holes - 0.1-5 main

holes looks for runs of zero bytes (a.k.a. holes) in the specified input files
(or the standard input), and prints the start addresses (in hexadecimal) as
well as the lengths (in decimal). When multiple input files are specified,
holes prefixes each line with the file name.
.
It can be used with fallocate(1), truncate(1), or virt-sparsify(1).