| SD and MMC Device Partitions | |
| ============================ | |
| Device partitions are additional logical block devices present on the | |
| SD/MMC device. | |
| As of this writing, MMC boot partitions as supported and exposed as | |
| /dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the | |
| parent /dev/mmcblkX. | |
| MMC Boot Partitions | |
| =================== | |
| Read and write access is provided to the two MMC boot partitions. Due to | |
| the sensitive nature of the boot partition contents, which often store | |
| a bootloader or bootloader configuration tables crucial to booting the | |
| platform, write access is disabled by default to reduce the chance of | |
| accidental bricking. | |
| To enable write access to /dev/mmcblkXbootY, disable the forced read-only | |
| access with: | |
| echo 0 > /sys/block/mmcblkXbootY/force_ro | |
| To re-enable read-only access: | |
| echo 1 > /sys/block/mmcblkXbootY/force_ro | |
| The boot partitions can also be locked read only until the next power on, | |
| with: | |
| echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on | |
| This is a feature of the card and not of the kernel. If the card does | |
| not support boot partition locking, the file will not exist. If the | |
| feature has been disabled on the card, the file will be read-only. | |
| The boot partitions can also be locked permanently, but this feature is | |
| not accessible through sysfs in order to avoid accidental or malicious | |
| bricking. |