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Message-ID: <5f4680cce78573ecfbbdc0dfca489710581b966f.camel@perches.com>
Subject: Re: mmotm 2019-07-04-15-01 uploaded (gpu/drm/i915/oa/)
From:   Joe Perches <joe@perches.com>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Cc:     Masahiro Yamada <yamada.masahiro@socionext.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Mark Brown <broonie@kernel.org>, linux-fsdevel@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-mm@kvack.org,
        Linux-Next Mailing List <linux-next@vger.kernel.org>,
        mhocko@suse.cz, mm-commits@vger.kernel.org,
        Michal Wajdeczko <michal.wajdeczko@intel.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Intel Graphics <intel-gfx@lists.freedesktop.org>,
        DRI <dri-devel@lists.freedesktop.org>,
        Chris Wilson <chris@chris-wilson.co.uk>
Date:   Thu, 04 Jul 2019 22:22:41 -0700
In-Reply-To: <20190704220931.f1bd2462907901f9e7aca686@linux-foundation.org>
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         <20190704220931.f1bd2462907901f9e7aca686@linux-foundation.org>
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On Thu, 2019-07-04 at 22:09 -0700, Andrew Morton wrote:
> diff(1) doesn't seem to know how to handle a zero-length file.
> 
> y:/home/akpm> mkdir foo
> y:/home/akpm> cd foo
> y:/home/akpm/foo> touch x
> y:/home/akpm/foo> diff -uN x y
> y:/home/akpm/foo> date > x
> y:/home/akpm/foo> diff -uN x y
> --- x   2019-07-04 21:58:37.815028211 -0700
> +++ y   1969-12-31 16:00:00.000000000 -0800
> @@ -1 +0,0 @@
> -Thu Jul  4 21:58:37 PDT 2019
> 
> So when comparing a zero-length file with a non-existent file, diff
> produces no output.

Why use the -N option ?

$ diff --help
[...]
  -N, --new-file                  treat absent files as empty

otherwise

$ cd $(mktemp -d -p .)
$ touch x
$ diff -u x y
diff: y: No such file or directory