Lenz Grimmer's blog

While browsing the fabolous ThinkWiki pages I stumbled over this little gem: the lt_hotswap kernel module finally allows me to eject the CD-ROM drive in my Thinkpad T42's UltraBay without having to shut down Linux first. This module makes sure that the device is properly unregistered from the kernel's device list. Now I can replace it with e.g. a second battery on the fly and don't have to shutdown the OS completely! The installation on my SUSE Linux 10.1 system was quite easy: after downloading the source tarball from the SourceForge.net download page I performed the following commands:

tar zxvf lt_hotswap-0.3.6.tar.gz
cd lt_hotswap-0.3.6
make
sudo make install
sudo rcacpid restart
modprobe lt_hotswap

You need to have the kernel-source package installed, as well as the gcc compiler, of course. Now when I eject the little lever that allows me to pull out the CD-ROM drive from the UltraBay, the following message appears in /var/log/messages:

lt_hotswap: Requesting IDE eject!
lt_hotswap: Attempting to eject

Now the CD-ROM drive can be safely pulled from the UltraBay and e.g. exchanged with an additional battery. Inserting the battery yields the following kernel message:

kernel: ACPI: Battery Slot [BAT1] (battery present)

The battery info also appears in /proc/acpi/battery and is fully operational. Unfortunately battery monitoring tools like KPowersave or gkrellm don't display the second battery, but at least the kernel is happily using it. I can remove the battery again, but this event does not seem to get registered properly - the second battery remains visible in /proc/acpi/battery, but shows zero capacity and the "present" state does not change. But at least replacing the CD-ROM drive with the battery now workes fine, which was my major concern. And it is still possible to re-insert the CD-ROM drive again:

kernel: ide1: BM-DMA at 0x1868-0x186f, BIOS settings: hdc:pio, hdd:pio
kernel: Probing IDE interface ide1...
kernel: hdc: HL-DT-STCD-RW/DVD DRIVE GCC-4242N, ATAPI CD/DVD-ROM drive
kernel: ide1 at 0x170-0x177,0x376 on irq 15
kernel: hdc: ATAPI 24X DVD-ROM CD-R/RW drive, 2048kB Cache, UDMA(33)

If you want to enable the lt_hotswap module at bootup, you need to add its name to the MODULES_LOADED_ON_BOOT variable in the /etc/sysconfig/kernel configuration file.

If your Laptop uses an external docking station to host a CD-ROM drive, there are some good news for you: according to Andreas Jaeger's blog, the upcoming openSUSE 10.2 will actually provide a generic Dockutils framework that will support docking/undocking functionality for different laptops and vendors. It will be interesting to find out if this covers UltraBay devices as well.