2.3. pstore filesystem with RAM backend (RAMOOPS)

Barebox supports the pstore filesystem known from the kernel. The main backend implementation is RAM. All other backends are currently not implemented by Barebox.

pstore is a filesystem to store kernel log or kernel panic messages. These messages are stored by the kernel in a specified RAM area which is never overwritten by any user. This data can be accessed after a reboot through /pstore in Barebox or the kernel. The pstore filesystem is automatically mounted at boot:

none on / type ramfs
none on /dev type devfs
none on /pstore type pstore

pstore may add additional warnings during boot due to wrong ECCs (no data written):

persistent_ram: found existing invalid buffer, size 791282217, start 1116786789
persistent_ram: uncorrectable error in header
persistent_ram: found existing invalid buffer, size 791282281, start 1133564005
persistent_ram: uncorrectable error in header
persistent_ram: found existing invalid buffer, size 791347753, start 1133564005
persistent_ram: uncorrectable error in header
persistent_ram: found existing invalid buffer, size 791347753, start 1133572197
persistent_ram: uncorrectable error in header
persistent_ram: found existing invalid buffer, size 774505001, start 1133564005
persistent_ram: uncorrectable error in header
persistent_ram: found existing invalid buffer, size 791282281, start 1133564005
persistent_ram: uncorrectable error in header
persistent_ram: found existing invalid buffer, size 791282217, start 1133564005
pstore: Registered ramoops as persistent store backend
ramoops: attached 0x200000@0x1fdf4000, ecc: 16/0

To use pstore/RAMOOPS both Barebox and Kernel have to be compiled with pstore and RAM backend support. The kernel receives the parameters describing the layout over the kernel command line. These parameters are automatically generated by Barebox. You can change these parameters in Barebox menuconfig. The RAMOOPS parameters for the Kernel are stored in the variable global.linux.bootargs.ramoops.

To see where the RAMOOPS area is located, you can execute iomem in Barebox. The RAMOOPS area is listed as ‘persistent ram’:

0x10000000 - 0x1fffffff (size 0x10000000) ram0
  0x17e7c0c0 - 0x1fcf817f (size 0x07e7c0c0) malloc space
  0x1fcf8180 - 0x1fcfffff (size 0x00007e80) board data
  0x1fd00000 - 0x1fd6eeff (size 0x0006ef00) barebox
  0x1fd6ef00 - 0x1fd88dff (size 0x00019f00) barebox data
  0x1fd88e00 - 0x1fd8c3db (size 0x000035dc) bss
  0x1fdf4000 - 0x1fe13fff (size 0x00020000) persistent ram
  0x1fe14000 - 0x1fe33fff (size 0x00020000) persistent ram
  0x1fe34000 - 0x1fe53fff (size 0x00020000) persistent ram
  0x1fe54000 - 0x1fe73fff (size 0x00020000) persistent ram
  0x1fe74000 - 0x1fe93fff (size 0x00020000) persistent ram
  0x1fe94000 - 0x1feb3fff (size 0x00020000) persistent ram
  0x1feb4000 - 0x1fed3fff (size 0x00020000) persistent ram
  0x1fed4000 - 0x1fef3fff (size 0x00020000) persistent ram
  0x1fef4000 - 0x1ff13fff (size 0x00020000) persistent ram
  0x1ff14000 - 0x1ff33fff (size 0x00020000) persistent ram
  0x1ff34000 - 0x1ff53fff (size 0x00020000) persistent ram
  0x1ff54000 - 0x1ff73fff (size 0x00020000) persistent ram
  0x1ff74000 - 0x1ff93fff (size 0x00020000) persistent ram
  0x1ff94000 - 0x1ffb3fff (size 0x00020000) persistent ram
  0x1ffb4000 - 0x1ffd3fff (size 0x00020000) persistent ram
  0x1ffd4000 - 0x1fff3fff (size 0x00020000) persistent ram
  0x1fff4000 - 0x1fff7fff (size 0x00004000) ttb
  0x1fff8000 - 0x1fffffff (size 0x00008000) stack

All pstore files that could be found are added to the /pstore directory. This is a read-only filesystem. If you disable the Kconfig option FS_PSTORE_RAMOOPS_RO, the RAMOOPS area is reset and its ECC recalculated. But that does not allow any writes from Barebox into that area.