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# frozen_string_literal: true
require 'aruba/file_size'
module Aruba
module Platforms
# Determinate disk usage
#
# @private
class DetermineDiskUsage
def call(paths)
size = paths.flatten.sum { |path| minimum_disk_space_used path }
FileSize.new(size)
end
private
# TODO: Aruba.config.physical_block_size could be allowed to be nil
# (So the unit size can be autodetected)
# Report minimum disk space used
#
# This estimates the minimum bytes allocated by the path.
#
# E.g. a 1-byte text file on a typical EXT-3 filesystem takes up 4096 bytes
# (could be more if it was truncated or less for sparse files).
#
# Both `File::Stat` and the `stat()` system call will report 8 `blocks`
# (each "usually" represents 512 bytes). So 8 * 512 is exactly 4096 bytes.
#
# (The "magic" 512 bye implied makes the value of "blocks" so confusing).
#
# Currently Aruba allows you to set what's called the `physical_block_size`,
# which is a bit misleading - it's the "512" value. So if you somehow have a
# "filesystem unit size" of 8192 (instead of a typical 4KB), set the
# `physical_block_size` to 1024 (yes, divide by 8: 8192/8 = 1024).
#
# Ideally, Aruba should provide e.g. `Aruba.config.fs_allocation_unit`
# (with 4096 as the default), so you wouldn't have to "divide by 8".
#
# (typical_fs_unit / typical_dev_bsize = 4096 / 512 = 8)
#
#
# @return [Integer]
# Total bytes allocate
#
# TODO: this is recommended over the above "blocks"
def minimum_disk_space_used(path)
# TODO: replace Aruba.config.physical_block_size
# with something like Aruba.config.fs_allocation_unit
dev_bsize = Aruba.config.physical_block_size
stat = File::Stat.new(path.to_s)
blocks = stat.blocks
return blocks * dev_bsize if blocks
typical_fs_unit = 4096
typical_dev_bsize = 512 # google dev_bsize for more info
block_multiplier = typical_fs_unit / typical_dev_bsize
fs_unit_size = dev_bsize * block_multiplier
fs_units = (stat.size + fs_unit_size - 1) / fs_unit_size
fs_units = 1 if fs_units.zero?
fs_units * fs_unit_size
end
end
end
end
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