Date: Thu, 29 Dec 2011 13:50:14 +0000 From: Chris Rees <utisoft@gmail.com> To: Kostik Belousov <kostikbel@gmail.com> Cc: hackers@freebsd.org Subject: Re: Checking for other kernel modules on load Message-ID: <CADLo83-Cz8KOafUNj-u6E=-8rcfwN3t544qzBrbEbtd_rHKD7g@mail.gmail.com> In-Reply-To: <20111229133516.GJ50300@deviant.kiev.zoral.com.ua> References: <CADLo838QjrUunABB=3R_d6NO9bnNAcKXM%2BZt3DRam3RnOGnxGw@mail.gmail.com> <B8D5A1B2-4790-48CA-AAC3-D4333D52ECEB@gsoft.com.au> <CADLo8382uPC6YmreCz8irVuiOhSwc2axJTgQRpVJk-%2B0Win8rQ@mail.gmail.com> <20111228135641.GV50300@deviant.kiev.zoral.com.ua> <CADLo83-OBNWzY_r_oFmUBjkNoCpifJ0_u9dYN52YTZ69X06o4Q@mail.gmail.com> <20111228150023.GY50300@deviant.kiev.zoral.com.ua> <CADLo83-zRNXWyPrs-7MtPfd2uz=56HsWtDaAoFGx8=S=ChQhwQ@mail.gmail.com> <20111229120333.GI50300@deviant.kiev.zoral.com.ua> <CADLo83-Dm8_k79zsfxJ_X6RW04AawcZaATcvZ86B3v26k32EmQ@mail.gmail.com> <20111229133516.GJ50300@deviant.kiev.zoral.com.ua>
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2011/12/29 Kostik Belousov <kostikbel@gmail.com>:
> On Thu, Dec 29, 2011 at 12:53:19PM +0000, Chris Rees wrote:
>> 2011/12/29 Kostik Belousov <kostikbel@gmail.com>:
>> > On Thu, Dec 29, 2011 at 11:46:57AM +0000, Chris Rees wrote:
>> >> 2011/12/28 Kostik Belousov <kostikbel@gmail.com>:
>> >> > On Wed, Dec 28, 2011 at 02:53:42PM +0000, Chris Rees wrote:
>> >> >> 2011/12/28 Kostik Belousov <kostikbel@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@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? =
=A0I could
>> >> >> >> >> even check for /dev/sndstat, though that doesn't seem elegan=
t 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 load=
ed is
>> >> >> > papering over some issue.
>> >> >>
>> >> >> True, although I figured that it was a simple conflict, possibly t=
o do
>> >> >> with sndstat.
>> >> >>
>> >> >> Also, I'm getting panics with the following patch, whether sound i=
s
>> >> >> loaded or not :)
>> >> >>
>> >> >> + =A0if (modfind("sound") >=3D 0)
>> >> >> + =A0 =A0{
>> >> >> + =A0 =A0 =A0cmn_err (CE_WARN, "A conflicting sound driver is alre=
ady loaded");
>> >> >> + =A0 =A0 =A0return EBUSY;
>> >> >> + =A0 =A0}
>> >> >> +
>> >> >>
>> >> >> Is there a better way to handle such conflicts?
>> >> >
>> >> > You have missed the point. There is some bug in oss driver that cau=
sing
>> >> > the panic. Presumed 'conflict' cannot cause the harm itself, beside=
s 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 p=
roblem
>> >> > you do a mis-service.
>> >> >
>> >> > And you still did not provided the panic message.
>> >>
>> >> I'm sorry, you're right. =A0However, 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 fro=
m
>> >> 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, AFAI=
R.
>> > So you get absolutely undeterministic behaviour which driver is refere=
nced
>> > by devfs node.
>> >
>> >> Chris
>> >>
>> >> [1] http://www.bayofrum.net/~crees/patches/oss-patch-kernel-OS-FreeBS=
D-os_freebsd.c
>> >
>> > I highly recommend to return error in case of any make_dev_p(9) failur=
e, 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?
>
> =A0 =A0 =A0 =A0error =3D make_dev_p();
> =A0 =A0 =A0 =A0if (error !=3D 0) {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0printf("Error creating device node /dev/%s=
: %d\n", name, error);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return (error);
> =A0 =A0 =A0 =A0}
>
No, that's what I wanted. Thank you.
Chris
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