Documentation/howto/using-topic-branches.txt - git - Git at Google

 Date: Mon, 15 Aug 2005 12:17:41 -0700
 From: tony.luck@intel.com
 Subject: Some tutorial text (was git/cogito workshop/bof at linuxconf au?)
 Abstract: In this article, Tony Luck discusses how he uses GIT
  as a Linux subsystem maintainer.

 Here's something that I've been putting together on how I'm using
 GIT as a Linux subsystem maintainer.

 -Tony

 Last updated w.r.t. GIT 0.99.9f

 Linux subsystem maintenance using GIT
 -------------------------------------

 My requirements here are to be able to create two public trees:

 1) A "test" tree into which patches are initially placed so that they
 can get some exposure when integrated with other ongoing development.
 This tree is available to Andrew for pulling into -mm whenever he wants.

 2) A "release" tree into which tested patches are moved for final
 sanity checking, and as a vehicle to send them upstream to Linus
 (by sending him a "please pull" request.)

 Note that the period of time that each patch spends in the "test" tree
 is dependent on the complexity of the change.  Since GIT does not support
 cherry picking, it is not practical to simply apply all patches to the
 test tree and then pull to the release tree as that would leave trivial
 patches blocked in the test tree waiting for complex changes to accumulate
 enough test time to graduate.

 Back in the BitKeeper days I achieved this by creating small forests of
 temporary trees, one tree for each logical grouping of patches, and then
 pulling changes from these trees first to the test tree, and then to the
 release tree.  At first I replicated this in GIT, but then I realised
 that I could so this far more efficiently using branches inside a single
 GIT repository.

 So here is the step-by-step guide how this all works for me.

 First create your work tree by cloning Linus's public tree:

  $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work

 Change directory into the cloned tree you just created

  $ cd work

 Set up a remotes file so that you can fetch the latest from Linus' master
 branch into a local branch named "linus":

  $ cat > .git/remotes/linus
  URL: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
  Pull: master:linus
  ^D

 and create the linus branch:

  $ git branch linus

 The "linus" branch will be used to track the upstream kernel.  To update it,
 you simply run:

  $ git fetch linus

 you can do this frequently (and it should be safe to do so with pending
 work in your tree, but perhaps not if you are in mid-merge).

 If you need to keep track of other public trees, you can add remote branches
 for them too:

  $ git branch another
  $ cat > .git/remotes/another
  URL: ... insert URL here ...
  Pull: name-of-branch-in-this-remote-tree:another
  ^D

 and run:

  $ git fetch another

 Now create the branches in which you are going to work, these start
 out at the current tip of the linus branch.

  $ git branch test linus
  $ git branch release linus

 These can be easily kept up to date by merging from the "linus" branch:

  $ git checkout test && git merge "Auto-update from upstream" test linus
  $ git checkout release && git merge "Auto-update from upstream" release linus

 Set up so that you can push upstream to your public tree (you need to
 log-in to the remote system and create an empty tree there before the
 first push).

  $ cat > .git/remotes/mytree
  URL: master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
  Push: release
  Push: test
  ^D

 and the push both the test and release trees using:

  $ git push mytree

 or push just one of the test and release branches using:

  $ git push mytree test
 or
  $ git push mytree release

 Now to apply some patches from the community.  Think of a short
 snappy name for a branch to hold this patch (or related group of
 patches), and create a new branch from the current tip of the
 linus branch:

  $ git checkout -b speed-up-spinlocks linus

 Now you apply the patch(es), run some tests, and commit the change(s).  If
 the patch is a multi-part series, then you should apply each as a separate
 commit to this branch.

  $ ... patch ... test  ... commit [ ... patch ... test ... commit ]*

 When you are happy with the state of this change, you can pull it into the
 "test" branch in preparation to make it public:

  $ git checkout test && git merge "Pull speed-up-spinlock changes" test speed-up-spinlocks

 It is unlikely that you would have any conflicts here ... but you might if you
 spent a while on this step and had also pulled new versions from upstream.

