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- .. SPDX-License-Identifier: GPL-2.0+
- PStore command
- ==============
- Design
- ------
- Linux PStore and Ramoops modules (Linux config options PSTORE and PSTORE_RAM)
- allow to use memory to pass data from the dying breath of a crashing kernel to
- its successor. This command allows to read those records from U-Boot command
- line.
- Ramoops is an oops/panic logger that writes its logs to RAM before the system
- crashes. It works by logging oopses and panics in a circular buffer. Ramoops
- needs a system with persistent RAM so that the content of that area can survive
- after a restart.
- Ramoops uses a predefined memory area to store the dump.
- Ramoops parameters can be passed as kernel parameters or through Device Tree,
- i.e.::
- ramoops.mem_address=0x30000000 ramoops.mem_size=0x100000 ramoops.record_size=0x2000 ramoops.console_size=0x2000 memmap=0x100000$0x30000000
- The same values should be set in U-Boot to be able to retrieve the records.
- This values can be set at build time in U-Boot configuration file, or at runtime.
- U-Boot automatically patches the Device Tree to pass the Ramoops parameters to
- the kernel.
- The PStore configuration parameters are:
- ======================= ==========
- Name Default
- ======================= ==========
- CMD_PSTORE_MEM_ADDR
- CMD_PSTORE_MEM_SIZE 0x10000
- CMD_PSTORE_RECORD_SIZE 0x1000
- CMD_PSTORE_CONSOLE_SIZE 0x1000
- CMD_PSTORE_FTRACE_SIZE 0x1000
- CMD_PSTORE_PMSG_SIZE 0x1000
- CMD_PSTORE_ECC_SIZE 0
- ======================= ==========
- Records sizes should be a power of 2.
- The memory size and the record/console size must be non-zero.
- Multiple 'dump' records can be stored in the memory reserved for PStore.
- The memory size has to be larger than the sum of the record sizes, i.e.::
- MEM_SIZE >= RECORD_SIZE * n + CONSOLE_SIZE + FTRACE_SIZE + PMSG_SIZE
- Usage
- -----
- Generate kernel crash
- ~~~~~~~~~~~~~~~~~~~~~
- For test purpose, you can generate a kernel crash by setting reboot timeout to
- 10 seconds and trigger a panic
- .. code-block:: console
- $ sudo sh -c "echo 1 > /proc/sys/kernel/sysrq"
- $ sudo sh -c "echo 10 > /proc/sys/kernel/panic"
- $ sudo sh -c "echo c > /proc/sysrq-trigger"
- Retrieve logs in U-Boot
- ~~~~~~~~~~~~~~~~~~~~~~~
- First of all, unless PStore parameters as been set during U-Boot configuration
- and match kernel ramoops parameters, it needs to be set using 'pstore set', e.g.::
- => pstore set 0x30000000 0x100000 0x2000 0x2000
- Then all available dumps can be displayed
- using::
- => pstore display
- Or saved to an existing directory in an Ext2 or Ext4 partition, e.g. on root
- directory of 1st partition of the 2nd MMC::
- => pstore save mmc 1:1 /
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