Migrate kernel-wiki:Kernel-Action-GitTheSource.md

docs/how-to/source-code/obtain-kernel-source-git.md

@@ -37,6 +37,90 @@ git clone https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jam
 
 See {ref}`exp-ubuntu-kernel-source-protocols` for more information.
 
+## Clone multiple releases using a shared reference repository
+
+Cloning a single kernel tree downloads several hundred megabytes of data. If
+you plan to work with more than one kernel release, you can save space and time
+by first downloading the upstream kernel tree and using it as a reference for
+subsequent clones:
+
+```{code-block} shell
+git clone https://kernel.ubuntu.com/ubuntu/linux.git
+git clone --reference linux https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy
+git clone --reference linux https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble
+```
+
+Each clone produces a new directory containing the full source and history.
+
+```{caution}
+Once two trees are linked this way, you cannot delete or move the upstream
+`linux` reference tree without manually updating
+`.git/objects/info/alternates` in each Ubuntu kernel tree that references it.
+```
+
+## Add multiple series as remotes
+
+If you are an advanced Git user, you can add each Ubuntu series as a remote to
+have all kernel series in a single Git repository, and switch between them
+using branches:
+
+```{code-block} shell
+git remote add jammy https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy
+git fetch jammy
+git checkout -b jammy --track jammy/master
+git checkout -b jammy-next --track jammy/master-next
+```
+
+## Work with multiple series in separate subdirectories
+
+To have the source for each kernel series available in its own subdirectory
+within a single Git repository, use `git subtree add`:
+
+```{code-block} shell
+git subtree add --prefix=jammy https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy master
+git subtree add --prefix=noble https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble master
+```
+
+This creates a `jammy/` subdirectory containing the Jammy kernel source and a
+`noble/` subdirectory containing the Noble kernel source, all within the same
+repository.
+
+To pull future updates into a subtree, specify the remote URL and ref
+explicitly — there is no automatic upstream tracking for subtrees:
+
+```{code-block} shell
+git subtree pull --prefix=jammy https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/jammy master
+```
+
+## Work with a specific kernel version using tags
+
+By default, cloning gives you the latest state of the `master` branch. To work
+with a specific previously released kernel version, use release tags. To list
+all available tags for a release:
+
+```{code-block} shell
+git tag -l Ubuntu-*
+```
+
+Example output:
+
+```{code-block} text
+Ubuntu-5.4.0-47.51
+Ubuntu-5.4.0-48.52
+Ubuntu-5.4.0-49.53
+Ubuntu-5.4.0-51.56
+Ubuntu-5.4.0-52.57
+...
+```
+
+To check out a specific version, create a branch pointing to that tag:
+
+```{code-block} shell
+git checkout -b temp Ubuntu-5.4.0-52.57
+```
+
+You can then work with that version — for example, by adding new commits.
+
 ## Related topics
 
 - {doc}`/explanation/ubuntu-linux-kernel-sources`
@@ -45,5 +129,3 @@ See {ref}`exp-ubuntu-kernel-source-protocols` for more information.
 % LINKS
 
 [git package]: https://packages.ubuntu.com/search?keywords=git
-
-% TODO: migrate the rest of the Wiki content