From mboxrd@z Thu Jan  1 00:00:00 1970
From: Yann E. MORIN <yann.morin.1998@free.fr>
Date: Fri, 24 Jul 2020 21:53:31 +0200
Subject: [Buildroot] [PATCH 08/11] package/pkg-generic.mk: detect files
 overwritten in TARGET_DIR and HOST_DIR
In-Reply-To: <20200501212318.GD15673@scaer>
References: <20200430095249.782597-1-thomas.petazzoni@bootlin.com>
 <20200430095249.782597-9-thomas.petazzoni@bootlin.com>
 <20200501212318.GD15673@scaer>
Message-ID: <20200724195331.GI2296@scaer>
List-Id: <buildroot.busybox.net>
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To: buildroot@busybox.net

Thomas, All,

On 2020-05-01 23:23 +0200, Yann E. MORIN spake thusly:
> On 2020-04-30 11:52 +0200, Thomas Petazzoni spake thusly:
[--SNIP--]
> > +ifeq ($(BR2_PER_PACKAGE_DIRECTORIES),y)
> > +# $(1): base directory to search in
> > +# $(2): suffix of file (optional)
> > +define pkg_detect_overwrite_before
> > +	cd $(1); \
> > +	LC_ALL=C find . -type f -exec md5sum {} \; > $($(PKG)_DIR)/.files$(2).md5

Note that this is very slow: it spawns a new md5sum process for each
file it encounters.

There is a better solution, though:

    find $(1) -type f -print0 |xargs -0 md5sum > $($(PKG)_DIR)/.files$(2).md5

Your original code took 11s (the second time, with a hot VFS cache),
while my proposal got it down to 2s (again, hot VFS cache).

We could also try to parallelise the job:

    find $(1) -type f -print0 |xargs -P $(PARALLEL_JOBS) -0 md5sum > $($(PKG)_DIR)/.files$(2).md5

Regards,
Yann E. MORIN.

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