On Wed, Apr 13, 2016 at 05:10:24PM +0000, Zoltán Balogh wrote:
>
> Hi Ben,
>
> I found only the definition of ofp_packet_in structure in chapter A.4.1 that
> mentions table_id.
>
> /* Packet received on port (datapath -> controller). */
> struct ofp_packet_in {
> struct ofp_header header;
> uint32_t buffer_id; /* ID assigned by datapath. */
> uint16_t total_len; /* Full length of frame. */
> uint8_t reason; /* Reason packet is being sent (one of OFPR_*) */
> uint8_t table_id; /* ID of the table that was looked up */
> uint64_t cookie; /* Cookie of the flow entry that was looked up. */
> struct ofp_match match; /* Packet metadata. Variable size. */
> /* Followed by:
> * - Exactly 2 all-zero padding bytes, then
> * - An Ethernet frame whose length is inferred from header.length.
> * The padding bytes preceding the Ethernet frame ensure that the IP
> * header (if any) following the Ethernet header is 32-bit aligned.
> */
> //uint8_t pad[2]; /* Align to 64 bit + 16 bit */
> //uint8_t data[0]; /* Ethernet frame */
> };
> OFP_ASSERT(sizeof(struct ofp_packet_in) == 32);
>
> The comment says that table_id member is "the ID of the table that was looked
> up".
>
> I investigated the action translator code in ofproto-dpif-xlate.c. I think it
> would be easy to store the current table ID in a new member of current
> xlate_ctx structure when action translation through the flow-chain is ongoing
> and a write_actions(output) or a write_actions(group) action is processed.
> So this way, the ID of the last table in the flow-chain that contains
> write_actions(output) or write_actions(group) could be stored. That could be
> done in xlate_write_actions().
>
> Then later, when the current action set is processed and there is an output
> action in the set, then this stored table_id could be used as table_id of
> current context when translating an output action and output port is
> CONTROLLER. This should be performed in xlate_output_action().
>
> What do you think? If it's ok, I would create a patch.
The table lookup is far removed from the output. The output is caused
by a group, which is in turn caused by the action set, which is in turn
from an action found by a table lookup. It's not at all obvious to me
that the table lookup is relevant.
What do other OpenFlow switches do?
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