powerpc/nvram: Fix an incorrect partition merge

[xinhui]

On 2016年06月03日 19:47, Michael Ellerman wrote:
> On Thu, 2015-10-12 at 07:30:02 UTC, xinhui wrote:
>> From: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
>>
>> When we merge two contiguous partitions whose signatures are marked
>> NVRAM_SIG_FREE, We need update prev's length and checksum, then write it
>> to nvram, not cur's. So lets fix this mistake now.
>>
>> Also use memset instead of strncpy to set the partition's name. It's
>> more readable if we want to fill up with duplicate chars .
>
> Does this ever happen in practice? ie. should we backport the fix to stable
> kernels?
>

I did not see that nvram warning in practice. BUT I suggest to backport it to stable kernel. :)

Let me recall the story. :)
In past days, I was using pstore to keep some kernel logs. and sometimes I found my own logs and the panic logs did not show.
pstore use a fixed-address reserved memory In x86 while nvram instead in ppc.

Then I spent some days to review the nvram codes.
And worked out three patches to fix all issues that I found in nvram. BUT looks like I only sent out two of them. :)
I lost the third patch maybe...

> Has it always been broken?
>

no. after nvram partition corruption hit, all nvram partitions will be erased and re-alloc after the second machine reboot.
I don't know who does it but i guess it is the firmware. :)

thanks
xinhui
> cheers
>