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Date:      Fri, 3 Jun 2016 18:14:45 +0100
From:      KILOREUX Emperex <kiloreux@gmail.com>
To:        freebsd-arch@freebsd.org
Cc:        =?UTF-8?B?SmVhbi1Tw6liYXN0aWVuIFDDqWRyb24=?= <dumbbell@freebsd.org>,  Koop Mast <kwm@freebsd.org>, eadler@freebsd.org
Subject:   API to link sysctl nodes to devices
Message-ID:  <CAN1JrQ2dd0WZi0_aaNdqH9xdy292tP2DYLxvKV9bfK93vYFLXw@mail.gmail.com>

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Hey,

As part of my participation GSOC, I have been working on an API spec to
link sysctl nodes to devices.

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.

- 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.



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