Re: [dm-crypt] [ANNOUNCE] cryptsetup 1.3.0-rc1 (test release candidate)

[Milan Broz <mbroz@redhat.com>]

On 03/22/2011 07:47 PM, Rudolf Deilmann wrote:
> On Mon, 21 Mar 2011 19:21:50 +0100
> Milan Broz <mbroz@redhat.com> wrote:
>> I added offset support, seems loopAES always uses offset==skip
>> (IOW initial vector is always related to absolute sector size on the
>> device).
> 
> No, loopAES supports both options. It depends on user input:
> 
> --
> -o offset
>    The data start is moved offset bytes into the specified file or
>    device. Normally offset is included in IV   (initialization
>    vector) computations. If offset is prefixed with @ character, then
>    offset is not included in IV computations. @ prefix functionality
>    may not be supported on some older kernels and/or loop drivers.

I wonder how I missed that. Ok, the we just allow --skip and if
it is not explicitly defined, it will behave as now.
So @offset => --skip 0 --offset $offset/512, right?

I added test for default offset (and verification with losetup passes),
so it is just that @ prefix mode missing now.

> Both options seems to be supported by dmcrypt/dmsetup. In the first case
> IV offset is always identic to the sector offset, in the second case IV
> offset is always zero.

yes, everything is supported, this is just userspace handling.

> (IV offset: 6th value at dmsetup table, sector offset: 8th value. I
> hope, I haven't muddle something )

FYI the documentation is in kernel itself
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob_plain;f=Documentation/device-mapper/dm-crypt.txt;hb=HEAD

Thanks,
Milan