From 15fb2ae896e6aad4ba947a5b4828f938575c9877 Mon Sep 17 00:00:00 2001
From: Colin Watson <cjwatson@ubuntu.com>
Date: Fri, 28 May 2010 11:51:50 +0100
Subject: [PATCH] Make grub-probe work with symbolic links under /dev/mapper as
 well as with real block devices.  The Linux world seems to be (at best) in
 transition here, and GRUB shouldn't get caught in the middle. *
 kern/emu/getroot.c (find_root_device): Follow symbolic links under
 /dev/mapper.

---
 ChangeLog.mapper-symlink |  8 ++++++++
 kern/emu/getroot.c       | 15 +++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)
 create mode 100644 ChangeLog.mapper-symlink

diff --git a/ChangeLog.mapper-symlink b/ChangeLog.mapper-symlink
new file mode 100644
index 000000000..afcfc6479
--- /dev/null
+++ b/ChangeLog.mapper-symlink
@@ -0,0 +1,8 @@
+2010-05-28  Colin Watson  <cjwatson@ubuntu.com>
+
+	Make grub-probe work with symbolic links under /dev/mapper as well
+	as with real block devices.  The Linux world seems to be (at best)
+	in transition here, and GRUB shouldn't get caught in the middle.
+
+	* kern/emu/getroot.c (find_root_device): Follow symbolic links under
+	/dev/mapper.
diff --git a/kern/emu/getroot.c b/kern/emu/getroot.c
index 6875044da..e62abe089 100644
--- a/kern/emu/getroot.c
+++ b/kern/emu/getroot.c
@@ -126,9 +126,20 @@ find_root_device (const char *dir, dev_t dev)
 	/* Ignore any error.  */
 	continue;
 
-      if (S_ISLNK (st.st_mode))
-	/* Don't follow symbolic links.  */
+      if (S_ISLNK (st.st_mode)) {
+#ifdef __linux__
+	if (strcmp (dir, "mapper") == 0) {
+	  /* Follow symbolic links under /dev/mapper/; the canonical name
+	     may be something like /dev/dm-0, but the names under
+	     /dev/mapper/ are more human-readable and so we prefer them if
+	     we can get them.  */
+	  if (stat (ent->d_name, &st) < 0)
+	    continue;
+	} else
+#endif /* __linux__ */
+	/* Don't follow other symbolic links.  */
 	continue;
+      }
 
       if (S_ISDIR (st.st_mode))
 	{