Changeset 0277ab8

Timestamp:

08/05/15 13:50:02 (6 years ago)

Author:

Shane Alcock <salcock@…>

Branches:

4.0.1-hotfixes, cachetimestamps, develop, dpdk-ndag, etsilive, libtrace4, master, ndag_format, pfring, rc-4.0.1, rc-4.0.2, rc-4.0.3, rc-4.0.4, ringdecrementfix, ringperformance, ringtimestampfixes

Children:

d280f48

Parents:

84d137d

Message:

Completed improvement of trace_strip_packet()

• Removed the trace_copy_packet() if the packet is not totally owned by libtrace. I think we can get away without it and we really don't want the performance hit when dealing with live captures.
• Replaced call to trace_get_layer3 with the old header parsing code from the previous version of trace_strip_packet(). The overhead of calling trace_get_layer3 was outweighing the performance gain from the change in memmove strategy.
• Removed ability to selectively strip VLAN or MPLS headers only -- this was not that useful and supporting it would make the code much more complex.
• Updated trace_get_layer3 to use the cached layer 2 header if available rather than making a call to trace_get_layer2 and getting it from there. This saves us a bit of function call overhead.
• Make sure we reset the layer 2 cached info if we shift the Ethernet header.
• Strip PPPoE in addition to MPLS and VLAN.

Location:

lib

Files:

• libtrace.h.in (modified) (2 diffs)
• protocols_l2.c (modified) (5 diffs)
• protocols_l3.c (modified) (1 diff)

lib/libtrace.h.in

@@ -1603 +1603 @@
 void *trace_get_link(const libtrace_packet_t *packet);
 
-/**
- * Supported masks for stripping headers from packets.
- */ 
-enum {
-        TRACE_STRIP_VLAN = 0x01, /**< Strip 802.1Q (VLAN tag) headers */
-        TRACE_STRIP_MPLS = 0x02  /**< Strip MPLS headers */
-};
-
-/** Strips certain headers from a given packet.
+/** Strips layer 2.5 headers from a given packet.
  * @param packet        The packet to strip headers from.
- * @param stripopts     A mask to indicate which headers should be stripped.
- * If multiple header types are to be stripped, these should be ORed together
- * to create the full mask. A mask of zero will strip all strippable headers.
  *
  * @return The packet with the requested headers removed (if they were
@@ -1636 +1625 @@
  * the original packet being returned unmodified.
  *
- * @note Depending on the input source, this function may need to copy the
- * original packet to be able to safely modify the contents. This may have
- * a major impact on performance so avoid stripping packets unless absolutely
- * necessary.
- */
-DLLEXPORT libtrace_packet_t *trace_strip_packet(libtrace_packet_t *packet,
-                int stripopts);
+ */
+DLLEXPORT libtrace_packet_t *trace_strip_packet(libtrace_packet_t *packet);
 
 /** Get a pointer to the IPv4 header (if any) for a given packet

lib/protocols_l2.c

@@ -101 +101 @@
 }
 
-libtrace_packet_t *trace_strip_packet(libtrace_packet_t *packet, 
-                int stripopts) {
+libtrace_packet_t *trace_strip_packet(libtrace_packet_t *packet) {
 
         libtrace_ether_t *ethernet;
@@ -108 +107 @@
         uint16_t ethertype;
         uint32_t remaining;
-        libtrace_packet_t *copy;
-        char *payload;
+        char *nextpayload;
         uint16_t finalethertype = 0;
         uint16_t caplen, removed = 0;
@@ -130 +128 @@
         }
 
