source/netmap: read one packet in its own function

NetmapReadPackets walked the slots of a single packet inline while also
driving the per ring iteration. Move the slot walk into
NetmapReadOnePacket so the ring loop only picks the next packet and the
slot handling can be changed on its own.

No functional change.

Ticket: #8777

src/source-netmap.c

@@ -705,6 +705,44 @@ static void NetmapProcessPacket(NetmapThreadVars *ntv, const struct nm_pkthdr *p
     (void)TmThreadsSlotProcessPkt(ntv->tv, ntv->slot, p);
 }
 
+/* read the packet at ring->cur into hdr and move the ring past the slots it
+ * used. a packet can be split over several slots, so walk on until the slot
+ * that has NS_MOREFRAG cleared. */
+static void NetmapReadOnePacket(struct netmap_ring *ring, struct nm_pkthdr *hdr)
+{
+    u_int i = ring->cur;
+    struct netmap_slot *slot = &ring->slot[i];
+    u_char *oldbuf;
+
+    hdr->slot = slot;
+    oldbuf = hdr->buf = (u_char *)NETMAP_BUF(ring, slot->buf_idx);
+    hdr->len = hdr->caplen = slot->len;
+
+    /* loop through the ring slots to get packet data */
+    while (slot->flags & NS_MOREFRAG) {
+        /* packet can be fragmented across multiple slots, */
+        /* so loop until we find the slot with the flag    */
+        /* cleared, signalling the end of the packet data. */
+        u_char *nbuf;
+        u_int oldlen = slot->len;
+        i = nm_ring_next(ring, i);
+        slot = &ring->slot[i];
+        hdr->len += slot->len;
+        nbuf = (u_char *)NETMAP_BUF(ring, slot->buf_idx);
+
+        if (oldbuf != NULL && nbuf - oldbuf == ring->nr_buf_size &&
+                oldlen == ring->nr_buf_size) {
+            hdr->caplen += slot->len;
+            oldbuf = nbuf;
+        } else {
+            oldbuf = NULL;
+        }
+    }
+
+    hdr->ts = ring->ts;
+    ring->head = ring->cur = nm_ring_next(ring, i);
+}
+
 /**
  * \brief Copy netmap rings data into Packet structures.
  * \param *d nmport_d (or nm_desc) netmap if structure.
@@ -733,45 +771,12 @@ static TmEcode NetmapReadPackets(struct nmport_d *d, int cnt, NetmapThreadVars *
 
         /* cycle through the non-empty ring slots to fetch their data */
         for (; !nm_ring_empty(ring) && cnt != got; got++) {
-            u_int idx, i;
-            u_char *oldbuf;
-            struct netmap_slot *slot;
-
             if (hdr.buf) { /* from previous round */
                 NetmapProcessPacket(ntv, &hdr);
             }
 
-            i = ring->cur;
-            slot = &ring->slot[i];
-            idx = slot->buf_idx;
             d->cur_rx_ring = cur_rx_ring;
-            hdr.slot = slot;
+            NetmapReadOnePacket(ring, &hdr);
-            oldbuf = hdr.buf = (u_char *)NETMAP_BUF(ring, idx);
-            hdr.len = hdr.caplen = slot->len;
-
-            /* loop through the ring slots to get packet data */
-            while (slot->flags & NS_MOREFRAG) {
-                /* packet can be fragmented across multiple slots, */
-                /* so loop until we find the slot with the flag    */
-                /* cleared, signalling the end of the packet data. */
-                u_char *nbuf;
-                u_int oldlen = slot->len;
-                i = nm_ring_next(ring, i);
-                slot = &ring->slot[i];
-                hdr.len += slot->len;
-                nbuf = (u_char *)NETMAP_BUF(ring, slot->buf_idx);
-
-                if (oldbuf != NULL && nbuf - oldbuf == ring->nr_buf_size &&
-                        oldlen == ring->nr_buf_size) {
-                    hdr.caplen += slot->len;
-                    oldbuf = nbuf;
-                } else {
-                    oldbuf = NULL;
-                }
-            }
-
-            hdr.ts = ring->ts;
-            ring->head = ring->cur = nm_ring_next(ring, i);
         }
     }