Re: [libvirt] [PATCH 6/9] qemu: support unmanaged target tap dev for <interface type='ethernet'>

If managed='no', then the tap device must already exist, and setting of MAC address and online status (IFF_UP) is skipped. NB: we still set IFF_VNET_HDR and IFF_MULTI_QUEUE as appropriate, because those bits must be properly set in the TUNSETIFF we use to set the tap device name of the handle we've opened - if IFF_VNET_HDR has not been set and we set it the request will be honored even when running libvirtd unprivileged; if IFF_MULTI_QUEUE is requested to be different than how it was created, that will result in an error from the kernel. This means that you don't need to pay attention to IFF_VNET_HDR when creating the tap devices, but you *do* need to set IFF_MULTI_QUEUE if you're going to use multiple queues for your tap device. NB2: /dev/vhost-net normally has permissions 600, so it can't be opened by an unprivileged process. This would normally cause a warning message when using a virtio net device from an unprivileged libvirtd. I've found that setting the permissions for /dev/vhost-net permits unprivileged libvirtd to use vhost-net for virtio devices, but have no idea what sort of security implications that has. I haven't changed libvrit's code to avoid *attempting* to open /dev/vhost-net - if you are concerned about the security of opening up permissions of /dev/vhost-net (probably a good idea at least until we ask someone who knows about the code) then add <driver name='qemu'/> to the interface definition and you'll avoid the warning message. Note that virNetDevTapCreate() is the correct function to call in the case of an existing device, because the same ioctl() that creates a new tap device will also open an existing tap device. Resolves: https://bugzilla.redhat.com/1723367 (partially) Signed-off-by: Laine Stump <laine(a)redhat.com&gt; --- src/qemu/qemu_interface.c | 77 +++++++++++-------- src/qemu/qemu_process.c | 2 +- src/util/virnetdev.h | 2 +- .../net-eth-unmanaged-tap.args | 32 ++++++++ tests/qemuxml2argvmock.c | 16 +++- tests/qemuxml2argvtest.c | 1 + 6 files changed, 96 insertions(+), 34 deletions(-) create mode 100644 tests/qemuxml2argvdata/net-eth-unmanaged-tap.args