Checking for other kernel modules on load

[Chris Rees]

2011/12/29 Kostik Belousov <kostikbel at gmail.com>:
> On Thu, Dec 29, 2011 at 11:46:57AM +0000, Chris Rees wrote:
>> 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.
> On 8.2, there is no check in the devfs for duplicated cdev names, AFAIR.
> So you get absolutely undeterministic behaviour which driver is referenced
> by devfs node.
>
>> Chris
>>
>> [1] http://www.bayofrum.net/~crees/patches/oss-patch-kernel-OS-FreeBSD-os_freebsd.c
>
> I highly recommend to return error in case of any make_dev_p(9) failure, and
> not only EEXIST.

That'd be great-- but I can't work out how to do it :(

Do I need to return a different value?

Chris