From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Robbie Harwood <rharwood@redhat.com>
Date: Tue, 7 Mar 2023 18:59:40 -0500
Subject: [PATCH] blscfg: check for mounted /boot in emu

Irritatingly, BLS defines paths relatives to the mountpoint of the
filesystem which contains its snippets, not / or any other fixed
location.  So grub2-emu needs to know whether /boot is a separate
filesysem from / and conditionally prepend a path.

Signed-off-by: Robbie Harwood <rharwood@redhat.com>
---
 grub-core/commands/blscfg.c | 54 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 49 insertions(+), 5 deletions(-)

diff --git a/grub-core/commands/blscfg.c b/grub-core/commands/blscfg.c
index dbd0899acf..6e398fc175 100644
--- a/grub-core/commands/blscfg.c
+++ b/grub-core/commands/blscfg.c
@@ -40,8 +40,9 @@ GRUB_MOD_LICENSE ("GPLv3+");
 #include "loadenv.h"
 
 #define GRUB_BLS_CONFIG_PATH "/loader/entries/"
+
 #ifdef GRUB_MACHINE_EMU
-#define GRUB_BOOT_DEVICE ""
+#define GRUB_BOOT_DEVICE "/boot"
 #else
 #define GRUB_BOOT_DEVICE "($root)"
 #endif
@@ -54,8 +55,50 @@ struct keyval
 
 static struct bls_entry *entries = NULL;
 
+/* Cache probing in frob_boot_device().  Used for linux entry also.
+ * Always true in non-emu, meaning to prefix things with GRUB_BOOT_DEVICE. */
+static int separate_boot = -1;
+
 #define FOR_BLS_ENTRIES(var) FOR_LIST_ELEMENTS (var, entries)
 
+/* BLS appears to make paths relative to the filesystem that snippets are
+ * on, not /.  Attempt to cope. */
+static char *frob_boot_device(char *tmp)
+{
+#ifdef GRUB_MACHINE_EMU
+  grub_file_t f;
+  char *line = NULL;
+
+  if (separate_boot != -1)
+    goto probed;
+
+  separate_boot = 0;
+
+  f = grub_file_open ("/proc/mounts", GRUB_FILE_TYPE_CONFIG);
+  if (f == NULL)
+    goto probed;
+
+  while ((line = grub_file_getline (f)))
+    {
+      if (grub_strstr (line, " " GRUB_BOOT_DEVICE " "))
+	{
+	  separate_boot = 1;
+	  grub_free (line);
+	  break;
+	}
+
+      grub_free(line);
+    }
+
+  grub_file_close (f);
+ probed:
+  if (!separate_boot)
+    return grub_stpcpy (tmp, " ");
+#endif
+
+  return grub_stpcpy (tmp, " " GRUB_BOOT_DEVICE);
+}
+
 static int bls_add_keyval(struct bls_entry *entry, char *key, char *val)
 {
   char *k, *v;
@@ -842,7 +885,7 @@ static void create_entry (struct bls_entry *entry)
       for (i = 0; early_initrds != NULL && early_initrds[i] != NULL; i++)
 	{
 	  grub_dprintf ("blscfg", "adding early initrd %s\n", early_initrds[i]);
-	  tmp = grub_stpcpy (tmp, " " GRUB_BOOT_DEVICE);
+	  tmp = frob_boot_device (tmp);
 	  tmp = grub_stpcpy (tmp, initrd_prefix);
 	  tmp = grub_stpcpy (tmp, early_initrds[i]);
 	  grub_free(early_initrds[i]);
@@ -851,7 +894,7 @@ static void create_entry (struct bls_entry *entry)
       for (i = 0; initrds != NULL && initrds[i] != NULL; i++)
 	{
 	  grub_dprintf ("blscfg", "adding initrd %s\n", initrds[i]);
-	  tmp = grub_stpcpy (tmp, " " GRUB_BOOT_DEVICE);
+	  tmp = frob_boot_device (tmp);
 	  tmp = grub_stpcpy (tmp, initrds[i]);
 	}
       tmp = grub_stpcpy (tmp, "\n");
@@ -888,7 +931,7 @@ static void create_entry (struct bls_entry *entry)
         }
       char *tmp = dt;
       tmp = grub_stpcpy (dt, "devicetree");
-      tmp = grub_stpcpy (tmp, " " GRUB_BOOT_DEVICE);
+      tmp = frob_boot_device (tmp);
       if (add_dt_prefix)
         tmp = grub_stpcpy (tmp, prefix);
       tmp = grub_stpcpy (tmp, devicetree);
@@ -907,7 +950,8 @@ static void create_entry (struct bls_entry *entry)
 			"linux %s%s%s%s\n"
 			"%s%s",
 			savedefault ? "savedefault\n" : "",
-			GRUB_BOOT_DEVICE, clinux, options ? " " : "", options ? options : "",
+			separate_boot ? GRUB_BOOT_DEVICE : "",
+			clinux, options ? " " : "", options ? options : "",
 			initrd ? initrd : "", dt ? dt : "");
 
   grub_normal_add_menu_entry (argc, argv, classes, id, users, hotkey, NULL, src, 0, &index, entry);