linux-kernel - Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem

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Message-ID: <20090623182941.GA2045@elf.ucw.cz>
Date:	Tue, 23 Jun 2009 20:29:41 +0200
From:	Pavel Machek <pavel@....cz>
To:	Marco <marco.stornelli@...il.com>
Cc:	Tim Bird <tim.bird@...sony.com>,
	Jamie Lokier <jamie@...reable.org>,
	Linux Embedded <linux-embedded@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Daniel Walker <dwalker@....ucsc.edu>
Subject: Re: [PATCH 00/14] Pramfs: Persistent and protected ram filesystem

On Tue 2009-06-23 20:07:23, Marco wrote:
> Pavel Machek wrote:
> > On Mon 2009-06-22 14:50:01, Tim Bird wrote:
> >> Pavel Machek wrote:
> >>>> block of fast non-volatile RAM that need to access data on it using a
> >>>> standard filesytem interface."
> >>> Turns a block of fast RAM into 13MB/sec disk. Hmm. I believe you are
> >>> better with ext2.
> >> Not if you want the RAM-based filesystem to persist over a kernel
> >> invocation.
> > 
> > Yes, you'll need to code Persistent, RAM-based _block_device_. 
> 
> First of all I have to say that I'd like to update the site and make it
> clearer but at the moment it's not possible because I'm not the admin
> and I've already asked to the sourceforge support to have this possibility.
> 
> About the comments: sincerely I don't understand the comments. We have
> *already* a fs that takes care to remap a piace of ram (ram, sram,
> nvram, etc.), takes care of caching problems, takes care of write

Well, it looks pramfs design is confused. 13MB/sec shows that caching
_is_ useful for pramfs. So...?

> You are talked about journaling. This schema works well for a disk, but
> what about a piece of ram? What about a crazy kernel that write in that
> area for a bug? Do you remember for example the e1000e bug? It's not

I believe you need both journaling *and* write protection. How do you
handle power fault while writing data?
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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