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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="SPECIAL-DEVS"
>Devices requiring special
configuration</A
></H1
><P
>Some devices require a bit of extra configuration beyond the
normal aliasing of a device to a module. </P
><P
></P
><UL
><LI
><P
>Character devices on major number 10: <A
HREF="special-devs.html#MISCDEVS"
>The miscellaneous
devices</A
></P
></LI
><LI
><P
><A
HREF="special-devs.html#SCSIDEVS"
>SCSI devices</A
>
</P
></LI
><LI
><P
><A
HREF="special-devs.html#PRE-POST"
>Devices that require
special initialization</A
></P
></LI
></UL
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="MISCDEVS"
>char-major-10 : Mice, watchdogs and randomness</A
></H2
><P
>Hardware devices are usually identified through their
major device numbers, e.g. ftape is
<TT
CLASS="LITERAL"
>char-major-27</TT
>. However, if you look through
the entries in <TT
CLASS="FILENAME"
>/dev</TT
> for char major 10,
you will see that this is a bunch of very different devices,
including </P
><P
></P
><UL
><LI
><P
>Mice of various sorts (bus mice, PS/2
mice)</P
></LI
><LI
><P
>Watchdog devices </P
></LI
><LI
><P
>The kernel <TT
CLASS="FILENAME"
>random</TT
>
device </P
></LI
><LI
><P
>APM (Advanced Power Management) interface
</P
></LI
></UL
><P
>These devices are controlled by several different
modules, not a single one, and therefore the kerneld
configuration for these <I
CLASS="EMPHASIS"
>misc. devices</I
>
use the major number <I
CLASS="EMPHASIS"
>and</I
> the minor
number: </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias char-major-10-1 psaux # For PS/2 mouse
alias char-major-10-130 wdt # For WDT watchdog</PRE
></TD
></TR
></TABLE
><P
>You need a kernel version 1.3.82 or later to use this;
earlier versions do not pass the minor number to kerneld,
making it impossible for kerneld to figure out which of the
misc. device modules to load. </P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="SCSIDEVS"
>Loading SCSI drivers: The
<TT
CLASS="LITERAL"
>scsi_hostadapter</TT
> entry</A
></H2
><P
>Drivers for SCSI devices consist of a driver for the
SCSI host adapter (e.g. an Adaptec 1542), and a driver for the
type of SCSI device you use, e.g. a hard disk, a CD-ROM or a
tape-drive. All of these can be loaded as modules. However,
when you want to access e.g. the CD-ROM drive that is
connected to the Adaptec card, the kernel and kerneld only
knows that it needs to load the <TT
CLASS="FILENAME"
>sr_mod</TT
>
module in order to support SCSI CD-ROM's; it does not know
what SCSI controller the CD-ROM is connected to, and hence
does not know what module to load to support the SCSI
controller. </P
><P
>To resolve this, you can add an entry for the SCSI
driver module to your <TT
CLASS="FILENAME"
>/etc/conf.modules</TT
>
that tells kerneld which of the many possible SCSI controller
modules it should load: </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> alias scd0 sr_mod # sr_mod for SCSI CD-ROM's ...
alias scsi_hostadapter aha1542 # ... need the Adaptec driver</PRE
></TD
></TR
></TABLE
><P
>This only works with kernel version 1.3.82 or later. </P
><P
>This works if you have only one SCSI controller. If you
have more than one, things become a little more
difficult.</P
><P
>In general, you cannot have kerneld load a driver for a
SCSI host adapter, if a driver for another host adapter is
already installed. You must either build both drivers into
your kernel (not as modules), or load the modules
manually.</P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>There <I
CLASS="EMPHASIS"
>is</I
> a way that you can
have kerneld load multiple SCSI drivers. James Tsiao came up
with this idea:</P
><BLOCKQUOTE
CLASS="BLOCKQUOTE"
><P
> You can easily have kerneld load the second scsi
driver by setting up the dependency in your modules.dep by
hand. You just need an entry like:</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> /lib/modules/2.0.30/scsi/st.o: /lib/modules/2.0.30/scsi/aha1542.o</PRE
></TD
></TR
></TABLE
><P
>To have kerneld load the
<TT
CLASS="FILENAME"
>aha1542.o</TT
> before it loads
<TT
CLASS="FILENAME"
>st.o</TT
>. My machine at home is set up
almost exactly like the setup above, and it works fine for
all my secondary scsi devices, including tape, cd-rom, and
generic scsi devices. The drawback is that
<B
CLASS="COMMAND"
>depmod -a</B
> can't autodetect these
dependencies, so the user needs to add them by hand, and
not run <B
CLASS="COMMAND"
>depmod -a</B
> on boot up. But once
it is set up, kerneld will autoload the
<TT
CLASS="FILENAME"
>aha1542.o</TT
> just
fine.</P
></BLOCKQUOTE
></BLOCKQUOTE
></DIV
><P
>You should be aware, that this technique only works if
you have different kinds of SCSI devices on the two
controllers, for example, hard disks on one controller, and
cd-rom drives, tapes or generic SCSI devices on another.</P
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="PRE-POST"
>When loading a module isn't enough: The
<TT
CLASS="LITERAL"
>post-install</TT
> entry</A
></H2
><P
>Sometimes, just loading the module is not enough to get
things working. For instance, if you have your sound card
compiled as a module, it is often convenient to set a certain
volume level. Only problem is, the setting vanishes the next
time the module is loaded. Here is a neat trick from Ben
Galliart (<TT
CLASS="EMAIL"
><<A
HREF="mailto:bgallia@luc.edu"
>bgallia@luc.edu</A
>></TT
>): </P
><BLOCKQUOTE
CLASS="BLOCKQUOTE"
><P
>The final solution required installing the <A
HREF="ftp://sunsite.unc.edu/pub/Linux/apps/sound/mixers/"
TARGET="_top"
> <SPAN
CLASS="PRODUCTNAME"
>setmix</SPAN
> package</A
> and then
adding the following line to my
<TT
CLASS="FILENAME"
>/etc/conf.modules</TT
>: </P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>post-install sound /usr/local/bin/setmix -f /etc/volume.conf</PRE
></TD
></TR
></TABLE
></BLOCKQUOTE
><P
>What this does is that after the sound module is loaded,
kerneld runs the command indicated by the
<TT
CLASS="LITERAL"
>post-install sound</TT
> entry. So the sound
module gets configured with the command
<B
CLASS="COMMAND"
>/usr/local/bin/setmix -f
/etc/volume.conf</B
>.</P
><P
>This may be useful for other modules as well, for
example the <TT
CLASS="FILENAME"
>lp</TT
> module can be configured
with the <TT
CLASS="FILENAME"
>tunelp</TT
> program by adding
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> post-install lp tunelp options</PRE
></TD
></TR
></TABLE
><P
>For kerneld to recognize these options, you will need a
version of kerneld that is 1.3.69f or later.</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>An earlier version of this mini-HOWTO mentioned a
pre-remove option, that might be used to run a command just
before kerneld removed a module. However, this has never
worked and its use is therefore discouraged - most likely,
this option will disappear in a future kerneld release. The
whole issue of module settings is undergoing some change at
the moment, and may look different on your system by the
time you read this. </P
></BLOCKQUOTE
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