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

Fri May 4 17:05:12 UTC 2012

No.

On Fri, May 04, 2012 at 10:16:14AM +0800, YIMIN CHEN wrote:
> 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?