Re: How to get the size of the loop-device?

[Markus Laire <malaire@xxxxxxxxx>]

On 2/1/06, Jari Ruusu <jariruusu@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Markus Laire wrote:
> > Once I have a working loop device, e.g. /dev/loop5, how can I get the
> > size of this device in bytes for bash-script?
>
> sectors=`blockdev --getsize /dev/loop5`
> fullsize=`echo ${sectors}' * 512' | bc`
> halfsize=`echo ${sectors}' * 256' | bc`
>
> What are you trying to do?

I'm writing a script which double-encrypts a single swap-area and /tmp
with random keys.

If I simply use two loop-devices for both, I need 4 sets of random keys.

So I'm trying this setup which only needs 2 sets of random keys:
(I don't want to waste the entropy)
(Note: I intend to use 2 different ciphers, but currently I only have
AES working)

losetup -e AES256 -H random /dev/loop7 "$DEV"
losetup -e AES256 -H random /dev/loop6 /dev/loop7
losetup -s $halfsize /dev/loop4 /dev/loop6
losetup -o $halfsize /dev/loop5 /dev/loop6
mkswap /dev/loop4 > /dev/null
mke2fs -m 0 /dev/loop5 &> /dev/null
swapon /dev/loop4
mount -t ext2 /dev/loop5 /tmp
chmod 1777 /tmp

--
Markus Laire

-
Linux-crypto:  cryptography in and on the Linux system
Archive:       http://mail.nl.linux.org/linux-crypto/