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SubjectRe: How to write patches
Jeff's descriprion is very informative, but his emphasis
is somewhat different from what I find difficult with patches.
First, for the life of me I was unable to remeber which
argument goes first (DaveM was mad every time). Second, I kept
forgetting to keep the base tree a diff against that instead of
the latest tree.

So, here is the patch release cycle in my view, with all
small details.

1. I pick a "base" tree which I will hack on. Suppose that
we start with 2.2.17-pre22. So, I download linux-2.2.16.tar.bz2
from Linus place and patch-pre22.bz2 from Alan's place.
THESE MUST BE SAVED after I unpack them.

2. I unpack. Note that I have base release in the directory name.

bzip -d < linux-2.2.16.tar.bz2| tar xf -
mv linux linux-2.2.17-pre22
bzip -d < patch-pre22.bz2| patch -d linux-2.2.17-pre22 -p1

3. One way or another, I make two trees, one of which is "base"
and another is "work".

mkdir linux-2.2.17-pre22-p3
(cd linux-2.2.17-pre22 && tar cf - .)| (cd linux-2.2.17-pre22-p3 && tar xf -)

4. Hack

cd linux-2.2.17-pre22-p3
make oldconfig
(make dep && make bzImage) > build.out 2>&1
........... etc.

The step #4 will take some time, and kernel will get developed
while we sit on it. Normally it takes me anywhere from 3 weeks
to 3 months to come up with something useable.

5. Time to diff and submit, but Oops, Linus published 2.2.17!
Now you will see how it all REALLY works.

5a. Unpack

bzip -d < linux-2.2.17.tar.bz2| tar xf -
mv linux linux-2.2.17

6. Diff your base tree and your changed tree. Do not settle
for .orig files! Diff whole thing!

6a. Get dontdiff from Tigran, it's helpful

6b. Diff, but notice the argument order!!

diff -urN --exclude-from=dontdiff \
linux-2.2.17-pre22 linux-2.2.17-pre22-p3 > linux-2.2.17-pre22-p3.diff

6c. In most cases you need to remove junk from your diff,
even with dontdiff.

7. Apply your diff to the new tree (remember,
never touch the base tree):

mkdir linux-2.2.17-p3
(cd linux-2.2.17 && tar cf - .)| (cd linux-2.2.17-p3 && tar xf -)
patch -d linux-2.2.17-p3 -p1 < linux-2.2.17-pre22-p3.diff

If I am lucky, my patch applies cleanly or with a small
fuzz factor. But otherwise there may be a conflict that I
shall resolve by hand:

find linux-2.2.17-p3 -name '*.rej'
# perhaps cat something.rej >> something && vi something

This part is actually important. If I sent linux-2.2.17-pre22-p3.diff
to Alan, he would try to apply it against then-current 2.2.17
(if not 2.2.18-pre2), get the same conflict, and dump the patch
into the void. Always resolve yourself, do not ride the maintainer.

8. Now I can send the patch to Alan and wait.

9. Once my patch is tentatively applied, say, in 2.2.18-pre2,
I re-download it, and do the whole thing again to make sure
that it was applied right. Alan has a habit of editing patches
on the fly, so I must keep tabs on it.

10. By this time 2.2.17-pre22 base are obsolete so we may
delete them (but evacuate good .config first or you'd start
from defconfig again):

cp linux-2.2.17-pre22-p3/.config linux-2.2.18-pre3/
rm -rf linux-2.2.17-pre22 linux-2.2.17-pre22-p3
# Sometimes I keep linux-2.2.17-pre22-p3.diff a little longer
# after the base moved on, for the sake of slower paced collegues.

And the ball just keeps rolling.

-- Pete
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