[PATCH v4 1/2] address the case where there are multiple values for the same kernel arg

[Coiby Xu]

When updating the kernel command line in /etc/default/grub, grubby only
replaces a given entry if it is the last entry on the command line.
In all other cases it appends a new entry to it. This behavior makes it
quite likely that there are multiple entries of the same parameter on
the command line, e.g.
GRUB_CMDLINE_LINUX="crashkernel=110M crashkernel=220M fadump=on
crashkernel=330M".

In such an situation _update_kernel_cmdline_in_grub_etc_default only
updates/removes the last entry. Which is usually not what you
want as the kernel (for crashkernel) takes the last entry it can find.

Thus make sure the case with multiple entries of the same parameter is
handled properly by removing all occurrences of given parameter first.

Note
1. sed command group and conditional control has been used to get rid of
   grep.
2. Fully supporting kernel cmdline as documented in
   Documentation/admin-guide/kernel-parameters.rst is complex and in
   foreseeable future a full implementation is not needed. So simply
   document the unsupported cases instead.

Reported-by: Philipp Rudo <prudo(a)redhat.com&gt;
Suggested-by: Philipp Rudo <prudo(a)redhat.com&gt;
Signed-off-by: Coiby Xu <coxu(a)redhat.com&gt;
---
 kdumpctl | 54 ++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 40 insertions(+), 14 deletions(-)

diff --git a/kdumpctl b/kdumpctl
index 9fd76ac..978aee1 100755
--- a/kdumpctl
+++ b/kdumpctl
@@ -1399,25 +1399,49 @@ _get_all_kernels_from_grubby()
 }
 
 GRUB_ETC_DEFAULT="/etc/default/grub"
-# modify the kernel command line parameter in default grub conf
+# Update a kernel parameter in default grub conf
+#
+# If a value is specified, it will be inserted in the end. Otherwise it
+# would remove given kernel parameter.
+#
+# Note this function doesn't address the following cases,
+# 1. The kernel ignores everything on the command line after a '--'. So
+#    simply adding the new entry to the end will fail if the cmdline
+#    contains a --.
+# 2. If the value for a parameter contains spaces it can be quoted using
+#    double quotes, for example param="value with spaces". This will
+#    break the [^[:space:]\"] regex for the value.
+# 3. Dashes and underscores in the parameter name are equivalent. So
+#    some_parameter and some-parameter are identical.
+# 4. Some parameters, e.g. efivar_ssdt, can be given multiple times.
+# 5. Some kernel parameters, e.g. quiet, doesn't have value
 #
 # $1: the name of the kernel command line parameter
-# $2: new value. If empty, the parameter would be removed
-_update_kernel_cmdline_in_grub_etc_default()
+# $2: new value. If empty, given parameter would be removed
+_update_kernel_arg_in_grub_etc_default()
 {
-	local _para=$1 _val=$2 _para_val _regex
+	local _para=$1 _val=$2 _para_val
 
 	if [[ -n $_val ]]; then
 		_para_val="$_para=$_val"
 	fi
 
-	_regex='^(GRUB_CMDLINE_LINUX=.*)([[:space:]"])'"$_para"'=[^[:space:]"]*(.*)$'
-	if grep -q -E "$_regex" "$GRUB_ETC_DEFAULT"; then
-		sed -i -E
's/'"$_regex"'/\1\2'"$_para_val"'\3/'
"$GRUB_ETC_DEFAULT"
-	elif [[ -n $_para_val ]]; then
-		# If the kernel parameter doesn't exist, put it in the first
-		sed -i -E 's/^(GRUB_CMDLINE_LINUX=")/\1'"$_para_val"' /'
"$GRUB_ETC_DEFAULT"
-	fi
+	# Update the command line /etc/default/grub, i.e.
+	# on the line that starts with 'GRUB_CMDLINE_LINUX=',
+ #       1) remove $para=$val if the it's the first arg
+ #       2) remove all occurences of $para=$val
+ #       3) insert $_para_val to end
+ #       4) remove duplicate spaces left over by 1) or 2) or 3)
+ #       5) remove space at the beginning of the string left over by 1) or 2) or 3)
+ #       6) remove space at the end of the string left over by 1) or 2) or 3)
+ sed -i -E "/^GRUB_CMDLINE_LINUX=/ {
+         s/\"${_para}=[^[:space:]\"]*/\"/g;
+         s/[[:space:]]+${_para}=[^[:space:]\"]*/ /g;
+         s/\"$/ ${_para_val}\"/
+         s/[[:space:]]+/ /g;
+         s/(\")[[:space:]]+/\1/g;
+         s/[[:space:]]+(\")/\1/g;
+         }" "$GRUB_ETC_DEFAULT"
 }
 
 reset_crashkernel()
@@ -1496,10 +1520,12 @@ reset_crashkernel()
 	#   - set the dump mode as kdump for non-ppc64le cases
 	#   - retrieved the default crashkernel value for given dump mode
 	if [[ $_grubby_kernel_path == ALL && -n $_dump_mode ]]; then
-		_update_kernel_cmdline_in_grub_etc_default crashkernel "$_crashkernel"
+		_update_kernel_arg_in_grub_etc_default crashkernel "$_crashkernel"
 		# remove the fadump if fadump is disabled
-		[[ $_fadump_val == off ]] && _fadump_val=""
-		_update_kernel_cmdline_in_grub_etc_default fadump "$_fadump_val"
+		if [[ $_fadump_val == off ]]; then
+			_fadump_val=""
+		fi
+		_update_kernel_arg_in_grub_etc_default fadump "$_fadump_val"
 	fi
 
 	# If kernel-path not specified, either
-- 
2.34.1