[PATCH] Support dropin files for Linux kernel parameters

[Simon Rowe]

Kernel parameters actually cover a range of purposes, including
userspace like systemd. They also need setting for a variety of
reasons:

  * as distro defaults
  * to provide configuration for a package
  * for an admin to set desired behaviour

Having these all combined in a single line (like GRUB_CMDLINE_LINUX)
is unwieldy, it is hard to make changes without impacting another
usecase.

Add optional support for dropin files in the directories:

  * /usr/lib/kernel.d/
  * /etc/kernel.d/

where the contents of each file with the '.conf' suffix is evaluated
(excluding comments) and appended to any other kernel parameters
defined via GRUB_CMDLINE_LINUX etc. Files in /etc/kernel.d/ completely
replace those of the same name in /usr/lib/kernel.d/. This allows a
distro or installer to set parameters but then for an admin to
override them.

Signed-off-by: Simon Rowe <simon.rowe@nutanix.com>
---
 util/grub-mkconfig_lib.in   | 18 ++++++++++++++++++
 util/grub.d/10_linux.in     |  8 +++++---
 util/grub.d/20_linux_xen.in |  8 +++++---
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/util/grub-mkconfig_lib.in b/util/grub-mkconfig_lib.in
index 08953287c..7aaa747f1 100644
--- a/util/grub-mkconfig_lib.in
+++ b/util/grub-mkconfig_lib.in
@@ -348,3 +348,21 @@ grub_add_tab () {
   sed -e "s/^/$grub_tab/"
 }
 
+kernel_params_from_files () {
+  # Read Linux kernel parameters from dropin files.
+
+  file_bases=""
+
+  for f in /etc/kernel.d/*.conf /usr/lib/kernel.d/*.conf; do
+    [ -r $f ] || continue
+    file_bases="$file_bases $(basename $f)"
+  done
+
+  for b in $(echo $file_bases | tr ' ' '\n' | sort -u); do
+    if [ -r /etc/kernel.d/$b ]; then
+      grep -v '^#' /etc/kernel.d/$b | tr '\n' ' '
+    elif [ -r /usr/lib/kernel.d/$b ]; then
+      grep -v '^#' /usr/lib/kernel.d/$b | tr '\n' ' '
+    fi
+  done
+}
diff --git a/util/grub.d/10_linux.in b/util/grub.d/10_linux.in
index cc393be7e..fba3775f9 100644
--- a/util/grub.d/10_linux.in
+++ b/util/grub.d/10_linux.in
@@ -275,6 +275,8 @@ for linux in ${reverse_sorted_list}; do
     fi
   fi
 
+  extra_kernel_params=$(kernel_params_from_files)
+
   # The GRUB_DISABLE_SUBMENU option used to be different than others since it 
was
   # mentioned in the documentation that has to be set to 'y' instead of 'true' 
to
   # enable it. This caused a lot of confusion to users that set the option to 
'y',
@@ -285,7 +287,7 @@ for linux in ${reverse_sorted_list}; do
 
   if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xtrue ]; 
then
     linux_entry "${OS}" "${version}" simple \
-    "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}"
+    "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT} 
${extra_kernel_params}"
 
     submenu_indentation="$grub_tab"
     
@@ -298,10 +300,10 @@ for linux in ${reverse_sorted_list}; do
   fi
 
   linux_entry "${OS}" "${version}" advanced \
-              "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}"
+              "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT} 
${extra_kernel_params}"
   if [ "x${GRUB_DISABLE_RECOVERY}" != "xtrue" ]; then
     linux_entry "${OS}" "${version}" recovery \
-                "${GRUB_CMDLINE_LINUX_RECOVERY} ${GRUB_CMDLINE_LINUX}"
+                "${GRUB_CMDLINE_LINUX_RECOVERY} ${GRUB_CMDLINE_LINUX} 
${extra_kernel_params}"
   fi
 done
 
diff --git a/util/grub.d/20_linux_xen.in b/util/grub.d/20_linux_xen.in
index 94dd8be13..089f6de43 100644
--- a/util/grub.d/20_linux_xen.in
+++ b/util/grub.d/20_linux_xen.in
@@ -336,6 +336,8 @@ for current_xen in ${reverse_sorted_xen_list}; do
            fi
        fi
 
+       extra_kernel_params=$(kernel_params_from_files)
+
        # The GRUB_DISABLE_SUBMENU option used to be different than others 
since it was
        # mentioned in the documentation that has to be set to 'y' instead of 
'true' to
        # enable it. This caused a lot of confusion to users that set the 
option to 'y',
@@ -346,7 +348,7 @@ for current_xen in ${reverse_sorted_xen_list}; do
 
        if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != 
xtrue ]; then
            linux_entry "${OS}" "${version}" "${xen_version}" simple \
-               "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}" 
"${GRUB_CMDLINE_XEN} ${GRUB_CMDLINE_XEN_DEFAULT}"
+               "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}" 
"${GRUB_CMDLINE_XEN} ${GRUB_CMDLINE_XEN_DEFAULT} ${extra_kernel_params}"
 
            submenu_indentation="$grub_tab$grub_tab"
     
@@ -360,10 +362,10 @@ for current_xen in ${reverse_sorted_xen_list}; do
        fi
 
        linux_entry "${OS}" "${version}" "${xen_version}" advanced \
-           "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}" 
"${GRUB_CMDLINE_XEN} ${GRUB_CMDLINE_XEN_DEFAULT}"
+           "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}" 
"${GRUB_CMDLINE_XEN} ${GRUB_CMDLINE_XEN_DEFAULT} ${extra_kernel_params}"
        if [ "x${GRUB_DISABLE_RECOVERY}" != "xtrue" ]; then
            linux_entry "${OS}" "${version}" "${xen_version}" recovery \
-               "${GRUB_CMDLINE_LINUX_RECOVERY} ${GRUB_CMDLINE_LINUX}" 
"${GRUB_CMDLINE_XEN}"
+               "${GRUB_CMDLINE_LINUX_RECOVERY} ${GRUB_CMDLINE_LINUX}" 
"${GRUB_CMDLINE_XEN} ${extra_kernel_params}"
        fi
     done
     if [ x"$is_top_level" != xtrue ]; then
-- 
2.22.3