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    SubjectRe: [PATCH 1/1] lib: remove leading spaces before tabs
    On Wed, Jun 09, 2021 at 02:44:54PM -0700, Joe Perches wrote:
    > 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@huawei.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@huawei.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

    If you care about parallelism, the checkpatch should be doing it itself.

    Currently it's one perl interpreter with a single queue vs. zillions of perl
    invocations (with all downsides of this). And I'm not sure which one is a
    winning.

    And yes, I'm aware of why xargs is ever exists (including handling of the
    special file names).

    > > 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.

    --
    With Best Regards,
    Andy Shevchenko


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