Re: [PATCH V2] nvme: report capacity 0 for non supported ZNS SSDs

From: Hannes Reinecke <hare@suse.de>
To: "hch@lst.de" <hch@lst.de>, Keith Busch <kbusch@kernel.org>
Cc: "axboe@kernel.dk" <axboe@kernel.dk>,
	"Niklas.Cassel@wdc.com" <Niklas.Cassel@wdc.com>,
	"javier@javigon.com" <javier@javigon.com>,
	"sagi@grimberg.me" <sagi@grimberg.me>,
	"joshi.k@samsung.com" <joshi.k@samsung.com>,
	"Klaus B. Jensen" <k.jensen@samsung.com>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	Javier Gonzalez <javier.gonz@samsung.com>
Subject: Re: [PATCH V2] nvme: report capacity 0 for non supported ZNS SSDs
Date: Wed, 4 Nov 2020 15:26:46 +0100	[thread overview]
Message-ID: <23e10fd1-d20c-cf77-4dc0-dd8b0774fd7a@suse.de> (raw)
In-Reply-To: <20201102185851.GA21349@lst.de>

On 11/2/20 7:58 PM, hch@lst.de wrote:
> On Mon, Nov 02, 2020 at 10:33:55AM -0800, Keith Busch wrote:
>> I can see this going one of two ways:
>>
>>   a) Set up the existing controller character device with a generic
>>      disk-less request_queue to the IO queues accepting IO commands to
>>      arbitrary NSIDs.
>>
>>   b) Each namespace that can't be supported gets their own character
>>      device.
>>
>> I'm leaning toward option "a". While it doesn't create handles to unique
>> namespaces, it has more resilience to potentially future changes. And I
>> recall the target side had a potential use for that, too.
> 
> The problem with a) is that it can't be used to give users or groups
> access to just one namespaces, so it causes a real access control
> nightmare.  The problem with b) is that now applications will break
> when we add support for new command sets or features.  I think
> 
>    c) Each namespace gets its own character device, period.
> 
> is the only sensible option.
> 
I hardly dare to mention bsg here; but the is pretty similar to what it 
set out to do ...

Or yet another interface?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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