41 lines
1.3 KiB
Plaintext
41 lines
1.3 KiB
Plaintext
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.
|