# DP: Add support for specifying the root device using UUIDs on the
# DP: kernel command line like this without the need for an initrd:
# DP: linux ... root=UUID=ce40d6b2-18eb-4a75-aefe-7ddb0995ce63
# DP:
# DP: Written © 2010 by Thorsten Glaser <tg@debian.org>
# DP: Idea from 1999 by David Balazic <david.balazic@uni-mb.si>

--- linux-2.6.36/block/genhd.c~	Wed Oct 20 22:30:22 2010
+++ linux-2.6.36/block/genhd.c	Sat Nov 20 23:14:03 2010
@@ -35,7 +35,7 @@ struct kobject *block_depr;
 static DEFINE_MUTEX(ext_devt_mutex);
 static DEFINE_IDR(ext_devt_idr);
 
-static struct device_type disk_type;
+struct device_type disk_type;
 
 /**
  * disk_get_part - get partition
@@ -1019,7 +1019,7 @@ static char *block_devnode(struct device *dev, mode_t 
 	return NULL;
 }
 
-static struct device_type disk_type = {
+struct device_type disk_type = {
 	.name		= "disk",
 	.groups		= disk_attr_groups,
 	.release	= disk_release,
--- linux-2.6.36/init/do_mounts.c~	Wed Oct 20 22:30:22 2010
+++ linux-2.6.36/init/do_mounts.c	Sat Nov 20 23:16:07 2010
@@ -32,6 +32,84 @@ static int __initdata root_wait;
 
 dev_t ROOT_DEV;
 
+#ifdef CONFIG_EXT2_FS
+/* support for root=UUID=ce40d6b2-18eb-4a75-aefe-7ddb0995ce63 bootargs */
+
+#include <linux/buffer_head.h>
+#include <linux/ext2_fs.h>
+
+__u8 root_dev_label[16];
+int root_dev_type;	/* 0 = normal (/dev/hda1, 0301); 1 = UUID; 3 = bad */
+
+/* imported from block/genhd.c after removing its static qualifier */
+extern struct device_type disk_type;
+
+static __u8 __init fromhex(char c)
+{
+	if (c >= '0' && c <= '9')
+		return (c - '0');
+	c &= ~32;
+	if (c >= 'A' && c <= 'F')
+		return (c - 'A' + 10);
+	return (0xFF);
+}
+
+static void __init parse_uuid(const char *s)
+{
+	int i;
+	__u8 j, k;
+
+	if (strlen(s) != 36 || s[8] != '-' || s[13] != '-' ||
+	    s[18] != '-' || s[23] != '-')
+		goto bad_uuid;
+	for (i = 0; i < 16; i++) {
+		if (*s == '-')
+			++s;
+		j = fromhex(*s++);
+		k = fromhex(*s++);
+		if (j == 0xFF || k == 0xFF)
+			goto bad_uuid;
+		root_dev_label[i] = (j << 4) | k;
+	}
+	return;
+ bad_uuid:
+	/* we cannot panic here, defer */
+	root_dev_type = 3;
+}
+
+static int __init check_dev(dev_t devt, int blocksize)
+{
+	/* most of this taken from fs/ext2/super.c */
+
+	struct buffer_head * bh;
+	struct ext2_super_block * es;
+	struct block_device *bdev;
+	unsigned long sb_block = 1;
+	unsigned long logic_sb_block;
+	unsigned long offset = 0;
+	int rv = 0;
+
+	bdev = bdget(devt);
+
+	if (blocksize != BLOCK_SIZE) {
+		logic_sb_block = (sb_block*BLOCK_SIZE) / blocksize;
+		offset = (sb_block*BLOCK_SIZE) % blocksize;
+	} else {
+		logic_sb_block = sb_block;
+	}
+
+	if (!(bh = __bread(bdev, logic_sb_block, blocksize)))
+		return (0);
+	es = (struct ext2_super_block *)(((char *)bh->b_data) + offset);
+	if (le16_to_cpu(es->s_magic) == EXT2_SUPER_MAGIC) {
+		if (!memcmp(es->s_uuid, root_dev_label, 16))
+			rv = 1;
+	}
+	brelse(bh);
+	return (rv);
+}
+#endif /* CONFIG_EXT2_FS for UUID support */
+
 static int __init load_ramdisk(char *str)
 {
 	rd_doload = simple_strtol(str,NULL,0) & 3;
@@ -148,6 +226,13 @@ done:
 static int __init root_dev_setup(char *line)
 {
 	strlcpy(saved_root_name, line, sizeof(saved_root_name));
+#ifdef CONFIG_EXT2_FS
+	root_dev_type = 0;
+	if (!strncmp(line, "UUID=", 5)) {
+		root_dev_type = 1;
+		parse_uuid(line + 5);
+	}
+#endif /* CONFIG_EXT2_FS for UUID support */
 	return 1;
 }
 
@@ -333,6 +418,45 @@ void __init change_floppy(char *fmt, ...)
 
 void __init mount_root(void)
 {
+#ifdef CONFIG_EXT2_FS
+	/* UUID support */
+	if (root_dev_type == 1) {
+		int blocksize;
+
+		/* from block/genhd.c printk_all_partitions */
+		struct class_dev_iter iter;
+		struct device *dev;
+
+		class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
+		while (root_dev_type && (dev = class_dev_iter_next(&iter))) {
+			struct gendisk *disk = dev_to_disk(dev);
+			struct disk_part_iter piter;
+			struct hd_struct *part;
+			if (get_capacity(disk) == 0 ||
+			    (disk->flags & GENHD_FL_SUPPRESS_PARTITION_INFO))
+				continue;
+			blocksize = queue_logical_block_size(disk->queue);
+
+			disk_part_iter_init(&piter, disk, DISK_PITER_INCL_PART0);
+			while (root_dev_type && (part = disk_part_iter_next(&piter))) {
+				/* avoid empty or too small partitions */
+				if (part->nr_sects < 8)
+					continue;
+				if (check_dev(part_devt(part), blocksize)) {
+					ROOT_DEV = part_devt(part);
+					root_dev_type = 0;
+				}
+			}
+			disk_part_iter_exit(&piter);
+		}
+		class_dev_iter_exit(&iter);
+	}
+	if (root_dev_type == 1)
+		printk(KERN_ERR "VFS: Unable to find root by UUID %s.\n", saved_root_name + 5);
+	else if (root_dev_type == 3)
+		panic("Badly formatted UUID %s was supplied as kernel parameter root", saved_root_name + 5);
+#endif /* CONFIG_EXT2_FS for UUID support */
+
 #ifdef CONFIG_ROOT_NFS
 	if (MAJOR(ROOT_DEV) == UNNAMED_MAJOR) {
 		if (mount_nfs_root())