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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Johannes Schindelin <Johannes.Schindelin@gmx.de>,
	git@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: current git kernel has strange problems during bisect
Date: Sun, 11 Jan 2009 11:13:30 -0800 (PST)	[thread overview]
Message-ID: <alpine.LFD.2.00.0901111113150.6528@localhost.localdomain> (raw)
In-Reply-To: <200901111620.03345.borntraeger@de.ibm.com>


On Sun, 11 Jan 2009, Christian Borntraeger wrote:
> 
> I think we should really avoid merging subtrees to the linux kernel. It 
> makes bisecting a real PITA. Furthermore, It is unlikely, but what if 
> the problem is part of the 581 changesets from btrfs?

Umm, yes? 

The thing is, btrfs was developed as an outside module. There are two 
choices: import it with history, or import it without history. The history 
is interesting, so importing _with_ it is a much nicer one. But that does 
mean that btrfs introduces into the kernel tree the same behaviour we've 
had in the git development tree for a long time - multiple root commits, 
and "independent" branches that get merged.

It's actually very natural for git, and the btrfs tree actually was 
re-done with "git filter-branch" to move all the history so that it is in 
fs/btrfs, rather than moving around from the root like the _original_ 
development was done. So it's not technically a subtree merge, it's a 
regular merge with just two different root commits - one for the original 
base kernel development, one for the original btrfs kernel development.

For bisect, it's indeed somewhat annoying, and we could have perhaps done 
some things a bit differently, but it's about the closest you can get to 
"real history" without making the first btrfs merge-point a _total_ 
disaster.

For bisect purposes, if you know you're not chasing down a btrfs issue, 
you can do

	git bisect good 34353029534a08e41cfb8be647d734b9ce9ebff8

where that commit 34353029 is the last one which has _just_ the btrfs 
files. The next commit is when it does "Merge Btrfs into fs/btrfs", and 
that one has the whole kernel tree again.

			Linus

  parent reply	other threads:[~2009-01-11 19:15 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-01-11 15:02 current git kernel has strange problems during bisect Christian Borntraeger
2009-01-11 15:07 ` Christian Borntraeger
2009-01-11 15:14   ` Johannes Schindelin
2009-01-11 15:20     ` Christian Borntraeger
2009-01-11 16:31       ` Boaz Harrosh
2009-01-11 19:13       ` Linus Torvalds [this message]
2009-01-11 19:42         ` Sam Ravnborg
2009-01-11 19:47           ` Alexey Zaytsev
2009-01-11 23:02             ` Pierre Habouzit
2009-01-12  4:51               ` Christian Couder
2009-01-12  5:03                 ` Christian Couder
2009-01-11 20:04           ` Linus Torvalds
2009-01-11 21:39             ` Christian Borntraeger
2009-01-11 22:27               ` Daniel Barkalow
2009-01-13 20:26               ` Kyle Moffett
2009-01-15 16:54                 ` Andreas Bombe
2009-01-15 23:13                   ` Kyle Moffett
2009-01-11 21:54             ` Sam Ravnborg
2009-01-11 22:17             ` Alexey Zaytsev
2009-01-11 22:32               ` Sam Ravnborg
2009-01-11 22:34               ` Daniel Barkalow
2009-01-11 20:29         ` Andi Kleen
2009-01-11 20:51           ` Johannes Schindelin

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