linux-kernel - Re: [RFC] new -stable tag variant, Git workflow question

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Date:	Thu, 19 Nov 2009 10:15:16 -0800
From:	Greg KH <gregkh@...e.de>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Wright <chrisw@...s-sol.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC] new -stable tag variant, Git workflow question

On Thu, Nov 12, 2009 at 10:11:57AM -0600, James Bottomley wrote:
> On Wed, 2009-11-11 at 20:41 -0800, Greg KH wrote:
> > On Wed, Nov 11, 2009 at 12:50:24PM -0600, James Bottomley wrote:
> > > On Tue, 2009-11-10 at 11:37 -0800, Greg KH wrote:
> > > > On Tue, Nov 10, 2009 at 09:29:48AM -0500, James Bottomley wrote:
> > > > > On Mon, 2009-11-09 at 20:14 -0800, Greg KH wrote:
> > > > > > > A further question is, i can see using this tagging scheme in the future 
> > > > > > > in merge commits log messages too - will your scripts notice that too?
> > > > > > 
> > > > > > Hm, I don't think we look at merges as there's nothing there to actually
> > > > > > commit.
> > > > > > 
> > > > > > > For example if there's a few commits left in tip:*/urgent branches 
> > > > > > > (tip:sched/urgent, tip:core/urgent, tip:x86/urgent, etc.) by the time 
> > > > > > > v2.6.32 is released, i will then merge them into tip:sched/core, 
> > > > > > > tip:core/core, tip:x86/core, etc. - and i could use the merge commit as 
> > > > > > > a notification area to 'activate' them for -stable backporting via a 
> > > > > > > merge commit.
> > > > > > > 
> > > > > > > This is how such merge commits would look like:
> > > > > > > 
> > > > > > >   Merge branch 'core/urgent' into core/rcu
> > > > > > > 
> > > > > > >   Merge reason: Pick up urgent fixes that did not make it into .32.0
> > > > > > > 
> > > > > > >   Cc: <stable@...nel.org> # .32.x: 83f5b01: rcu: Fix long-grace-period race
> > > > > > >   Signed-off-by: Ingo Molnar <mingo@...e.hu>
> > > > > > > 
> > > > > > > This is not so rare of a situation as it might seem - for the trees i 
> > > > > > > maintain it happens in almost every release cycle - i typically skip 
> > > > > > > urgent branch merges after -rc8/-rc9, unless they are very-very-urgent 
> > > > > > > fixes - but they'd still be eligible for -stable.
> > > > > > 
> > > > > > Ok, that would be good and fine with me.
> > > > > > 
> > > > > > James, would your script pick this up, or does it need to also pay
> > > > > > attention to merge commits?
> > > > > 
> > > > > No ... because merge commits should effectively be empty (and when
> > > > > they're not you can't generate an applyable diff).  If I understand the
> > > > > workflow, the desire is to have the whole branch sent to stable by
> > > > > tagging the merge commit.  That's possible ... it's exactly the same
> > > > > logic I use in the commit scripts for the SCSI tree, so it should be
> > > > > possible to extract the logic.
> > > > > 
> > > > > By the looks of the above it's only a few commits, or is it the entire
> > > > > branch?
> > > > 
> > > > I'm thinking the commit would be the merge, right Ingo?  So it would
> > > > just be a single commit that has the marker in it.
> > > 
> > > OK, so I can make it send you this just by removing the --no-merge flag
> > > from the git rev-list the script uses to sift through what changed
> > > (which I've already done).
> > > 
> > > The slight problem is that further down, to generate the patch the
> > > script uses git format-patch -k --stdout commit^..commit.  For a merge
> > > commit, this will generate a patch equivalent to the entire branch that
> > > was merged, even though the commit message will only pick out some of
> > > these ... is this OK?
> > > 
> > > If not, I can look at using git show instead to generate the patches (it
> > > will effectively generate null diffs for merge points with the stable
> > > tag, which is closer to what you want).
> > > 
> > > Alternatively, if you pick up the commits from Linus' tree anyway, I
> > > could just stop producing diffs, which will save email bandwidth and
> > > then be automatically correct whether the commit is a merge or not.
> > 
> > No, I'd like to keep diffs, and use Linus's suggestion to get the
> > correct diff, I have had that same bug in some scripts I have written as
> > well.
> 
> OK, so git show --pretty=email -u --stat -M --cc <commit>
> 
> seems to be what works well (the options are -u to generate diff plus
> stats, -M to detect renames and --cc to try to generate a diff for merge
> points showing if there have been non trivial fix ups).
> 
> I've attached a sample below of what it will look like for a stable
> tagged merge point.  As you can see, because this is a simple merge, the
> diff is empty.

Looks great to me, thanks for doing this.

greg k-h
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