#! /bin/sh
###
### Establish snapshots of LVM logical volumes
###
### (c) 2011 Mark Wooding
###

###----- Licensing notice ---------------------------------------------------
###
### This program is free software; you can redistribute it and/or modify
### it under the terms of the GNU General Public License as published by
### the Free Software Foundation; either version 2 of the License, or
### (at your option) any later version.
###
### This program is distributed in the hope that it will be useful,
### but WITHOUT ANY WARRANTY; without even the implied warranty of
### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
### GNU General Public License for more details.
###
### You should have received a copy of the GNU General Public License
### along with this program; if not, write to the Free Software Foundation,
### Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

set -e
quis=${0##*/}

###--------------------------------------------------------------------------
### Parse the command line.

## Provide help or version information.
usage="usage: $quis DEVICE [KEY=VALUE ...]"
version="$quis, version 1.0.0"
case "$#,$1" in
  0,*) echo >&2 "$usage"; exit 1 ;;
  *,-v | *,--version) echo "$version"; exit ;;
  *,-h | *,--help)
    cat <<EOF
$version
$usage

Option keys:
  op=OPERATION          \`snap' to create snapshot, or \`unsnap' to remove.
  snapsz=SIZE		Size to reserve for snapshot storage.
  tag=TAG               Disambiguation tag to append to logical volume name.
EOF
    exit
    ;;
esac

## Scan the option keys.
dev=$1; shift
Oop=snap Otag=snap Osnapsz=100M
win=t
for i in "$@"; do
  case "$i" in
    ?*=*) ;;
    *) echo >&2 "$quis: malformed option \`$i'"; exit 1 ;;
  esac
  k=${i%%=*} v=${i#*=}
  case "$k" in *.lvm) k=${k%.lvm} ;; ?*.?*) continue ;; esac
  case "$k" in
    op | tag | snapsz) eval "O$k=\$v" ;;
    *) echo >&2 "$quis: unknown option \`$k'"; win=nil ;;
  esac
done
case $win in nil) exit 1 ;; esac

## Check the device name.
case "$dev" in
  ?*/?*) ;; *) echo >&2 "$quis: device \`$dev' should be VG/LV"; exit 1 ;;
esac
vg=${dev%%/*} lv=${dev#*/}

###--------------------------------------------------------------------------
### Take or remove the snapshot.

case "$Oop" in

  snap)
    case "$Osnapsz" in
      *%*) szarg="extents" ;;
      *) szarg="size" ;;
    esac
    lvcreate >/dev/null --snapshot \
      --$szarg="$Osnapsz" \
      --name="$lv.$Otag" \
      "$vg/$lv"
    echo "$vg/$lv.$Otag"
    ;;

  unsnap)
    ## LVM snapshot removal is full of awful bugs, mostly to do with races
    ## with udev.  We have a handy script which does the necessary.  May it
    ## not be needed for long.
    lvm-rmsnap >/dev/null "$vg/$lv.$Otag"
    ;;

  *)
    echo >&2 "$quis: unknown operation \`$Oop'"
    exit 1
    ;;

esac

###----- That's all, folks --------------------------------------------------