[question] Partial sector issue while discard in qcow2 image

[Lin Ma]

Hi all,

During  woring to add GET LBA STATUS support in qemu scsi emulation layer, I encountered

an unmap issue with qcow2 image, It's likely about how to unmap partial clusters. e.g.:

With these default values:

* the default value of s->qdev.blocksize: 512

* the default value of s->cluster_size of qcow2 image: 65536

Running 'sg_unmap -l 1024 -n 32 /dev/sda' hits the condition

'if (!QEMU_IS_ALIGNED(offset | bytes, s->cluster_size))' in the function qcow2_co_pdiscard,

Then it won't perform qcow2_cluster_discard(), So the corresponding clusters won't be discard

in this situation, Correct?

Of cause, with the default blocksize and cluster_size, The below examples won't hit the condition 'if (!QEMU_IS_ALIGNED...'.

sg_unmap -l 1024 -n 128 /dev/sda

or

sg_unmap -l 256 -n 128 /dev/sda

Thanks,

Lin