[libvirt] [PATCH 4/4] util: use netlink to create bridge devices

[John Ferlan]

On 03/23/2015 03:43 PM, Laine Stump wrote:
> Just as it is possible to delete a bridge device with the netlink
> RTM_DELLINK message, one can be created with the RTM_NEWLINK
> message. Because of differences in the format of the message, it's not
> as straightforward as with virNetlinkDelLink() to create a single
> utility function that can be used to create any type of interface, so
> the new netlink version of virNetDevBridgeCreate() does its own
> construction of the netlink message and calls virNetlinkCommand()
> itself.
> 
> This doesn't provide any extra functionality, just provides symmetry
> with the previous commit.
> 
> NB: We *could* alter the API of virNetDevBridgeCreate() to take a MAC
> address, and directly program that mac address into the bridge (by
> adding an IFLA_ADDRESS attribute, as is done in
> virNetDevMacVLanCreate()) rather than separately creating the "dummy
> tap" (e.g. virbr0-nic) to maintain a fixed mac address on the bridge,
> but the commit history of virnetdevbridge.c shows that the presence of
> this dummy tap is essential in some older versions of the kernel
> (between 2.6.39 and 3.1 or 3.2, possibly?) to proper operation of IPv6
> DAD, and I don't want to take the chance of breaking something that I
> don't have the time/setup to test (my RHEL6 box is at kernel
> 2.6.32-544, and the next lowest kernel I have is 3.17)
> ---
>  src/util/virnetdevbridge.c | 78 +++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 77 insertions(+), 1 deletion(-)
> 
What's here seems reasonable - I don't have "history" on my side to
answer the older versions of the kernel query...

One other difference between this and virNetDevMacVLanCreate is the
error path that handles *retry if the name is already in use...  Whether
that's a worthy addition here or not is your call...

ACK -

John