Now the number of actions is limited, as a practical matter, to the size
of the buffer that the kernel provides for Netlink dumps, which is usually
4096 bytes. A flow statistics entry must fit in a single one of these
buffers. Actions are 8 bytes each, so this is about 500 actions
considering overhead.
This changes the kernel switch implementation to use the kernel Netlink
"dump" interface to allow flow stats that don't fit in the socket buffer
to be dumped gradually as the caller drains the socket buffer.
One of the changes here is a bug fix for nla_unreserve. Because Netlink
attributes' lengths are rounded up to a multiple of 4 bytes, reducing
the length of the payload by N bytes doesn't necessarily reduce the
length of the skb by N bytes. Instead, we need to know the original
length and final length of the attribute. This means that using 'len'
as a difference in bytes doesn't really make sense, so this changes
'len' to be the new length of the attribute payload and renames the
function to nla_shrink to (IMO) better reflect what it is now doing.
Since we have to release the RCU read lock between calls to the dump
function, we need table iterators that persist across RCU epochs. One
way to do this would be to add new "iterator_save" and "iterator_restore"
functions, but this seemed like overkill since there would then be a
total of 5 iterator functions that have only one user (flow stats dumping).
Instead, this patch refactors table iteration into a single "iterate"
function that takes a callback. This simplifies the table iteration code
significantly.
This change also modifies dpctl to understand the new format of flow
stats.
This has two notable omissions. First, only at most 4k of flow statistics
are reported. Second, aggregate statistics are not yet supported. Both
of these are fairly easily fixable, just not fixed yet.
We want to allow multiple OpenFlow connections to a switch, so that
dpctl and other management tools can also connect to a switch that
is connecte to the controller. These tools will want to fetch the
information in the data_hello message, but currently this can only
be done by sending a control_hello message, which changes the
switch configuration state. So breaking the hello messages up into
multiple different messages, only some of which affect configuration
state, cures the problem.
Also, clean up the kernel datapath a bit, by adding helper functions
for allocating and resizing Generic Netlink messages that encapsulate
OpenFlow messages.
This is required on the Quanta platform, which needs to down a semaphore
inside the timeout implementation.
Also, add a 2.4 compatibility implementation of kthread so that both
2.4 and 2.6 can use the kthread API.
Ben Pfaff
Justin Pettit
Ben Pfaff
Martin Casado