Subject: Re: Can't find the revelant commit with git-log

From: Francis Moreau <[email-masked]>
Date: Tue, 25 Jan 2011 18:44:49 +0100

René Scharfe <[email-masked]> writes:

> Am 25.01.2011 10:01, schrieb Francis Moreau:
>>
>> The project is the Linux kernel, and I'm trying to look for changes
>> which happened between v2.6.27 and v2.6.28. The changes happened in the
>> following file: drivers/pci/intel-iommu.c where a function has been
>> removed:
>> 
>>    $ git --version
>>    git version 1.7.4.rc3
>> 
>>    $ cd ~/linux-2.6/drivers/pci/
>>    $ git grep blacklist v2.6.27 -- drivers/pci/intel-iommu.c
>>    $
>> 
>> No ouput... hmm, I know it's in... oh maybe the path is incorrect
>> 
>>    $ git git grep blacklist v2.6.27 -- intel-iommu.c
>>    v2.6.27:intel-iommu.c:static int blacklist_iommu(const struct dmi_system_id *id)
>>    v2.6.27:intel-iommu.c:          .callback = blacklist_iommu,
>> 
>> ah, so Git failed previously without any comments on the wrong
>> path... maybe it should ?
>
> Good idea.
>

Actually I _think_ I encoutered this behaviour for other commands as well,
like git-show or git-log, I don't remember.

>
>> So at that point I know that in the revision v2.6.27, there's a function
>> called "blacklist_iommu" in drivers/pci/intel-iommu.c
>> 
>> Now take a look if it's still there in v2.6.28:
>> 
>>    $ git git grep blacklist v2.6.28 -- intel-iommu.c
>>    $
>> 
>> This time nothing is printed but I know that the command is correct.
>> 
>> So now I'm interested in looking for the commit which removed this
>> function. Fo this I'm trying to use git-log(1):
>> 
>>    $ git log --full-history --follow -S'static int blacklist_iommu(const struct dmi_system_id *id)' v2.6.27..v2.6.28 -- intel-iommu.c
>>    $ echo $?
>>    0
>> 
>> I tried different options but it fails.
>> 
>> Also I found that passing the exact string to '-S' is annoying, are
>> there any way to just pass a part of the string such as
>> "-Sblacklist_iommu" ?
>
> This (-Sblacklist_iommu) works for me.
>

Hmm, I thought I tried this and it didn't work, but that's obviously
wrong.

>
>> Sorry if I miss the revelant git-log's option, but there're so many...
>
> Try -m (show full diff for merge commits), as the change you're looking
> for seems to have been introduced by a merge, not a regular commit.
>
> 	$ opts="--stat -Sblacklist_iommu -m --oneline"
> 	$ revs="v2.6.27..v2.6.28"
>
> 	$ git log $opts $revs -- drivers/pci/intel-iommu.c
>
> This returns nothing.  Hmm.  Let's try this instead:
>
> 	$ git log $opts $revs -- drivers/pci/
> 	057316c (from 3e2dab9) Merge branch 'linus' into test
> 	 drivers/pci/intel-iommu.c |  307 ++++++++++++++++++++------------------------
> 	 1 files changed, 140 insertions(+), 167 deletions(-)
> 	6b2ada8 (from 3b7ecb5) Merge branches 'core/softlockup', 'core/softirq', 'core/resources', 'core/printk' and 'core/misc' into core-v28-for-linus
> 	 drivers/pci/intel-iommu.c |  187 ++++++--------------------------------------
> 	 1 files changed, 26 insertions(+), 161 deletions(-)
> 	d847059 (from 725c258) Merge branch 'x86/apic' into x86-v28-for-linus-phase4-B
> 	 drivers/pci/intel-iommu.c |  185 ++++++---------------------------------------
> 	 1 files changed, 25 insertions(+), 160 deletions(-)
> 	725c258 (from 129d6ab) Merge branches 'core/iommu', 'x86/amd-iommu' and 'x86/iommu' into x86-v28-for-linus-phase3-B
> 	 drivers/pci/intel-iommu.c |   25 ++++++++++++++++++++++++-
> 	 1 files changed, 24 insertions(+), 1 deletions(-)
> 	6e03f99 (from 9821626) Merge branch 'linus' into x86/iommu
> 	 drivers/pci/intel-iommu.c |   23 +++++++++++++++++++++++
> 	 1 files changed, 23 insertions(+), 0 deletions(-)
>
> Strange, why did we need to remove the last path component to get these
> results which say that exactly the file we previously specified was changed?

ah... I think I've been hit by this, since I tried '-m' too but see
nothing and was not smart enough to remove the filename from the path.

> Also interesting, and matching the above results in that we see the need for
> the -m flag confirmed:
>
> 	$ for merge in 057316c 6b2ada8 d847059 725c258 6e03f99
> 	do
> 		a=$(git show $merge | grep -c blacklist_iommu)
> 		b=$(git show -m $merge | grep -c blacklist_iommu)
> 		echo $merge $a $b
> 	done
> 	057316c 0 2
> 	6b2ada8 0 2
> 	d847059 0 2
> 	725c258 0 2
> 	6e03f99 0 2
>
> IAW: the combined diff for the five found merges doesn't show any changes to
> a line containing the string "blacklist_iommu", but the full diffs do.
>
> Let's check for the presence of the string in the merge results and their
> parents:
>
> 	$ for merge in 057316c 6b2ada8 d847059 725c258 6e03f99
> 	  do
> 		for rev in $(git show $merge | grep ^Merge:)
> 		do
> 			t=parent
> 			case $rev in
> 			Merge:)
> 				echo
> 				rev=$merge
> 				t=merge
> 				;;
> 			esac
> 			if git grep -q blacklist_iommu $rev -- drivers/pci/
> 			then
> 				echo "$t $rev: found"
> 			else
> 				echo "$t $rev: not found"
> 			fi
> 		done
> 	done
>
> 	merge 057316c: not found
> 	parent 3e2dab9: found
> 	parent 2515ddc: not found
> 	
> 	merge 6b2ada8: not found
> 	parent 278429c: not found
> 	parent 3b7ecb5: found
> 	parent 77af7e3: not found
> 	parent 1516071: not found
> 	parent 1fa63a8: not found
> 	parent 8546232: not found
> 	
> 	merge d847059: not found
> 	parent 725c258: found
> 	parent 11494547: not found
> 	
> 	merge 725c258: found
> 	parent 3dd392a: found
> 	parent 72d3105: found
> 	parent 129d6ab: not found
> 	parent 1e19b16: found
> 	
> 	merge 6e03f99: found
> 	parent 9821626: not found
> 	parent 6bfb09a: found
>
> Hmm, seems like the function is gone since d847059.  Does all of this help
> you in any way?

Yes it does, but one question I'm wondering is: is it possible to do
this more user friendly ? ;)

Thanks
-- 
Francis