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

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Message-ID: <2ea1731b0906242332n305a8ebbgf37b259171741ea8@mail.gmail.com>
Date:	Thu, 25 Jun 2009 08:32:08 +0200
From:	Marco Stornelli <marco.stornelli@...il.com>
To:	Jamie Lokier <jamie@...reable.org>
Cc:	Pavel Machek <pavel@....cz>, Tim Bird <tim.bird@...sony.com>,
	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

2009/6/24 Jamie Lokier <jamie@...reable.org>:
> Pavel Machek wrote:
>> On Tue 2009-06-23 20:07:23, Marco wrote:
>> > 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?
>
> I think this is basically right.
>
> write protection for the crazy kernels, and journalling for
> powerfail/crash during updates.
>
> Journalling can be extremely simple.  It can be just one memory block
> at a fixed location, double-buffering all writes.
>
> Pramfs already has checksums, which makes that easier.  You just write
> to the buffer area first, with checksum, then write to the final area.
> Mount looks at the buffer area, and if the checksum is fine, copies
> the contents to the destination block.
>
> That's all it takes to be resistant against power failures and crashes
> during writes.  Probably <100 lines of code.
>
> -- Jamie
>

It seems a reasonable request.

Marco
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