bcache block interface ongoing support [LWN.net]

bcache block interface ongoing support

Posted May 24, 2018 12:54 UTC (Thu) by TimSmall (guest, #96681)
In reply to: bcache block interface ongoing support by nix
Parent article: An update on bcachefs

I was assuming that this would not involve the lvm tool set (or metadata etc.), but instead that a user space bcache-specific tool could be written to setup device mapper mappings to use dm-cache directly (within the constraints of dm-cache). This would involve fully draining (write-back → write-through → nocache) and discarding the cache device contents - so that there's a way to end up with the same (cached) content without moving the entire contents of the backing store (but keeping the bcache metadata headers etc. on the backing store device).

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bcache block interface ongoing support

Posted May 24, 2018 14:53 UTC (Thu) by nix (subscriber, #2304) [Link]

Thinking about it, you could do that in the dynamic state of the system with just a dm-linear that skips the start of the device. You'd definitely need something to get that set up though (with low enough requirements that it could run from an initramfs and link against musl etc). It would not exactly be entirely transparent, unless "bcache" remains as a block device that just does that and passes everything through, or that thunks to dm-cache for everything (now *that* would be neat, get any improvements with that layer without compatibility problems!).