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The bootcount documentation was using "unattended" while it probably intending to say "unintended" Signed-off-by: Vasileios Amoiridis <vasileios.amoiridis@cern.ch> Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
58 lines
1.9 KiB
ReStructuredText
58 lines
1.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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Boot Count Limit
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================
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This is enabled by CONFIG_BOOTCOUNT_LIMIT.
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This allows to detect multiple failed attempts to boot Linux.
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After a power-on reset, the ``bootcount`` variable will be initialized to 1, and
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each reboot will increment the value by 1.
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If, after a reboot, the new value of ``bootcount`` exceeds the value of
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``bootlimit``, then instead of the standard boot action (executing the contents
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of ``bootcmd``), an alternate boot action will be performed, and the contents of
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``altbootcmd`` will be executed.
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If the variable ``bootlimit`` is not defined in the environment, the Boot Count
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Limit feature is disabled. If it is enabled, but ``altbootcmd`` is not defined,
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then U-Boot will drop into interactive mode and remain there.
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It is the responsibility of some application code (typically a Linux
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application) to reset the variable ``bootcount`` to 0 when the system booted
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successfully, thus allowing for more boot cycles.
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CONFIG_BOOTCOUNT_FS
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--------------------
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This adds support for maintaining boot count in a file on a filesystem.
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Tested filesystems are FAT and EXT. The file to use is defined by:
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CONFIG_SYS_BOOTCOUNT_FS_INTERFACE
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CONFIG_SYS_BOOTCOUNT_FS_DEVPART
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CONFIG_SYS_BOOTCOUNT_FS_NAME
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The format of the file is:
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.. list-table::
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:header-rows: 1
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* - type
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- entry
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* - u8
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- magic
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* - u8
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- version
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* - u8
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- bootcount
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* - u8
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- upgrade_available
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To prevent unintended usage of ``altbootcmd``, the ``upgrade_available``
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variable is used.
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If ``upgrade_available`` is 0, ``bootcount`` is not saved.
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If ``upgrade_available`` is 1, ``bootcount`` is saved.
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So a userspace application should take care of setting the ``upgrade_available``
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and ``bootcount`` variables to 0, if the system boots successfully.
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This also avoids writing the ``bootcount`` information on all reboots.
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