Re: [dm-devel] newbie question regarding target_type's map callback

[Krzysztof Błaszkowski <kb sysmikro com pl>]

On Sun, 2011-06-19 at 02:48 +0100, Alasdair G Kergon wrote:
> All I can suggest is studying the existing upstream targets to
> understand better how they work and perhaps avoid problems like the ones
> you are seeing.

How about DM_MAPIO_REQUEUE ?


> 
> What is your target trying to do?

it is just a simple model target now which passes back requests from
inbox queue to dm_io() on a single backend dev in context of target's
work queue.

> (Why is split_io important? 

well, for same reason like dm-stripe. i may need this in the future for
switching backend devices dynamically according to bio LBA. This is why
i want to have a bio of size not bigger than split_io.


>  Did you implement a merge fn?)


no, i didn't. i don't know a purpose of merge fn.

I can see that e.g. dm-stripe doesn't use this callback in 2.6.33 kernel
while dm-stripe from 2.6.39 uses it.

furthermore dm-linear from 2.6.33 and .39 utilize .merge but split_io is
0.

> 
> Alasdair
> 


-- 
Krzysztof Blaszkowski