revert/undo rebase

rebase 後發現 fail，要 rollback 怎辦？

列出 reflog，用 git log 找出 rebase 之前的那個 head 是哪一個，然後用 reset --hard 切過去。

git reflog
afa93f0 HEAD@{0}: rebase: tidy up the driver/misc/Makefile, keeps the 9.4 kernel content, just append the new source added by us
7a3b48e HEAD@{1}: checkout: moving from rtk2 to 7a3b48ec1ba6eee2298ee654c0cee1e06f464fed^0
f4fbe68 HEAD@{2}: checkout: moving from rtk to rtk2
6d5d23c HEAD@{3}: checkout: moving from rtk to rtk
6d5d23c HEAD@{4}: checkout: moving from rtk2 to rtk
f4fbe68 HEAD@{5}: checkout: moving from debug_suspend_wakeup to rtk2
4c13583 HEAD@{6}: commit: add more comment : wake_lock_internal & alarm.c
d8cf098 HEAD@{7}: rebase: add a lot message to trace the lock sequence
fe3b73a HEAD@{8}: rebase: use external sd as boot
f4fbe68 HEAD@{9}: checkout: moving from debug_suspend_wakeup to f4fbe680ef41ed3d38ecc1f49a8b2c32a294c178^0
733e20f HEAD@{10}: checkout: moving from rtk2 to debug_suspend_wakeup
f4fbe68 HEAD@{11}: commit: tidy up the driver/misc/Makefile, keeps the 9.4 kernel content, just append the new source added by us
6d5d23c HEAD@{12}: checkout: moving from rtk to rtk2
6d5d23c HEAD@{13}: checkout: moving from imx_r9.4 to rtk
901321c HEAD@{14}: checkout: moving from rtk to imx_r9.4
6d5d23c HEAD@{15}: checkout: moving from 37bace68774d42fc2bea3b2aa2fb8aafb3a6f5a0 to rtk
37bace6 HEAD@{16}: checkout: moving from rtk to 37bace68774d42fc2bea3b2aa2fb8aafb3a6f5a0
6d5d23c HEAD@{17}: checkout: moving from debug_suspend_wakeup to rtk

reflog 會列出每次 operation, HEAD 變動的 log，後面列的是HEAD 的 latest log。

所以可以猜出 HEAD@{11} 大概是 rebase 之前的 head.
... rebase 包含很多動作，rollback, patch them, patch mine... 所以HEAD 變動很多次。

為了確認，可以用 git log 看一下
git log --pretty=oneline HEAD@{11}
f4fbe680ef41ed3d38ecc1f49a8b2c32a294c178 tidy up the driver/misc/Makefile, keeps the 9.4 kernel content, just append the new source added by us
6d5d23c54c2198831014b13d2f85f6f353f9e878 merge from 9.1: dimmer & brake gpio initial setting
911b3e5a7aced34f107715ebe4a1c09f8228c683 switch the sdcard init sequence, to make emmc as mmc0 always
a56e643558b691e5db349f0e630acc8e4e768cd4 Merge branch 'rtk' of git://robot/linux-2.6.35.y into rtk
8269efc25f3339750c7c9d05be88bc3232930f05 fix bug: system data abort due to audio-p driver
698afa31b154d7ea6ac6a3ba8664678e14fbbc97 fix bug: system data abort due to audio-p driver

這樣確認是了。

reset --hard 過去：
git reset --hard HEAD@{11}

---

ref :

• http://stackoverflow.com/questions/134882/undoing-a-git-rebase
• http://gitfu.wordpress.com/2008/04/06/git-reflog-no-commits-left-behind/
• http://jeffkreeftmeijer.com/2010/the-mighty-reflog-and-the-amazing-bisect/
• http://quirkygba.blogspot.com/2008/11/recovering-history-with-git-reflog.html
• http://freeasinbeard.org/post/318519782/reflog-and-fsck-your-git-disaster-recovery-toolkit

internal -- staging area

這一篇說得很清楚 (http://ihower.tw/blog/archives/2591 ).

staging area 是一塊 git 用來紀錄 commit command 要"提交的東西" 的區域)。
所以當你commit 過後，staging area 是空的。
用 git add, 就會把 add 的 file 加到 staging area 裡。

平時用的
$git commit -a a option ，意指..將修改過的檔案add 到 staging area，
所以這樣 commit ，會自動把修改過的 file commit 進去。

要是不加 -a 選項，就要在commit 之前，用 git add 把要 commit 的 file 加到 staging area。
然後 commit 才會 commit這些 file 進去。

要把 staging area 裡的 file 拿出來，用:
$git reset HEAD filename
這樣，那個 file 就會從 staging area 移出來，恢復到還沒被加入 staging area 的狀態 (原來是 untracked 就是 untracked, 是unstaging 就是 unstaging)，修改的內容不會消失。

因為有 staging area，所以 diff 分為以下三種：
$git diff
比較 working 跟 staging area

$git diff --cached
拿staging area 的file 跟 HEAD 的內容 (上次commit)比較

$git diff HEAD
比較 working 跟 HEAD 的不同。