[Bug 1741860] Re: Use the kernel default for crashkernel offset

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Title:
  Use the kernel default for crashkernel offset

Status in The Ubuntu-power-systems project:
  In Progress
Status in makedumpfile package in Ubuntu:
  In Progress
Status in makedumpfile source package in Xenial:
  In Progress
Status in makedumpfile source package in Bionic:
  In Progress
Status in makedumpfile source package in Disco:
  In Progress
Status in makedumpfile source package in Eoan:
  In Progress

Bug description:
  [Impact]

   * The value chosen for ppc64el of 128MB aligns with that of the
  kernel default. That may change some day, so it would be best to let
  the kernel decide what value it should use. If the value does change
  and the kernel is not allowed to choose a value, this may stop the
  kernel from booting on a production system.

  [Test Case]

   Run `cat /etc/default/grub.d/kdump-tools.cfg`

   * Expected result: there is no offset specified at the end of the
  line (.e.g, @128M).

   * Actual result: For Xenial, Bionic, Disco, and Eoan there are
  offsets specified.

  [Regression Potential]

   * Right now, the offset described in the kdump-tools.cfg aligns with
  that of what the kernel would select, so since they are the same we
  would expect no change in operation.

  
  Original bug description follows:
  -----------------------------------------

  == Comment: #0 - Hari Krishna Bathini <hbathini at in.ibm.com> - 2018-01-08 01:06:41 ==
  ---Problem Description---
  A default offset of 128MB is enforced for crashkernel by kdump-tools utility
  overriding the kernel default.

  While the kernel default offset for crashkernel is also 128MB, that may change
  and the right thing to do would be to let the kernel decide on the offset of
  crashkernel in the default scenario..

  Get rid of "@128M" in kdump-tools.cfg file

  Contact Information = hbathini at in.ibm.com

  ---uname output---
  na

  Machine Type = na

  ---Debugger---
  A debugger is not configured

  ---Steps to Reproduce---
   # cat /etc/default/grub.d/kdump-tools.cfg
  GRUB_CMDLINE_LINUX_DEFAULT="$GRUB_CMDLINE_LINUX_DEFAULT crashkernel=2G-4G:320M,4G-32G:512M,32G-64G:1024M,64G-128G:2048M,128G-:4096M at 128M"
  ---

  The offset is specified via kdump-tools where as the kernel may be the right place to
  set an offset by default..

  Userspace tool common name: kdump-tools

  The userspace tool has the following bit modes: 64-bit

  Userspace rpm: kdump-tools

  Userspace tool obtained from project website:  na

  *Additional Instructions for hbathini at in.ibm.com:
  -Attach ltrace and strace of userspace application.

  == Comment: #3 - MAMATHA INAMDAR <mainamdar at in.ibm.com> - 2018-01-08 03:05:05 ==
  This bug is opened to follow-up other bug based on the comment 19
  https://bugzilla.linux.ibm.com/show_bug.cgi?id=152905#c19 (Canonical Launchpad 	1676884 )

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