On 2019-09-04 02:23, Jorge Fernandez Monteagudo wrote:
Hi all!
Is it possible to get a crypted btrfs in a file? Currently I'm doing this to
get a crypted ISO filesystem in a file:
# genisoimage -R -J -iso-level 4 -o iso.img <dir_to_put_in_the_image>
# fallocate iso-crypted.img -l $(stat --printf="%s" iso.img)
# cryptsetup -d <key_to_crypt_iso> create test iso-crypted.img
# dd if=iso.img of=/dev/mapper/test bs=512
# sync
# cryptsetup remove test >
Is it possible to do something similar in btrfs? Is there something similar to
'genisoimage' in btrfs ? Or, at least, given a directory, is it possible to
know the outcome size of the filesystem to create an empty file with fallocate
and create a btrfs in a loop device like:
# fallocate btrfs-crypted.img -l <btrfs_size_for_dir_to_put_in_the_image>
# losetup /dev/loop0 btrfs-crypted.img
# mkfs.btrfs /dev/loop0
then we can mount the loop0, copy the files, unmount and then crypt the
btrfs-crypted.img like the ISO one.
What you want here is mkfs.btrfs with the `-r` and `--shrink` options.
So, for your specific example, replace the genisoimage command from your
first example with this and update the file names appropriately:
# mkfs.btrfs -r <dir_to_put_in_the_image> --shrink btrfs.img
Note that you don't need and shouldn't use a loop mount for the target
file for the `mkfs` command. It will generate the file at the
appropriate size automatically (and as a general rule, `mkfs` for any
filesystem works just fine without a loop mount, you just need to have a
file of the right size for most of them).
