This builds on earlier work that implemented netdev object refcounting.
However, rather than requiring explicit create and destroy calls,
these operations are now performed automatically based on the referenece
count. This is important because in certain situations it is not
possible to know whether a netdev has already been created. A
workaround existed (which looked fairly similar to this paradigm) but
introduced it's own issues. This simplifies and unifies the API.
This change adds netdev_create() and netdev_destroy() functions to allow
the creation of network devices through the netdev library. Previously,
network devices had to already exist or be created on demand through
netdev_open(). This caused problems such as not being able to specify
TAP devices as ports in ovs-vswitchd, which this patch fixes.
This also lays the groundwork for adding GRE and VDE support.
An option to zero the TCP flags when querying flow stats was added
to the kernel datapath to support NetFlow active timeouts. This
adds that same support to the user datapath.
netdev_open() can always be used in place of netdev_open_tap(). The
former is going to be generalized to support pluggable network device
types, so it makes sense to use it everywhere.
To make the netdev code more portable, it needs to support returning error
codes from functions that don't have them. This commit changes
netdev_get_mtu() to return an error code and updates its caller.
(Currently netdev_get_mtu() won't ever return an error, but other future
implementations might.)
At startup, the vswitch needs to delete datapaths that are not configured
by the administrator. Until now this was done by knowing the possible
names of Linux datapaths. This commit cleans up by allowing each
datapath class to enumerate its existing datapaths and their names.
