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