templates: Add GRUB_DISABLE_UUID

The grub-mkconfig and 10_linux scripts by default attempt to use a UUID to
set the root kernel command line parameter and the $root GRUB environment
variable.

The former can be disabled by setting the GRUB_DISABLE_LINUX_UUID variable
to "true", but there is currently no way to disable the latter.

The generated grub config uses the search command with the --fs-uuid option
to find the device that has to be set as $root, i.e:

 search --no-floppy --fs-uuid --set=root ...

This is usually more reliable but in some cases it may not be appropriate,
so this patch introduces a new GRUB_DISABLE_UUID variable that can be used
to disable searching for the $root device by filesystem UUID.

When disabled, the $root device will be set to the value specified in the
device.map as found by the grub-probe --target=compatibility_hint option.

When setting GRUB_DISABLE_UUID=true, the GRUB_DISABLE_LINUX_UUID and
GRUB_DISABLE_LINUX_PARTUUID variables will also be set to "true" unless
these have been explicitly set to "false".

That way, the GRUB_DISABLE_UUID variable can be used to force using the
device names for both GRUB and Linux.

Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Nicholas Vinson <nvinson234@gmail.com>

docs/grub.texi

@@ -1441,6 +1441,15 @@ enable the use of partition UUIDs, set this option to @samp{false}.
 If this option is set to @samp{true}, disable the generation of recovery
 mode menu entries.
 
+@item GRUB_DISABLE_UUID
+Normally, @command{grub-mkconfig} will generate menu entries that use
+universally-unique identifiers (UUIDs) to identify various filesystems to
+search for files.  This is usually more reliable, but in some cases it may
+not be appropriate.  To disable this use of UUIDs, set this option to
+@samp{true}. Setting this option to @samp{true}, will also set the options
+@samp{GRUB_DISABLE_LINUX_UUID} and @samp{GRUB_DISABLE_LINUX_PARTUUID} to
+@samp{true}, unless they have been explicilty set to @samp{false}.
+
 @item GRUB_VIDEO_BACKEND
 If graphical video support is required, either because the @samp{gfxterm}
 graphical terminal is in use or because @samp{GRUB_GFXPAYLOAD_LINUX} is set,

util/grub-mkconfig.in

@@ -158,6 +158,15 @@ if test -f ${sysconfdir}/default/grub ; then
   . ${sysconfdir}/default/grub
 fi
 
+if [ "x${GRUB_DISABLE_UUID}" = "xtrue" ]; then
+  if [ -z "${GRUB_DISABLE_LINUX_UUID}" ]; then
+    GRUB_DISABLE_LINUX_UUID="true"
+  fi
+  if [ -z "${GRUB_DISABLE_LINUX_PARTUUID}" ]; then
+    GRUB_DISABLE_LINUX_PARTUUID="true"
+  fi
+fi
+
 # XXX: should this be deprecated at some point?
 if [ "x${GRUB_TERMINAL}" != "x" ] ; then
   GRUB_TERMINAL_INPUT="${GRUB_TERMINAL}"
@@ -224,6 +233,7 @@ export GRUB_DEFAULT \
   GRUB_TERMINAL_INPUT \
   GRUB_TERMINAL_OUTPUT \
   GRUB_SERIAL_COMMAND \
+  GRUB_DISABLE_UUID \
   GRUB_DISABLE_LINUX_UUID \
   GRUB_DISABLE_LINUX_PARTUUID \
   GRUB_DISABLE_RECOVERY \

util/grub-mkconfig_lib.in

@@ -156,7 +156,7 @@ prepare_grub_to_access_device ()
   if [ "x$fs_hint" != x ]; then
     echo "set root='$fs_hint'"
   fi
-  if fs_uuid="`"${grub_probe}" --device $@ --target=fs_uuid 2> /dev/null`" ; then
+  if [ "x${GRUB_DISABLE_UUID}" != "xtrue" ] && fs_uuid="`"${grub_probe}" --device $@ --target=fs_uuid 2> /dev/null`" ; then
     hints="`"${grub_probe}" --device $@ --target=hints_string 2> /dev/null`" || hints=
     echo "if [ x\$feature_platform_search_hint = xy ]; then"
     echo "  search --no-floppy --fs-uuid --set=root ${hints} ${fs_uuid}"
@@ -173,7 +173,7 @@ grub_get_device_id ()
   IFS='
 '
   device="$1"
-  if fs_uuid="`"${grub_probe}" --device ${device} --target=fs_uuid 2> /dev/null`" ; then
+  if [ "x${GRUB_DISABLE_UUID}" != "xtrue" ] && fs_uuid="`"${grub_probe}" --device ${device} --target=fs_uuid 2> /dev/null`" ; then
     echo "$fs_uuid";
   else
     echo $device |sed 's, ,_,g'