LVM, defvs and initrd (for lvm rootfs)

I have a system that I am trying to boot with an LVM root filesystem. The kernel is a 2.4.8 (Mandrake variant) and is using devfs.

The LVM version is unfortunately only 0.9.1_beta3 because that is what is in the stock kernel at the moment (IIRC). I am trying to get Mandrake to update to the latest 1.0.* release but they are resisting taking what is not the stock kernel until they have some internal expertise on LVM. This would be a good reason for you guys to get the 1.0.* code pushed up to Linus. :-)

Anyhow, I am successfully booting the system fully with the root filesystem on LVM so I know my initrd is (somewhat :-) correct. The problem I am having is that once I am booted, the /dev/<volume group/ directory is empty. I think this has something to do with the fact that when the lvm kernel module is actually loaded (and the devfs nodes registered), the system is booted on the initrd root filesystem which then gets thrown away (along with the devfs /dev/ directory) when the real root is mounted.

Here is the order of operations during boot as I can determine them:

1.  mount initrd
2.  kernel mounts devfs
3   load lvm module (which creates devfs nodes)
3.  vgscan, vchange -a y
4.  mount real root (on lvm partition)
5.  kernel mounts devfs again (on real root)
6.  unmount initrd

I think the lvm nodes are created successfully in step 3 but get lost when devfs is mounted a second time in step 5.

Here is the (relevant) kernel output during the boot. The line nubmers on the left of course were just added here so that I could annotate below.

1. Linux version 2.4.8-11mdk ([email protected]) (gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release / Linux-Mandrake 8.1)) #1 Wed Aug 22 16:22:21 CEST 2001 [ snip ]
2. Kernel command line: BOOT_IMAGE=linux ro root=3a00 devfs=mount
[ snip ]
3. devfs: v0.107 (20010709) Richard Gooch ([email protected])
4. devfs: boot_options: 0x2
[ snip ]

5.  RAMDISK: Compressed image found@block 0
6.  Uncompressing...............................................................................................................................done.
7.  Freeing initrd memory: 1282k freed
8.  VFS: Mounted root (ext2 filesystem).
9.  Mounted devfs on /dev

10. LVM version 0.9.1_beta3 by Heinz Mauelshagen (25/01/2001)
11. lvm -- Module successfully initialized
12, devfs: devfs_register(): device already registered: "group" 13, devfs: devfs_register(): device already registered: "lvol1" 14, devfs: devfs_register(): device already registered: "1" 15, VFS: Mounted root (ext2 filesystem) readonly.
16, change_root: old root has d_count=2
17, Mounted devfs on /dev
18, Freeing unused kernel memory: 708k freed

Notice in line 2, the kernel command line does include "devfs=mount". Notice in lines 5-8, the initial ramdisk is detected and mounted. In line 9, the kernel mounts devfs. Lines 10-11 are the loading of the lvm driver and lines 12-14 are errors from devfs about devices that exist, I guess. I am not sure why I am getting these.

See on line 15, the real root filesystem (on the LVM LV) is mounted successfully (yay!) and on line 17, devfs is mounted again -- by the kernel.

The system boots fine onto the LVM based root filesystem. The problem is that the device nodes in /dev/VG (group, lvol1 and 1) are missing an uncreatable.

Is my theory correct? Is there a way to work around this?

Thanx,
b.

Brian J. Murrell

Hi,

Run vgscan (without parameters) at the end of rc.sysinit.

Bye,
Bas.

----- Original Message -----
From: "Brian J. Murrell" <[email protected]>
To: <[email protected]>
Sent: Monday, September 03, 2001 6:09 AM
Subject: [linux-lvm] LVM, defvs and initrd (for lvm rootfs)

egcs-2.91.66 19990314/Linux (egcs-1.1.2 release / Linux-Mandrake 8.1)) #1 Wed Aug 22 16:22:21 CEST 2001

Uncompressing............................................................... ................................................................done.

Should have mentioned... I have tried this. vgscan tries to create the /dev/<volume group/* nodes (with mknod(2)) but it fails, presumably because devfs[d] does not allow it (the node creation with mknod(2))? I have not looked much into devfs[d] yet.

b.

Brian J. Murrell

I believe this issue was fixed in a later revision of the LVM tools, (i don't remember when precisely)
try upgrading tools.

L.

Luca Berra -- [email protected]
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Excellent! That was (and wasn't) what I was hoping to hear. :-)

Thanx,
b.

Brian J. Murrell