linux-kernel - Re: [PATCH] tools/counter: Add checking directory exists for make clean

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Message-ID: <ZKtZ1WB9LdszbxU+@fedora>
Date:   Sun, 9 Jul 2023 21:07:33 -0400
From:   William Breathitt Gray <william.gray@...aro.org>
To:     Anh Tuan Phan <tuananhlfc@...il.com>
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org, rongtao@...tc.cn,
        ricardo@...dini.net, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tools/counter: Add checking directory exists for make
 clean

On Fri, Jul 07, 2023 at 09:08:35PM +0700, Anh Tuan Phan wrote:
> rmdir requires the directory exist so it causes "make -C tools clean"
> failed if someone only builds other tools but not counter. This commit
> adds checking the directory exist before doing rmdir.
> 
> Signed-off-by: Anh Tuan Phan <tuananhlfc@...il.com>
> ---
>  tools/counter/Makefile | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/counter/Makefile b/tools/counter/Makefile
> index a0f4cab71fe5..2907f3b3094b 100644
> --- a/tools/counter/Makefile
> +++ b/tools/counter/Makefile
> @@ -40,7 +40,9 @@ $(OUTPUT)counter_example: $(COUNTER_EXAMPLE)
>  clean:
>  	rm -f $(ALL_PROGRAMS)
>  	rm -rf $(OUTPUT)include/linux/counter.h
> -	rmdir -p $(OUTPUT)include/linux
> +	@if [ -d $(OUTPUT)include/linux ]; then \
> +		rmdir -p $(OUTPUT)include/linux; \
> +	fi
>  	find $(or $(OUTPUT),.) -name '*.o' -delete -o -name '\.*.d' -delete
> 
>  install: $(ALL_PROGRAMS)
> -- 
> 2.34.1

Hi Anh,

Please CC <linux-iio@...r.kernel.org> and <linux-kernel@...r.kernel.org>
as well in the future so Counter users and developers can become aware
of relevant patches.

One worry I have with this approach is the possible race condition where
the check for existence succeeds but the directory is deleted by another
agent before our rmdir executes. However, I'm not sure how we could
achieve such behavior atomically to prevent the issue.

One alternative I've considered is perhaps a single find command to
search for and delete empty directories:

    find $(or $(OUTPUT),.) -type d -empty -delete

But this will delete directories not created by the makefile which I
consider an unexpected behavior for the user (or at least very rude of
the script to do).

Perhaps we should delete the directory tree explicitly:

    rm -df $(OUTPUT)include/linux
    rm -df $(OUTPUT)include

Although we lose the symmetry of rmdir to our previous mkdir, this
should prevent the race condition issue and succeed whether the
directories still exist or not.

William Breathitt Gray

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