User-Space MPLS actions and matches

This patch implements use-space datapath and non-datapath code
to match and use the datapath API set out in Leo Alterman's patch
"user-space datapath: Add basic MPLS support to kernel".

The resulting MPLS implementation supports:
* Pushing a single MPLS label
* Poping a single MPLS label
* Modifying an MPLS lable using set-field or load actions
  that act on the label value, tc and bos bit.
* There is no support for manipulating the TTL
  this is considered future work.

The single-level push pop limitation is implemented by processing
push, pop and set-field/load actions in order and discarding information
that would require multiple levels of push/pop to be supported.

e.g.
   push,push -> the first push is discarded
   pop,pop -> the first pop is discarded

This patch is based heavily on work by Ravi K.

Cc: Ravi K <rkerur@gmail.com>
Reviewed-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.6
* Non-trivial rebase
* Track dl_type changes in ofpact_check__() and ofpacts_check()
  to allow pre-requisite checks to work correctly in the presence
  of mpls_push and mpls_pop actions.
* Do not modify datapath.
  Accordingly, the changes suggested by Yamahata-san which were
  incorporated in v2.5 to the datapath patch "datapath: Add basic MPLS
  support to kernel"

v2.5
* As suggested by Yamahata-san
  - Do not guard against label == 0 for
    OVS_ACTION_ATTR_SET_MPLS in validate_actions().
    A label of 0 is valid
  - Remove comment stipulating that if
    the top_label element of struct sw_flow_key is 0 then
    there is no MPLS label. An MPLS label of 0 is valid
    and the correct check if ethertype is
    ntohs(ETH_TYPE_MPLS) or ntohs(ETH_TYPE_MPLS_MCAST)
* Update tests for TTL fix provided by
  "flow: Set ip_ttl in flow_compose()"
* Do not initialise ih and ih6 in flow_extract()
  until after calling parse_mpls() and parse_remaining_mpls()
  as those functions may change the value of b.data.
* Do not add spurious debug code to execute_controller_action()
* Do not reset packet->l3 in pop_mpls(),
  it is already the correct value

v2.4
* Make use of set_mpls_lse_*() in flow_set_mpls_*()

v2.3
* As suggested by Ben Pfaff
  - Remove noise-only change from execute_set_action()
  - Guard against running off the end of packets in parse_remaining_mpls()
  - Ensure there is sufficient data before reading IP header in flow_extract()
  - Omit formating mpls in flow_format if there is no MPLS header
  - Fix spelling errors in parse_mpls_onward()
  - Fix coding style in flow_compose()
  - Use inner_dl_type where possible in flow_compose()
  - Correct bitwise logic in mpls_set_any_*()
  - Do not define NXM constants for MPLS as the OXM constants may be used
    with NXM.
  - Disable writing of MPLS BOS by setting 'writable' to false for
    OXM_OF_MPLS_BOS.
  - Rename format_mpls_lse_values() as mpls_lse_from_components()
    as it is not a format helper.
  - Fix coding style in mpls_lse_from_components()
  - Evaluate check_expectations() outside of MAX
    as MAX evaluates its arguments more than once.
  - Remove noise-change from parse_8021q_onward()
  - Remove noise-change from commit_set_nw_action()
  - Move action checking logic from ofpact_check__() to
    ofpact_from_openflow11() and ofpact_from_nxast()
  - Remove noise-change from ofpact_format
  - Fix typos in ofpact_push
  - Correct comment in ofputil_usable_protocols()
    MPLS BoS bit match was added in OpenFlow 1.3
  - Add a helper function to return the pointer to the eth_type of a packet
    and use this to vastly simplify set_ethertype() and get_ethertype()
  - Correct size logic in get_label_ttl_and_tc() using
    ofpbuf_tail(packet) - packet->l3
  - Refactor get_label_ttl_and_tc to return an MPLS tag
    rather than broken out TTL, TC and value. Also,
    rename as get_lse()
  - Remove set_new_mpls_lse and open code its logic.
  - Correct code style of if block in pop_mpls()
  - Do not add unused IP6_TC()
  - Do not make spurious change to subfacet_should_install()
  - Remove assert() from execute_controller_action() as it
    is not obviously useful.
  - Make use of set_mpls_lse_values() in compose_mpls_push_action()
  - Do not make spurious change for REG_LOAD in do_xlate_actions()
  - Do not at test-mpls, it is not used
* As suggested by Yamahata-san
  - Use MPLS_xxx_MASK >> MPLS_xxx_SHIFT in mf_is_value_valid() and
  - Track MPLS stack depth and use it to determine if the MPLS label should
    be pushed, popped or modified
  - No longer use 0 as a special MPLS LSE value
* s/mpls_stack/mpls_bos/
  This is in keeping with the naming used in the OpenFlow 1.3 specification
* Fold user-space datapath back into this patch,
  there seem to be mutual dependencies.
* Remove stray structure definitions: nx_action_mpls_label,
  nx_action_mpls_tc, nx_action_mpls_ttl
* Remove check_expectations_mpls() and use check_expectations() directly
  instead.  The logic of check_expectations_mpls() is not relevant to the
  current incantation of the patch-set as it includes support for MPLS
  matches in the datapath.
* Removed unused TTL manipulation code

