linux-kernel - Re: pktcdvd -> sysfs warning with 2.6.27

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Date:	Mon, 13 Oct 2008 22:28:13 +0100
From:	Nix <nix@...eri.org.uk>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org, Peter Osterlund <petero2@...ia.com>,
	a.zummo@...ertech.it
Subject: Re: pktcdvd -> sysfs warning with 2.6.27

On 12 Oct 2008, Greg KH uttered the following:
> Perhaps some other kernel code is registering with that same major/minor
> number, making it already present in sysfs.  Where does that sysfs file
> link to before you load your driver?

Exactly so. This is probably *not* a regression after all: the only
change I made to my 2.6.27 config (weeks before actually rebooting, so I
forgot) was to build in the CMOS RTC driver, in a hopeless attempt to
make hrtimers work on this old hardware (I knew it was hopeless but
tried anyway). (Unsurprisingly it didn't work:
<http://www.ussg.iu.edu/hypermail/linux/kernel/0810.1/1033.html> worked,
thank *you* Jeff, I have glitch-free pulseaudio and microsecond sleeps
and several of my programs are happier!)

And, looky here, a smoking gun:

hades:~# ls -l /sys/dev/char/254:0 /dev/rtc*
lrwxrwxrwx 1 root root 0 2008-10-13 22:16 /sys/dev/char/254:0 -> ../../devices/platform/rtc_cmos/rtc/rtc0
hades:~# ls -l 
lrwxrwxrwx 1 root root      4 2008-10-13 21:57 /dev/rtc -> rtc0
crw-r--r-- 1 root root 254, 0 2008-10-13 21:57 /dev/rtc0

hades:~# pktsetup cdrw /dev/cdrw
hades:~# ls -l /dev/pktcdvd/
total 0
brw-r----- 1 root root  254,  0 2008-10-13 22:23 cdrw
crw-r--r-- 1 root root   10, 63 2008-10-13 21:57 control
brw-rw---- 1 root cdrom 254,  0 2008-10-13 22:23 pktcdvd0

Am I right in assuming that this sort of isn't going to work? :)

Major 254 is listed as LOCAL/EXPERIMENTAL USE in devices.txt. I don't
consider either pktcdvd or the rtc drivers as LOCAL/EXPERIMENTAL: the
former in particular has been in the kernel for years.

They could do with proper device numbers. No matter what this is going
to break some non-udev setups :(
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