Questions about the USB HID device drivers

[Warner Losh]

On Mon, Feb 18, 2019 at 2:04 PM Apollo D. Sharpe, Sr. via freebsd-usb <
freebsd-usb at freebsd.org> wrote:

> On 2/18/19 3:26 AM, Hans Petter Selasky wrote:
> > Each devicename has a uniq prefix followed by a uniq unit number.
>
> So, we just end up dumping ALL device nodes in /dev...
>

Yes and no. If the unique prefix has / in it, devfs puts it in a subdir.


> > Character device nodes are automatically created. However it is
> > possible for user-space applications to create symbolic links
> > afterwards in /dev .
>
> ...and leave it to user-space to create the hierarchy within /dev? Is
> there a technical reason that kernel drivers don't automatically
> subscribe to a hierarchy, or is this just historic inertia? It seems
> funny to me that such decisions are left to user-space applications.
>

Way back in the days of yore, it was 100% userland to create the hierarchy.
You did your mknod and that was that. We had big tables of major numbers
that mapped device names to the kernel.

There were problems with this: not the least was that major numbers were a
limited resource and soon ran out. Now, devfs manages everything. You can
get it to create many different hierarchies. see devfs(8) for details.

Warner