Re: [PATCH 1/4] block: introduce submit_bio_noacct_add_head

antlists
2020-12-30T17:54:28Z

On 30/12/2020 17:06, John Stoffel wrote:
> Danny> "Provide a way for stacking block device to re-submit
>
> Danny> the bio which should be handled first."
>
> Danny> I will fix it.
>
> Great, though my second question is*why* it needs to be handled
> first? What is the difference between stacked and un-stacked devices
> and how could it be done in a way that doesn't require a seperate
> function like this?

Is this anything to do with what's on my mind as a database guy? I've
heard that things like RAID and LVM have difficulty providing write
barriers.

I want to be confident that, at EVERY level of the stack, I can put a
barrier in that guarantees that everything written by user-space BEFORE
the barrier is handled before anything written AFTER the barrier. That
way, I can be confident that, after a problem, I know whether I can
safely roll the log forward or back.

Cheers,
Wol