Re: [PATCH 0/2] nvme: Add kernel API for admin command

Keith Busch
2019-09-17T16:39:13Z

On Mon, Sep 16, 2019 at 12:13:24PM +0000, Baldyga, Robert wrote:
> Ok, fair enough. We want to keep things hidden behind certain layers,
> and that's definitely a good thing. But there is a problem with these
> layers - they do not expose all the features. For example AFAIK there
> is no clear way to use 512+8 format via block layer (nor even a way
> to get know that bdev is formatted to particular lbaf). It's impossible
> to use it without layering violations, which nobody sees as a perfect
> solution, but it is the only one that works.

I think your quickest path to supporting such a format is to consider
each part separately, then bounce and interleave/unmix the data +
metadata at another layer that understands how the data needs to be laid
out in host memory. Something like this RFC here:

http://lists.infradead.org/pipermail/linux-nvme/2018-February/015844.html

It appears connecting to infradead lists is a bit flaky at the moment,
so not sure if you'll be able to read the above link right now.

Anyway, the RFC would have needed a bit of work to be considered, like
using a mempool for the purpose, but it does generically make such
formats usable through the block stack so maybe try flushing out that
idea.