docs: update component documentation

docs/howto/code/components/snapcraft.yaml

@@ -7,7 +7,7 @@ confinement: strict
 
 components:
   translations:
-    type: test
+    type: standard
     summary: Translations modules
     description: Translations modules
     version: "1.0"

docs/reference/bases.rst

@@ -86,6 +86,8 @@ channel.
 Snaps with a ``devel`` build base must have a ``grade`` of ``devel`` and cannot
 be promoted to ``stable`` or ``candidate`` channels.
 
+.. _kernel-snap-reference:
+
 Kernel snaps
 ^^^^^^^^^^^^
 

docs/reference/components.rst

@@ -1,10 +1,48 @@
 Components
-**********
+==========
 
 .. include:: /reuse/components-intro.rst
 
-Components employ a `Craft Parts`_ feature called ``partitions``. See
-:ref:`component and partitions<components-and-partitions>` for an explanation
-on how they are related.
+Like snaps, components are packaged a squashfs file. When installed, the
+component is mounted at the path ``$SNAP/../components/$SNAP_REVISION/`` so
+the host snap can access it.
+
+Types
+-----
+
+A component must declare a ``type`` in the project's ``snapcraft.yaml`` file.
+For some types, Snapcraft may place requirements on the files of a component
+and snapd may have special handling for the component.
+
+Standard
+~~~~~~~~
+
+The ``standard`` type is the general use type for components. It should be used
+when no specific type applies. Snapcraft has no requirements or special
+handling for this type.
+
+Kernel-modules
+~~~~~~~~~~~~~~
+
+The ``kernel-modules`` type should only be used for
+:ref:`kernel snaps<kernel-snap-reference>`. These components are for kernel
+modules and firmware that are made available to the system after installation.
+This type allows the kernel to find firmware and for users to load kernel
+modules with ``modprobe``.
+
+Static modules should be organized under ``modules/<kernel-version>/`` in the
+component, where ``<kernel-version>`` is the version reported by ``uname -r``.
+
+Firmware should be organized under ``firmware/`` in the component.
+
+Modules and firmware may be dynamically generated by the component's
+``install`` or ``refresh`` hooks:
+
+- Modules generated by a hook should be placed in
+  ``$SNAP_DATA/modules/<kernel-version>/``.
+- Firmware generated by a hook should be placed in ``$SNAP_DATA/firmware/``.
+
+To allow loading of dynamically generated modules and firmware, the snap's
+``meta/kernel.yaml`` file must declare ``dynamic-modules: $SNAP_DATA``.
 
 .. include:: /common/craft-parts/reference/partition_specific_output_directory_variables.rst