#!/bin/sh
exit 1  #Not actually a script.

VG=xenvg
DISK=/dev/mapper/36090a028407d6e2b2589a45cdb971489
HALFSIZETiB=5.23
TMPDM=tmpfoo
TMPDEV=/dev/mapper/$TMPDM
TMPDM2=tmpbar
TMPDEV2=/dev/mapper/$TMPDM2
METADATASIZE=3.5m

#  - pvresize the old PV to half the space
pvresize --setphysicalvolumesize=${HALFSIZETiB}t $DISK

#  - dmsetup create a device in the latter half
dmstart=$(python -c "print int(($HALFSIZETiB + 0.01) * 1024 * 1024 * 1024 * 2)")
dmlen=$(python -c "print int(($HALFSIZETiB - 0.02) * 1024 * 1024 * 1024 * 2)")
#foreach host:
dmsetup create $TMPDM --table "0 $dmlen linear $DISK $dmstart"
#done

#  - pvcreate a temporary PV on the new device
pvcreate $TMPDEV

#  - vgextend with the temporary PV
vgextend $VG $TMPDEV

#  - pvmove all the LVs to the temporary PV
#    (something like
#      for lv in $(LVs for running VMs on this host); do
#        #some lvchange -a commands
#        pvmove -n $lv <oldpv> <newpv>
#        #possibly more lvchange -a to restore old state
#      done)

movelv () {
  echo pvmoving $1...
  lvchange -an $1
  pvmove -i 10 -n $1 $2
}

#FOREACH host:
for lv in $(lvs -o lv_name --noheadings $VG); do
  movelv $VG/$lv $DISK
done
#done

# hopefully empty:
lvs $VG -o lv_name,devices | grep $DISK
# if not, do some more movelv

# This is possible if some LVs were used on more than one host during
# migration.


#  - pvremove the old PV
vgreduce $VG $DISK
pvremove $DISK

#  - pvcreate a new PV in the old space,
#     with --setphysicalvolumesize <half size>
#     and with --metadatasize <huge>    (the point of this exercise)
shortsize=$(python -c "print $HALFSIZETiB - 0.01")t
dmsetup create $TMPDM2 --table "0 $((2 * 1024 * 4)) linear $DISK 0"
pvcreate $TMPDEV2 --setphysicalvolumesize $shortsize --metadatasize $METADATASIZE
dmsetup remove $TMPDM2
pvscan
vgextend $VG $DISK

#  - pvmove all the LVs back

#FOREACH host:
for lv in $(lvs -o lv_name --noheadings $VG); do
  movelv $VG/$lv $TMPDEV
done
#done

# hopefully empty:
lvs $VG -o lv_name,devices | grep $TMPDEV
# if not, do some more movelv

#  - pvremove the temporary PV
vgreduce $VG $TMPDEV
pvremove $TMPDEV
dmsetup remove $TMPDM

#  - pvresize the new PV to use the whole space
pvresize $DISK
