Date: Sun, 5 Jun 2016 23:53:54 -0400 From: Warner Losh <wlosh@bsdimp.com> To: KILOREUX Emperex <kiloreux@gmail.com> Cc: Poul-Henning Kamp <phk@phk.freebsd.dk>, Koop Mast <kwm@freebsd.org>, eadler@freebsd.org, =?utf-8?Q?Jean-S=C3=A9bastien_P=C3=A9dron?= <dumbbell@freebsd.org>, freebsd-arch@freebsd.org Subject: Re: API to link sysctl nodes to devices Message-ID: <070D3C32-9631-49AD-85FB-53A4865AFA08@bsdimp.com> In-Reply-To: <CAN1JrQ1eSr3%2BrPuF5d6USX=V_cTjzuAG=VXd7pFphO%2BEk2gE%2BQ@mail.gmail.com> References: <CAN1JrQ2dd0WZi0_aaNdqH9xdy292tP2DYLxvKV9bfK93vYFLXw@mail.gmail.com> <13621.1465030369@critter.freebsd.dk> <CAN1JrQ1eSr3%2BrPuF5d6USX=V_cTjzuAG=VXd7pFphO%2BEk2gE%2BQ@mail.gmail.com>
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> On Jun 5, 2016, at 11:07 PM, KILOREUX Emperex <kiloreux@gmail.com> =
wrote:
>=20
> Hey,
>=20
> Thanks for your feedback, but we have been over this and what you are
> proposing seems pretty interesting, can you please elaborate on how =
that
> could be implemented inside the kernel, or give more details about it, =
also
> it seems a bit cool if we could do both of them together, so what do =
you
> think about sysctl nodes, is there any disadvantages for the =
implementation
> of such API ?
>=20
> On Sat, Jun 4, 2016 at 9:52 AM, Poul-Henning Kamp <phk@phk.freebsd.dk>
> wrote:
>=20
>> --------
>> In message <
>> CAN1JrQ2dd0WZi0_aaNdqH9xdy292tP2DYLxvKV9bfK93vYFLXw@mail.gmail.com>
>> , KILOREUX Emperex writes:
>>=20
>>> As part of my participation GSOC, I have been working on an API spec =
to
>>> link sysctl nodes to devices.
>>=20
>> It's not really the sysctl nodes as such you should focus on, but
>> rather on the gap between (the increasingly inaccurately named)
>> newbus and devfs.
>>=20
>> The poster-boy example is how you get from USB bus coordinates to
>> /dev/da* or /dev/{tty|cua}U* devices.
>>=20
>> devd(8) seems to know the linkage and usually I resort to /etc/devd
>> entries like this to make it liveable:
>>=20
>> attach 1000 {
>> match "device-name" "uftdi[0-9]*";
>> match "vendor" "0x0403";
>> match "product" "0x6001";
>> match "sernum" "FTHAV9UU";
>> action "ln -s /dev/cua$ttyname /dev/bbb1";
>> };
>>=20
>> notify 1000 {
>> match "system" "USB";
>> match "subsystem" "DEVICE";
>> match "type" "DETACH";
>> match "vendor" "0x0403";
>> match "product" "0x6001";
>> match "sernum" "FTHAV9UU";
>> action "rm -f /dev/bbb1";
>> };
For /dev/da* we created a geom creation event that should be used =
instead of a USB insertion event, which removed the strain we had. For =
uftdi vs ttyUx thing, though, there=E2=80=99s a problem. We could do a =
device creation event as well (there may already be one), but there=E2=80=99=
s no way to connect the /dev/ttyUx back to the newbus device_t node, =
which can be used look up info about the device to do interesting things =
with. One way to do this would be dev.uftdi.0.%devnodes: ttyU2 ttyU3, =
which would require some new APIs for adding a dev_t to a device_t. But =
that might be backwards. I=E2=80=99d like something more like =
devnode.ttyU2.device: uftdi0 would do the trick (or uftdi.0, since =
device names can have numbers in them, which is why the sysctl nodes =
under dev are the way they are). Note =E2=80=98devnode=E2=80=99 is just =
a name, I=E2=80=99m agnostic, but given that dev is already taken (and =
its an API for many device drivers, so changing it would be difficult) =
=E2=80=98devnode=E2=80=99 seems the next best thing, but I=E2=80=99m =
open to other names.
Of course, having a stronger coupling between device_t and dev_t would =
allow us to detect when /dev/foo isn=E2=80=99t destroyed when the =
device_t created it gets detached.
As for sysctl, there=E2=80=99s already a sysctl tree that=E2=80=99s =
tightly coupled to a device instance that any device can take advantage =
of. I=E2=80=99m not sure what you need here, unless it=E2=80=99s what I =
described in the last paragraph.
Warner=
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