meta-facebook/recipes-fb/emmc-init/files/emmc-init.service

[Unit]
Description=eMMC initialize check
Before=mnt-data.mount
Requires=dev-mmcblk0.device
After=dev-mmcblk0.device

[Service]
ExecStart=/usr/libexec/emmc-init/emmc-init
Type=oneshot
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target