linux-kernel - Re: [PATCH] checkpatch: Add test for commit id formatting style in commit log

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Date:	Sun, 10 Aug 2014 14:28:01 -0700
From:	Joe Perches <joe@...ches.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Git Mailing List <git@...r.kernel.org>
Subject: Re: [PATCH] checkpatch: Add test for commit id formatting style in
 commit log

On Sun, 2014-08-10 at 23:08 +0200, Geert Uytterhoeven wrote:
> Hi Joe,

Hi Geert.

> On Thu, Jul 3, 2014 at 12:00 AM, Joe Perches <joe@...ches.com> wrote:
> > Commit logs have various forms of commit id references.
> >
> > Try to standardize on a 12 character long lower case
> > commit id along with a description of parentheses and
> > the quoted subject line
> >
> > ie: commit 0123456789ab ("commit description")
> 
> Now this is in mainline, checkpatch starts complaining about my "too long"
> (40 chars) commit IDs in commit messages :-(
> 
> 40 chars may be too long (but it's quick to copy-and-paste, as "git show"
> shows that by default), but 12 sounds a bit short, as that's only 48 bits.

Right now, this test allows 12 to 16 byte length commit ids
without emitting a warning.

Andrew wanted this test, I don't care how long the commit id
is in the commit log.

> According to the Birthday Paradox (en.wikiipedia.org/wiki/Birthday_problem),
> there's a probability of 50% of a collision if you use 48 bits IDs in a
> repository with ca. 16 milion (2^24) objects. A Linux kernel repository
> counts ca. 4 million objects, so we're getting close...
> 
> So soon we'll get "error: short SHA1 is ambiguous".
> 
> BTW, is there actually an easy way to make "git show" show all options for
> an ambiguous SHA1?

Not so far as I know, but I'm nothing like a git expert.

The script I used before adding this to checkpatch was:

$ cat format_commit.sh 
#!/bin/bash

regex1="^error: short SHA1 $1 is ambiguous\."
regex2="fatal: ambiguous argument '$1': unknown revision or path not in the working tree\."

tmp=$(mktemp --tmpdir format_commit.XXXXXXXXXXXXX)

git log --format='%H ("%s")' -1 $1 > $tmp 2>&1

read line < $tmp

rm -f $tmp

if [[ $line =~ $regex1 ]] ; then
    echo "checking commits $1..."
    git rev-list --remotes | grep -i "^$1" |
    while read line ; do
        git log --format='%H ("%s")' -1 $line | 
        echo "commit $(cut -c 1-12,41-)"
    done
elif [[ $line =~ $regex2 ]] ; then
    echo "No matching commit"
    exit 1
else
    echo "commit $(echo $line | cut -c1-12,41-)"
fi

exit 0
$

so that using "$ format_commit.sh 1234" looks
at _all_ the commit references by using git rev-list
then greps that output for the matches, but it is
darn slow...

$ time ./format_commit.sh 1234
checking commits 1234...
commit 1234351cba95 ("xfs: introduce xlog_copy_iovec")
commit 1234471e2d11 ("perf header: Fix numa topology printing")
commit 1234f4bada54 ("hwrng: Kconfig: remove dependency for atmel-rng driver")
commit 12340313cf94 ("MAINTAINERS: add new cgroup list to CC notice")
commit 12346037a718 ("UBIFS: dump more in the lprops debugging check")
commit 12342c475f5d ("iwlwifi: proper monitor support")
commit 1234010684bb ("Add notation that the Asus W5F laptop has a short cable instead of 80-wire.")
commit 123411f2d0da ("[CPUFREQ] dprintf format fixes in cpufreq/speedstep-centrino.c")

real	0m24.535s
user	0m21.668s
sys	0m5.332s

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