| .. SPDX-License-Identifier: GPL-2.0+ | |
| Boot Count Limit | |
| ================ | |
| This is enabled by CONFIG_BOOTCOUNT_LIMIT. | |
| This allows to detect multiple failed attempts to boot Linux. | |
| After a power-on reset, the "bootcount" variable will be initialized to 1, and | |
| each reboot will increment the value by 1. | |
| If, after a reboot, the new value of "bootcount" exceeds the value of | |
| "bootlimit", then instead of the standard boot action (executing the contents of | |
| "bootcmd"), an alternate boot action will be performed, and the contents of | |
| "altbootcmd" will be executed. | |
| If the variable "bootlimit" is not defined in the environment, the Boot Count | |
| Limit feature is disabled. If it is enabled, but "altbootcmd" is not defined, | |
| then U-Boot will drop into interactive mode and remain there. | |
| It is the responsibility of some application code (typically a Linux | |
| application) to reset the variable "bootcount" to 0 when the system booted | |
| successfully, thus allowing for more boot cycles. | |
| CONFIG_BOOTCOUNT_EXT | |
| -------------------- | |
| This adds support for maintaining boot count in a file on an EXT filesystem. | |
| The file to use is defined by: | |
| CONFIG_SYS_BOOTCOUNT_EXT_INTERFACE | |
| CONFIG_SYS_BOOTCOUNT_EXT_DEVPART | |
| CONFIG_SYS_BOOTCOUNT_EXT_NAME | |
| The format of the file is: | |
| ==== ================= | |
| type entry | |
| ==== ================= | |
| u8 magic | |
| u8 version | |
| u8 bootcount | |
| u8 upgrade_available | |
| ==== ================= | |
| To prevent unattended usage of "altbootcmd", the "upgrade_available" variable is | |
| used. | |
| If "upgrade_available" is 0, "bootcount" is not saved. | |
| If "upgrade_available" is 1, "bootcount" is saved. | |
| So a userspace application should take care of setting the "upgrade_available" | |
| and "bootcount" variables to 0, if the system boots successfully. | |
| This also avoids writing the "bootcount" information on all reboots. |