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On 09/09/2011 12:39 PM, Vaibhav Jain wrote:
On Fri, Sep 9, 2011 at 11:12 AM, Kai
Meyer <kai@xxxxxxxxxx>
wrote:
On 09/09/2011 09:05 AM, Vaibhav Jain
wrote:
Hi,
I am not able to understand how diff between two trees
of which one is just contains hardlinks to another's
files (cp -al )ing
works.I am asking this question here because I need to
build a custom kernel for which I need to generate
patch. So the
documentation suggests to create a hardlink copy of
the kernel source tree using cp -al and then make
changes to
one of the trees and run a diff.I am wondering that if
files are hardlinks then changes to one copy will
affect another in which case
diff should give no output.
Also, the patch I created looks a little odd as it
contains complete modified files instead of just the
differences.
Please help!
Make the hard link copy like normal. Then delete the
directory that you are making changes to (in the hard link
directory), then copy the files over with out hard links.
That way "most" of the kernel tree is hard linked, and just
the portion you want to work on is a copy. That way the diff
will work.
Otherwise, skip the hard link part all together, and just
make a full copy. Uses lots of disk space and takes longer
to diff.
-Kai Meyer
Hi Kai,
Thanks for the reply. I need just one more favour.
Could you please look at this document describing the procedure to
build
custom fedora kernel. It mentions the step to create hardlink to
generate but doesn't
talk about deleting anything ?I just need to confirm if the
article is not accurate or if there is
any error in my understanding.
Whenever I follow it I get a patch that contains all of the
content of the changed files rather than just the changes.
Here is the relevant portion :
Copy the
Source Tree and Generate a Patch
This step is for applying a patch to the kernel source. If a
patch is not needed, proceed to "Configure Kernel Options".
Copy the source tree to preserve the original tree while making
changes to the copy:
The second cp command hardlinks the .orig
and .new trees to make diff run
faster. Most text editors know how to break the hardlink
correctly to avoid problems.
Using vim on FC14, it treated the hard link as a hard link and
thus the above technique failed. It was necessary to repeat the
original copy used for the .orig directory for the .new
directory. Note that this uses twice the space.
Make changes directly to the code in the .new
source tree, or copy in a modified file. This file might come
from a developer who has requested a test, from the upstream
kernel sources, or from a different distribution.
After the .new source tree is modified, generate
a patch. To generate the patch, run diff against
the entire .new and .orig source
trees with the following command:
cd ~/rpmbuild/BUILD
diff -uNrp kernel-2.6.$ver.$fedver.orig kernel-2.6.$ver.$fedver.new > ../SOURCES/linux-2.6-my-new-patch.patch
"Using vim on FC14, it treated the hard link as a hard link and
thus the above technique failed. It was necessary to repeat the
original copy used for the .orig directory for the .new directory.
Note that this uses twice the space."
It means to say that some editors, like VIM, edit files in-place,
and some files copy the original contents into some other buffer
(memory or temporary file), and then effectively delete the file
you're editing, and copy the modified file into place. The hard-link
instructions are a "trick" to save time and space when you are
modifying large code base, like the kernel. If your favorite editor
is behaving like the observed behavor of VIM, then you will need to
delete the hard link file, and put a regular copy of the file in
place before making changes.
