[PATCH] use UUIDs for cross-disk installs (Re: Issue with boot != root and chainloading)

[Robert Millan <rmh@aybabtu.com>]

[-- Attachment #1: Type: text/plain, Size: 1600 bytes --]

On Fri, Jul 25, 2008 at 05:47:00PM -0400, Pavel Roskin wrote:
> On Fri, 2008-07-25 at 23:08 +0200, Robert Millan wrote:
> > On Thu, Jul 24, 2008 at 12:49:05PM -0400, Pavel Roskin wrote:
> > > 
> > > As I said, GRUB uses its internal ID instead of BIOS ID.  We need to fix
> > > it.
> > 
> > Why not just remove that logic and use UUIDs instead?  It would also simplify
> > the code both in grub-setup and in kernel, maybe even make it smaller.
> 
> I have no objections to that plan.  We'll need UUID search functionality
> on core.img.  I understand you implemented it already.  Is it committed?

Yes.  There's a virtual disk in fs_uuid.mod which can be optionaly loaded in.

> Where should we put the root UUID in core.img?

In grub_prefix.  It already supports this, since it was needed for root-in-LVM
setups.

See attached patch.  I'm afraid it doesn't make kernel smaller as promised;
I expected to get rid of make_install_device() in kernel, but later noticed
that this is still needed for non-cross installs.

2008-07-26  Robert Millan  <rmh@aybabtu.com>

        * include/grub/i386/pc/kernel.h (GRUB_KERNEL_MACHINE_DATA_END):
        Increase from 0x50 to 0x60.
        * util/i386/pc/grub-install.in: Detect cross-disk installs, and
        use UUIDs to identify the root drive for them.  If that's not
        possible, abort.
        * util/i386/pc/grub-setup.c (setup): Do not special-case, or even
        check, for cross-disk installs.

-- 
Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What good is a phone call… if you are unable to speak?
(as seen on /.)

[-- Attachment #2: uuid_boot.diff --]
[-- Type: text/x-diff, Size: 4397 bytes --]

2008-07-26  Robert Millan  <rmh@aybabtu.com>

	* include/grub/i386/pc/kernel.h (GRUB_KERNEL_MACHINE_DATA_END):
	Increase from 0x50 to 0x60.
	* util/i386/pc/grub-install.in: Detect cross-disk installs, and
	use UUIDs to identify the root drive for them.  If that's not
	possible, abort.
	* util/i386/pc/grub-setup.c (setup): Do not special-case, or even
	check, for cross-disk installs.

Index: include/grub/i386/pc/kernel.h
===================================================================
--- include/grub/i386/pc/kernel.h	(revision 1733)
+++ include/grub/i386/pc/kernel.h	(working copy)
@@ -41,7 +41,7 @@
 #define GRUB_KERNEL_MACHINE_PREFIX		0x20
 
 /* End of the data section. */
-#define GRUB_KERNEL_MACHINE_DATA_END		0x50
+#define GRUB_KERNEL_MACHINE_DATA_END		0x60
 
 /* The size of the first region which won't be compressed.  */
 #if defined(ENABLE_LZO)
Index: util/i386/pc/grub-install.in
===================================================================
--- util/i386/pc/grub-install.in	(revision 1733)
+++ util/i386/pc/grub-install.in	(working copy)
@@ -233,15 +233,34 @@
 # Device abstraction module, if any (lvm, raid).
 devabstraction_module=`$grub_probe --target=abstraction --device ${grub_device}`
 
+# The order in this list is critical.  Be careful when modifying it.
+modules="$modules $fs_module $partmap_module biosdisk $devabstraction_module"
+
+prefix_drive=
 if [ "x${devabstraction_module}" = "x" ] ; then
-    prefix_drive=
+    if echo "${install_device}" | grep -qx "(.*)" ; then
+      install_drive="${install_device}"
+    else
+      install_drive="`$grub_probe --target=drive --device ${install_device}`"
+    fi
+    grub_drive="`$grub_probe --target=drive --device ${grub_device}`"
+
+    # Strip partition number
+    install_drive="`echo ${install_drive} | sed -e s/,[0-9]*//g`"
+    grub_drive="`echo ${grub_drive} | sed -e s/,[0-9]*//g`"
+    if [ "x${grub_drive}" != "x${install_drive}" ] ; then
+        uuid="`$grub_probe --target=fs_uuid --device ${grub_device}`"
+        if [ "x${uuid}" = "x" ] ; then
+          echo "You attempted a cross-disk install, but the filesystem containing ${grubdir} does not support UUIDs." 1>&2
+          exit 1
+        fi
+        prefix_drive="(UUID=${uuid})"
+        modules="$modules fs_uuid"
+    fi
 else
     prefix_drive=`$grub_probe --target=drive --device ${grub_device}`
 fi
 
-# The order in this list is critical.  Be careful when modifying it.
-modules="$modules $fs_module $partmap_module biosdisk $devabstraction_module"
-
 grub_prefix="${prefix_drive}`make_system_path_relative_to_its_root ${grubdir}`" || exit 1
 
 $grub_mkimage --output=${grubdir}/core.img --prefix=${grub_prefix}/ $modules || exit 1
Index: util/i386/pc/grub-setup.c
===================================================================
--- util/i386/pc/grub-setup.c	(revision 1733)
+++ util/i386/pc/grub-setup.c	(working copy)
@@ -339,18 +339,12 @@
 	  if (grub_disk_write (dest_dev->disk, embed_region.start, 0, core_size, core_img))
 	    grub_util_error ("%s", grub_errmsg);
 
-	  /* The boot image and the core image are on the same drive,
-	     so there is no need to specify the boot drive explicitly.  */
-	  *boot_drive = 0xff;
+	  /* FIXME: can this be skipped?  */
+	  *boot_drive = 0xFF;
+	  *root_drive = 0xFF;
+
 	  *kernel_sector = grub_cpu_to_le64 (embed_region.start);
 
-          /* If the root device is different from the destination device,
-             it is necessary to embed the root drive explicitly.  */
-          if (root_dev->disk->id != dest_dev->disk->id)
-            *root_drive = (grub_uint8_t) root_dev->disk->id;
-          else
-            *root_drive = 0xFF;
-
 	  /* Write the boot image onto the disk.  */
 	  if (grub_disk_write (dest_dev->disk, 0, 0, GRUB_DISK_SECTOR_SIZE,
 			       boot_img))
@@ -480,15 +474,8 @@
   
   *kernel_sector = grub_cpu_to_le64 (first_sector);
 
-  /* If the destination device is different from the root device,
-     it is necessary to embed the boot drive explicitly.  */
-  if (root_dev->disk->id != dest_dev->disk->id)
-    *boot_drive = (grub_uint8_t) root_dev->disk->id;
-  else
-    *boot_drive = 0xFF;
-
-  /* When the core image is not embedded, the root device always follows
-     the boot device.  */
+  /* FIXME: can this be skipped?  */
+  *boot_drive = 0xFF;
   *root_drive = 0xFF;
 
   *install_dos_part = grub_cpu_to_le32 (dos_part);