Re: pktcdvd -> sysfs warning with 2.6.27

[Kay Sievers]

On Tue, Oct 14, 2008 at 7:27 AM, Peter Osterlund <petero2@xxxxxxxxx> wrote:
> Greg KH <greg@xxxxxxxxx> writes:
>
>> On Mon, Oct 13, 2008 at 10:28:13PM +0100, Nix wrote:
>>> 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? :)
>>
>> Yes, you are right :)
>
> I don't think so. One is a character device and the other is a block
> device. Block devices didn't use to collide with character devices.
> Has that changed recently?

No, that's still true.

>>> 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.
>>
>> Both of those should get "real" majors assigned to them.  It's not ok to
>> randomly go grabbing major:minor numbers like this for code that is in
>> mainline.
>
> It's not about random grabbing. It's about getting a dynamically
> assigned number. The pktcdvd driver once had static numbers, but at
> the time when the driver was merged into the mainline kernel, dynamic
> numbers were considered better. Therefore I changed the driver to use
> dynamic numbers.

The pktcdvd driver allocates a dynamic block major, which is fine. But
doesn't it use the same number, and now not allocated, for the char
devices it uses? That looks like something that needs to fixed, right?

  static void pkt_sysfs_dev_new(struct pktcdvd_device *pd)
  {
    if (class_pktcdvd) {
      pd->dev = device_create_drvdata(class_pktcdvd, NULL,
                                                pd->pkt_dev, NULL,
                                                "%s", pd->name);

Thanks,
Kay
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