On 7/13/23 18:30, Laine Stump wrote: > When I implemented passt support in libvirt, I saw the --mac-addr > option on the passt commandline, immediately assumed that this was > used for setting the guest interface's mac address somewhere within > passt, and read no further. As a result, "--mac-addr" is always added > to the passt commandline, specifying the setting from > <mac addr='blah'/> in the guest's interface config. > > But as pointed out in this bugzilla comment: > > https://bugzilla.redhat.com/2184967#c8 > > That is *not at all* what passt's --mac-addr option does. Instead, it > is used to force the *remote* mac address for incoming traffic to a > specific value. So setting --mac-addr results in all traffic on the > interface having the same (the guest's) mac address for both source > and destination in all traffic. Surprisingly, this still works, so > nobody noticed it during testing. > > The proper thing is to not specify any mac address to passt - the > remote MAC addresses can and should remain untouched, and the local > MAC address will end up being known to passt and beyond just by the > guest sending out packets with that MAC address. > > Reported-by: Laszlo Ersek <lersek@xxxxxxxxxx> > Signed-off-by: Laine Stump <laine@xxxxxxxxxx> > --- > src/qemu/qemu_passt.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/src/qemu/qemu_passt.c b/src/qemu/qemu_passt.c > index 3679bf75fc..d36856e92e 100644 > --- a/src/qemu/qemu_passt.c > +++ b/src/qemu/qemu_passt.c > @@ -176,7 +176,6 @@ qemuPasstStart(virDomainObj *vm, > g_autofree char *passtSocketName = qemuPasstCreateSocketPath(vm, net); > g_autoptr(virCommand) cmd = NULL; > g_autofree char *pidfile = qemuPasstCreatePidFilename(vm, net); > - char macaddr[VIR_MAC_STRING_BUFLEN]; > bool needUnlink = false; > size_t i; > > @@ -187,7 +186,6 @@ qemuPasstStart(virDomainObj *vm, > virCommandAddArgList(cmd, > "--one-off", > "--socket", passtSocketName, > - "--mac-addr", virMacAddrFormat(&net->mac, macaddr), > "--pid", pidfile, > NULL); > I've been thinking more about this. It is certainly an improvement. Per my reading of the passt manual, "--mac-addr" and "--gateway" should either be specified together, or none of them should be specified; and this change satisfies that condition. Reviewed-by: Laszlo Ersek <lersek@xxxxxxxxxx>
