[PATCH v2 2/3] block: support PI at non-zero offset within metadata

[Keith Busch]

On Thu, Feb 01, 2024 at 06:31:25PM +0530, Kanchan Joshi wrote:
> Block layer integrity processing assumes that protection information
> (PI) is placed in the first bytes of each metadata block.
> 
> Remove this limitation and include the metadata before the PI in the
> calculation of the guard tag.

Very late reply, but I am just now discovering the consequences of this
patch.

We have drives with this format, 64b metadata with PI at the end. With
previous kernels, we had written data to these drives. Those kernel
versions disabled the GUARD generation, so the metadata was written
without it, and everything was fine.

Now we upgrade to 6.9+, and this kernel enables the GUARD check. All the
data previously written to this drive is unreadable because the GUARD is
invalid.

Not sure exactly what to do about this, but it is a broken kernel
upgrade path, so wanted to throw that information out there.