API to link sysctl nodes to devices

[Hans Petter Selasky]

Hi,

On 06/03/16 19:14, KILOREUX Emperex wrote:
> Hey,
>
> As part of my participation GSOC, I have been working on an API spec to
> link sysctl nodes to devices.
>

Can you clarify a bit what you mean by "device". The term "device" was a 
bit too generic for me :-) I suppose you mean a "character device", right?

Can you give some examples of properties for a character device, which 
can be exposed trough these sysctls you propose ?

> And I cam up with few ideas that I need some feedback on before proceeding
> to the implementation on the kernel.
>
> - We need devices to have their propoer sysctl trees, and thus every device
> linked will have its own id as the head of its syctl tree.
>
> For example a device with id 0x94, would have it's sysctl root look like
> dev.fs.0x94 where the below parameters can be accessed after that.

Would it be better to have a direct mapping between character device 
name, including directories and dev.fs.xxx , like /dev/cuaU0 maps to 
dev.fs.cuaU0.xxx ?

>
> - We want to give device drivers the ability to create and delete sysctl
> nodes as they want, thus proposing a proper interface for it.
>
>
> So I have been thinking so far to enable the creation of the root for those
> sysctl nodes on the system initialization, to allow existing device drivers
> to link their device on the tree.
>
> Also we want to propose a new function similar to make_dev, supposed we
> name it make_dev_sys, that gets the device id and links it on the tree of
> existing sysctl nodes, and for the purpose of keeping track of the
> available sysctl nodes for each device, I thought of proposing a change to
> the device switching table "cdevsw" to keep systcl context tracked for the
> device.
>
> Would any modification to cdevsw break backward compatibility ?
> Please provide us with any feedback you have on this proposition and any
> defects you seeing in the logic.
>
> Your help is much appreciated.

--HPS