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To: linux-kernel@vger.kernel.org
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: /dev/random probs in 2.4test(12-pre3)
Date: 1 Dec 2000 10:18:56 -0800
Organization: Transmeta Corporation, Santa Clara CA
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Copyright: Copyright 2000 H. Peter Anvin - All Rights Reserved
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Followup to:  <Pine.LNX.4.10.10012011720050.23462-100000@sphinx.mythic-beasts.com>
By author:    Matthew Kirkwood <matthew@hairy.beasts.org>
In newsgroup: linux.dev.kernel
>
> Hi,
> 
> It looks like the random driver in 2.4test will return a
> short read, rather than blocking.  This is breaking vpnd
> (http://sunsite.dk/vpnd/) which breaks with "failed to
> gather random data" or similar.
> 
> Here's a sample strace:
> 
> open("/dev/random", O_RDONLY)           = 3
> read(3, "q\321Nu\204\251^\234i\254\350\370\363\"\305\366R\2708V"..., 72) = 29
> close(3)                                = 0
> 
> Have the semantics of the device changed, or is vpnd doing
> something wrong?
> 

vpnd is doing something wrong: it's assuming short reads won't
happen.  /dev/random will block if there is NOTHING to be read;
however, if there are bytes to be read, it will return them even if it
is less than the user asked for.

	-hpa
-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
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