git rebase 经验
By cwhuang, 2009 年 06 月 17 日為了玩 Android，學會了 git 的初步使用。不過僅止於基本的 git checkout、git log、git diff、git status、git commit 等。這幾天為了協助同事將 Android 移植到廠商的板子上，必須將廠商提供的 kernel 與 Android kernel 做結合。為此請教一些 git 高手。經過一番練習，總算對 git rebase 的使用有了初步的掌握。也漸漸了解了 git 的強大威力，為什麼高手都愛用… 特別將這段經驗記載在這邊，給有興趣的人參考。有兩個 git repositories 要做合併。一個是廠商提供的 kernel：git://git.kernel.org/pub/scm/linux/kernel/git/kki_ap/samsung-ap-2.6.git 另一個是 Android 的 kernel：git://android.git.kernel.org/kernel/common.git 首先，先建立一個工作目錄$ mkdir kernel-git$ cd kernel-git$ git initInitialized empty Git repository in /home/cwhuang/git/kernel-git/.git/ 然後加入兩個遠端的 repositories：$ git remote add samsung git://git.kernel.org/pub/scm/linux/kernel/git/kki_ap/samsung-ap-2.6.git$ git remote add android git://android.git.kernel.org/kernel/common.git 將遠端 repositories 的資料取回：$ git fetch samsungremote: Counting objects: 11677, done.remote: Compressing objects: 100% (2462/2462), done.remote: Total 10383 (delta 7976), reused 10138 (delta 7743)Receiving objects: 100% (10383/10383), 5.04 MiB, done.Resolving deltas: 100% (7976/7976), completed with 324 local objects.From git://git.kernel.org/pub/scm/linux/kernel/git/kki_ap/samsung-ap-2.6.git * [new branch] master -> samsung/master * [new tag] v2.6.28.6-samsung-v1 -> v2.6.28.6-samsung-v1From git://git.kernel.org/pub/scm/linux/kernel/git/kki_ap/samsung-ap-2.6.git * [new tag] v2.6.28-rc4-s3c64xx -> v2.6.28-rc4-s3c64xx * [new tag] v2.6.28-rc4-s5pc1xx -> v2.6.28-rc4-s5pc1xx * [new tag] v2.6.28-rc5-s3c64xx -> v2.6.28-rc5-s3c64xx * [new tag] v2.6.28-rc5-s5pc1xx -> v2.6.28-rc5-s5pc1xx * [new tag] v2.6.28-rc6-s3c64xx -> v2.6.28-rc6-s3c64xx * [new tag] v2.6.28-rc6-s5pc1xx -> v2.6.28-rc6-s5pc1xx * [new tag] v2.6.28-rc7-s3c64xx -> v2.6.28-rc7-s3c64xx * [new tag] v2.6.28-rc7-s5pc1xx -> v2.6.28-rc7-s5pc1xx * [new tag] v2.6.28-rc8-s3c64xx -> v2.6.28-rc8-s3c64xx * [new tag] v2.6.28-rc8-s5pc1xx -> v2.6.28-rc8-s5pc1xx * [new tag] v2.6.28-rc8-s5pc1xx-v1 -> v2.6.28-rc8-s5pc1xx-v1 * [new tag] v2.6.28.6-samsung -> v2.6.28.6-samsung$ git fetch androidremote: Counting objects: 1077412, done.remote: Compressing objects: 100% (176782/176782), done.Receiving objects: 100% (1077412/1077412), 263.30 MiB | 28369 KiB/s, done.remote: Total 1077412 (delta 896526), reused 1076403 (delta 895639)Resolving deltas: 100% (896526/896526), done.From git://android.git.kernel.org/kernel/common.git * [new branch] 2.6.27 -> android/2.6.27 * [new branch] 2.6.29 -> android/2.6.29From git://android.git.kernel.org/kernel/common.git * [new tag] v2.6.12 -> v2.6.12 * [new tag] v2.6.12-rc2 -> v2.6.12-rc2(skipped...) * [new tag] v2.6.29-rc8 -> v2.6.29-rc8 看看有哪些 branches?$ git branch -a android/2.6.27 android/2.6.29 samsung/master 在合併之前，先了解一下已存在的 branches。我們可以先看看這些 branches 的共同祖先(common ancestor)：$ git merge-base samsung/master android/2.6.273fa8749e584b55f1180411ab1b51117190bac1e5$ git show 3fa8749e584b55f1180411ab1b51117190bac1e5commit 3fa8749e584b55f1180411ab1b51117190bac1e5Author: Linus Torvalds Date: Thu Oct 9 15:13:53 2008 -0700 Linux 2.6.27diff --git a/Makefile b/Makefileindex ce9eceb..16e3fbb 100644--- a/Makefile+++ b/Makefile@@ -1,7 +1,7 @@ VERSION = 2 PATCHLEVEL = 6 SUBLEVEL = 27-EXTRAVERSION = -rc9+EXTRAVERSION = NAME = Rotary Wombat # *DOCUMENTATION*$ git merge-base samsung/master android/2.6.294a6908a3a050aacc9c3a2f36b276b46c0629ad91$ git show 4a6908a3a050aacc9c3a2f36b276b46c0629ad91commit 4a6908a3a050aacc9c3a2f36b276b46c0629ad91Author: Linus Torvalds Date: Wed Dec 24 15:26:37 2008 -0800 Linux 2.6.28 Happy holidays..diff --git a/Makefile b/Makefileindex 4c8d797..71e98e9 100644--- a/Makefile+++ b/Makefile@@ -1,7 +1,7 @@ VERSION = 2 PATCHLEVEL = 6 SUBLEVEL = 28-EXTRAVERSION = -rc9+EXTRAVERSION = NAME = Erotic Pickled Herring # *DOCUMENTATION* 因此 branch samsung/master 和 android/2.6.27 都是從 v2.6.27 來的，而 samsung/master 和 android/2.6.29 則從 v2.6.28 而來。