Re: [Ksummit-discuss] Allowing something Change-Id (or something like it) in kernel commits

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Thu, Aug 22, 2019 at 06:05:29PM -0700, Olof Johansson wrote:
> On Thu, Aug 22, 2019 at 5:45 PM Olof Johansson <olof@lixom.net> wrote:
> >
> > On Thu, Aug 22, 2019 at 5:43 PM Guenter Roeck <linux@roeck-us.net> wrote:
> > >
> > > On 8/22/19 5:30 PM, Olof Johansson wrote:
> > > > On Thu, Aug 22, 2019 at 5:17 PM Linus Torvalds
> > > > <torvalds@linux-foundation.org> wrote:
> > > >>
> > > >> On Thu, Aug 22, 2019 at 4:40 PM Doug Anderson <dianders@chromium.org> wrote:
> > > >>>
> > > >>> The Linux kernel has always viewed these Change-Id tags as obnoxious
> > > >>> and useless spam.  Anyone who accidentally leaves a Change-Id in their
> > > >>> patch when posting to the mailing list is told to please re-post their
> > > >>> patch without the Change-Id.  In this email, I will attempt to argue
> > > >>> that the Linux kernel ought to relax this restriction and allow
> > > >>> (possibly even encourage) Change-Ids.
> > > >>
> > > >> No.
> > > >>
> > > >> Not without some ground rules.
> > > >>
> > > >>> To begin with, let me make sure we're on the same page about what
> > > >>> Change-Ids are.  As I understand it:
> > > >>>
> > > >>> * A change ID is much alike a UUID.  It is locally generated on a
> > > >>> developer's computer and is (in theory) unique across the universe.
> > > >>
> > > >> Completely irrelevant.
> > > >>
> > > >> The point of an UUID is not just that it's unique, but THAT YOU CAN
> > > >> LOOK SOMETHING UP USING IT!
> > > >>
> > > >> A "change ID" that I can't use to look anything up with is completely
> > > >> pointless and should be removed from kernel history.
> > > >>
> > > >> But if you have something unique that is actually useful for looking
> > > >> things up, then by all means. But it needs to be useful for
> > > >> _everybody_.
> > > >>
> > > >>> * When a developer keeps the same Change-Id across two patches they
> > > >>> are making the assertion that the two patches are either the same or
> > > >>> should be treated as two versions of the same logical change.
> > > >>
> > > >> .. and we have better ways to do that.
> > > >>
> > > >> For example, we are actively encouraging things like message ID's
> > > >> (which are _also_ a form of locally generated UUID, they just are more
> > > >> than the silly purely numerical one).
> > > >>
> > > >> That gives you the origin of something, but it also gives you the
> > > >> development history and context.
> > > >>
> > > >> But note that how when it comes to message ID's we encourage them in a
> > > >> form that actually also helps look that information up, ie the
> > > >> preferred form isn't just the message ID (although that exists), it's
> > > >> a link like
> > > >>
> > > >>      Link: https://lore.kernel.org/r/20190723065733.4899-5-leon@kernel.org
> > > >>
> > > >> instead of
> > > >>
> > > >>     Message-ID: 20190723065733.4899-5-leon@kernel.org
> > > >>
> > > >> even though technically they have just as much actual information in theory.
> > > >>
> > > >> Do you see people complaining about that kind of UUID? No.  Because it
> > > >> gives useful information to the project, and when something happens,
> > > >> people can look things up and _use_ that kind of UUID.
> > > >
> > > > For the actual open projects, the answer to this might be relative
> > > > easy: Most gerrit instances can feed a mailing list with emails of
> > > > both the initial patch, and later comments.
> > > >
> > > > Said emails would obviously have a Message-ID, and if the list is
> > > > added to lore, it can be referenced there.
> > > >
> > > > Note, even if the Change-Id had a full URL, there would be no archival
> > > > guarantee in the same way as lore gives us, so that approach alone
> > > > isn't useful. A URL to a "forever" mailing list archive seems like the
> > > > most stable possible reference.
> > > >
> > > > This doesn't address the full issue Doug was looking to solve, which
> > > > is the reverse mapping of "posted patch" to "previous version of the
> > > > patch". Patchwork tries to guess this, but it's best effort. I don't
> > > > have a great answer to this, besides possibly in-reply-to threading
> > > > and associating back that way via the email trail.
> > > >
> > >
> > > Wouldn't a direct link to the Gerrit instance solve the problem ?
> > > After all,
> > >
> > > Link: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/1759334
> > >
> > > points to the same Gerrit entry as
> > >
> > > Change-Id: I5a2e33424e7fb19fed13afb854ae6546ef9bfa35
> > >
> > > and there would be no need to look anything up.
> >
> > Nope, for the same reason I already mentioned: In 2 years when Google
> > deprecates Chromium and EOL's the product and project (see: Reader,
> > Google+, Youtube messaging), there will be no way to get to the
> > history. (I know, unlikely in this case, but URLs move without
> > redirects, etc).
> >
> > Lore solves that, since it's externally archived.
> 
> Actually, it seems like the outgoing email already has suitable headers.
> 
> I looked up a random review, and viewed raw message:
> 
> https://groups.google.com/a/chromium.org/forum/#!original/chromium-os-reviews/Y2R_LLKytQw/M0TRRzfoAgAJ
> 
> X-Gerrit-Change-Id: I50d72612569743198825afdf41200c15db759076
> X-Gerrit-Change-Number: 1762035
> X-Gerrit-ChangeURL:
> <https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/1762035>
> X-Gerrit-Commit: 5b7dff2b2cb0b1a8769a53d59e387772ae569243
> 
> Since that would be captured in a mail archive, you could easily get
> it from there if needed.
> 
> Based on this, there's no reason to use opaque Change-Id, all the
> functionality needed can be reached through the mail URLs we already
> agreed are reasonable to use.
> 
> 
> (Someone should maybe tell Hao that he has the email address
> misspelled in his S-o-b).

This is however Gerrit-specific and I do not believe that Doug is
proposing to tie it all to Gerrit. I should be able to stick Change-Id
or tag we settle upon onto my outgoing patches and have it there without
any Gerrit involvement.

Thanks.

-- 
Dmitry