[PATCH] reimplement grub-reboot to nor depend on GRUB_DEFAULT=saved

[Andrey Borzenkov <arvidjaar@gmail.com>]

Use separate environment variable next_entry to indicate one time
boot entry. CMOS button still takes precedent. It makes grub-reboot
usable also when GRUB_DEFAULT is set to explicit value.

It retains support for prev_saved_entry for compatibility. Also
grub-reboot will restore saved_entry from prev_saved_entry first time
it is called.

As a side effect it also fixes a problem that saved_entry is lost
after two consequitive grub-reboot calls.

Signed-off-by: Andrey Borzenkov <arvidjaar@gmail.com>

---

Is there any reason why onetime reboot is restricted to the cases
when we use saved menu entry? The implementation looks straightforward;
are there any drawbacks I miss?

 util/grub-reboot.in      |   17 ++++++-----------
 util/grub-set-default.in |    1 +
 util/grub.d/00_header.in |   14 +++++++++++++-
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/util/grub-reboot.in b/util/grub-reboot.in
index 1a91d36..d132e4f 100644
--- a/util/grub-reboot.in
+++ b/util/grub-reboot.in
@@ -46,8 +46,6 @@ export TEXTDOMAINDIR="@localedir@"
 usage () {
     gettext_printf "Usage: %s [OPTION] MENU_ENTRY\n" "$self"
     gettext "Set the default boot menu entry for GRUB, for the next boot only."; echo
-    gettext_printf "This requires setting GRUB_DEFAULT=saved in %s/default/grub.\n" "$sysconfdir"
-    echo
     print_option_help "-h, --help" "$(gettext "print this message and exit")"
     print_option_help "-v, --version" "$(gettext "print the version information and exit")"
     dirmsg="$(gettext_printf "expect GRUB images under the directory DIR/%s instead of the %s directory" "@grubdirname@" "$grubdir")"
@@ -129,17 +127,14 @@ fi
 
 grubdir=`echo "${bootdir}/@grubdirname@" | sed 's,//*,/,g'`
 
-prev_saved_entry=`$grub_editenv ${grubdir}/grubenv list | sed -n 's/^saved_entry=//p'`
+# Restore saved_entry if it was set by previous version
+prev_saved_entry=`$grub_editenv ${grubdir}/grubenv list | sed -n 's/^prev_saved_entry=//p'`
 if [ "$prev_saved_entry" ]; then
-    $grub_editenv ${grubdir}/grubenv set prev_saved_entry="$prev_saved_entry"
-else
-    # We need some non-empty value for prev_saved_entry so that GRUB will
-    # recognise that grub-reboot has been used and restore the previous
-    # saved entry. "0" is the same as an empty value, i.e. the first menu
-    # entry.
-    $grub_editenv ${grubdir}/grubenv set prev_saved_entry=0
+    $grub_editenv ${grubdir}/grubenv set saved_entry="$prev_saved_entry"
+    $grub_editenv ${grubdir}/grubenv unset prev_saved_entry
 fi
-$grub_editenv ${grubdir}/grubenv set saved_entry="$entry"
+
+$grub_editenv ${grubdir}/grubenv set next_entry="$entry"
 
 # Bye.
 exit 0
diff --git a/util/grub-set-default.in b/util/grub-set-default.in
index ea18da1..d607318 100644
--- a/util/grub-set-default.in
+++ b/util/grub-set-default.in
@@ -130,6 +130,7 @@ fi
 grubdir=`echo "${bootdir}/@grubdirname@" | sed 's,//*,/,g'`
 
 $grub_editenv ${grubdir}/grubenv unset prev_saved_entry
+$grub_editenv ${grubdir}/grubenv unset next_entry
 $grub_editenv ${grubdir}/grubenv set saved_entry="$entry"
 
 # Bye.
diff --git a/util/grub.d/00_header.in b/util/grub.d/00_header.in
index 3da5d12..c3c1f43 100644
--- a/util/grub.d/00_header.in
+++ b/util/grub.d/00_header.in
@@ -51,13 +51,25 @@ if [ "x$GRUB_BUTTON_CMOS_ADDRESS" != "x" ]; then
     cat <<EOF
 if cmostest $GRUB_BUTTON_CMOS_ADDRESS ; then
    set default="${GRUB_DEFAULT_BUTTON}"
+elif [ "\${next_entry}" ] ; then
+   set default="\${next_entry}"
+   set next_entry=
+   savenev next_entry
+   set boot_once=true
 else
    set default="${GRUB_DEFAULT}"
 fi
 EOF
 else
     cat <<EOF
-set default="${GRUB_DEFAULT}"
+if [ "\${next_entry}" ] ; then
+   set default="\${next_entry}"
+   set next_entry=
+   savenev next_entry
+   set boot_once=true
+else
+   set default="${GRUB_DEFAULT}"
+fi
 EOF
 fi
 cat <<EOF
-- 
tg: (16e3c9b..) u/boot-once (depends on: master)