[ovs-dev] Is there a way to have a flow perform tbl_lookup twice?

YIMIN CHEN ymchen.nbzj at gmail.com
Fri May 4 02:16:14 UTC 2012


Hi Ben,

My goal is to implement a decap action that would decap a packet with
external IP addresses, and then have the decapped packet, with
internal IP addresses, do a flow lookup again.

Can this be achieved using resubmit?

Thanks!
Yimin

On Fri, May 4, 2012 at 9:37 AM, Ben Pfaff <blp at nicira.com> wrote:
> You can read PORTING in the root of the tree.
>
> It would be best if you'd explain your goal first, instead of doing a
> deep dive into implementation details.
>
> On Fri, May 04, 2012 at 09:20:38AM +0800, YIMIN CHEN wrote:
>> Hi Ben,
>>
>> Thank you for the detailed information!  I read this part of the code,
>> and have some confusion. Can you please review the following to see if
>> my understanding of code is correct?
>>
>> 1) ofproto/ code is userspace code, and datapath/ code is the actual dp code.
>> 2) ofproto handles the rule insertion from control plane, and datapath
>> handles the actual flow lookup.
>> 3) resubmit is handled in userspace? I saw the resubmit logic
>> xlate_nicira_action() is in ofproto I didn't see find any code in
>> datapath that handles resubmit, not even in ovs-ofctl.c. Is
>> xlate_nicira_action() doing flow insertion with resubmit action or
>> actually performing the dp actions? I am confused.
>>
>> What is the relationship between ofproto userspace and the dp code?
>> what is the difference between xlate table action and odp action?
>>
>> I think I am very confused, if there is any documentation I can read
>> to understand this design better, would you please give me a pointer?
>>
>> Thanks!
>> Yimin
>>
>> On Thu, May 3, 2012 at 11:30 AM, Ben Pfaff <blp at nicira.com> wrote:
>> > It's documented in nicira-ext.h:
>> >
>> > /* Action structures for NXAST_RESUBMIT and NXAST_RESUBMIT_TABLE.
>> >  *
>> >  * These actions search one of the switch's flow tables:
>> >  *
>> >  *    - For NXAST_RESUBMIT_TABLE only, if the 'table' member is not 255, then
>> >  *      it specifies the table to search.
>> >  *
>> >  *    - Otherwise (for NXAST_RESUBMIT_TABLE with a 'table' of 255, or for
>> >  *      NXAST_RESUBMIT regardless of 'table'), it searches the current flow
>> >  *      table, that is, the OpenFlow flow table that contains the flow from
>> >  *      which this action was obtained.  If this action did not come from a
>> >  *      flow table (e.g. it came from an OFPT_PACKET_OUT message), then table 0
>> >  *      is the current table.
>> >  *
>> >  * The flow table lookup uses a flow that may be slightly modified from the
>> >  * original lookup:
>> >  *
>> >  *    - For NXAST_RESUBMIT, the 'in_port' member of struct nx_action_resubmit
>> >  *      is used as the flow's in_port.
>> >  *
>> >  *    - For NXAST_RESUBMIT_TABLE, if the 'in_port' member is not OFPP_IN_PORT,
>> >  *      then its value is used as the flow's in_port.  Otherwise, the original
>> >  *      in_port is used.
>> >  *
>> >  *    - If actions that modify the flow (e.g. OFPAT_SET_VLAN_VID) precede the
>> >  *      resubmit action, then the flow is updated with the new values.
>> >  *
>> >  * Following the lookup, the original in_port is restored.
>> >  *
>> >  * If the modified flow matched in the flow table, then the corresponding
>> >  * actions are executed.  Afterward, actions following the resubmit in the
>> >  * original set of actions, if any, are executed; any changes made to the
>> >  * packet (e.g. changes to VLAN) by secondary actions persist when those
>> >  * actions are executed, although the original in_port is restored.
>> >  *
>> >  * Resubmit actions may be used any number of times within a set of actions.
>> >  *
>> >  * Resubmit actions may nest to an implementation-defined depth.  Beyond this
>> >  * implementation-defined depth, further resubmit actions are simply ignored.
>> >  *
>> >  * NXAST_RESUBMIT ignores 'table' and 'pad'.  NXAST_RESUBMIT_TABLE requires
>> >  * 'pad' to be all-bits-zero.
>> >  *
>> >  * Open vSwitch 1.0.1 and earlier did not support recursion.  Open vSwitch
>> >  * before 1.2.90 did not support NXAST_RESUBMIT_TABLE.
>> >  */
>> > struct nx_action_resubmit {
>> >    ovs_be16 type;                  /* OFPAT_VENDOR. */
>> >    ovs_be16 len;                   /* Length is 16. */
>> >    ovs_be32 vendor;                /* NX_VENDOR_ID. */
>> >    ovs_be16 subtype;               /* NXAST_RESUBMIT. */
>> >    ovs_be16 in_port;               /* New in_port for checking flow table. */
>> >    uint8_t table;                  /* NXAST_RESUBMIT_TABLE: table to use. */
>> >    uint8_t pad[3];
>> > };
>> > OFP_ASSERT(sizeof(struct nx_action_resubmit) == 16);
>> >
>> > and in ovs-ofctl(8):
>> >
>> >              resubmit:port
>> >              resubmit([port],[table])
>> >                     Re-searches  this OpenFlow flow table (or the table whose
>> >                     number is specified by  table)  with  the  in_port  field
>> >                     replaced  by port (if port is specified) and executes the
>> >                     actions found, if any, in addition to any  other  actions
>> >                     in this flow entry.
>> >
>> >                     Recursive  resubmit actions are obeyed up to an implemen‐
>> >                     tation-defined maximum depth.   Open  vSwitch  1.0.1  and
>> >                     earlier  did  not  support recursion; Open vSwitch before
>> >                     1.2.90 did not support table.
>> >
>> >
>> > On Thu, May 03, 2012 at 09:54:08AM +0800, YIMIN CHEN wrote:
>> >> Hi Ben,
>> >>
>> >> Thank you for  your reply! I saw there is some code about resubmit
>> >> Nicira extension action, but that seems to be in userspace ofproto.c,
>> >> not in datapath, so I didn't know that is related. Could you help
>> >> clarify for me how does resubmit work?
>> >>
>> >>
>> >> Thanks!
>> >> Yimin
>> >>
>> >> On Wed, May 2, 2012 at 12:40 PM, Ben Pfaff <blp at nicira.com> wrote:
>> >> > On Wed, May 02, 2012 at 10:53:10AM +0800, YIMIN CHEN wrote:
>> >> >> I am looking at ovs dp code, and is looking at a correct way for a
>> >> >> flow to traverse the table twice. The goal is like this:
>> >> >>
>> >> >> flow lookup => tbl_lookup()
>> >> >> perform actions => execute_actions() which changes the packet
>> >> >> flow lookup using the new packet => tbl_lookup()
>> >> >> perform actions on the new packet => execute_actions.
>> >> >
>> >> > Do you want the "resubmit" Nicira extension action?



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