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[Launchpad Bug Tracker <1248492@xxxxxxxxxxxxxxxxxx>]

** Branch linked: lp:ubuntu/precise-proposed/linux-lts-saucy

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https://bugs.launchpad.net/bugs/1248492

Title:
  [saucy] [armhf] use pstore to save console log messages

Status in “linux” package in Ubuntu:
  Fix Released
Status in “linux” source package in Saucy:
  Fix Committed
Status in “linux” source package in Trusty:
  Fix Released

Bug description:
  SRU Justification:

  Impact: on platforms when there's a persistent memory storage (or when
  ram is not cleared during bootup like on arm), pstore and it's pstore-
  ram backend can be used to to save log messages on a previously
  defined and unallocated memory portion. Unfortunately, if we want to
  save bootup messages, we need the pstore-ram backend to be build in.

  Fix: apply the attached patch and recompile.

  Test: e.g., for a 256MB board, bootup a kernel with the following
  parameters:

  "mem=128M ramoops.mem_address=0x8000000 ramoops.mem_size=1048576"

  mem will tell the kernel to use only the first 128MB of ram, while ramoops address and size will the pstore where to find its storage and how big it is.
  Later on you can retrieve those messages from the u-boot command line dumping that memory region (mdw 0x8000000...) or you can bootup another kernel, mount pstore and retrieve the logs stored there:

  mount -t pstore  - /sys/fs/pstore
  cp /sys/fs/pstore/dmesg* .

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