Date: Wed, 8 Jun 2016 09:21:59 +0200 From: =?UTF-8?Q?Jean-S=c3=a9bastien_P=c3=a9dron?= <jean-sebastien.pedron@dumbbell.fr> To: freebsd-arch@freebsd.org Subject: Re: API to link sysctl nodes to devices Message-ID: <3ef10748-1e8c-c937-80f2-677091e25a8f@dumbbell.fr> In-Reply-To: <10046161.dJvFbDNaVq@ralph.baldwin.cx> References: <CAN1JrQ2dd0WZi0_aaNdqH9xdy292tP2DYLxvKV9bfK93vYFLXw@mail.gmail.com> <10046161.dJvFbDNaVq@ralph.baldwin.cx>
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From: =?UTF-8?Q?Jean-S=c3=a9bastien_P=c3=a9dron?=
<jean-sebastien.pedron@dumbbell.fr>
To: freebsd-arch@freebsd.org
Message-ID: <3ef10748-1e8c-c937-80f2-677091e25a8f@dumbbell.fr>
Subject: Re: API to link sysctl nodes to devices
References: <CAN1JrQ2dd0WZi0_aaNdqH9xdy292tP2DYLxvKV9bfK93vYFLXw@mail.gmail.com>
<10046161.dJvFbDNaVq@ralph.baldwin.cx>
In-Reply-To: <10046161.dJvFbDNaVq@ralph.baldwin.cx>
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On 06/06/2016 20:19, John Baldwin wrote:
> More detail on what you actually want is needed I think. We already h=
ave
> sysctl device nodes for newbus devices (dev.X.y).
The main reason behind this project is to be able to implement an
equivalent of Linux' libudev. libudev is based on sysfs to list devices
and query generic or arbitrary informations on those devices.
One consumer of this API on Linux is Mesa, the userland part of the
video drivers providing 3D acceleration and so on. Mesa has a file
descriptor on an entry in /dev (eg. /dev/dri/card0). It passes this file
descriptor to libudev to query informations such as:
o the PCI ID of the graphics card
o the name of the driver ("i915", "nouveau", "radeon", etc.)
Another consumer is libinput, an input stack implementation not tied to
the X.Org server, usable by Wayland compositors. libinput uses libudev
to enumerate input devices and query them, but I never studied what
exactly it needs.
Today, on FreeBSD, Mesa uses the "hw.dri" sysctl tree (which is specific
to graphics card) to get the required informations. But we can't do that
for any kind of devices.
To sum up, we need a way to list devices and get various informations,
in a non-graphics-card-specific way.
There is devinfo(3) but I don't see a way to associate a result from
devinfo(3) to a file descriptor from /dev. Likewise for the "dev" sysctl
tree.
> The drm2 code insists on using its own private tree instead of=20
> dev.drmn.0.y though which might be the source of some confusion.
I agree it should be unifed.
> If the goal is to know which device_t a
> given cdev is associated with, I think having a way to ask that and the=
n use
> nodes for the device_t is more straightforward than having an indirecti=
on
> with a separate sysctl tree with opaque cookies for names.
>=20
> (That is, if you had a 'QUERY_DEVICET_NAME' ioctl that character device=
> drivers could optionally implement. Note that only the device driver
> really knows the mapping from cdev to device_t. We could perhaps provi=
de
> a wrapper where you could add the device_t as an arg via make_dev_s() a=
nd
> have the devfs ioctl handler handle QUERY_DEVICET_NAME in that layer us=
ing
> the arg passed to make_dev_s(). I would perhaps have the ioctl return =
the
> name and unit broken out so it is easier to generate the sysctl path.)
I see. That's a good idea, thank you! We'll discuss this further.
--=20
Jean-S=E9bastien P=E9dron
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