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diff --git a/Documentation/howto/rebase-from-internal-branch.txt b/Documentation/howto/rebase-from-internal-branch.txt new file mode 100644 index 000000000000..02cb5f758d6f --- /dev/null +++ b/Documentation/howto/rebase-from-internal-branch.txt @@ -0,0 +1,164 @@ +From: Junio C Hamano <gitster@pobox.com> +To: git@vger.kernel.org +Cc: Petr Baudis <pasky@suse.cz>, Linus Torvalds <torvalds@osdl.org> +Subject: Re: sending changesets from the middle of a git tree +Date: Sun, 14 Aug 2005 18:37:39 -0700 +Abstract: In this article, JC talks about how he rebases the + public "pu" branch using the core Git tools when he updates + the "master" branch, and how "rebase" works. Also discussed + is how this applies to individual developers who sends patches + upstream. +Content-type: text/asciidoc + +How to rebase from an internal branch +===================================== + +-------------------------------------- +Petr Baudis <pasky@suse.cz> writes: + +> Dear diary, on Sun, Aug 14, 2005 at 09:57:13AM CEST, I got a letter +> where Junio C Hamano <junkio@cox.net> told me that... +>> Linus Torvalds <torvalds@osdl.org> writes: +>> +>> > Junio, maybe you want to talk about how you move patches from your "pu" +>> > branch to the real branches. +>> +> Actually, wouldn't this be also precisely for what StGIT is intended to? +-------------------------------------- + +Exactly my feeling. I was sort of waiting for Catalin to speak +up. With its basing philosophical ancestry on quilt, this is +the kind of task StGIT is designed to do. + +I just have done a simpler one, this time using only the core +Git tools. + +I had a handful of commits that were ahead of master in pu, and I +wanted to add some documentation bypassing my usual habit of +placing new things in pu first. At the beginning, the commit +ancestry graph looked like this: + + *"pu" head + master --> #1 --> #2 --> #3 + +So I started from master, made a bunch of edits, and committed: + + $ git checkout master + $ cd Documentation; ed git.txt ... + $ cd ..; git add Documentation/*.txt + $ git commit -s + +After the commit, the ancestry graph would look like this: + + *"pu" head + master^ --> #1 --> #2 --> #3 + \ + \---> master + +The old master is now master^ (the first parent of the master). +The new master commit holds my documentation updates. + +Now I have to deal with "pu" branch. + +This is the kind of situation I used to have all the time when +Linus was the maintainer and I was a contributor, when you look +at "master" branch being the "maintainer" branch, and "pu" +branch being the "contributor" branch. Your work started at the +tip of the "maintainer" branch some time ago, you made a lot of +progress in the meantime, and now the maintainer branch has some +other commits you do not have yet. And "git rebase" was written +with the explicit purpose of helping to maintain branches like +"pu". You _could_ merge master to pu and keep going, but if you +eventually want to cherrypick and merge some but not necessarily +all changes back to the master branch, it often makes later +operations for _you_ easier if you rebase (i.e. carry forward +your changes) "pu" rather than merge. So I ran "git rebase": + + $ git checkout pu + $ git rebase master pu + +What this does is to pick all the commits since the current +branch (note that I now am on "pu" branch) forked from the +master branch, and forward port these changes. + + master^ --> #1 --> #2 --> #3 + \ *"pu" head + \---> master --> #1' --> #2' --> #3' + +The diff between master^ and #1 is applied to master and +committed to create #1' commit with the commit information (log, +author and date) taken from commit #1. On top of that #2' and #3' +commits are made similarly out of #2 and #3 commits. + +Old #3 is not recorded in any of the .git/refs/heads/ file +anymore, so after doing this you will have dangling commit if +you ran fsck-cache, which is normal. After testing "pu", you +can run "git prune" to get rid of those original three commits. + +While I am talking about "git rebase", I should talk about how +to do cherrypicking using only the core Git tools. + +Let's go back to the earlier picture, with different labels. + +You, as an individual developer, cloned upstream repository and +made a couple of commits on top of it. + + *your "master" head + upstream --> #1 --> #2 --> #3 + +You would want changes #2 and #3 incorporated in the upstream, +while you feel that #1 may need further improvements. So you +prepare #2 and #3 for e-mail submission. + + $ git format-patch master^^ master + +This creates two files, 0001-XXXX.patch and 0002-XXXX.patch. Send +them out "To: " your project maintainer and "Cc: " your mailing +list. You could use contributed script git-send-email if +your host has necessary perl modules for this, but your usual +MUA would do as long as it does not corrupt whitespaces in the +patch. + +Then you would wait, and you find out that the upstream picked +up your changes, along with other changes. + + where *your "master" head + upstream --> #1 --> #2 --> #3 + used \ + to be \--> #A --> #2' --> #3' --> #B --> #C + *upstream head + +The two commits #2' and #3' in the above picture record the same +changes your e-mail submission for #2 and #3 contained, but +probably with the new sign-off line added by the upstream +maintainer and definitely with different committer and ancestry +information, they are different objects from #2 and #3 commits. + +You fetch from upstream, but not merge. + + $ git fetch upstream + +This leaves the updated upstream head in .git/FETCH_HEAD but +does not touch your .git/HEAD or .git/refs/heads/master. +You run "git rebase" now. + + $ git rebase FETCH_HEAD master + +Earlier, I said that rebase applies all the commits from your +branch on top of the upstream head. Well, I lied. "git rebase" +is a bit smarter than that and notices that #2 and #3 need not +be applied, so it only applies #1. The commit ancestry graph +becomes something like this: + + where *your old "master" head + upstream --> #1 --> #2 --> #3 + used \ your new "master" head* + to be \--> #A --> #2' --> #3' --> #B --> #C --> #1' + *upstream + head + +Again, "git prune" would discard the disused commits #1-#3 and +you continue on starting from the new "master" head, which is +the #1' commit. + +-jc |