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1============================2SD and MMC Device Partitions3============================4 5Device partitions are additional logical block devices present on the6SD/MMC device.7 8As of this writing, MMC boot partitions as supported and exposed as9/dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the10parent /dev/mmcblkX.11 12MMC Boot Partitions13===================14 15Read and write access is provided to the two MMC boot partitions. Due to16the sensitive nature of the boot partition contents, which often store17a bootloader or bootloader configuration tables crucial to booting the18platform, write access is disabled by default to reduce the chance of19accidental bricking.20 21To enable write access to /dev/mmcblkXbootY, disable the forced read-only22access with::23 24 echo 0 > /sys/block/mmcblkXbootY/force_ro25 26To re-enable read-only access::27 28 echo 1 > /sys/block/mmcblkXbootY/force_ro29 30The boot partitions can also be locked read only until the next power on,31with::32 33 echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on34 35This is a feature of the card and not of the kernel. If the card does36not support boot partition locking, the file will not exist. If the37feature has been disabled on the card, the file will be read-only.38 39The boot partitions can also be locked permanently, but this feature is40not accessible through sysfs in order to avoid accidental or malicious41bricking.42