❯ cat hybris/droid-configs/sparse/usr/lib/systemd/system/dmsetup.service
[Unit]
Description=Setup dynamic partitions
Before=system.mount system_root.mount system_ext.mount vendor.mount product.mount local-fs.target systemd-modules-load.service droid-hal-init.service
DefaultDependencies=no

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/bash /usr/bin/droid/dmsetup.sh

[Install]
WantedBy=droid-hal-init.service

❯ cat hybris/droid-configs/sparse/usr/lib/systemd/system/system.mount
[Unit]
Description=Droid mount for /system
Before=local-fs.target systemd-modules-load.service

[Mount]
What=/system_root/system
Where=/system
Type=none
Options=bind

# Default is 90 which makes mount period too long in case of
# errors so drop it down a notch.
TimeoutSec=10

[Install]
WantedBy=local-fs.target

# From out/target/product/flame/vendor/etc/fstab.sm8150 :
# system                                                  /system                ext4    ro,barrier=1                                         wait,slotselect,avb=vbmeta_system,logical,first_stage_mount

❯ cat hybris/droid-configs/sparse/usr/lib/systemd/system/system_root.mount
[Unit]
Description=Droid mount for /system
Before=local-fs.target systemd-modules-load.service

[Mount]
What=/dev/mapper/dynpart-system_a
Where=/system_root
Type=ext4
Options=ro,barrier=1
# Options had SELinux context option:  

# Default is 90 which makes mount period too long in case of
# errors so drop it down a notch.
TimeoutSec=10

[Install]
WantedBy=local-fs.target

# From out/target/product/flame/vendor/etc/fstab.sm8150 :
# system                                                  /system                ext4    ro,barrier=1                                         wait,slotselect,avb=vbmeta_system,logical,first_stage_mount