Axel Axel - 6 months ago 18
Linux Question

Strange behaviour of Git: mysterious changes cannot be undone

I am seeing a behaviour in Git which seems very mysterious to me.
I keep a clone of the Linux repository from Github to play with Git locally. To be clear, I don't do much in this repository : I fetch changes, update

master
, checkout a specific version, and sometimes I try out a Git GUI to see what the visualization looks like on a big project.
TLDR version: I never did any changes to the files in it.

Strange behaviour



Earlier today, I checked-out
master
and pulled changes from Github. Everything seemed to go fine. But I suspect it actually didn't. This is what
git status
looks like now.

axel@macbook ~/Depots/linux $ git status
# On branch master
# Changes not staged for commit:
# (use "git add <file>..." to update what will be committed)
# (use "git checkout -- <file>..." to discard changes in working directory)
#
# modified: include/linux/netfilter/xt_connmark.h
# modified: include/linux/netfilter/xt_dscp.h
# modified: include/linux/netfilter/xt_mark.h
# modified: include/linux/netfilter/xt_rateest.h
# modified: include/linux/netfilter/xt_tcpmss.h
# modified: include/linux/netfilter_ipv4/ipt_ecn.h
# modified: include/linux/netfilter_ipv4/ipt_ttl.h
# modified: include/linux/netfilter_ipv6/ip6t_hl.h
# modified: net/ipv4/netfilter/ipt_ecn.c
# modified: net/netfilter/xt_dscp.c
# modified: net/netfilter/xt_hl.c
# modified: net/netfilter/xt_rateest.c
# modified: net/netfilter/xt_tcpmss.c
#
# Untracked files:
# (use "git add <file>..." to include in what will be committed)
#
# samples/hidraw/
no changes added to commit (use "git add" and/or "git commit -a")


Where do these changes come from, I wonder.
Now comes the worst part. Let us see what happens if I try to get rid of those files and check them out again.

axel@macbook ~/Depots/linux $ rm -Rf include net
axel@macbook ~/Depots/linux $ git checkout -- .
axel@macbook ~/Depots/linux $ git status
# On branch master
# Changes not staged for commit:
# (use "git add <file>..." to update what will be committed)
# (use "git checkout -- <file>..." to discard changes in working directory)
#
# modified: include/linux/netfilter/xt_CONNMARK.h
# modified: include/linux/netfilter/xt_DSCP.h
# modified: include/linux/netfilter/xt_MARK.h
# modified: include/linux/netfilter/xt_RATEEST.h
# modified: include/linux/netfilter/xt_TCPMSS.h
# modified: include/linux/netfilter_ipv4/ipt_ECN.h
# modified: include/linux/netfilter_ipv4/ipt_TTL.h
# modified: include/linux/netfilter_ipv6/ip6t_HL.h
# modified: net/ipv4/netfilter/ipt_ECN.c
# modified: net/netfilter/xt_DSCP.c
# modified: net/netfilter/xt_HL.c
# modified: net/netfilter/xt_RATEEST.c
# modified: net/netfilter/xt_TCPMSS.c
#
# Untracked files:
# (use "git add <file>..." to include in what will be committed)
#
# samples/hidraw/
no changes added to commit (use "git add" and/or "git commit -a")


Well, same thing.
The
git checkout
operation seems to produce files with mysterious changes.
I tried to investigate further, and I think I eliminated the possibility that these changes were caused by line-ending issues. See the beginning of a
git diff
below

diff --git a/include/linux/netfilter/xt_CONNMARK.h b/include/linux/netfilter/xt_CONNMARK.h
index 2f2e48e..efc17a8 100644
--- a/include/linux/netfilter/xt_CONNMARK.h
+++ b/include/linux/netfilter/xt_CONNMARK.h
@@ -1,6 +1,31 @@
-#ifndef _XT_CONNMARK_H_target
-#define _XT_CONNMARK_H_target
+#ifndef _XT_CONNMARK_H
+#define _XT_CONNMARK_H

-#include <linux/netfilter/xt_connmark.h>
+#include <linux/types.h>

-#endif /*_XT_CONNMARK_H_target*/
+/* Copyright (C) 2002,2004 MARA Systems AB <http://www.marasystems.com>
+ * by Henrik Nordstrom <hno@marasystems.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */


If I understand this right, this shows changes that cannot have been made by just changing some line endings, right?
Last thing I did was: try to find out the originator of the changes, but obviously that did not work. See the following
git blame
output.

axel@macbook ~/Depots/linux $ git blame include/linux/netfilter/xt_CONNMARK.h
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 1) #ifndef _XT_CONNMARK_H
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 2) #define _XT_CONNMARK_H
2e4e6a17 (Harald Welte 2006-01-12 13:30:04 -0800 3)
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 4) #include <linux/types.h>
0dc8c760 (Jan Engelhardt 2008-01-14 23:38:34 -0800 5)
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 6) /* Copyright (C) 2002,2004 MARA Systems AB <http://www.marasystems.com>
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 7) * by Henrik Nordstrom <hno@marasystems.com>
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 8) *
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 9) * This program is free software; you can redistribute it and/or modify
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 10) * it under the terms of the GNU General Public License as published by
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 11) * the Free Software Foundation; either version 2 of the License, or
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 12) * (at your option) any later version.
00000000 (Not Committed Yet 2011-10-25 20:00:56 +0200 13) */


Questions



What am I missing? When could I have gone wrong, and how to fix this?
Thanks for your tips and remarks!

Answer

The Linux source tree has filenames which differ in case only, which causes interesting failures on systems with case-insensitive filesystems.

You need a case-sensitive filesystem in order to work with the Linux source.

(include/linux/netfilter/xt_connmark.h and include/linux/netfilter/xt_CONNMARK.h are two different files in the Git repository, but only one can exist in your checkout at a time if your filesystem is case-insensitive.)

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