linux-kernel - Re: Reading large amounts from /dev/urandom broken

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Message-ID: <20140812091428.GA3950@amd.pavel.ucw.cz>
Date:	Tue, 12 Aug 2014 11:14:28 +0200
From:	Pavel Machek <pavel@....cz>
To:	Andrey Utkin <andrey.krieger.utkin@...il.com>
Cc:	Theodore Ts'o <tytso@....edu>, hannes@...essinduktion.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Reading large amounts from /dev/urandom broken

On Sun 2014-08-10 14:51:08, Andrey Utkin wrote:
> 2014-08-09 10:45 GMT+03:00 Pavel Machek <pavel@....cz>:
> > Warn about my quick benchmark?
> >
> > http://atrey.karlin.mff.cuni.cz/~pavel/quickbench.html
> >
> > I don't see what is insane about it. Yes, there might be more
> > effective generators of random bits, but that is not the point, this
> > is quick&dirty attempt at benchmark.
> >
> > Also people will use cat /dev/urandom > /dev/sdX (and similar) to
> > clean hard drives. There should be no need to warn about
> > that. (Performance is going to be disk-limited anyway).
> 
> I believe "cat /dev/urandom" doesn't result in reading with _block
> size_ more than 32 MB. As it was already explained by Theodore,
> currently single read() operation will return "short read" when
> requested to give more than 32 MB at once. You still can read more in
> consecuential reading acts.

Well, I still don't think this behaviour change is a good idea.

									Pavel
-- 
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