Re: [PATCH 21/21] nvme: Support atomic writes

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On 10/11/2023 06:29, Christoph Hellwig wrote:
Yes.

As for splitting, it is not permitted for atomic writes and only a single
bio is permitted to be created per write. Are more integrity checks
required?
I'm more worried about the problem where we accidentally add a split.
The whole bio merge/split path is convoluted and we had plenty of
bugs in the past by not looking at all the correct flags or opcodes.

Yes, this is always a concern.

Some thoughts on things which could be done:
- For no merging, ensure request length is a power-of-2 when enqueuing to block driver. This is simple but not watertight. - Create a per-bio checksum when the bio is created for the atomic write and ensure integrity when queuing to the block driver - a new block layer datapath which ensures no merging or splitting, but this seems a bit OTT

BTW, on topic of splitting, that NVMe virt boundary is a pain and I hope that we could ignore/avoid it for atomic writes.

Thanks,
John



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