Junio,
Thank you for the detailed explanation of what is apparently a common
question - which I just didn't know how to phrase to find the previous
discussions on simplified history.
Thanks,
Darren
On 07/02/2010 03:10 PM, Junio C Hamano wrote:
Darren Hart<dvhltc@xxxxxxxxxx> writes:
$ git checkout -b 2.6.33.5-rt23 v2.6.33.5-rt23
$ git log --pretty=oneline v2.6.33.5.. arch/powerpc/kernel
ef4afcc4401e92982f4ffd3fae6a9a6745a98596 Merge stable/linux-2.6.33.y into rt/2.6.33
...
92bfe2d63ed46764b0b0a6e9b63bb9e81023ab80 powerpc: realtime support
...
$ git whatchanged 92bfe2d6 -n1
commit 92bfe2d63ed46764b0b0a6e9b63bb9e81023ab80
...
:100644 100644 43e0734... 4bb9ce4... M arch/powerpc/kernel/entry_64.S
...
$ git log --pretty=oneline v2.6.33.5.. arch/powerpc/kernel/entry_64.S
<null>
This is expected, and it is by design.
$ git log --oneline --simplify-merges --full-history --graph \
v2.6.33.5..v2.6.33.5-rt23 -- arch/powerpc/kernel/entry_64.S
will give you a less simplified history. The first commit we find in its
output is:
* ef4afcc Merge stable/linux-2.6.33.y into rt/2.6.33
and if you look at that commit:
$ git show --pretty=short --stat -m ef4afcc -- arch/powerpc/kernel/
you will notice that:
- ef4afcc is a merge between ac43be5 and a00123d;
- arch/powerpc/kernel/entry_64.S has not changed between a00123d and this
merge result ef4afcc;
- There are many changes made to this path in the history leading to the
other parent of the merge, ac43be5.
- When Thomas created ef4afcc, after looking at ac43be5 and a00123d, he
took the version from a00123d. Effectively, what happend on the side
branch that led to ac43be5 did _not_ contribute to the end result at
all.
- There was no change to the path between v2.6.33.5 and a00123d (as they
are the same commit ;-).
- Hence there is nothing noteworthy to report when explaining how the
path came about since v2.6.33.5 and v2.6.33.5-rt23.
BTW, this has nothing to do with the path being the same between your HEAD
and v2.6.33.5. You can try:
$ git checkout v2.6.33.5-rt23
$ echo>>arch/powerpc/kernel/entry_64.S
$ git commit -m 'random change' arch/powerpc/kernel/entry_64.S
$ git log --oneline v2.6.33.5.. -- arch/powerpc/kernel/entry_64.S
b736245 random change
and notice that the change you just made is the only one that is needed to
explain how the file came into its current shape since the named bottom
version (v2.6.33.5).
If you look for "history simplification" in the list archive you will find
Linus explaining why this simplification is the right thing to do number
of times, but the short version is that "git log $path" by default gives
you _one_ possible and simplest explanation of how the $path came about
into its current shape, and "one possible and simplest" is what you want
most of the time, because "all possible explanations" is very expensive to
compute and often unreadable.
But the "--simplify-merges --full-history" trick I showed above may also
be another good thing to know.
--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
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