Checking for other kernel modules on load

[Chris Rees]

2011/12/28 Kostik Belousov <kostikbel at gmail.com>:
> On Wed, Dec 28, 2011 at 02:53:42PM +0000, Chris Rees wrote:
>> 2011/12/28 Kostik Belousov <kostikbel at gmail.com>:
>> > On Wed, Dec 28, 2011 at 12:23:58PM +0000, Chris Rees wrote:
>> >> On 28 December 2011 12:21, Daniel O'Connor <doconnor at gsoft.com.au> wrote:
>> >> >
>> >> > On 28/12/2011, at 22:07, Chris Rees wrote:
>> >> >> Is there a simple way to check for existence of a driver?  I could
>> >> >> even check for /dev/sndstat, though that doesn't seem elegant to me...
>> >> >
>> >> > kldstat -v, but really /dev/sndstat seems simpler and just as effective.
>> >> >
>> >>
>> >> Cheers-- I was thinking of a kernel-level function though.
>> >>
>> >> cognet@ suggested using modfind("sound"), I'll go with that.
>> > Obvious question is what the panic is. Checking for modules loaded is
>> > papering over some issue.
>>
>> True, although I figured that it was a simple conflict, possibly to do
>> with sndstat.
>>
>> Also, I'm getting panics with the following patch, whether sound is
>> loaded or not :)
>>
>> +  if (modfind("sound") >= 0)
>> +    {
>> +      cmn_err (CE_WARN, "A conflicting sound driver is already loaded");
>> +      return EBUSY;
>> +    }
>> +
>>
>> Is there a better way to handle such conflicts?
>
> You have missed the point. There is some bug in oss driver that causing
> the panic. Presumed 'conflict' cannot cause the harm itself, besides not
> allowing second driver to attach to the same device, and should not result
> in panic. Trying to implement a half-measure that only covers the problem
> you do a mis-service.
>
> And you still did not provided the panic message.

I'm sorry, you're right.  However, your guess was in fact correct;
make_dev was being called, which returned a null pointer because it
failed.

The patch at [1] stops the panic, however I was hoping that returning
EBUSY would abort loading the module... At the moment it loads the
module, and doesn't create the sndstat dev, which causes weird errors
with the oss binary commands.

Since this solves the panic and anyone should be able to work out from
the warning message what the problem is, AND this is a port that
apparently no-one else uses, should this be sufficient?

BTW, it only affects FreeBSD 9+, couldn't reproduce on my 8.2 dev
machine, but could once I upgraded it.

Chris

[1] http://www.bayofrum.net/~crees/patches/oss-patch-kernel-OS-FreeBSD-os_freebsd.c