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

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Date:   Mon, 20 Jan 2020 18:25:58 +0800
From:   Zhenzhong Duan <zhenzhong.duan@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     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 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:
> >
> > Hi Maintainers,
> >
> > I see there are 64 free slots(0-63) used for misc devices with dynamic
> > minor number. But PSMOUSE_MINOR(1) overlaps with that dynamic range.
> >
> > So if the dynamic minor number exhaust, psaux driver will fail with
> > "could not register psaux device, error: -16", is this expected?
> > Should we preserve a slot for psaux and serio_raw which use static
> > minor number PSMOUSE_MINOR?
>
> Is this a theoretical question, or are you actually running out of dynamic
> minor numbers? I would guess that if we change the limit to only allow
> dynamic minors 2 through 63, that would technically be a correct
> change, but the result would be that in the same situation another random
> driver fails, which is not much of an improvement, unless the dynamic
> minor numbers also continue into the range above 255.

It's theoretical question. Thanks for your explanation.

>
> 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 /*
> might as well give it one more than /dev/synth */
> drivers/staging/speakup/speakup_soft.c:#define SOFTSYNTHU_MINOR 27 /*
> might as well give it one more than /dev/synth */
> 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              183 /*
> official */
> 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?

Thanks
Zhenzhong