os-helpers-fs: add function to erase disks

The function overwrites the first 16 MiB of each partition (the default
LUKS2 header size), as well as the primary and backup GPT partition
tables.

Change-type: patch
Signed-off-by: Alex Gonzalez <[email protected]>

meta-balena-common/recipes-support/os-helpers/os-helpers/os-helpers-fs

@@ -467,3 +467,22 @@ split_bootpartition() {
 
     # Do not umount - flasher script will still copy configuration files
 }
+
+erase_disk() {
+    tdisk="${1}"
+    info "Erasing disk ${tdisk}"
+    _sector_size=$(lsblk -nlbo NAME,PHY-SEC,TYPE "/dev/${tdisk}" | grep disk |  awk '{print $2}')
+    _size=$(lsblk -nlbo NAME,SIZE,TYPE "/dev/${tdisk}" | grep disk |  awk '{print $2}')
+    _size_in_sectors=$( expr ${_size} / ${_sector_size} )
+    # Overwrite default LUKS2 header size of 16 MiB
+    _erased_sectors=$( expr 16 \* 1024 \* 1024 / ${_sector_size} )
+    # Erase the first sectors in each partition
+    for _ss in $(parted "/dev/${tdisk}" unit s print | awk '/^[ 0-9]/ {sub("s", ""); print $2}'); do
+            dd if=/dev/urandom of="/dev/${tdisk}" bs="${_sector_size}" count="${_erased_sectors}" seek="${_ss}" conv=sync
+    done
+    # Erase partition table
+    # GPT reserves 34 sector at the start of disk and end of disk as backup
+    GPT_RESERVED_LBA=34
+    dd if=/dev/urandom of="/dev/${tdisk}" bs="${_sector_size}" count="${GPT_RESERVED_LBA}" conv=sync
+    dd if=/dev/urandom of="/dev/${tdisk}" bs="${_sector_size}" seek="$(expr "${_size_in_sectors}" - "${GPT_RESERVED_LBA}" )" count="${GPT_RESERVED_LBA}" conv=sync
+}