[Qemu-discuss] qemu-kvm 0.15.1 discard feature

[Charles Chou]

Hi,
    Can someone tell me if the discard feature is fully implemented in 
qemu-kvm 0.15.1? From the source it seems to contain the necessary code 
for the block driver. However when I use a block device that is discard 
capable as a raw device for use with qemu-kvm as a data drive for the 
guest,, i.e., -hdb, and then created an ext4 fs. which is discard ready, 
but the deleted files did not seem to trigger the discard, i.e., the 
block space usage did not change.

    When I mkfs.ext4 on the block device directly and mount it on the 
qemu host machine, the discard feature works just fine. Is there a 
special option I need to use in qemu startup to let the quest OS know 
the block device is discard capable?

Thanks!
Charles Chou