Re: [dm-devel] Re: [PATCH] Implement barrier support for single device DM devices

[Alasdair G Kergon]

On Fri, Feb 15, 2008 at 03:20:10PM +0100, Andi Kleen wrote:
> On Fri, Feb 15, 2008 at 04:07:54PM +0300, Michael Tokarev wrote:
> > I wonder if it's worth the effort to try to implement this.

My personal view (which seems to be in the minority) is that it's a
waste of our development time *except* in the (rare?) cases similar to
the ones Andi is talking about.

But the decision has already been made for us in the block layer: 
dm is now pretty much required to support (zero-length) barriers.
Unfortunately we didn't get this finished in time for 2.6.25, but we
intend to get it done for 2.6.26:  Woe betide any callers today that
don't handle EOPNOTSUPP!

Alasdair
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