disk_to_dev(ns->disk)->kobj,
>> -					&nvm_dev_attr_group_12);
>> +		nvme_ns_id_attr_groups[1] = &nvm_dev_attr_group_12;
>>  		break;
>>  	case 2:
>> -		sysfs_remove_group(&disk_to_dev(ns->disk)->kobj,
>> -					&nvm_dev_attr_group_20);
>> +		nvme_ns_id_attr_groups[1] = &nvm_dev_attr_group_20;
> 
> This patch introduces a really ugly dependency between the NVMe core code and
> the lightnvm code, namely that the lightnvm code has to know at which position
> in the nvme_ns_id_attr_groups it can fill in its attribute group pointer. Have
> you considered to make nvme_nvm_register_sysfs() return an attribute group
> pointer such that the nvme_ns_id_attr_groups can be changed from a global into
> a static array?
> 
Wouldn't help much, as the 'nvme_ns_id_attr_groups' needs to be a global
pointer anyway as it's references from drivers/nvme/host/core.c and
drivers/nvme/host/multipath.c.

While I have considered having nvme_nvm_register_sysfs() returning a
pointer I would then have to remove the 'static' declaration from the
nvm_dev_attr_group_12/20.
Which I didn't really like, either.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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