linux-kernel - Re: [PATCH] Open Firmware device tree virtual filesystem

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Date:	Tue, 2 Jan 2007 12:26:21 +0100
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, devel@...top.org, dmk@...x.com,
	wmb@...mworks.com, hch@...radead.org, jg@...top.org
Subject: Re: [PATCH] Open Firmware device tree virtual filesystem

>> There is one big problem: text representation is useless
>> (to scripts etc.) unless it can be transformed back to binary;
>> i.e., it has to be possible to reliably detect _how_ some
>> property is represented into text, something that cannot be
>> done with how openpromfs handles it.
>
> Text is text is text for many propertiers,

Sure some properties contain (or _should_ contain!) just
one simple text string.  You can simply "cat" those when
they are binary in the filesystem too FWIW.

> in particular
> the ones you actually end up wanting to modify.

But that is just one simple use of the filesystem.  One that
doesn't work at all on PowerPC btw -- at kernel run time,
we don't have access to OF at all anymore.

> In order for a problem to exist, you have to show counter
> examples where the problem triggers and something fails.
>
> What in userspace wants to modify a OFW property, which
> is not text?

I never was talking about modifying.  Most things that
most users want to modify aren't normal OF properties
anyway, but configuration variables.  In some/many OF
implementations updating those via the device tree doesn't
work.

> In my experience all such cases are limited to ASCII text
> valued properties, such as device aliases, environment
> variables, and things like nvramrc.

If the text representation in the file system was unambiguous,
it wouldn't be useless for scripts anymore, merely very
inconvenient.

Segher

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