[PATCH 5/6] lightnvm: expose device geometry through sysfs

[m@bjorling.me (Matias Bjørling)]

On 06/30/2016 10:01 PM, J Freyensee wrote:
> On Wed, 2016-06-29@16:51 +0200, Matias Bj?rling wrote:
>> From: "Simon A. F. Lund" <slund at cnexlabs.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
>