#!/bin/bash

# lba2file: Given an LBA number and a drive in /dev/, print which
# filename(s), if any, use that sector.

# This is the opposite of `hdparm --fibmap /foo/bar`

# B9 May 2020

if [[ "$1" == "-b" ]]; then
    BYTESFLAG=Byte
    shift
fi

if [[ $# -lt 2 ]]; then
    echo "Usage: lba2file  [-b]  <sector number>  /dev/sdX"
    echo "	-b: Use byte address instead of sector"
    exit 1
fi

if [[ $(id -u) -ne 0 ]]; then
    echo "Please run as root using 'sudo $@'" >&2
    exit 1
fi

lba=$1
drive=$2
drive=${drive#/dev/}		# Remove /dev/ prefix, if any.

if [[ "$drive" =~ ^(.*)[0-9]$ ]]; then    # Either user specified a partition.
    searchparts="/sys/class/block/$drive"
    drive=${BASH_REMATCH[1]}
else				     # Or user specified a drive.
    shopt -s nullglob		     # Don't use '?' literally.
    searchparts=$(eval echo /sys/class/block/${drive}?)
fi

for partition in $searchparts; do
    device=/dev/${partition#/sys/class/block/}
    cd "$partition" || continue
    start=$(cat "$partition/start")
    partitionsize=$(cat "$partition/size")
    hwsectorsize=$(cat "/sys/class/block/$drive/queue/hw_sector_size")

    # Typically: e2blocksize==4096, hwsectorsize==512
    # Example: start=1048576, partitionsize=640133980160
    # Do a sanity check.
    if [[ -z "$start" || -z "$partitionsize" || -z "$hwsectorsize" ]]; then
	echo "Error reading data for $device" >&2
	continue
    fi

    # Scale everything to bytes since we'll use that for debugfs.
    start=$((start * hwsectorsize))
    partitionsize=$((partitionsize * hwsectorsize))

    # If not using byte flag, scale the address, too.
    if [[ -z "$BYTESFLAG" ]]; then
	byteaddress=$((lba * hwsectorsize))
    else
	byteaddress=$lba
    fi
    if [[ $byteaddress -lt $start ||
	  $byteaddress -ge $((start+partitionsize)) ]]; then
	#echo "Address $byteaddress is not within $partition"
	continue 		# Not in this partition
    fi

    if ! e2blocksize=$(tune2fs -l $device 2>/dev/null |
			   grep '^Block size' | egrep -o '[0-9]+'); then
	echo "Skipping $device, not an Ext2/3/4 partition" 
	continue
    fi

    # Scale address by filesystem blocksize to find filesystem block number
    e2blockaddress=$(( (byteaddress - start) / e2blocksize))
    
    Sector=${BYTESFLAG:-Sector}
    echo "Disk $Sector $lba is at filesystem block $e2blockaddress in $device"
    inode=$(debugfs -R "icheck $e2blockaddress" $device 2>/dev/null |
		   tail -1 | cut -f2)
    if [[ "$inode" && "$inode" != "<block not found>" ]]; then
	echo "$Sector is used by inode $inode"
	echo "Searching for filename(s)..."
	debugfs -R "ncheck $inode" $device 2>/dev/null
    else
	echo "$Sector is not in use."
    fi
done