2024-05-17-dracut-ext-kmods: add news item

Signed-off-by: Andrew Ammerlaan <andrewammerlaan@gentoo.org>

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+Title: Changes to dracut kernel module/microcode handling
+Author: Andrew Ammerlaan <andrewammerlaan@gentoo.org>
+Posted: 2024-05-17
+Revision: 1
+News-Item-Format: 2.0
+Display-If-Installed: sys-kernel/dracut
+Display-If-Installed: virtual/dist-kernel
+Display-If-Installed: sys-kernel/linux-firmware
+Display-If-Installed: sys-firmware/intel-microcode
+
+
+Impact
+====================
+
+Several changes were made regarding out-of-tree kernel modules, CPU
+microcode, and how these are handled in initial RAM file systems
+(initramfs) generated by sys-kernel/dracut for distribution kernels.
+Depending on the local Dracut and USE flag configuration, some
+configuration adjustments may be required as a result of these changes.
+
+Background (the problem)
+====================
+
+Previously Dracut implicitly included all out-of-tree kernel modules
+it could find. This leads to several problems:
+- It unnecessarily increases the size of the initramfs
+- It creates a bit of a mess when using distribution kernels, consider
+    the following:
+        1) Distribution kernel is upgraded
+        2) Initramfs for the new kernel is generated, it does not include
+            any out-of-tree kernel modules.
+        3) Portage triggers rebuild of the out-of-tree kernel modules
+        4) If zfs is installed, its rebuild will trigger an initramfs
+            re-installation. Otherwise no rebuild is triggered.
+    Problem: What is and is not included in the initramfs is now
+    ambiguous. It depends on the emerge order of the kernel modules
+    when zfs is used. And will completely change if at some later stage
+    regeneration of the initramfs is triggered manually via e.g.:
+        emerge --config sys-kernel/gentoo-kernel
+    As a result, Dracut's "--reproducible" setting is not working. And
+    the functionality of the initramfs may change (seemingly) at random.
+
+Background (the fix)
+====================
+
+Several things have been changed:
+- Out-of-tree kernel modules installed by portage are explicitly omitted
+    from the initramfs generated by Dracut by default.
+- Packages that install a kernel module for which it might make sense to
+    have it in the initramfs, have gained the "initramfs" USE flag. When
+    this flag is enabled, Dracut is instructed to include the installed
+    kernel modules. Packages for which it is essential that its kernel
+    modules are included in the initramfs have this new flag enabled
+    by default.
+- When distribution kernels are used (USE=dist-kernel), and a module
+    that should be in the initramfs is installed (USE=initramfs) the
+    initramfs is always re-generated.
+- The packages installing CPU microcode (sys-kernel/linux-firmware
+    and sys-firmware/intel-microcode) have been adjusted to mirror the
+    above changes for out-of-tree kernel modules. Both packages
+    have gained the "dist-kernel" USE flag, and the "initramfs" flag is
+    now enabled by default. When both flags are enabled, Dracut is
+    configured to include the installed microcode in the initramfs, and
+    then the initramfs is regenerated. When the "dist-kernel" flag is
+    disabled, the "initramfs" flag behaves as it previously did.
+
+User Action Required
+====================
+
+Users should double check two things:
+1) Please ensure that you are *not* globally enabling or disabling
+    the "initramfs" USE flag. Enabling it globally might result in an
+    unnecessarily large initramfs. Disabling it globally might result
+    in missing functionality in the initramfs. Which could lead to boot
+    failure if, for example, the zfs module is missing while the root
+    partition is a zfs.
+2) Any add_drivers, or omit_drivers lines in /etc/dracut.conf or
+    /etc/dracut.conf.d/* may override the Dracut configuration snippets
+    installed by the kernel module packages in
+    /usr/lib/dracut/dracut.conf.d.  Please review your Dracut
+    configuration files to ensure that you are not unintentionally
+    overriding the settings set by Portage.
+
+Frequently Asked Questions
+====================
+
+A package installing a kernel module I would like in my initramfs has
+not gained the "initramfs" USE flag. How do I proceed?
+
+    Please report a new bug on bugs.gentoo.org, requesting that the
+    package maintainer consider adding support to the package for
+    including the modules in the initramfs. In the meantime you can
+    locally override the configuration provided by the package (see
+    below). Note though that when distribution kernels are used,
+    regeneration of the initramfs must be triggered manually via e.g.:
+        emerge --config sys-kernel/gentoo-kernel
+
+How do I override the provided Dracut configuration snippets to
+include/exclude a custom list of modules?
+
+    To override the provided configuration snippet, create a new file
+    /etc/dracut.conf.d/10-PACKAGENAME.conf, replacing PACKAGENAME with
+    the name of the package providing the module. Add to this file:
+        omit_drivers+=" my list of drivers to omit "
+    and/or
+        add_drivers+=" my list of drivers to include "