Re: [gentoo-user] Re: kernel config hell

[Jerry McBride]

On Saturday 27 December 2008 10:48:19 am Harry Putnam wrote:
> Nikos Chantziaras <realnc@×××××.de> writes:
>
>
> [...]
>
> >>> Well, my bit of wisdom here: Don't use modules.  Do a "make
> >>> menuconfig", disable everything you don't need, and compile
> >>> everything you need in-kernel instead of as a module.
> >>
> >> I'd say the "disable everything you don't need" part is what Harry's
> >> mail is all about.
> >
> > Well, finding out what every installed module does isn't going to
> > help anyway.  I'd start with only the modules currently used after a
> > fresh boot (lsmod).  If you compile those in-kernel, it will boot.
> > Everything else can be tweaked later.
>
> Yeah, I talked about that in OP.  But the only kernel I've got working
> at the moment is a genkernel and it installs 80+ modules.
>
> rmmoding my way through those is what lead to my post.  Some indicate
> they are in use but I can see they aren't related to things I actually
> need.   Digging that bit of info up is what I've been talking about.
>
> > Dirk Heinrichs <dirk.heinrichs@××××××.de> writes:
> >
> > What could help you here is a "make xconfig". It's similar to "make
> > menuconfig" but has a nice QT user interface. I would recommend to
> > browse through it once and look at the help texts which are shown in
> > the lower right pane for each option you klick. Based on this
> > information, you can then decide wether or not to enable that option
> > or even compile it as module.
>
> I have looked at that before but didn't think it was any better than
> `menuconfig' and the '/' help tool.
>
> Many times the help provided doesn't really explain what a given
> setting does.  In fact in most cases it does not.
>
> What is really aggravating is that it doesn't even really tell you
> what exact thing in .config is being set with the various hundreds of
> options. I mean when you do set something, you don't really get to see
> what is being set inside of .config.
>
> I don't have X running currently so its a mute point, but is the help
> provided in xconfig and different than that available in `menuconfig'?
>
> >> Details:
> >> I'm at a point where any pared down kernel config I've built and
> >> tried has some terrible thing wrong with it. Usually involving udev
> >> and openrc someway or other... things not getting started or
> >> mounted etc etc.
> >
> > With udev, those things usually work automatically. However, you
> > must make sure that everything needed for accessing the root
> > filesystem must be compiled into the kernel. That usually includes
> > the driver for the chipset that operates your harddisks, harddisk
> > support and the filesystem used for /.
> >
> >> I'd think there would be some kind of cross reference somewhere that
> >> would connect module names to what they do, and what .config options
> >> are associated.
> >
> > I don't know of any. But in most cases, the module name is listed in
> > the help text.
> >
> >> Another path is to find the *.ko names in /lib/modules and use the
> >> absolute name to track them down in the kernel sources where there is
> >> usually a README of some sort in the tree leading to the *.ko.
> >
> > Somtimes, you can also simply guess by module name, for example:
> > joydev.ko -> Joy(stick)Dev(ice).
> >
> >> But my god what a slow and painful way to find out what these
> >> modules do.
> >
> > Yes, that's true. The browsing method may give you a rough overview
> > within an hour or two.
> >
> >> Just rmmod is another way but again a very slow and painful way.
> >> Maybe a module is used only occasionally and rmmodding may not show
> >> what it was for right away.  What ever fails may not happen
> >> immediately.
> >
> > Or try modprobe + dmesg instead. Usually a driver module tells
> > wether it has found some pice of supported hardware or not.
>
> Now that is a good piece of advice there... I did notice that rmmoding
> and modprobing can give you more info than you expect if you hit
> something that the module latches onto.
>
> I'm finding somewhat rough sledding in dmesg too.  I find the ethernet
> stuff with no problem and, by now, know what I need there.
>
> My hardware is pretty common stuff, not even any sata discs, all ata.
> and I'm still not sure which driver is needed there.
>
> On the last attempted kernel, I just went menuconfig on a copy of the
> genkernel .config and turned off a number of things I was pretty sure
> didn't apply to me (all wireless for example) or anything but ethernet
> under the network section. All firmware turned off.
> Stuff I've never needed before.
>
> Every thing mounted but still no network was started or any of the
> stuff listed in `rc-update show'.
>
> I was dumped out into a root shell where I was able to modprobe and
> '/etc/init.d/bla start' my way into a fully running system.
>
> So the stuff was there but something (I suspect udev) blocked it
> starting up like it should.
>
> At the same time a genkernel built kernel just boots as expected so
> clearly something was turned off that shouldn't have been.
>
> Right now my dmesg is clogged up with stuff since bootup so I'm going
> to reboot the genkernel built kernel and have a close look at dmesg
> (again for the 10th time ..) rmmod and modprobe and see what I find.


Jumping in the middle here....

On a new platform I usually just use lspci and "cat /proc/cpuinfo". From that 
I can determine what processor I have and what hardware is plugged into the 
pci bus... then all I have to consider is what gets plugged into the usb, 
firewire, parallel or serial ports... I've always rolled my own kernels and 
find it quite rewarding impressing the newbies with my efforts.

That said... always keep two kernels around... one you KNOW works and the 
other for fine tuning or testing.

Cheers and Merry Christmas.





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                             Jerome D. McBride
                                       
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