 Some time later when enough time has passed and testing done, you can pull the
 same branch into the "release" tree ready to go upstream.  This is where you
 see the value of keeping each patch (or patch series) in its own branch.  It
 means that the patches can be moved into the "release" tree in any order.

  $ git checkout release && git merge "Pull speed-up-spinlock changes" release speed-up-spinlocks

 After a while, you will have a number of branches, and despite the
 well chosen names you picked for each of them, you may forget what
 they are for, or what status they are in.  To get a reminder of what
 changes are in a specific branch, use:

  $ git-whatchanged branchname ^linus | git-shortlog

 To see whether it has already been merged into the test or release branches
 use:

  $ git-rev-list branchname ^test
 or
  $ git-rev-list branchname ^release

 [If this branch has not yet been merged you will see a set of SHA1 values
 for the commits, if it has been merged, then there will be no output]

 Once a patch completes the great cycle (moving from test to release, then
 pulled by Linus, and finally coming back into your local "linus" branch)
 the branch for this change is no longer needed.  You detect this when the
 output from:

  $ git-rev-list branchname ^linus

 is empty.  At this point the branch can be deleted:

  $ git branch -d branchname

 Some changes are so trivial that it is not necessary to create a separate
 branch and then merge into each of the test and release branches.  For
 these changes, just apply directly to the "release" branch, and then
 merge that into the "test" branch.

 To create diffstat and shortlog summaries of changes to include in a "please
 pull" request to Linus you can use:

  $ git-whatchanged -p release ^linus | diffstat -p1
 and
  $ git-whatchanged release ^linus | git-shortlog


 Here are some of the scripts that I use to simplify all this even further.

 ==== update script ====
 # Update a branch in my GIT tree.  If the branch to be updated
 # is "linus", then pull from kernel.org.  Otherwise merge local
 # linus branch into test|release branch

 case "$1" in
 test|release)
 	git checkout $1 && git merge "Auto-update from upstream" $1 linus
 	;;
 linus)
 	before=$(cat .git/refs/heads/linus)
 	git fetch linus
 	after=$(cat .git/refs/heads/linus)
 	if [ $before != $after ]
 	then
 		git-whatchanged $after ^$before | git-shortlog
 	fi
 	;;
 *)
 	echo "Usage: $0 linus|test|release" 1>&2
 	exit 1
 	;;
 esac

 ==== merge script ====
 # Merge a branch into either the test or release branch

 pname=$0

 usage()
 {
 	echo "Usage: $pname branch test|release" 1>&2
 	exit 1
 }

 if [ ! -f .git/refs/heads/"$1" ]
 then
 	echo "Can't see branch <$1>" 1>&2
 	usage
 fi

 case "$2" in
 test|release)
 	if [ $(git-rev-list $1 ^$2 | wc -c) -eq 0 ]
 	then
 		echo $1 already merged into $2 1>&2
 		exit 1
 	fi
 	git checkout $2 && git merge "Pull $1 into $2 branch" $2 $1
 	;;
 *)
 	usage
 	;;
 esac

 ==== status script ====
 # report on status of my ia64 GIT tree

 gb=$(tput setab 2)
 rb=$(tput setab 1)
 restore=$(tput setab 9)

 if [ `git-rev-list release ^test | wc -c` -gt 0 ]
 then
 	echo $rb Warning: commits in release that are not in test $restore
 	git-whatchanged release ^test
 fi

 for branch in `ls .git/refs/heads`
 do
 	if [ $branch = linus -o $branch = test -o $branch = release ]
 	then
 		continue
 	fi

 	echo -n $gb ======= $branch ====== $restore " "
 	status=
 	for ref in test release linus
 	do
 		if [ `git-rev-list $branch ^$ref | wc -c` -gt 0 ]
 		then
 			status=$status${ref:0:1}
 		fi
 	done
 	case $status in
 	trl)
 		echo $rb Need to pull into test $restore
 		;;
 	rl)
 		echo "In test"
 		;;
 	l)
 		echo "Waiting for linus"
 		;;
 	"")
 		echo $rb All done $restore
 		;;
 	*)
 		echo $rb "<$status>" $restore
 		;;
 	esac
 	git-whatchanged $branch ^linus | git-shortlog
 done
	Date: Mon, 15 Aug 2005 12:17:41 -0700
	From: tony.luck@intel.com
	Subject: Some tutorial text (was git/cogito workshop/bof at linuxconf au?)
	Abstract: In this article, Tony Luck discusses how he uses GIT
	as a Linux subsystem maintainer.

