[Lguest] Creating distro root disk image

[Rusty Russell]

On Thu, 2007-08-16 at 20:55 -0500, Jason Yeh wrote:
> This is the only image left on the hard disk:
> 
> jyeh at socrates:~/vmware/Ubuntu$ file guestos.img
> guestos.img: x86 boot sector; partition 1: ID=0x83, active, starthead 1,
> startsector 63, 40098177 sectors; partition 2: ID=0x5, starthead 254,
> startsector 40098240, 1831410 sectors, code offset 0x48
> 
> The lguest command is:
> sudo /home/jyeh/Dev/linux-2.6-git/Documentation/lguest/lguest 64m
> /home/jyeh/Dev/linux-2.6-git/vmlinux --tunnet=192.168.19.1
> --block=/home/jyeh/vmware/Ubuntu/guestos.img root=/dev/lgba

OK, the fast way of fixing this is to make a copy of the partition
without the boot sector on the front:

dd if=guestos.img of=guestos.img-part1 bs=512 skip=63

Then use --block=/home/jyeh/vmware/Ubuntu/guestos.img-part1

The better way is to apply this one-liner and boot with
"root=/dev/lgba1":
==
The lguest block device only requests one minor, which means
partitions don't work (eg "root=/dev/lgba1").

Let's follow the crowd and ask for 16.

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff -r f624b0b8f457 drivers/block/lguest_blk.c
--- a/drivers/block/lguest_blk.c	Fri Aug 17 11:18:01 2007 +1000
+++ b/drivers/block/lguest_blk.c	Fri Aug 17 12:45:11 2007 +1000
@@ -308,9 +308,13 @@ static int lguestblk_probe(struct lguest
 	}
 
 	/* This allocates a "struct gendisk" where we pack all the information
-	 * about the disk which the rest of Linux sees.  We ask for one minor
-	 * number; I do wonder if we should be asking for more. */
-	bd->disk = alloc_disk(1);
+	 * about the disk which the rest of Linux sees.  The argument is the
+	 * number of minor devices desired: we need one minor for the main
+	 * disk, and one for each partition.  Of course, we can't possibly know
+	 * how many partitions are on the disk (add_disk does that).
+	 *
+	 * Worst.  Interface.  Ever. */
+	bd->disk = alloc_disk(16);
 	if (!bd->disk) {
 		err = -ENOMEM;
 		goto out_unregister_blkdev;