linux-kernel - Re: [RFC PATCH 2/9] ntsync: Reserve a minor device number and ioctl range.

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Date: Tue, 23 Jan 2024 21:43:09 -0600
From: Elizabeth Figura <zfigura@...eweavers.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
 linux-api@...r.kernel.org, wine-devel@...ehq.org,
 André Almeida <andrealmeid@...lia.com>,
 Wolfram Sang <wsa@...nel.org>, Arkadiusz Hiler <ahiler@...eweavers.com>,
 Peter Zijlstra <peterz@...radead.org>
Subject:
 Re: [RFC PATCH 2/9] ntsync: Reserve a minor device number and ioctl range.

On Tuesday, 23 January 2024 18:54:02 CST Greg Kroah-Hartman wrote:
> On Tue, Jan 23, 2024 at 06:40:21PM -0600, Elizabeth Figura wrote:
> > Signed-off-by: Elizabeth Figura <zfigura@...eweavers.com>
> > ---
> 
> Note, we can't take patches without any changelog text, and you don't
> want us to :)
> 
> >  Documentation/admin-guide/devices.txt              | 3 ++-
> >  Documentation/userspace-api/ioctl/ioctl-number.rst | 2 ++
> >  drivers/misc/ntsync.c                              | 3 ++-
> >  include/linux/miscdevice.h                         | 1 +
> >  4 files changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/Documentation/admin-guide/devices.txt
> > b/Documentation/admin-guide/devices.txt index 94c98be1329a..041404397ee5
> > 100644
> > --- a/Documentation/admin-guide/devices.txt
> > +++ b/Documentation/admin-guide/devices.txt
> > @@ -376,8 +376,9 @@
> > 
> >  		240 = /dev/userio	Serio driver testing device
> >  		241 = /dev/vhost-vsock	Host kernel driver for virtio 
vsock
> >  		242 = /dev/rfkill	Turning off radio transmissions 
(rfkill)
> > 
> > +		243 = /dev/ntsync	NT synchronization primitive 
device
> > 
> > -		243-254			Reserved for local use
> > +		244-254			Reserved for local use
> 
> Why do you need a fixed minor number?  Can't your userspace handle
> dynamic numbers?  What systems require a static value?

I believe I added this because it's necessary for MODULE_ALIAS (and, more 
broadly, because I was following the example of vaguely comparable devices 
like /dev/loop-control). I suppose I could instead just remove MODULE_ALIAS 
(or even remove the ability to compile ntsync as a module entirely).

It's a bit difficult to figure out what's the preferred way to organize things 
like this (there not being a lot of precedent for this kind of driver) so I'd 
appreciate any direction.

--Zeb