[dm-devel] Re: [lvm-devel] dm-crypt - some info, and a few development questions

[Jon Bendtsen]

On Thu, Jul 17, 2003, at 11:36:01 2003 Joe Thornber 
dm-devel at sistina.com wrote:
 > On Thu, Jul 17, 2003 at 06:12:42PM +0200, Christophe Saout wrote:
 >> Would it be possible to do development of these things (especially
 >> the
 >> dm part) to an open place? I'm very interested in the inner workings 
   >> of
 >> device-mapper and the new 2.5/2.6 kernel block io code.
 >
 > Post your patches often, that way you'll get a lot more feedback.  I
 > tend to develop incremental patch sets.
 > (eg. http://people.sistina.com/~thornber/internal-patches/raid1/) this
 > allows people to see quickly what has changed.  I have a little perl
 > program that helps develop with such patchsets if you're interested.

to this mailing list, or the linux kernel development one ?


 >> If I had more time and would be able to understand these things
 >> better I
 >> would have written some code by now (perhaps porting some of the
 >> missing
 >> dm targets from 2.4 to 2.5 or so), but if I can see progress step by
 >> step I'll perhaps be able to help. Or at least test it.
 >
 > I'm working on the missing targets (snapshots and mirroring) already,
 > also these two are *far* more complex than your crypto target will be.

yeah i can imagien


 > Spend a day playing with dmsetup, and make sure you really understand
 > how to write target types.  The best way to learn is to try and write
 > a trivial target type, eg. a 'reverse' target that divides the device
 > into chunks and then reverses their order, ie. the first logical 
chunk > is
 > stored in the last logical chunk of the device.  This should only take
 > you ~150 lines of code (start with dm-linear.c and modify).

hmm, maybe the map into a file is a more trivial target ?


 >> And, I was just wondering, would it be theoretically possible to
 >> write a
 >> dm target that stores data in a file, so that it replaces what the
 >> loop device does? Or was dm not designed for this?
 >
 >> You could write a loop target, and people have suggested this
 >> already. It's not something that I'm interested in doing however.

Would it be an easy target to write, such that i could play with a 
dm-loop target before making the dm-crypt?



JonB