fstrimtest

#!/bin/bash

set -euo pipefail

fstype=$1

_du() { du -BM img; }
_fstrim() { fstrim --verbose mnt; }
_sync() { sync; sync; }

mkdir mnt
set -o noclobber
> img
truncate -s 5G img
dev=$(losetup --direct-io --find --show img)
mkfs."$fstype" -q "$dev"
mount -o nodiscard "$dev" mnt

for i in 1 2 3; do head -c 1G /dev/random >mnt/file$i; done; _sync
for i in 1 2  ; do rm                      mnt/file$i; done; _sync

_du
_fstrim; _sync
_du
_fstrim; _sync
_du
_fstrim; _sync
_du

umount mnt
rmdir mnt
losetup --detach "$dev"
rm img