Re: [PATCH] Consider user space generated checksum

On  July 13, mhtran@us.ibm.com wrote:

On alpha systems, the kernel computed checksum, csum_partial(), and user
space computed checksum are different.  As a consequence, the kernel MD
driver aborts detection of MD superblock.  This means running mdadm
--assemble -f or -U summaries will not always work.

Weird... arch/alpha/checksum.c seem to do a 16 bit checksum rather
than the 32bit csum that i386 does.  It's mostly used for network code
and IP uses 16bit csum, but it is odd that it claims to return a 32
bit  number, but really it will always be 16bit...

I have been wondering... Should MD driver use csum_partial() at all?

Well, as we seem to want a 32bit checksum, I guess we cannot.  But for
historical reasons, we probably have to.

I guess a patch much like yours is needed.  I'll add something to make
sure version-1 superblock are a bit more predictable.

NeilBrown