Update gentoo kernel

In gentoo, everything gets updated via portage using "emerge". For the kernel, emerge only updates the source. You have to manually configure, compile, and install the kernel source into a kernel binary. This is to allow you to keep your kernel tuned for your machine.

Set up Symlink to Kernel Source

Gentoo installs the source in different "slots", here:

/usr/src/linux-#kernelversion#-gentoo-#gentooreleaseversion#

I don't use the [symlink] USE flag for gentoo-sources. If you use it, it will symlink the latest downloaded source, as soon as you download it, to:

/usr/src/linux

I prefer to do this manually when I have time to actually install the kernel, so the pointer to the kernel header files matches the installed kernel - that seems important! When you are ready to install the kernel, set up the symlink as follows:

cd /usr/src
rm linux
ln -s linux-#kernelversion#-gentoo-#gentooreleaseversion# linux

Steps To Install Kernel

su -
emerge sys-kernel/gentoo-sources
Check the /usr/src/linux symlink, as described above.
cd /usr/src/linux
make menuconfig (and configure - see Configure MythTV kernel)
make && make modules_install
mount /boot (if needed)
ls /boot
cp arch/x86_64/boot/bzImage /boot/kernel-genkernel-x86)64-#kernelversion#-gentoo-#gentooreleaseversion#_mdm-menuconfig
emacs /boot/grub/grub.conf (and add your shiny new kernel to the default top of the list)
(optional) emerge -av --unmerge "<gentoo-sources-2.6.##"
(optional) purge older kernels from /boot/ (and /usr/src/ if previous step didn't do the trick)

Post-kernel-installation Steps

There are certain packages that are kernel-specific, and must be installed AFTER the kernel is updated. Note that this is only necessary if you are changing kernel versions, NOT if you just adjust the settings on an already-installed kernel.

install nvidia or ati binary driver ([nvidia-drivers], [ati-drivers])
(old) install a new ivtv that matches the new kernel version
"If your (ntfs3g) driver stops working after you have upgraded your kernel then you should reinstall fuse."
lirc (for LCD display, and maybe some day, a remote) :>

In theory you can use the following to automatically reinstall kernel-dependent modules:

module-rebuild rebuild

But I used a more manual approach, as module-rebuild didn't work:

module-rebuild list                   # to see what it WOULD rebuild
emerge ati-drivers
eselect opengl set ati
reboot
emacs /etc/portage/package.mask       # adjust ivtv version if needed
                                      # it has to match your kernel version
                                      # comment out ivtv line to get latest version
emerge sys-fs/fuse
emerge lirc
update-modules
reboot

Even better, if you have just adjusted the kernel, and not bumped up the version, just do this:

module-rebuild list                   # to see what it WOULD rebuild
emerge ati-drivers sys-fs/fuse lirc
update-modules
eselect opengl set ati
reboot

If you've done an emerge of media-video/nvidia-settings, you can run it to adjust the resolution, etc., dynamically in X.