[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]

Re: [libvirt PATCH 0/3] Eliminate old tap/macvtap teardown stomping on new tap setup



On 8/24/20 6:23 AM, Laine Stump wrote:
The problem and solution are very well described in patches 2 and 3,
but in short - because we (libvirt for macvtap, the kernel for tap)
always try to assign the lowest numbered names possible to macvtap and
tap devices, we sometimes create a new tap for a new guest using the
same name as an old tap for an old guest that is shutting down
simultaneous to setting up the new guest/tap. This can lead to the old
guest teardown stomping on the new guest setup.

These patches eliminate that problem by changing the strategy to do
our best to *not* reuse tap / macvtap device names, but instead use a
monotonically incrementing counter to name the devices.

One possibly undesirable side effect of this (and the other) patch is
that the longer a host is running without reboot, the higher the
numbers tap device names will get. While users are accustomed to
always seeing vnet0 and vnet1, they may be a bit surprised to now see
vnet39283 or macvtap735. It has been pointed out to me that the same
thing happened with PIDs a few years ago, and while it looked strange
at first, everyone is now accustomed to it.

Laine Stump (3):
   util: make locking versions of virNetDevMacVLan(Reserve|Release)Name()
   util: assign macvtap names using a monotonically increasing integer
   util: assign tap device names using a monotonically increasing integer

  src/libvirt_private.syms    |   1 +
  src/qemu/qemu_process.c     |  22 +++++++-
  src/util/virnetdevmacvlan.c | 109 +++++++++++++++++++++++++++---------
  src/util/virnetdevtap.c     |  79 +++++++++++++++++++++++++-
  src/util/virnetdevtap.h     |   4 ++
  5 files changed, 186 insertions(+), 29 deletions(-)


Reviewed-by: Michal Privoznik <mprivozn redhat com>

Michal


[Date Prev][Date Next]   [Thread Prev][Thread Next]   [Thread Index] [Date Index] [Author Index]