[dm-devel] Bcache

Mike Snitzer snitzer at redhat.com
Fri Mar 16 01:45:53 UTC 2012

On Thu, Mar 15 2012 at  6:59pm -0400,
Kent Overstreet <koverstreet at google.com> wrote:

> On Thu, Mar 15, 2012 at 04:17:32PM -0400, Mike Snitzer wrote:
> > Your interest should be in getting the hard work you've put into bcache
> > upstream.  That's unlikely to happen until you soften on your reluctance
> > to embrace existing appropriate kernel interfaces.
> I don't really care what you think my priorities should be. I write code
> first and foremost for myself, and the one thing I care about is good
> code.
> I'd love to have bcache in mainline, seeing more use and getting more
> improvements - but if that's contingent on making it work through dm,
> sorry, not interested.
> If you want to convince me that dm is the right way to go you'll have
> much better luck with technical arguments.

We have quite a lot of code that illustrates how to implement DM
targets.  DM isn't forcing undue or cumbersome constraints that prevent
it's use for complex targets with in-kernel metadata -- again dm-thinp
proves this.

It is your burden to even begin to substantiate _why_ both DM and MD are
inadequate frameworks for virtual block device drivers.

> > Baseless and unspecific assertions don't help your cause -- dm-thinp
> > disproves your unconvincing position (manages it's metadata in kernel,
> > etc).
> I'm not the only one who's read the dm code and found it lacking - and
> anyways, I'm not really out to convince anyone. 

Like other kernel code, DM is approachable for those who are willing to
put the time in to understand it.  Your hand-waving (and now proxy)
critiques leave us nothing to work with.

> > > Kind of presumptuous, don't you think?
> > 
> > Not really, considering what I'm responding to at the moment ;)
> Maybe you should consider how you word things...

Say what?  Nice projection.  Luckily the thread is public for all to see.

I initially thought Christoph's feedback in this thread was harsh; now
it seems eerily prophetic.

Lets stop wasting our time on this thread.  Maybe we can be more
constructive in the future.

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