[linux-lvm] LVM and RedHat 7.1

[Tom Dawes-Gamble]

HI,

I have been playing with LVM on RedHat 7.1 I've used the standard RedHat 
kernel source RPM and the LVMbeta9 tools.  

When building a root on LVM I found the HOW-TO at 

http://www.sistina.com/lvm/doc/lvm_howto/Converting_a_root_filesys.html
didn't document that need for a "ramdisk=" option to the lilo.conf
entry for the root on LVM part. ( I've enter a bug report for that. )

I also made the stupid error of not putting ramdisk and and support for
initrd in the kernel. You you think that should be clearer in the 
HOW-TO?  

The  LVM root file system howto at 
http://www.the-infinite.org/archive/docs/lvm/howto-boot-off-root-lv.txt
does however document it.  Though is refers to ramdisk_size= rather than
ramdisk=. 

I was not able to get parted compiled on RH 7.1 but the version I used
was brand new.  The older stable parted refused to shrink my original root 
taking up the whole disk apart from /boot and some swap. 

Apart from that the whole job of setting up root on LVM went like a dream.

Now for the main purpose of this message.

The /etc/rc.d/rc.sysint script in RH 7.1 has some code to activate the
LVM devices but it didn't work for me.  So I have rewritten it so that 
it should work for all scenarios.  As shipped it only works correctly for 
LVM built in to the kernel if LVM is a module it fails.

As I see it there are four possible LVM kernel configurations.

1) No LVM
2) LVM built in (Not a module)
3) LVM loadable module
4) LVM with root on LVM and loadable module.

The released rc.sysinit tests for the presence of /proc/lvm and /sbin/vgchange
to determine if vgscan and vgchange should be run.

The /proc/lvm will only exist if LVM is built in or root is on LVM.
So the script fails if you have a LVM as a loadable module.

So this is my idea as to how to have a generic rc.sysinit that caters for 
all four configurations.

# LVM initialization

# If /proc/lvm exists but lvm-mod.o does not then LVM is built in therefor
# we need to activate the Volume Groups.
if [ -e /proc/lvm -a ! -e /lib/modules/$(uname -r)/kernel/drivere/md/lvm-mod.o ]
        then
	# If /etc/lvmtab doesn't exist then run vgscan.
        if [ ! -f /etc/lvmtab ]; then
                action $"Scaning for LVM devices:" /sbin/vgscan 
        fi
        action $"Activate LVM devices:" /sbin/vgchange -a y
fi

#  If /proc/lvm is not there but we have lvm-mod.o then we are not root on LVM
#  so we need to activate the Volume Groups.
if [ ! -e /proc/lvm -a -e /lib/modules/$(uname -r)/kernel/drivers/md/lvm-mod.o ] 
        then
	# If /etc/lvmtab doesn't exist then run vgscan.
        if [ ! -f /etc/lvmtab ]; then
                action $"Scaning for LVM devices:" /sbin/vgscan 
        fi
        action $"Activate LVM devices:" /sbin/vgchange -a y
fi

# End of LVM initialization.

That should cover all four cases.

1) No LVM. Nothing to do.  
	The first if fails since there is no /proc/lvm.
	The second if fails since there is no lvm-mod.o module.

2) LVM built in LVM.
	The first if passes since there is a .proc.lvm and no lvm-mod.o module.  
	The second if fails since /proc/lvm exists after running vgchange.

3) LVM loadable module.
	The first if fails since there is no /proc/lvm and there is an 
	lvm-mod.o module. 
	The second if passes for the same reasons.

4) LVM root on LVM. Nothing to since VG activated by initrd linuxrc.
	The first if fails since there is an lvm-mod.o.
	The second if fails since /proc/lvm exists.

Have I forgotten anything?

Am I doing anything bad?

Should I post a patch for rc.systinit?

Can anyone else test this for me?

I note there is no deactivation of the VG in the shutdown.  But other messages
indicate this is not really a problem.  So I have not bothered doing anything 
about that.

Best regards,
Tom.

-- 
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