	Here's something that I've been putting together on how I'm using
	GIT as a Linux subsystem maintainer.

	-Tony

	Last updated w.r.t. GIT 0.99.9f

	Linux subsystem maintenance using GIT
	-------------------------------------

	My requirements here are to be able to create two public trees:

	1) A "test" tree into which patches are initially placed so that they
	can get some exposure when integrated with other ongoing development.
	This tree is available to Andrew for pulling into -mm whenever he wants.

	2) A "release" tree into which tested patches are moved for final
	sanity checking, and as a vehicle to send them upstream to Linus
	(by sending him a "please pull" request.)

	Note that the period of time that each patch spends in the "test" tree
	is dependent on the complexity of the change. Since GIT does not support
	cherry picking, it is not practical to simply apply all patches to the
	test tree and then pull to the release tree as that would leave trivial
	patches blocked in the test tree waiting for complex changes to accumulate
	enough test time to graduate.

	Back in the BitKeeper days I achieved this by creating small forests of
	temporary trees, one tree for each logical grouping of patches, and then
	pulling changes from these trees first to the test tree, and then to the
	release tree. At first I replicated this in GIT, but then I realised
	that I could so this far more efficiently using branches inside a single
	GIT repository.

	So here is the step-by-step guide how this all works for me.

	First create your work tree by cloning Linus's public tree:

	$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work

	Change directory into the cloned tree you just created

	$ cd work

	Set up a remotes file so that you can fetch the latest from Linus' master
	branch into a local branch named "linus":

	$ cat > .git/remotes/linus
	URL: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
	Pull: master:linus
	^D

	and create the linus branch:

	$ git branch linus

	The "linus" branch will be used to track the upstream kernel. To update it,
	you simply run:

	$ git fetch linus

	you can do this frequently (and it should be safe to do so with pending
	work in your tree, but perhaps not if you are in mid-merge).

	If you need to keep track of other public trees, you can add remote branches
	for them too:

	$ git branch another
	$ cat > .git/remotes/another
	URL: ... insert URL here ...
	Pull: name-of-branch-in-this-remote-tree:another
	^D

	and run:

	$ git fetch another

	Now create the branches in which you are going to work, these start
	out at the current tip of the linus branch.

	$ git branch test linus
	$ git branch release linus

	These can be easily kept up to date by merging from the "linus" branch:

	$ git checkout test && git merge "Auto-update from upstream" test linus
	$ git checkout release && git merge "Auto-update from upstream" release linus

	Set up so that you can push upstream to your public tree (you need to
	log-in to the remote system and create an empty tree there before the
	first push).

	$ cat > .git/remotes/mytree
	URL: master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
	Push: release
	Push: test
	^D

	and the push both the test and release trees using:

	$ git push mytree

	or push just one of the test and release branches using:

	$ git push mytree test
	or
	$ git push mytree release

	Now to apply some patches from the community. Think of a short
	snappy name for a branch to hold this patch (or related group of
	patches), and create a new branch from the current tip of the
	linus branch:

	$ git checkout -b speed-up-spinlocks linus

	Now you apply the patch(es), run some tests, and commit the change(s). If
	the patch is a multi-part series, then you should apply each as a separate
	commit to this branch.

	$ ... patch ... test ... commit [ ... patch ... test ... commit ]*

	When you are happy with the state of this change, you can pull it into the
	"test" branch in preparation to make it public:

	$ git checkout test && git merge "Pull speed-up-spinlock changes" test speed-up-spinlocks

	It is unlikely that you would have any conflicts here ... but you might if you
	spent a while on this step and had also pulled new versions from upstream.

