[gentoo-user] how to partition a dm-crypt disk?

[Caveman Al Toraboran]

hi - why can't i use fdisk to partition a dm-crypt
disk?

tried to `sudo fdisk /dev/mapper/ea`, which is created by:

> `sudo cryptsetup open --type plain /dev/sda ea`

fdisk shows my partitions:

> Device                  Start        End    Sectors   Size Type
> /dev/mapper/ea-part1     2048   10487807   10485760     5G Linux filesystem
> /dev/mapper/ea-part2 10487808 1953525134 1943037327 926.5G Linux filesystem

but, as i save that partition table, i get this
error:

> Command (m for help): w
> The partition table has been altered.
> Failed to add partition 1 to system: Invalid argument
> Failed to add partition 2 to system: Invalid argument

if i repeat the execution of fdisk, i see that
partition table, and if i hit `w`, it saves
without showing that error.

then, as i go to run `mkfs.ext4` on them, i can't
see them under `/dev/mapper/`.

rgrds,
cm.