linux-kernel - [PATCH v9 8/8] powerpc/fadump: update documentation about 'fadump_extra

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Message-Id: <151075915192.14434.3165385149109943093.stgit@hbathini.in.ibm.com>
Date:   Wed, 15 Nov 2017 20:49:21 +0530
From:   Hari Bathini <hbathini@...ux.vnet.ibm.com>
To:     linuxppc-dev <linuxppc-dev@...abs.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        lkml <linux-kernel@...r.kernel.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Ankit Kumar <ankit@...ux.vnet.ibm.com>,
        Michal Suchánek <msuchanek@...e.de>,
        Mahesh J Salgaonkar <mahesh@...ux.vnet.ibm.com>
Subject: [PATCH v9 8/8] powerpc/fadump: update documentation about
 'fadump_extra_args=' parameter

With the introduction of 'fadump_extra_args=' parameter to pass additional
parameters to fadump (capture) kernel, update documentation about it.

Signed-off-by: Hari Bathini <hbathini@...ux.vnet.ibm.com>
Signed-off-by: Michal Suchanek <msuchanek@...e.de>
---
 Documentation/powerpc/firmware-assisted-dump.txt |   20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/Documentation/powerpc/firmware-assisted-dump.txt b/Documentation/powerpc/firmware-assisted-dump.txt
index bdd344a..5705f55 100644
--- a/Documentation/powerpc/firmware-assisted-dump.txt
+++ b/Documentation/powerpc/firmware-assisted-dump.txt
@@ -162,7 +162,19 @@ How to enable firmware-assisted dump (fadump):
 
 1. Set config option CONFIG_FA_DUMP=y and build kernel.
 2. Boot into linux kernel with 'fadump=on' kernel cmdline option.
-3. Optionally, user can also set 'crashkernel=' kernel cmdline
+3. A user can pass additional command line parameters as a space
+   separated quoted list through 'fadump_extra_args=' parameter,
+   to be enforced when fadump is active. For example, parameter
+   'fadump_extra_args="nr_cpus=1 numa=off udev.children-max=2"'
+   will be changed to 'fadump_extra_args nr_cpus=1  numa=off
+   udev.children-max=2' in-place when fadump is active. This
+   parameter has no affect when fadump is not active. Multiple
+   instances of 'fadump_extra_args=' can be passed. This provision
+   can be used to reduce memory consumption during dump capture by
+   disabling unwarranted resources/subsystems like CPUs, NUMA
+   and such. Value with spaces can be passed as
+   'fadump_extra_args="parameter=\"value with spaces\""'
+4. Optionally, user can also set 'crashkernel=' kernel cmdline
    to specify size of the memory to reserve for boot memory dump
    preservation.
 
@@ -172,6 +184,12 @@ NOTE: 1. 'fadump_reserve_mem=' parameter has been deprecated. Instead
       2. If firmware-assisted dump fails to reserve memory then it
          will fallback to existing kdump mechanism if 'crashkernel='
          option is set at kernel cmdline.
+      3. Special parameters like '--' passed inside fadump_extra_args are also
+         just left in-place. So, the user is advised to consider this while
+         specifying such parameters. It may be required to quote the argument
+         to fadump_extra_args when the bootloader uses double-quotes as
+         argument delimiter as well. eg
+        append = " fadump_extra_args=\"nr_cpus=1 numa=off udev.children-max=2\""
 
 Sysfs/debugfs files:
 ------------