linux-kernel - Re: [PATCH] checkpatch: Allow not using -f with files that are in git

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Date:   Fri, 28 Aug 2020 11:17:23 -0700
From:   Joe Perches <joe@...ches.com>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andy Whitcroft <apw@...dowen.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] checkpatch: Allow not using -f with files that are in
 git

On Tue, 2020-08-25 at 14:23 +0200, Rasmus Villemoes wrote:
> On 25/08/2020 02.09, Joe Perches wrote:
> > If a file exists in git and checkpatch is used without the -f
> > flag for scanning a file, then checkpatch will scan the file
> > assuming it's a patch

[]

> > +sub git_is_single_file {
> > +	my ($filename) = @_;
> > +
> > +	return 0 if ((which("git") eq "") || !(-e "$gitroot"));
> > +
> > +	my $output = `${git_command} ls-files -- $filename`;
> > +	my $count = $output =~ tr/\n//;
> > +	return $count eq 1 && $output =~ m{^${filename}$};
> > +}
> 
> Isn't that somewhat expensive to do for each file?

Just FYI:  Not really.

On my 4 year old laptop git ls-files -- <file> takes
about .02 seconds.

$ time git ls-files -- 'net/l2tp/l2tp_ip.c'
net/l2tp/l2tp_ip.c

real	0m0.013s
user	0m0.009s
sys	0m0.004s

Even uncached, it's quite quick.

# sync; echo 3 > /proc/sys/vm/drop_caches
$ time git ls-files -- 'net/l2tp/l2tp_ip.c'
net/l2tp/l2tp_ip.c

real	0m0.079s
user	0m0.004s
sys	0m0.037s

cheers, Joe