Date:	Tue, 21 Jul 2009 15:38:08 -0400
From:	John Lanza <jdlanza@...il.com>
To:	tridge@...ba.org
Cc:	Boaz Harrosh <bharrosh@...asas.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Martin Steigerwald <Martin@...htvoll.de>,
	Jan Engelhardt <jengelh@...ozas.de>,
	Theodore Tso <tytso@....edu>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Pavel Machek <pavel@....cz>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	linux-fsdevel@...r.kernel.org,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>, corbet@....net,
	jcm@...masters.org, torvalds@...ux-foundation.org
Subject: Re: CONFIG_VFAT_FS_DUALNAMES regressions

Resending in plain text.......

On Tue, Jul 21, 2009 at 11:06 AM, John Lanza<jdlanza@...il.com> wrote:
> If I understand the proposal (which I think I do), Tridge is correct.
> If a patent prohibits a system from performing steps "A" and "B",
> simply separating the steps into separate modules, or utilities, won't
> avoid infringement.
>
> I'm happy to answer specific questions, but it might be best to do
> that separately from lkml.
>
> johnl
>
> On Tue, Jul 21, 2009 at 9:04 AM, <tridge@...ba.org> wrote:
>> Hi Boaz,
>>
>>  > I guess you tried putting a zero at first char and it breaks everybody?
>>
>> It works with some devices, but with many it doesn't. A space followed
>> by a nul works with quite a lot of devices, but not enough (the last
>> patch used a space followed by a nul).
>>
>> I went to a large electronics store and told them I wanted to buy
>> devices that didn't work with my computer. They were very helpful, and
>> as a result I was able to test a lot of devices. That is what led to
>> the design of this patch (plus the feedback from people like Jan and
>> his IOneIt MP3 player).
>>
>>  > I guess (35^6)*8*7 is not that bad
>>
>> yes, but luckily For the WinXP bluescreen the probability of the crash
>> is actually much lower than that figure would give. With the same
>> modelling assumptions of WinXP memory slots for 8.3 entries that Paul
>> used for the last patch, it comes out as less than a 1 in 10k chance
>> for a full directory (ie. 32767 long filenames). For 100 files in a
>> directory it is around 1 chance in 10^11. I'm sure Paul will do the
>> full expansion and modelling if anyone wants more precise numbers.
>>
>> For the chkdsk rename, the probability is much easier to calculate as
>> it is just the usual birthday expansion (see wikipedia for simple
>> formula for that). That is what gives 0.5% for 32767 files in a
>> directory, and 4.8x10^-8 for for 100 files.
>>
>> Basically it won't happen very often. In each case the probability is
>> rougly 75x less than it was for the last patch.
>>
>>  > What if we had a user mode utility that does these short-names
>>  > renames that a user can optionally run after umount? since it
>>  > only writes the (random) short-names it's also safe.
>>
>> While I will defer to John Lanza if you want a more complete legal
>> view on this, I think it is likely that separating the steps of the
>> patent between programs within one system is not a safe enough legal
>> strategy to be used.
>>
>> Please do keep thinking about it though. There could well be some
>> simple combination which is legally safe and also technically
>> completely satisfactory. If you think you have hit on a winner, you
>> may wish to discuss it with John Lanza in private first though, so it
>> can be fine tuned before being presented publicly.
>>
>> Cheers, Tridge
>>
>
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