[PATCH 21/21] nvme: Support atomic writes
John Garry
john.g.garry at oracle.com
Fri Nov 10 00:44:45 PST 2023
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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