Hi, I have launched a qemu process with the following options related to emulated disk:
-drive file=disk.qcow2,if=none,id=disk0,l2-cache-size=8M,format=qcow2,discard=on,detect-zeroes=unmap,aio=io_uring
-device virtio-blk-pci,drive=disk0,scsi=off,bootindex=2
If I download files on guest OS to increase the used disk space, I can observe that the disk file size is increased too. But if I delete the downloaded files on the guest OS, the behavior on the host side is strange. By using ls -alh or du --apparent-size commands I saw that the file size has not decreased after deletion. But by using du -hs or qemu-img info commands I observe that the disk file size has been decreased successfully.
I know that this is because of sparse blocks. But is there any way to tell the underlying filesystem to use write operations on sparsed blocks?
I am using qemu version 5.2.0 and my host operating system is debian 11. I even use fstrim command on guest OS but it doesn't have any impact.