I'm running Xen 4.2 and I'm trying to figure out how to enable feature-discard on my paravirtualized domU's. As I understand it, I must have discard enabled in order to run fstrimon my domUs and relay trim instructions back down to the block device.
Currently, when I run fstrim -v / on my domUs, I get this on RHEL7:
fstrim: /: the discard operation is not supported
Or this on a RHEL6 guest:
fstrim: /: FITRIM ioctl failed: Operation not supported
I can see from the output of xenstore-ls that feature-discard is set to 0 for all of my domU's: