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Date: Wed, 5 Nov 2025 15:53:09 +0100
From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Keith Busch <kbusch@meta.com>,
	linux-block@vger.kernel.org, martin.petersen@oracle.com,
	axboe@kernel.dk
Subject: Re: [RFC PATCH] blk-integrity: support arbitrary buffer alignment
Message-ID: <20251105145309.GA26042@lst.de>
References: <20251104224045.3396384-1-kbusch@meta.com> <20251105141504.GC22325@lst.de> <aQtiYd69E-3G_PC4@kbusch-mbp>
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On Wed, Nov 05, 2025 at 07:42:41AM -0700, Keith Busch wrote:
> This generally does pass 'void *' to contiguous protection data. If the
> actual protection payload is spread across multiple segments, though, we
> don't have contiguous data, so we have to bounce it through something.
> Declaring the union on the stack provides this memory for that unusual
> case. If the bip segment is big enough, we point the 'void *' directly
> at it; if not, we point it to the temporary onstack allocation. Using
> a union ensures that it's definitely big enough for any checksum type.

The union contains pointers, which are always 8 bytes.  But I guess
I can see now how this didn't blow up, assuming this was only tested
on classic PI, as the tuples are just 8 bytes and you just used the
pointer as storage?  I.e. these aren't supposed to be pointers, but
values?