From mboxrd@z Thu Jan  1 00:00:00 1970
From: "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: compat: autofs v5 packet size ambiguity - update
Date: Wed, 22 Feb 2012 09:45:56 -0800
Message-ID: <4F4529D4.6070008@zytor.com>
References: <CA+55aFzhS69QSoN1j+Z2md116u+3OfniAoE0QMo6xyBjDyjbEw@mail.gmail.com> <20120221.221609.218135609185671883.davem@davemloft.net> <CA+55aFwvmZGDzO_8wwYfH8HsLE=qCmLkJfeMyCe4PVvOYbDMHQ@mail.gmail.com> <CA+55aFzv3X3yW8WZGMZO+aKa=qWi2w8=zn2DP-Q3jRry8Ermyw@mail.gmail.com> <CA+55aFyh1NmBt0LwR3+iD6B-Xa8wAs-nGJ0MBouPhTzWUi8W5g@mail.gmail.com> <1329889428.2193.45.camel@perseus.themaw.net> <4F4484F0.9070501@zytor.com> <CA+55aFwUvuaGdnpwVQLQLF=DdqROmKqz65v+_DXHbebNhPqkLg@mail.gmail.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ian Kent <raven@themaw.net>, David Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org, autofs@vger.kernel.org, Thomas Meyer <thomas@m3y3r.de>, Al Viro <viro@zeniv.linux.org.uk>

On 02/22/2012 08:10 AM, Linus Torvalds wrote:
> 
> But yeah, writing fixed-size data and then having a reader that reads
> fixed-size data is just not a very good approach. It's doubly bad when
> the "fixed size" isn't an explicit size that is documented in the
> protocol, but depends on data structures.
> 

Incidentally, a valid user space workaround for this problem would be to
just read all the data off the pipe but consider the packet length to be
NAME_MAX rather than NAME_MAX+1; then simply discard all-zero ints
received on input since a packet always starts with the autofs version
number.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.