	Some time later when enough time has passed and testing done, you can pull the
	same branch into the "release" tree ready to go upstream. This is where you
	see the value of keeping each patch (or patch series) in its own branch. It
	means that the patches can be moved into the "release" tree in any order.

	$ git checkout release && git merge "Pull speed-up-spinlock changes" release speed-up-spinlocks

	After a while, you will have a number of branches, and despite the
	well chosen names you picked for each of them, you may forget what
	they are for, or what status they are in. To get a reminder of what
	changes are in a specific branch, use:

	$ git-whatchanged branchname ^linus \| git-shortlog

	To see whether it has already been merged into the test or release branches
	use:

	$ git-rev-list branchname ^test
	or
	$ git-rev-list branchname ^release

	[If this branch has not yet been merged you will see a set of SHA1 values
	for the commits, if it has been merged, then there will be no output]

	Once a patch completes the great cycle (moving from test to release, then
	pulled by Linus, and finally coming back into your local "linus" branch)
	the branch for this change is no longer needed. You detect this when the
	output from:

	$ git-rev-list branchname ^linus

	is empty. At this point the branch can be deleted:

	$ git branch -d branchname

	Some changes are so trivial that it is not necessary to create a separate
	branch and then merge into each of the test and release branches. For
	these changes, just apply directly to the "release" branch, and then
	merge that into the "test" branch.

	To create diffstat and shortlog summaries of changes to include in a "please
	pull" request to Linus you can use:

	$ git-whatchanged -p release ^linus \| diffstat -p1
	and
	$ git-whatchanged release ^linus \| git-shortlog


	Here are some of the scripts that I use to simplify all this even further.

	==== update script ====
	# Update a branch in my GIT tree. If the branch to be updated
	# is "linus", then pull from kernel.org. Otherwise merge local
	# linus branch into test\|release branch

	case "$1" in
	test\|release)
	git checkout $1 && git merge "Auto-update from upstream" $1 linus
	;;
	linus)
	before=$(cat .git/refs/heads/linus)
	git fetch linus
	after=$(cat .git/refs/heads/linus)
	if [ $before != $after ]
	then
	git-whatchanged $after ^$before \| git-shortlog
	fi
	;;
	*)
	echo "Usage: $0 linus\|test\|release" 1>&2
	exit 1
	;;
	esac

	==== merge script ====
	# Merge a branch into either the test or release branch

	pname=$0

	usage()
	{
	echo "Usage: $pname branch test\|release" 1>&2
	exit 1
	}

	if [ ! -f .git/refs/heads/"$1" ]
	then
	echo "Can't see branch <$1>" 1>&2
	usage
	fi

	case "$2" in
	test\|release)
	if [ $(git-rev-list $1 ^$2 \| wc -c) -eq 0 ]
	then
	echo $1 already merged into $2 1>&2
	exit 1
	fi
	git checkout $2 && git merge "Pull $1 into $2 branch" $2 $1
	;;
	*)
	usage
	;;
	esac

	==== status script ====
	# report on status of my ia64 GIT tree

	gb=$(tput setab 2)
	rb=$(tput setab 1)
	restore=$(tput setab 9)

	if [ `git-rev-list release ^test \| wc -c` -gt 0 ]
	then
	echo $rb Warning: commits in release that are not in test $restore
	git-whatchanged release ^test
	fi

	for branch in `ls .git/refs/heads`
	do
	if [ $branch = linus -o $branch = test -o $branch = release ]
	then
	continue
	fi

	echo -n $gb ======= $branch ====== $restore " "
	status=
	for ref in test release linus
	do
	if [ `git-rev-list $branch ^$ref \| wc -c` -gt 0 ]
	then
	status=$status${ref:0:1}
	fi
	done
	case $status in
	trl)
	echo $rb Need to pull into test $restore
	;;
	rl)
	echo "In test"
	;;
	l)
	echo "Waiting for linus"
	;;
	"")
	echo $rb All done $restore
	;;
	*)
	echo $rb "<$status>" $restore
	;;
	esac
	git-whatchanged $branch ^linus \| git-shortlog
	done