Re: [libvirt] [PATCH 2/2 (v3)] util: fallback to ioctl(SIOCBRDELBR) if netlink RTM_DELLINK fails

commit 09778e09 switched from using ioctl(SIOCBRDELBR) for bridge device deletion to using a netlink RTM_DELLINK message, which is the more modern way to delete a bridge (and also doesn't require the bridge to be ~IFF_UP to succeed). However, although older kernels (e.g. 2.6.32, in RHEL6/CentOS6) support deleting *some* link types with RTM_NEWLINK, they don't support deleting bridges, and there is no compile-time way to figure this out. This patch moves the body of the SIOCBRDELBR version of virNetDevBridgeDelete() into a static function, calls the new function from the original, and also calls the new function from the RTM_DELLINK version if the RTM_DELLINK message generates an EOPNOTSUPP error. Since RTM_DELLINK is done from the subordinate function virNetlinkDelLink, which is also called for other purposes (deleting a macvtap interface), a function pointer called "fallback" has been added to the arglist of virNetlinkDelLink() - if that arg != NULL, the provided function will be called when (and only when) RTM_DELLINK fails with EOPNOTSUPP. Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1252780 (part 2) --- Another idea for doing this I came up with during review of the others... src/util/virnetdevbridge.c | 41 ++++++++++++++++++++++++++++++----------- src/util/virnetdevmacvlan.c | 2 +- src/util/virnetlink.c | 13 +++++++++++-- src/util/virnetlink.h | 5 ++++- 4 files changed, 46 insertions(+), 15 deletions(-)