linux-kernel - Re: [PATCH 5/6] lightnvm: expose device geometry through sysfs

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Message-ID: <577619D9.1080209@bjorling.me>
Date:	Fri, 1 Jul 2016 09:20:57 +0200
From:	Matias Bjørling <m@...rling.me>
To:	J Freyensee <james_p_freyensee@...ux.intel.com>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	axboe@...com, keith.busch@...el.com,
	linux-nvme@...ts.infradead.org, dm-devel@...hat.com
Cc:	"Simon A. F. Lund" <slund@...xlabs.com>
Subject: Re: [PATCH 5/6] lightnvm: expose device geometry through sysfs

On 06/30/2016 10:01 PM, J Freyensee wrote:
> On Wed, 2016-06-29 at 16:51 +0200, Matias Bjørling wrote:
>> From: "Simon A. F. Lund" <slund@...xlabs.com>
>>
>> For a host to access an Open-Channel SSD, it has to know its
>> geometry,
>> so that it writes and reads at the appropriate device bounds.
>>
>> Currently, the geometry information is kept within the kernel, and
>> not
>> exported to user-space for consumption. This patch exposes the
>> configuration through sysfs and enables user-space libraries, such as
>> liblightnvm, to use the sysfs implementation to get the geometry of
>> an
>> Open-Channel SSD.
>>
>> The sysfs entries are stored within the device hierarchy, and can be
>> found using the "lightnvm" device type.
>>
>> An example configuration looks like this:
>>
>> /sys/class/nvme/
>> └── nvme0n1
>>     ├── capabilities: 3
>>     ├── device_mode: 1
>>     ├── channel_parallelism: 0
>>     ├── erase_max: 1000000
>>     ├── erase_typ: 1000000
>>     ├── flash_media_type: 0
>>     ├── media_capabilities: 0x00000001
>>     ├── media_type: 0
>>     ├── multiplane: 0x00010101
>>     ├── num_blocks: 1022
>>     ├── num_channels: 1
>>     ├── num_luns: 4
>>     ├── num_pages: 64
>>     ├── num_planes: 1
>>     ├── page_size: 4096
>>     ├── prog_max: 100000
>>     ├── prog_typ: 100000
>>     ├── read_max: 10000
>>     ├── read_typ: 10000
>>     ├── sector_oob_size: 0
>>     ├── sector_size: 4096
>>     ├── media_manager: gennvm
>>     ├── ppa_format: 0x380830082808001010102008
>>     ├── vendor_opcode: 0
>>     └── version: 1
>>
>
> That is an awful lot of new things to add under nvme0n1-type sysfs
> entries when there is already a decent amount of stuff under it.
>

You are right. These are rightfully placed under /lightnvm in the sysfs 
path. The description is wrong, will update it. Thanks Jay.

> Any chance these new things could be stuck under a separate sysfs
> directory under each nvmeXnY device?  If these things are mainly
> beneficial to LightNVM, it will be easier for a LightNVM newbie to
> find, recognize, and consider all the important things in an Open
> Channel SSD solution if it's under a separate directory.  And for
> current SSD solutions that don't seem to need these things exposed in
> sysfs for operation, it will make what is directly under nvmeXnY
> directories less cluttered.
>
> Thanks,
> Jay
>