Re: [libvirt] [PATCHv3 4/4] util: set src_pid for virNetlinkCommand when appropriate

Until now, the nl_pid of the source address of every message sent by virNetlinkCommand has been set to the value of getpid(). Most of the time this doesn't matter, and in the one case where it does (communication with lldpad), it previously was the proper thing to do, because the netlink event service (which listens on a netlink socket for unsolicited messages from lldpad) coincidentally always happened to bind with a local nl_pid == getpid(). With the fix for: https://bugzilla.redhat.com/show_bug.cgi?id=816465 that particular nl_pid is now effectively a reserved value, so the netlink event service will always bind to something else (coincidentally "getpid() + (1 << 22)", but it really could be anything). The result is that communication between lldpad and libvirtd is broken (lldpad gets a "disconnected" error when it tries to send a directed message).

The solution to this problem cause by a solution, is to query the

netlink event service's nlhandle for its "local_port", and send that as the source nl_pid (but only when sending to lldpad, of course - in other cases we maintain the old behavior of sending getpid()). There are two cases where a message is being directed at lldpad - one in virNetDevLinkDump, and one in virNetDevVPortProfileOpSetLink. The case of virNetDevVPortProfileOpSetLink is simplest to explain - only if !nltarget_kernel, i.e. the message isn't targetted for the kernel, is the dst_pid set (by calling virNetDevVPortProfileGetLldpadPid()), so only in that case do we call virNetlinkEvenServiceLocalPid() to set src_pid.

For virNetDevLinkDump, it's a bit more complicated. The call to virNetDevVPortProfileGetLldpadPid() was effectively up one level (in virNetDevVPortProfileOpCommon), although obscured by an unnecessary passing of a function pointer. This patch removes the function pointer, and calls virNetDevVPortProfileGetLldpadPid() directly in virNetDevVPortProfileOpCommon - if it's doing this, it knows that it should also call virNetlinkEventServiceLocalPid() to set src_pid too; then it just passes src_pid and dst_pid down to virNetDevLinkDump. Since (src_pid == 0 && dst_pid == 0) implies that the kernel is the destination, there is no longer any need to send nltarget_kernel as an arg to virNetDevLinkDump, so it's been removed. The disparity between src_pid being int and dst_pid being uint32_t may be a bit disconcerting to some, but I didn't want to complicate virNetlinkEventServiceLocalPid() by having status returned separately from the value.