core-admin/common/block-snapshot

#!/bin/bash

# Usage: block-snapshot add|remove img-file cow-file
#
# This creates dm-snapshot device on given arguments

dir=$(dirname "$0")
. "$dir/block-common.sh"

get_dev() {
  dev=$1

  if [ -L "$dev" ]; then
    dev=$(readlink -f "$dev") || fatal "$dev link does not exist."
  fi

  if [ -f "$dev" ]; then
    file=$dev

    inode=$(stat -c '%i' "$file")
    devnum=$(stat -c '%D' "$file")
    if [ -z "$inode" ] || [ -z "$devnum" ]
    then
      release_lock "block"
      fatal "Unable to lookup $file: dev: $devnum inode: $inode"
    fi

    dev_list=$(losetup -a | grep ' \[0*'${devnum}'\]:'${inode} | cut -d : -f 1)
    for loopdev in $dev_list; do
      # found existing loop to this file
      echo $loopdev
      return
    done


    # assign new loop device
    loopdev=$(losetup -f 2>/dev/null || find_free_loopback_dev)
    if [ "$loopdev" = '' ]
    then
      release_lock "block"
      fatal 'Failed to find an unused loop device'
    fi

    do_or_die losetup "$loopdev" "$file"
    echo $loopdev
  else
    test -e "$dev" || fatal "$dev does not exist."
    test -b "$dev" || fatal "$dev is not a block device nor file."
  fi
}

get_dm_snapshot_name() {
  base=$1
  cow=$2

  echo snapshot-$(stat -c '%D:%i' "$base")-$(stat -c '%D:%i' "$cow")
}

create_dm_snapshot() {
  local base_dev cow_dev base_sz

  dm_devname=$1
  base=$2
  cow=$3

  if [ ! -e /dev/mapper/$dm_devname ]; then
    # prepare new snapshot device
    base_dev=$(get_dev $base)
    cow_dev=$(get_dev $cow)
    base_sz=$(blockdev --getsz $base_dev)
    do_or_die dmsetup create $dm_devname --table "0 $base_sz snapshot $base_dev $cow_dev P 256"
  fi

}

create_dm_snapshot_origin() {
  local base_dev base_sz

  dm_devname=$1
  base=$2

  if [ ! -e /dev/mapper/$dm_devname ]; then
    # prepare new snapshot-origin device
    base_dev=$(get_dev $base)
    base_sz=$(blockdev --getsz $base_dev)
    do_or_die dmsetup create $dm_devname --table "0 $base_sz snapshot-origin $base_dev"
  fi
}

t=$(xenstore_read_default "$XENBUS_PATH/type" 'MISSING')


case "$command" in
  add)
    case $t in
      snapshot|origin)
        p=$(xenstore_read "$XENBUS_PATH/params")
        base=${p/:*/}
        cow=${p/*:/}

        if [ -L "$base" ]; then
          base=$(readlink -f "$base") || fatal "$base link does not exist."
        fi

        if [ -L "$cow" ]; then
          cow=$(readlink -f "$cow") || fatal "$cow link does not exist."
        fi

        # first ensure that snapshot device exists (to write somewhere changes from snapshot-origin)
        dm_devname=$(get_dm_snapshot_name "$base" "$cow")

        claim_lock "block"

        # prepare snapshot device
        create_dm_snapshot $dm_devname "$base" "$cow"

        if [ "$t" == "snapshot" ]; then
          #that's all for snapshot, store name of prepared device
          xenstore_write "$XENBUS_PATH/node" "/dev/mapper/$dm_devname"
          write_dev /dev/mapper/$dm_devname
        elif [ "$t" == "origin" ]; then
          # for origin - prepare snapshot-origin device and store its name
          dm_devname=origin-$(stat -c '%D:%i' "$base")
          create_dm_snapshot_origin $dm_devname "$base"
          xenstore_write "$XENBUS_PATH/node" "/dev/mapper/$dm_devname"
          write_dev /dev/mapper/$dm_devname
        fi

        release_lock "block"
        exit 0
        ;;
    esac
    ;;
  remove)
    case $t in
      snapshot|origin)
        node=$(xenstore_read "$XENBUS_PATH/node")

        if [ -z "$node" ]; then
          fatal "No device node to remove"
        fi

        if [ ! -e "$node" ]; then
          fatal "Device $node does not exists"
        fi

        claim_lock "block"

        use_count=$(dmsetup info $node|grep Open|awk '{print $3}')

        # do not remove snapshot if snapshot origin is still present
        if [ "${node/snapshot/}" != "$node" -a -e "/dev/mapper/origin-$(echo $node|cut -d- -f2)" ]; then
          use_count=1
        fi

        if [ "$use_count" -gt 0 ]; then
          log info "Device $node still in use - not removing"
          release_lock "block"
          exit 0
        fi

        # get list of used (loop) devices
        deps="$(dmsetup deps $node | cut -d: -f2 | sed -e 's#(7, \([0-9]\+\))#/dev/loop\1#g')"

        # if this is origin
        if [ "${node/origin/}" != "$node" ]; then
          # remove unused snapshots
          for snap in /dev/mapper/snapshot-$(echo $node|cut -d- -f2)-*; do
            use_count=$(dmsetup info $snap|grep Open|awk '{print $3}')
            if [ "$use_count" -eq 0 ]; then
              # unused snapshot - remove it
              deps="$deps $(dmsetup deps $snap | cut -d: -f2 | sed -e 's#(7, \([0-9]\+\))#/dev/loop\1#g')"
              log debug "Removing $snap"
              dmsetup remove $snap
            fi
          done
        fi
	
	if [ -e $node ]; then
          log debug "Removing $node"
          dmsetup remove $node
	fi

        # try to free loop devices
        for dev in $deps; do
          if [ -b "$dev" ]; then
            log debug "Removing $dev"
            losetup -d $dev || true 2> /dev/null
          fi
        done

        release_lock "block"
        
        exit 0
        ;;
    esac
    ;;
esac

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