Re: Aerospace and linux

[Brian Gordon]

Thank you both.    This has been very helpful for me.

I think I read two conclusions:
1) R/O is a small percentage of RAM
2) To cover this small precentage would be non-trivial

Thank you both very much for your time and knowledge, I'll move along now.



On Thu, Jun 10, 2010 at 12:46 PM, Chris Friesen <cfriesen@xxxxxxxxxx> wrote:
> On 06/10/2010 12:38 PM, Brian Gordon wrote:
>
>> On the more exotic end, I have also seen systems that have dual
>> redundant processors / memories.  Then they add compare logic between
>> the redundant processors that compare most pins each clock cycle.   If
>> any pins are not identical at a clock cycle, then something has gone
>> wrong (SEU, hardware failure, etc..)
>
> Some phone switches do this.  Some of them also have at least two copies
> of everything in memory and will do transactional operations that can be
> rolled back if there is a hardware glitch.
>
>> So, some pages of RAM are going to be read-only and the data in those
>> pages came from some source (file system?).   Can anyone describe a
>> high level strategy to occasionaly provide some coverage of this data?
>
>> So far I have thought about page descriptors adding an MD5 hash
>> whenever they are read-only and first being "loaded/mapped?" and then
>> a background daemon could occasionaly verify.
>
> Makes sense to me.  You might also pick an on-disk format with extra
> checksumming so you could compare the on-disk checksum with the
> in-memory checksum.
>
> Chris
>
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