linux-kernel - Re: [PATCH 1/1] lib: remove leading spaces before tabs

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Date:   Wed, 09 Jun 2021 14:44:54 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Andy Shevchenko <andy@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] lib: remove leading spaces before tabs

On Wed, 2021-06-09 at 13:30 +0300, Andy Shevchenko wrote:
> On Wed, Jun 9, 2021 at 9:21 AM Leizhen (ThunderTown)
> <thunder.leizhen@...wei.com> wrote:
> > On 2021/6/9 13:15, Leizhen (ThunderTown) wrote:
> > > On 2021/6/9 0:03, Joe Perches wrote:
> > > > On Tue, 2021-06-08 at 17:00 +0800, Leizhen (ThunderTown) wrote:
> > > > > On 2021/6/8 16:44, Andy Shevchenko wrote:
> > > > > > On Tue, Jun 8, 2021 at 10:14 AM Zhen Lei <thunder.leizhen@...wei.com> wrote:
> > > > > > > 
> > > > > > > 1) Run the following command to find and remove the leading spaces before
> > > > > > >    tabs:
> > > > > > >    find lib/ -type f | xargs sed -r -i 's/^[ ]+\t/\t/'
> > > > > > 
> > > > > > Hint for the future, try to use what Git provides, for example `git
> > > > > > ls-files -- lib/`.
> > > > > 
> > > > > Okay, thanks. I learned a new trick.
> 
> > > > For instance:
> > > > 
> > > > $ git diff --stat lib
> > > > $ git ls-files lib/ | \
> > > >   xargs ./scripts/checkpatch.pl --types=SPACE_BEFORE_TAB --fix-inplace
> > 
> > I just tried it. It's too slow.
> 
> If checkpath accepts infinite positional arguments, then proper way of
> use (that's how I do with simple perl regexps) is to
> 
> scripts/checkpatch.pl --types=SPACE_BEFORE_TAB --fix-inplace -- $(git ls-files lib/)

That won't always work:

$ git ls-files | xargs | wc -c
2716737

Nothing accepts infinite positional arguments.
You are always limited by the maximum length of a command line

$ getconf ARG_MAX
2097152

xargs has:

$ xargs --show-limits
Your environment variables take up 3517 bytes
POSIX upper limit on argument length (this system): 2091587
POSIX smallest allowable upper limit on argument length (all systems): 4096
Maximum length of command we could actually use: 2088070
Size of command buffer we are actually using: 131072
Maximum parallelism (--max-procs must be no greater): 2147483647

> Seems like we have a shell lesson :-)

Maybe so.

Using xargs allows use of -P to invoke parallelism.
Or you could just use gnu parallel instead of xargs.

Using './scripts/checkpatch.pl -- $(git ls-files <path>)' will only
allow a single process to be invoked for the files to be scanned.