Date:	Tue, 23 Feb 2016 15:49:30 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Junio C Hamano <gitster@...ox.com>,
	Fengguang Wu <fengguang.wu@...el.com>,
	Xiaolong Ye <xiaolong.ye@...el.com>, git@...r.kernel.org,
	ying.huang@...el.com, philip.li@...el.com, julie.du@...el.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/PATCH 1/1] format-patch: add an option to record base tree info

"H. Peter Anvin" <hpa@...or.com> writes:

> On February 23, 2016 12:35:12 PM PST, Junio C Hamano <gitster@...ox.com> wrote:
>>ebiederm@...ssion.com (Eric W. Biederman) writes:
>>
>>> Junio C Hamano <gitster@...ox.com> writes:
>>>
>>>> It is valuable for a testing organization to say "We tested this
>>>> series on top of version X.  We know it works, we have tested on a
>>>> lot more hardware than the original developer had, we know this is
>>>> good to go."  It is a valuable service.
>>>>
>>>> But that is valuable only if version X is still relevant, isn't it?
>>>>
>>>> Is the relevance of a version something that is decided by a
>>>> developer who submits a patch series, or is it more of an attribute
>>>> of the project and where the current integration is happening?
>>>> Judging from the responses from Dan to this thread, I think the
>>>> answer is the latter, and for the purpose of identifying the
>>>> relevant version(s), the project does not even care about the exact
>>>> commit, but it wants to know more about which branch the series is
>>>> targetted to.
>>>>
>>>> With that understanding, I find it hard to believe that it buys the
>>>> project much for the "base" commit to be recorded in a patch series
>>>> and automated testing is done by applying the patches to that exact
>>>> commit, which possibly is no-longer-relevant, even though it may
>>>> help shielding the testing machinery from "you tested with a wrong
>>>> version" complaints.
>>>>
>>>> Isn't it more valuable for the test robot to say "this may or may
>>>> not have worked well with whatever old version the patch series was
>>>> based on, but it no longer is useful to the current tip of the
>>>> 'master'"?  If you consider what benefit the project would gain by
>>>> having such a robot, that is the conclusion I have to draw.
>>>>
>>>> So I still am not convinced that this "record base commit" is a
>>>> useful thing to do.
>>>
>>> So I don't know what value this has to the git project.
>>
>>Oh, don't worry, I wasn't talking about value this may have to the
>>Git project at all.  "The value to the project" I mentioned in my
>>response was all about the value to the kernel project.
>>
>>> The value of Fengguag's automated testing to the kernel project is to
>>> smoke out really stupid things.
>>
>>I'll snip your bullet points, but as I wrote, I do understand the
>>value of prescreening test.
>>
>>What I was questioning was what value it gives to that testing to
>>use "the developer based this patch on this exact commit" added to
>>each incoming patch, and have Fengguag's testing machinery test a
>>patch with a base version that may no longer be relevant in the
>>context of the project.  Compared to that, wouldn't "this no longer
>>applies to the branch the series targets" or "this still applies
>>cleanly, but no longer compiles because the surrounding API has
>>changed" be much more valuable?
>>
>>In your other message, you mentioned the "index $old..$new" lines,
>>and it is possible to use them to find a tree that the patch cleanly
>>applies to, but it will not uniquely identify _the_ version the
>>patch submitter used.  IMHO, finding such _a_ tree from the recent
>>history of the branch that the patch targets and testing the patch
>>on top of that tree (as opposed to testing the patch in the exact
>>context the developer worked on) would give the project a better
>>value.
>
> Personally, as a maintainer, I would love to see the tree ID and
> ideally also the commit ID a series is based on.  The commit ID is in
> some ways less useful since it is non-recreatable (and therefore will
> never match for anything but the first patch of a series), but could
> be useful to the maintainer.
>
> As far as putting in a bunch of metainformation that has to be
> manually or semimanually obtained, there are a lot of issues with
> that, as it way too easily turns into wrong information or potential
> information leaks that might make corporate contributors
> uncomfortable.

I would really love to hear from Fengguag about where this is a
practical problem, but I expect the flock of x86 topic tress is probably
one of those cases where there are problems for automation to figure out
which tree a patch applies to in practice.  The mailing list for x86
patches is linux-kernel.  Even if you filter by x86@...nel.org to detect
it is an x86 patch which topic branch a patch goes to was not clear to
me from a quick skim of recent lkml x86 patches.

So I could really respect a patch header line that said:
tree abcdef0123456789...0123456789abcdef

Where the numbers where the truncated tree hash before and after a patch
was applied.  That would seem to give a little bit of extra sanity
checking in the application of git diffs as well.

Eric

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