mxgrub: add grub.cfg consistency check

'check_grub_menu_and_boot_dir' compares the content
of the boot-menu (grub.cfg), and the filesystem content
in /boot.

mxgrub/mxgrub

@@ -42,6 +42,51 @@ sub check_mbr {
 
 }
 
+sub check_grub_menu_and_boot_dir {
+  my $distmaster=`distmaster`; chop $distmaster;
+  my $missing_in_menu=0;
+  my $missing_in_boot=0;
+  my $inconsistent = 1;
+
+  my @kernels_menu = grep {/menuentry.+?mariux-\d/} split m/\n/, read_file('/boot/grub/grub.cfg');
+  @kernels_menu = map {/["']mariux-[\d\.]+-(\d+)['"]/; "mariux.$1"} @kernels_menu;
+
+  my @tmp = grep {/mariux\.\d+/} scandir('/boot');
+  my %installed;
+  for (@tmp) {
+    $installed{$_} = 0; # filesystem data (should have no dupes).
+  }
+
+  for my $k (@kernels_menu) {
+    if (defined $installed{$k}) {
+      $installed{$k}+=1; # mind, the top menu entry occurs twice.
+    } else {
+      $missing_in_boot++;
+    }
+  }
+
+  for my $k (keys %installed) {
+    $missing_in_menu++ if $installed{$k} < 1;
+  }
+
+  if ($missing_in_boot == 0 and $missing_in_boot == 0) {
+    $inconsistent = 0;
+  }
+
+  warn << "EOF" if $inconsistent;
+
+  Note: GRUB menu and installed kernels differ.
+
+    $missing_in_boot Kernel(s) from the menu are missing in '/boot'.
+    $missing_in_menu Kernel(s) aren't listed in the menu.
+
+  Consider a rewrite of grub.cfg (on $distmaster):
+
+           $0 --update
+
+EOF
+}
+
 sub check_grub_installation {
   my $fingerprint='[ab]*.mod'; # this 'scans' just a dozen, and not 200 files.
   my $sum_lib  = ` cat /usr/lib/grub/i386-pc/$fingerprint | md5sum `;
@@ -280,6 +325,7 @@ sub cmd_initramfs {
 }
 
 check_grub_installation();
+check_grub_menu_and_boot_dir();
 
 our ($opt_list,$opt_update,$opt_initramfs,$opt_test);