From: Ben Pfaff Date: Wed, 19 Sep 2012 22:38:29 +0000 (-0700) Subject: ofp-actions: Improve explanation of 'compat' member in struct ofpact. X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2ac3c572267c550302eee88d4f584b3694d88f88;p=openvswitch ofp-actions: Improve explanation of 'compat' member in struct ofpact. Suggested-by: Justin Pettit Signed-off-by: Ben Pfaff --- diff --git a/lib/ofp-actions.h b/lib/ofp-actions.h index 75ccc26e..46e2d79a 100644 --- a/lib/ofp-actions.h +++ b/lib/ofp-actions.h @@ -108,7 +108,31 @@ enum { * * Each action is a structure "struct ofpact_*" that begins with "struct * ofpact", usually followed by other data that describes the action. Actions - * are padded out to a multiple of OFPACT_ALIGNTO bytes in length. */ + * are padded out to a multiple of OFPACT_ALIGNTO bytes in length. + * + * The 'compat' member is special: + * + * - Most "struct ofpact"s correspond to one particular kind of OpenFlow + * action, at least in a given OpenFlow version. For example, + * OFPACT_SET_VLAN_VID corresponds to OFPAT10_SET_VLAN_VID in OpenFlow + * 1.0. + * + * For such actions, the 'compat' member is not meaningful and generally + * should be zero. + * + * - A few "struct ofpact"s correspond to multiple OpenFlow actions. For + * example, OFPACT_SET_TUNNEL can be NXAST_SET_TUNNEL or + * NXAST_SET_TUNNEL64. In these cases, if the "struct ofpact" originated + * from OpenFlow, then we want to make sure that, if it gets translated + * back to OpenFlow later, it is translated back to the same action type. + * (Otherwise, we'd violate the promise made in DESIGN, in the "Action + * Reproduction" section.) + * + * For such actions, the 'compat' member should be the original action + * type. (If the action didn't originate from OpenFlow, then setting + * 'compat' to zero should be fine: code to translate the ofpact to + * OpenFlow must tolerate this case.) + */ struct ofpact { enum ofpact_type type; /* OFPACT_*. */ enum ofputil_action_code compat; /* Original type when added, if any. */