Re: [libvirt] [PATCHv2] Support vhost-net mode at qemu startup for virtio network devices.

Attempt to turn on vhost-net mode for devices of type NETWORK, BRIDGE, and DIRECT (macvtap). * src/qemu/qemu_conf.h: add vhostfd to qemuBuildHostNetStr prototype add qemudOpenVhostNet prototype new flag to set when :,vhost=" found in qemu help * src/qemu/qemu_conf.c: * set QEMUD_CMD_FLAG_VNET_HOST is ",vhost=" found in qemu help * qemudOpenVhostNet - opens /dev/vhost-net to pass to qemu if everything is in place to use it. * qemuBuildHostNetStr - add vhostfd to commandline if it's not empty (higher levels decide whether or not to fill it in) * qemudBuildCommandLine - if /dev/vhost-net is successfully opened, add its fd to tapfds array so it isn't closed on qemu exec, and populate vhostfd_name to be passed in to commandline builder. * src/qemu/qemu_driver.c: add filler 0 for new arg to qemuBuildHostNetStr, along with a note that this must be implemented in order for hot-plug of vhost-net virtio devices to work properly (once qemu "netdev_add" monitor command is implemented).