Re: [PATCH] Add short author date to Fixes tag

[Alejandro Colomar <alx@kernel.org>]

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D'oh!  I forgot to add the In-Reply-To tag.

I meant to reply to
<https://lore.kernel.org/all/52541f79-ba1c-49c9-a576-45c3472d1c79@intel.com/T/#mf183db5f382b4a39cf52a4a1d2ca8f96697c312e>


On 2026-02-25T01:56:08+0100, Alejandro Colomar wrote:
> Hi Steven, Greg,
> 
> [I'll reply to several sub-threads at once.]
> 
> 
> [Message-ID: <20250113095101.4e0fff91@gandalf.local.home>]
> On Mon, Jan 13, 2025 at 09:51:01AM -0500, Steven Rostedt wrote:
> > Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> 
> > > $ git help fixes
> > > 'fixes' is aliased to 'show --format='Fixes: %h ("%s")' -s'
> >
> > Hmm, I've just been manually adding the Fixes tags ;-) That's because when
> > I add a fixes tag, I also do a more in depth analysis to make sure the
> > commit being tagged is really the cause of the problem. A lot of my fixes
> > tags are due to very subtle bugs, and a lot of times its a combination of
> > event that happened.
> 
> I also precede the generation of the fixes tag with an in-depth
> analysis.  However, that doesn't conflict with using a git alias to
> generate it, once I've reached a conclusion.  I use this alias to
> generate them, and it's quite handy:
> <https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING.d/git#n46>
> 
> >
> > That said, maybe one day I'll use a script or alias in the future.
> 
> 
> [Message-ID: <20250111120935.769ab9a3@gandalf.local.home>]
> On Sat, Jan 11, 2025 at 6:08 PM Steven Rostedt <rostedt@goodmis.org> wrote:
> > On Fri, 10 Jan 2025 16:21:35 -0800
> > Jacob Keller <jacob.e.keller@intel.com> wrote:
> >
> > > I personally find the date helpful as it can help place a commit without
> > > needing to take the extra time to do a lookup.
> >
> > I've never found dates to be meaningful. I'm always more concerned about
> > when a commit was added to mainline. Thus the version where the commit was
> > added is very important for me.
> 
> Indeed.  I agree with this, and it's a quite important difference.
> The commit dates are strictly increasing, which means you can use the
> date to perform a search of a commit, if there's a collision in the
> hash (and possibly in the subject).
> 
> I documented this in the man-pages project, where I require the commit
> date to appear in Fixes tags.
> <https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING.d/patches/trailer#n16>
> 
> > This is why I keep a bare clone of Linus's
> > tree and commonly do:
> >
> >  $ git describe --contains fd3040b9394c
> > v5.19-rc1~159^2~154^2
> >  $ git describe --contains a76053707dbf
> > v5.15-rc1~157^2~376^2~4
> >
> > I can easily see that a76053707dbf was added in 5.15 and fd3040b9394c was
> > added in 5.19. The amount of work needed to add dates to Fixes tags would
> > greatly exceed the amount of added work someone would need to do to do the
> > above operations if they wanted to know the order of commits.
> 
> 
> [Message-ID: <2025011032-gargle-showing-7500@gregkh>]
> Greg wrote (Fri, 10 Jan 2025 13:32:22 +0100):
> > Please no, you will break all of our tooling and scripts that parse
> > these types of fields.  The git commit id and commit header is all we
> > need to properly determine this type of information, no need to add a
> > date in here at all.
> > 
> [...]
> > 
> > So I don't think you need to add a date here.  Dates also really do not
> > mean much with commits, what matters is what release a commit is in, not
> > when it was originally made.  We have commits that take years to show up
> > in a release, so if you only look at a date, you will be mistaken many
> > times as it's not showing what came before what many times (i.e. we
> > apply commits out-of-date-order all the time.)
> 
> As I said above, I agree that the commit date is the right choice.
> Author dates can be out-of-date-order by years.  Commit dates are
> necessarily in order, though.
> 
> 
> [Message-ID: <20250110080331.04645768@gandalf.local.home>]
> Steven wrote (Fri, 10 Jan 2025 08:03:31 -0500):
> > How can it lead to misjudgment? If you have two or more hashes matching, do
> > you really think they'll have the same subjects?
> 
> The possibility isn't zero.  Statistically, it's quite low.  However,
> it's non-zero.
> 
> $ git log --format=tformat:'%s' | sort | uniq -c | sort | tail
>     248 Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
>     263 Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6
>     275 Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
>     293 Merge tag 'arm64-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
>     314 Merge branch 'akpm' (patches from Andrew)
>     315 Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
>     318 Merge tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
>     324 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
>     369 Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm
>     670 Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
> $ git log --format=tformat:'%s' | grep -v ^Merge | sort | uniq -c | sort | tail
> grep: (standard input): binary file matches
>      22 drm/amd/display: Clean up some inconsistent indenting
>      25 Auto-update from upstream
>      26 [ARM] Update mach-types
>      26 pmdomain: Merge branch fixes into next
>      30 s390: update defconfigs
>      32 tools arch x86: Sync the msr-index.h copy with the kernel sources
>      38 [SPARC64]: Update defconfig.
>      52 mmc: Merge branch fixes into next
>      59 drm/i915: Convert wait_for(I915_READ(reg)) to intel_wait_for_register()
>      62 batman-adv: Start new development cycle
> 
> Subjects repeat every now and then, and the entropy in some subjects is
> actually quite low.
> 
> If you include the commit date in a Fixes tag, then you preclude the
> entire possibility of a commit reference clash, because you won't have
> two patches committed in the same date with the same subject and same
> hash (unless you *really* try)
> 
> 
> [Message-ID: <2025011115-energize-edge-c9c7@gregkh>]
> Greg wrote (Sat, 11 Jan 2025 06:48:53 +0100):
> > And if it isn't long enough, tools like:
> >	https://lore.kernel.org/r/20241226220555.3540872-1-sashal@kernel.org
> > can help figure it out as well.
> 
> That uses hash+subject.  This may be not enough in some cases (see how
> much subjects repeat, in the logs above).  And importantly, a fixes tag
> may become ambiguous *after* it has been written, so you can't predict
> much.
> 
> By having a commit date in the Fixes tag, you could even simplify the
> script to just do a binary search in case of ambiguity.  Let's say I
> want to find the following commit (arbitrarily taken from the first
> Fixes tag I've found in my copy of linux.git):
> 
> 	a2e459555c5f (2023-08-09; "shmem: stable directory offsets")
> 
> We could find it, with a trivial command line.  We only even need two
> characters of the hash:
> 
> 	$ git log --oneline --after='2023-08-08' --before='2023-08-10' \
> 	| grep ^a2;
> 	a2e459555c5f shmem: stable directory offsets
> 
> No need for a huge script to disambiguate.  This is even typo-resistant,
> as one could eventually find something that is similar enough, if one
> had such a field with a typo (in any of the three fields).  You'd be
> able to search by the other two fields, and two fields should be
> _usually_ enough for disambiguating, and the third one could corroborate
> the typo.
> 
> So, what would you think of having the commit date in commit references
> such as Fixes tags?
> 
> 
> Have a lovely night!
> Alex
> 
> -- 
> <https://www.alejandro-colomar.es>



-- 
<https://www.alejandro-colomar.es>

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