v2.2
* Manual Rebase

v2.1
* Reinstate user-space datapath changes
* Update to use datapath API set out in Leo Alterman's
  kernel datapath patch "datapath: Add basic MPLS support to kernel"
* Do not add:
  - OFPAT11_COPY_TTL_OUT/NXAST_COPY_TTL_OUT,
  - OFPAT11_COPY_TTL_IN/NXAST_COPY_TTL_IN.
  - OFPAT11_DEC_MPLS_TTL/NXAST_DEC_MPLS_TTL
  Add support for these later. Jesse Gross has commented that "It is envisaged
  this will be done "using set and some form of resubmit if necessary (as we do
  for IP)"
* Do not add:
  - OFPAT11_SET_MPLS_LABEL/NXAST_SET_MPLS_LABEL
  - OFPAT11_SET_MPLS_TC/NXAST_SET_MPLS_TC
  - OFPAT11_SET_MPLS_TTL/NXAST_SET_MPLS_TTL
  These may be handled by load/set-field actions.
* Remove inner_mpls_lse from struct flow
  - The new objective is to only support one layer of MPLS labels at this time
* Rearrange action handling logic (again):
  - Logic to commit commit all MPLS actions is now in commit_mpls_action()
    which is called by commit_odp_actions().
  - Logic to compose push actions is in compose_mpls_push_action()
  - Logic to compose pop actions is in compose_mpls_pop_action()
  - There is no logic to compose mpls_set actions,
    compose_mpls_lse_action() has been removed.
  - This seems consistent with the handling of other actions.
* Correct mpls formatting in format_odp_action(),
  an error introduced by me.
* s/commit_mpls_/compose_mpls_/
  This seems to be more in keeping with the current naming convention.
* s/mpls_stack/mpls_bos/i
  This seems to be more in keeping with the wording in
  the OpenFlow 1.3 specification

v2.0
* Rebase to current master
  - First by Isaku Yamahata in July;
  - Then by me more recently.
* Remove datapath changes
  - This is intended to provide a first step for
    merging MPLS. The uers-space chagges seem
    largely uncontroversial while the datapath
    changes were incomplete with respect to
    agreement on the implementation for TTL actions
    and offloads.
* Correct dec_mpls_ttl to decrement TTL by 1 rather than 2
  - Fix by Isaku Yamahata
* Bug fixes to allow test suite to pass
* Make sparse clean
* Introduce encap_dl_type element to struct flow.
  This is used to store the dl_type of the encapsulated packet
  and is used by odp_flow_key_to_flow() and flow_compose() to
  allow eth_from_packet_or_flow() to be able to handle
  e.g. an MPLS encoded IPv4 packet.
* update packet.c:get_label_ttl_and_tc() to treat unknown eth type
  asn an error.
* Remove datapath changes

Previous Revisions by Ravi K
Add support for dec_mpls_ttl action

This adds support for the OpenFlow 1.1+ dec_mpls_ttl action.
And also adds an NX dec_mpls_ttl action.

The handling of the TTL modification is entirely handled in userspace.

Reviewed-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.6
* Rebase

v2.5
* First post
Add support for set_mpls_ttl action

This adds support for the OpenFlow 1.1+ set_mpls_ttl action.
And also adds an NX set_mpls_ttl action.

The handling of the TTL modification is entirely handled in userspace.

Reviewed-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.6
* Rebase

v2.5
* First post
Add support for copy_ttl_out action

This adds support for the OpenFlow 1.1+ copy_ttl_out action.
And also adds an NX copy_ttl_out action.

The implementation does not support copying in the case where the outermost
header is IP as it is unclear to me that Open vSwtich has a notion of an
inner IP header to copy the TLL from.

The handling of the TTL modification is entirely handled in userspace.

Reviewed-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.6
* Non-trivial rebase

v2.5
* First post
Add support for copy_ttl_in action

This adds support for the OpenFlow 1.1+ copy_ttl_in action.
And also adds an NX copy_ttl_out action.

The implementation does not support copying in the case where the outermost
header is IP as it is unclear to me that Open vSwtich has a notion of an
inner IP header to copy the TLL from.

The implementation does not support copying in the case where the
outermost and next-to-otermost header is MPLS due to limitations
in the current MPLS implementation which only supports modifying
the outermost MPLS header.

The handling of the TTL modification is entirely handled in userspace.

Reviewed-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.7
* Correct typo in changelog

v2.6
* Non-trivial rebase

v2.5
* First post