linux-kernel - Re: Question about dynamic minor number of misc device

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Date:   Tue, 21 Jan 2020 08:56:37 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Zhenzhong Duan <zhenzhong.duan@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Question about dynamic minor number of misc device

On Mon, Jan 20, 2020 at 11:13 PM Theodore Y. Ts'o <tytso@....edu> wrote:
>
> On Mon, Jan 20, 2020 at 11:59:32AM +0100, Arnd Bergmann wrote:
> > On Mon, Jan 20, 2020 at 11:26 AM Zhenzhong Duan
> > <zhenzhong.duan@...il.com> wrote:
> > > On Mon, Jan 20, 2020 at 6:03 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > > On Mon, Jan 20, 2020 at 9:33 AM Zhenzhong Duan <zhenzhong.duan@...il.com> wrote:
> > > > On a  related note, I checked for drivers that call misc_register()
> > > > with a minor number that is not defined in include/linux/misc.h
> > > > and found a bunch, including some that have conflicting numbers,
> > > > conflicting names  or numbers from the dynamic range:
> > > >
> > > > drivers/staging/speakup/devsynth.c:#define SYNTH_MINOR 25
> > > > drivers/staging/speakup/speakup_soft.c:#define SOFTSYNTH_MINOR 26 /*
> > > > drivers/staging/speakup/speakup_soft.c:#define SOFTSYNTHU_MINOR 27 /*
> > > > drivers/macintosh/via-pmu.c:#define PMU_MINOR           154
> > > > drivers/macintosh/ans-lcd.h:#define ANSLCD_MINOR                156
> > > > drivers/auxdisplay/charlcd.c:#define LCD_MINOR          156
> > > > drivers/char/applicom.c:#define AC_MINOR 157
> > > > drivers/char/nwbutton.h:#define BUTTON_MINOR 158
> > > > arch/arm/include/asm/nwflash.h:#define FLASH_MINOR               160
> > > > drivers/sbus/char/envctrl.c:#define ENVCTRL_MINOR       162
> > > > drivers/sbus/char/flash.c:#define FLASH_MINOR   152
> > > > drivers/sbus/char/uctrl.c:#define UCTRL_MINOR   174
> > > > drivers/char/toshiba.c:#define TOSH_MINOR_DEV 181
> > > > arch/um/drivers/random.c:#define RNG_MISCDEV_MINOR
> > > > drivers/auxdisplay/panel.c:#define KEYPAD_MINOR         185
> > > > drivers/video/fbdev/pxa3xx-gcu.c:#define MISCDEV_MINOR  197
> > > > kernel/power/user.c:#define SNAPSHOT_MINOR      231
> > > > drivers/parisc/eisa_eeprom.c:#define    EISA_EEPROM_MINOR 241
> > > >
> > > > If you would like to help clean that up, you are definitely welcome
> > > > to send patches.
> > >
> > > Ok, should that be a patch for all drivers or seperate patch for each driver?
> >
> > I think one patch to move the ones with unique names would be fine,
> > but then separate patches for
> >
> > - FLASH_MINOR move and rename to avoid conflict
> > - change speakup to dynamic minors
> > - support for high dynamic minor numbers if you are really motivated
> >   (probably nobody needs these)
>
> Are we sure that reassigning minor device number conflits isn't going
> to break systems?  Especially those on random, older, architectures
> they might not be using udev.

To clarify: the only numbers that I think should be changed to dynamic
allocation are for drivers/staging/speakup. While this is a fairly old
subsystem, I would expect that it being staging means we can be a
little more progressive with the changes.

      Arnd