#!/bin/bash

# Overview of backup process
#  1) Read and parse configuration file
#  2) Loop through each backup
#  3) Create a FS snapshot using LVM
#  4) Mount the snapshot FS
#  5) Mount our backup file in a loop filesystem (we can guarantee the space
#     will be present this way, and it allows selective recovery of files if
#     need be)
#  6) rsync the differences between the snapshot FS and the backup FS
#  7) Unmount the backup FS
#  8) Unmount the snapshot FS
#  9) Delete the snapshot LVM (leaving it will degrade performance)
# 10) Repeat 3-9 if necessary

# Save the old IFS variable so that we can restore it when we're done
ORIGIFS=$IFS
IFS=$(echo -en "\n\b")

# User where the reports of the backup are sent to
MAILTO=root

# Read from the configuration file any exclude filters for the rsync output
LOG_EXCLUDE=$(cat "$PWD/backup.conf" | egrep "^[ \t]*LOG_EXCLUDE=" |
              cut -d'=' -f 2-)
LOG_FILE=/tmp/backup$$.log

# Get each line from the configuration file one at a time, ignoring anything
# that starts with a pound (#) sign
for i in $(cat "$PWD/backup.conf" | egrep -v "^[ \t]*#.*|^[ \t]*LOG_EXCLUDE=.*"); do
	# Parse out the locations we need
	VOL=$(echo $i | sed "s@^\([^:]*\):\(.*\)@\1@")
	TARG=$(echo $i | sed "s@^\([^:]*\):\(.*\)@\2@")

	# Check to make sure the paths are valid
	[ -b $VOL ]  || { echo "Source volume not valid: $VOL. Skipping";
	                  continue; }
	[ -f $TARG ] || { echo "Target image not valid: $TARG. Skipping";
	                  continue; }

	# Get necessary information about the source volume.
	# Get only the necessary line, and not the headers, and then compress the
	# info so it is only separated by a single space (makes finding fields
	# easier in the next steps). There will be an extra space at the beginning, 
	# so fields are 1 greater than what they seem.
	#
	# Make sure the volume is a LVM Logical Volume
	lvs -a $VOL 2>/dev/null 1>/dev/null || {
		echo "$VOL not an LVM Logical Volume ($?). Skipping."; continue; }
	# Now we actually collect the info
	INFO=$(lvs -a $VOL | tail -n 1 | sed 's/[ ][ ]*/ /g')
	# Field 1: Logical Volume Name
	VOL_NAME=$(echo $INFO | cut -d' ' -f 2)
	# Field 2: Volume Group Name
	GROUP_NAME=$(echo $INFO | cut -d' ' -f 3)
	# Field 3: Attributes - Not needed right now, but may come in handy
	ATTRS=$(echo $INFO | cut -d' ' -f 4)
	# Field 4: Volume Size
	VOL_SIZE=$(echo $INFO | cut -d' ' -f 5)

	# Now we just create a name for the snapshot volume, and then we can
	# create it
	SNAP_NAME=${VOL_NAME}$$
	SNAP_PATH=/dev/${GROUP_NAME}/${SNAP_NAME}
	lvcreate -s -L${VOL_SIZE} -n $SNAP_NAME $VOL >/dev/null || {
		echo "Snapshot of '${GROUP_NAME}/${SNAP_NAME}' failed ($?). Skipping.";
		continue; }
	
	# Mount our filesystems at temporary mount locations
	SNAP_MOUNT=/tmp/backup-$SNAP_NAME
	TARG_MOUNT=/tmp/backup-target$$
	mkdir $SNAP_MOUNT || {
		echo "Failed to create snapshot mount point ($?). Skipping.";
		cleanup; continue; }
	mkdir $TARG_MOUNT || {
		echo "Failed to create target mount point ($?). Skipping.";
		cleanup; continue; }
	mount $SNAP_PATH $SNAP_MOUNT || {
		echo "Mounting snapshot failed ($?). Skipping.";
		cleanup; continue; }
	mount -o loop $TARG $TARG_MOUNT || {
		echo "Mounting target image failed ($?). Skipping.";
		cleanup; continue; }

	# Update the backup file system with files from the snapshot
	# IMPORTANT!!: The trailing slash on the source is necessary for it to
	# work in the expected way, or else all backups will end up within a
	# subdirectory with the name $SNAP_MOUNT
	rsync -aHEAXxv --stats --delete --ignore-errors $SNAP_MOUNT/ $TARG_MOUNT | \
		egrep -v "$LOG_EXCLUDE" >> $LOG_FILE

	# Cleanup stuff is put into a function so that it can be called before
	# an exit call
	function cleanup() {
		# Unmount the backups and remove the temporary dirs
		# Errors may occur here, but we don't really care. Just pipe the errors
		# to /dev/null
		umount $SNAP_MOUNT 2>/dev/null 1>/dev/null
		umount $TARG_MOUNT 2>/dev/null 1>/dev/null
		[ -d $SNAP_MOUNT ] && rmdir $SNAP_MOUNT
		[ -d $TARG_MOUNT ] && rmdir $TARG_MOUNT

		# Delete the snapshot
		[ -b $SNAP_PATH ] && lvremove -f $SNAP_PATH >/dev/null
	}
	# Now call our cleanup routine on normal completions
	cleanup
done

# Mail the log file, and then delete the file
mail -s "Backups on $(hostname)" $MAILTO < $LOG_FILE
rm $LOG_FILE

# Restore the IFS
IFS=$ORIGIFS