On Wed, Jan 08, 2014 at 11:45:39PM +0100, Paolo Bonzini wrote: > Il 08/01/2014 23:24, Richard W.M. Jones ha scritto: > > It's extremely difficult to know when it's safe to add this parameter. > > Qemu gives no indication of when using discard=.. is safe (ie. won't > > cause qemu to fail to start up or fail in some other way). It's even > > worse when we have to go via libvirt which itself doesn't expose > > qemu's capabilities upwards. > > It is a bug that "-help" doesn't list discard=on, but QMP > query-command-line-options lists it correctly. > > libvirt could safely ignore discard if the underlying QEMU does not > support it, but that's not how it was implemented. Currently, > explicitly specifying either discard='on' and discard='off' will cause > the VM to fail to start if QEMU does not support it. There are > tradeoffs in both solutions...
That sucks .. for me ... Can't we have an option like discard=ifpossible? libguestfs would use this, since we'd always prefer to honour discard requests from our kernel. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v
