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

[Jon Bendtsen]

Joe Thornber wrote:
> Hi Jon,
> 
> Firstly I suggest you split this project into 2 chunks.  First
> concentrate on the device-mapper encryption target, and use dmsetup to
> do all of your testing.  When this is complete come back and talk to
> us about what work would need to be done on the tools to integrate it
> into LVM2.

We are 2 people, can we both work on the device-mapper driver?


> Make sure you read the source code for the existing targets,
> especially the simple ones like 'linear' and 'stripe'. 

Already done that, i'm going through the LVM2 stuff next.


> The 2.4 version of dm has a very useful extra target method that
> allows you to catch the io when it has completed.  You should use this
> to perform decryption.  I have attached a patch that adds this
> functionality to 2.5, this has had limited testing, so it would be
> helpful if you could keep me informed of any successes/failures you
> have with it.

i'll guess i'll try your patch first, so it also can receive some 
testing. Which 2.5 does it work on ?


> Encryption will require you to encrypt into your own data pages so you
> will have to think about how to manage these pages (maybe look at the
> page handling in kcopyd (2.4, make sure you grab the latest code from
> our ftp site).  Remember that you cannot allocate memory from within a
> dm target except GFP_NOIO, so use mempools to ensure progress.

i figured i would have to do that, but not that i cant allocate memory.


> First work out what the dm-crypt target parameters are going to be,
> and what metadata you need to store (the 1024 bytes you mentioned).  I
> suggest you keep the metadata seperate from the actual encrypted
> device, since this will allow you to add/remove encryption from
> existing LVs (without changing their size).

Okay, i'll take your advice.


> dm-devel at sistina.com is the right list for this discussion, or mail me
> directly if you want.

It is not mentioned from the page with the LVM mailing lists, but google 
found it. I'm subscribed now



JonB