Make debug=file show which file filters get run.

If one of the file filters breaks things, it's hard to figure out where
it has happened.

This makes grub log which filter is being run, which makes it easier to
figure out where you are in the sequence of events.

Signed-off-by: Peter Jones <pjones@redhat.com>

grub-core/kern/file.c

@@ -30,6 +30,14 @@ void (*EXPORT_VAR (grub_grubnet_fini)) (void);
 
 grub_file_filter_t grub_file_filters[GRUB_FILE_FILTER_MAX];
 
+static char *filter_names[] = {
+    [GRUB_FILE_FILTER_VERIFY] = "GRUB_FILE_FILTER_VERIFY",
+    [GRUB_FILE_FILTER_GZIO] = "GRUB_FILE_FILTER_GZIO",
+    [GRUB_FILE_FILTER_XZIO] = "GRUB_FILE_FILTER_XZIO",
+    [GRUB_FILE_FILTER_LZOPIO] = "GRUB_FILE_FILTER_LZOPIO",
+    [GRUB_FILE_FILTER_MAX] = "GRUB_FILE_FILTER_MAX"
+};
+
 /* Get the device part of the filename NAME. It is enclosed by parentheses.  */
 char *
 grub_file_get_device_name (const char *name)
@@ -121,6 +129,9 @@ grub_file_open (const char *name, enum grub_file_type type)
     if (grub_file_filters[filter])
       {
 	last_file = file;
+	if (filter < GRUB_FILE_FILTER_MAX)
+	  grub_dprintf ("file", "Running %s file filter\n",
+			filter_names[filter]);
 	file = grub_file_filters[filter] (file, type);
 	if (file && file != last_file)
 	  {