-        /* Copy the packet as we need to be sure that the packet
-         * payload is contiguous. This won't be guaranteed for live
-         * formats, for instance.
+        if (remaining <= sizeof(libtrace_ether_t))
+                return packet;
+
+        caplen = trace_get_capture_length(packet);
+        ethertype = ntohs(ethernet->ether_type);
+        dest = ((char *)ethernet) + sizeof(libtrace_ether_t);
+        nextpayload = dest;
+        remaining -= sizeof(libtrace_ether_t);
+
+        /* I'd normally use trace_get_layer3 here, but it works out faster
+         * to do it this way (mostly less function call overhead).
+         *
+         * XXX This approach is going to just strip everything between the
+         * Ethernet and IP headers -- is there a use case where someone
+         * might want to selectively strip headers?
          */
-        if (packet->buf_control == TRACE_CTRL_EXTERNAL) {
-                copy = trace_copy_packet(packet);
-                trace_destroy_packet(packet);
-                packet = copy;
-
-                /* Re-grab the ethernet header from the copy */
-                ethernet = (libtrace_ether_t *)trace_get_layer2(packet,
-                        &linktype, &remaining);
-
-        }
-
-        payload = (char *)trace_get_layer3(packet, &ethertype, &remaining);
-        caplen = trace_get_capture_length(packet);
-        dest = ((char *)ethernet) + sizeof(libtrace_ether_t);
-
-        if (payload == NULL || remaining == 0)
-                return packet;
-
-        if (payload == dest)
-                return packet;
-
-        ethernet->ether_type = ntohs(ethertype);
-        trace_set_capture_length(packet, caplen - (payload - dest));
-        memmove(payload - (dest - (char *)packet->payload), packet->payload, 
-                        (dest - (char *)packet->payload));
-        packet->payload = payload - (dest - (char *)packet->payload);
-        packet->l2_header = NULL;
-        packet->l3_header = NULL;
-        packet->l4_header = NULL;
-        
-        /*
-        payload = trace_get_payload_from_layer2(ethernet, linktype,
-                        &ethertype, &remaining);
-
         while (!done) {
 
-                if (payload == NULL || remaining == 0)
+                if (nextpayload == NULL || remaining == 0)
                         break;
 
@@ -177 +153 @@
 
                 case TRACE_ETHERTYPE_8021Q:
-                        payload = (void *)trace_get_payload_from_vlan(payload,
+                        nextpayload = (char *)trace_get_payload_from_vlan(
+                                        nextpayload,
                                         &ethertype, &remaining);
-                        if (stripopts == 0 || (stripopts & TRACE_STRIP_VLAN))
-                        {
-                                removed += (oldrem - remaining);
-                                //memmove(dest, payload, remaining);
-                                //payload = dest;
-
-                        } else {
-                                if (finalethertype == 0) {
-                                        finalethertype = TRACE_ETHERTYPE_8021Q;
-                                }
-                                //dest = payload;
-                        }
+                        removed += (oldrem - remaining);
                         break;
 
                 case TRACE_ETHERTYPE_MPLS:
-                        payload = (void *)trace_get_payload_from_mpls(payload,
+                        nextpayload = (char *)trace_get_payload_from_mpls(
+                                        nextpayload,
                                         &ethertype, &remaining);
-                        if (stripopts == 0 || (stripopts & TRACE_STRIP_MPLS))
-                        {
-                                removed += (oldrem - remaining);
-                                //memmove(dest, payload, remaining);
-                                //payload = dest;
-
-                        } else {
-                                if (finalethertype == 0) {
-                                        finalethertype = TRACE_ETHERTYPE_MPLS;
-                                }
-                                //dest = payload;
-                        }
+                        removed += (oldrem - remaining);
+                        break;
+                case TRACE_ETHERTYPE_PPP_SES:
+                        nextpayload = (char *)trace_get_payload_from_pppoe(
+                                        nextpayload,
+                                        &ethertype, &remaining);
+                        removed += (oldrem - remaining);
                         break;
 
@@ -219 +181 @@
                 }
         }
-                */
-        /* Update the preceding headers to match the new packet contents */
+
+        if (nextpayload != NULL) {
+
+                ethernet->ether_type = ntohs(finalethertype);
+                trace_set_capture_length(packet, caplen - removed);
+                memmove(nextpayload - (dest - (char *)packet->payload), 
+                        packet->payload, 
+                        (dest - (char *)packet->payload));
+                packet->payload = nextpayload - (dest - (char *)packet->payload);
+                packet->l2_header = NULL;
+                packet->link_type = finalethertype;
+        }
+        
         return packet;
 

lib/protocols_l3.c

@@ -245 +245 @@
         }
 
-        link = trace_get_layer2(packet,&linktype,remaining);
+        if (packet->l2_header) {
+                link = packet->l2_header;
+                linktype = packet->link_type;
+                *remaining = packet->l2_remaining;
+        } else {
+                link = trace_get_layer2(packet,&linktype,remaining);
+        }
         iphdr = trace_get_payload_from_layer2(
                         link,