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

[Christoph Hellwig]

On Tue, Jan 30, 2024 at 10:42:05PM +0530, Kanchan Joshi wrote:
> The block integrity subsystem assumes that PI appears first in the
> metadata buffer.
> Abolish this assumption by adding the ability to handle PI starting at
> a non-zero offset.
> Calculation of the guard tag includes the metadata buffer up to this
> offset.

Maybe rewrite this as:

Block layer integrity processing currently assumes that protection
information is placed in the first bytes of each metadata block.
Remove this this limitation and include the metadata before the
protection information in the calculation of the guard tag.

>  {
>  	unsigned int i;
> +	u8 offset = iter->pi_offset;

Nit: I find it more readable if variables that are initialized at
declaration time come first.  Also (with a few exceptions) it's nice
to read longer declarations first.