事實上，不難驗證 samsung/master 是從 v2.6.28.6 改來的。可以用 gitk 這個圖形化工具來看看從 v2.6.27 到 android/2.6.27 的變化：$ gitk v2.6.27..android/2.6.27 同樣的，samsung/master 的變化是：$ gitk v2.6.28..samsung/master 我們要決定如何進行合併。可以將 samsung 的修改合併到 Android kernel，也可以將 Android 的修改合併到 samsung kernel。我決定選擇後者，因為從 gitk 可以看出 Android 的變化相當簡單而清楚，就是單線發展而已。相對的，samsung kernel 就併來併去，線條亂七八糟，看得眼花瞭亂。因此將 Android 的修改併到 samsung kernel，應該比較簡單而容易成功。可以用 git rebase 來進行合併。首先，建立一個新的本地 branch 來保存合併結果：$ git branch --track samsung-android samsung/master 然後用 git rebase 指令，將 v2.6.27 到 android/2.6.27 的修改，一個一個的 apply 到 samsung-android 這個 branch 中：$ git rebase --whitespace=fix --onto samsung-android v2.6.27 android/2.6.27First, rewinding head to replay your work on top of it...Applying: PM: Add wake lock api.Applying: PM: Add early suspend api.Applying: PM: Implement wakelock api.Applying: PM: Implement early suspend apiApplying: PM: Enable early suspend through /sys/power/stateApplying: PM: Add user-space wake lock api.Applying: PM: wakelock: Abort task freezing if a wake lock is held.Applying: PM: earlysuspend: Add console switch when user requested sleep state changes.Applying: PM: earlysuspend: Removing dependence on console.Applying: rtc: Add android alarm driver.Applying: rtc: Try to prevent RTC errors from accumulating.Applying: ledtrig-sleep: Add led trigger for sleep debugging.error: patch failed: drivers/leds/Makefile:29error: drivers/leds/Makefile: patch does not applyUsing index info to reconstruct a base tree...Falling back to patching base and 3-way merge...Auto-merged drivers/leds/KconfigAuto-merged drivers/leds/MakefileApplying: PM: Wait for console in resume.Applying: PM: Fix suspend_console/resume_console use only one semaphore.Applying: switch: switch class and GPIO drivers.Applying: lowmemorykiller: Initial support for 2.6.27error: patch failed: drivers/misc/Kconfig:475error: drivers/misc/Kconfig: patch does not applyerror: patch failed: drivers/misc/Makefile:30error: drivers/misc/Makefile: patch does not applyUsing index info to reconstruct a base tree...Falling back to patching base and 3-way merge...Auto-merged drivers/misc/KconfigCONFLICT (content): Merge conflict in drivers/misc/KconfigAuto-merged drivers/misc/MakefileCONFLICT (content): Merge conflict in drivers/misc/MakefileFailed to merge in the changes.Patch failed at 0016. 由這些訊息可看出，前 15 個修改被成功的 apply 上去，但第 16 個產生 conflicts。先用 git status 看看問題出在哪裡：$ git statusdrivers/misc/Kconfig: needs mergedrivers/misc/Makefile: needs merge# Not currently on any branch.# Changes to be committed:# (use "git reset HEAD ..." to unstage)## new file: drivers/misc/lowmemorykiller.c## Changed but not updated:# (use "git add ..." to update what will be committed)## unmerged: drivers/misc/Kconfig# unmerged: drivers/misc/Makefile# 可以看出有兩個檔案有 conflicts，必須手動修改。例如，在 drivers/misc/Makefile 裡 conflicts 大約在 35 至 39 行：<<<<<<< HEAD:drivers/misc/Makefileobj-$(CONFIG_C2PORT) += c2port/=======obj-$(CONFIG_LOW_MEMORY_KILLER) += lowmemorykiller.o>>>>>>> lowmemorykiller: Initial support for 2.6.27:drivers/misc/Makefile 不難看出，這兩行都要加到 Makefile 中。因此我改成：obj-$(CONFIG_C2PORT) += c2port/obj-$(CONFIG_LOW_MEMORY_KILLER) += lowmemorykiller.o 接著$ git add drivers/misc/Makefile 用同樣的方法修改 drivers/misc/Kconfig，然後$ git rebase --continue 如此會繼續合併的過程。當然可能產生其它的 conflicts，都用類似的方法修正，直到 rebase 完成。如果覺得某個產生 conflicts 的修改是不必要的，可以跳過：$ git rebase --skip 如果覺得 conflicts 太複雜了，不知要麼修改，想要放棄，可以$ git rebase --abort 如此會放棄所有的合併結果，而將 source tree 回到合併前的狀態。