linux-kernel - Re: [RFC PATCH] lightnvm: expose configuration through sysfs

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Date:	Wed, 27 Apr 2016 20:20:33 +0200
From:	Matias Bjørling <mb@...htnvm.io>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	"Simon A. F. Lund" <slund@...xlabs.com>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] lightnvm: expose configuration through sysfs

On 04/27/2016 07:41 PM, Greg KH wrote:
> On Wed, Apr 27, 2016 at 10:18:57AM -0700, Simon A. F. Lund wrote:
>> --- a/include/linux/lightnvm.h
>> +++ b/include/linux/lightnvm.h
>> @@ -174,6 +174,7 @@ struct nvm_id_group {
>>   	u16	cpar;
>>
>>   	struct nvm_id_lp_tbl lptbl;
>> +	struct kobject kobj;
>>   };
>>
>>   struct nvm_addr_format {
>> @@ -205,6 +206,7 @@ struct nvm_target {
>>   	struct list_head list;
>>   	struct nvm_tgt_type *type;
>>   	struct gendisk *disk;
>> +	struct kobject kobj;
>>   };
>>
>>   struct nvm_tgt_instance {
>> @@ -360,6 +362,8 @@ struct nvm_dev {
>>
>>   	struct mutex mlock;
>>   	spinlock_t lock;
>> +
>> +	struct kobject kobj;
>>   };
>>
>>   static inline struct ppa_addr generic_to_dev_addr(struct nvm_dev *dev,
>
> Never use "raw" kobjects in a driver for a device.  You just guaranteed
> that userspace tools will not see these devices or attributes, which
> implies you didn't really test this using libudev :(
>
> Please use real devices, attached to the real devices your disks already
> have in the tree.
>
> And are you sure you didn't just mess up your reference counting by
> now having the lifecycle of these structures be dictated by the kobject?
>
> thanks,
>
> greg k-h
>

Hi Greg,

Thanks for the feedback.

lightnvm doesn't have anything to hook up with in the /dev/block/* until 
a device is exposed through a target. A device goes into a staging area, 
and then later is configured to expose a block device.

In the case of NVMe device driver, the driver brings up a device, 
identifies it as a lightnvm device, then calls nvm_register and 
registers the device. It skips the registration as a block device.

At the nvm_register point, the user can list the available devices 
through an ioctl, and then choose a target to put on top. The target 
will then expose it as a block device.

This might not be the ideal way. I like your input on what would be the 
proper way to expose such a device.

-Matias