datapath: Add basic MPLS support to kernel

Allow datapath to recognize and extract MPLS labels into flow keys
and execute actions which push, pop, and set labels on packets.

Based heavily on work by Leo Alterman and Ravi K.

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

---

v2.3
* s/mpls_stack/mpls_bos/
  This is in keeping with the naming used in the OpenFlow 1.3 specification

v2.2
* Call skb_reset_mac_header() in skb_cb_set_mpls_stack()
  eth_hdr(skb) is non-NULL when called in skb_cb_set_mpls_stack().
* Add a call to skb_cb_set_mpls_stack() in ovs_packet_cmd_execute().
  I apologise that I have mislaid my notes on this but
  it avoids a kernel panic. I can investigate again if necessary.
* Use struct ovs_action_push_mpls instead of
  __be16 to decode OVS_ACTION_ATTR_PUSH_MPLS in validate_actions(). This is
  consistent with the data format for the attribute.
* Indentation fix in skb_cb_mpls_stack(). [cosmetic]

v2.1
* Manual rebase

Previous version(s) by Leo Alterman
nx-match: Do not check pre-requisites for load actions

There are (or at least will be) cases where this check can produce false
positives.  For example, a flow which matches a non-MPLS packet and then
applies an MPLS push action followed by an action to load the MPLS label.

I believe this is the same problem that was recently discussed in
relation to set-field. In that case my understanding is that consensus
was to omit the check and potentially revisit the problem later.

Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.2
* No change

v2.1
* Initial post
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: Isaku Yamahata <yamahata@valinux.co.jp>
Cc: Ravi K <rkerur@gmail.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

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