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

Marco Stornelli
2009-06-25T06:32:21Z

2009/6/24 Jamie Lokier <jamie@shareable.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