[PATCH v2 2/2] hw/net: Added basic IPv6 fragmentation

[andrew@daynix.com]

From: Andrew <andrew@daynix.com>

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1708065
Overall, there was an issue that big frames of IPv6 doesn't sent.
With network backend with 'virtual header' - there was an issue
in 'plen' field. Overall, during TSO, 'plen' would be changed,
but with 'vheader' this field should be set to the size of the
payload itself instead of '0'.
For software offload - there is added basic IPv6 fragmentation.
The basic IPv6 fragmentation - adding 'frag' extension to
the packet, overall shares some logic with IPv4. It works,
but there are still issues with a combination of
extensions - in the future, it would require refactoring
work to implement workflow with IPv6 and extension.
e1000e driver doesn't set the 'plen' field for IPv6 for big packets
if TSO is enabled. "Jumbo option" isn't added yet, until
qemu supports packets greater than 64K.

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
---
 hw/net/net_tx_pkt.c | 30 ++++++++++++--
 hw/net/net_tx_pkt.h | 14 +++++++
 include/net/eth.h   | 15 +++++--
 net/eth.c           | 99 ++++++++++++++++++++++++++++++++++++++++++---
 4 files changed, 147 insertions(+), 11 deletions(-)

diff --git a/hw/net/net_tx_pkt.c b/hw/net/net_tx_pkt.c
index 331c73cfc0..74044c6618 100644
--- a/hw/net/net_tx_pkt.c
+++ b/hw/net/net_tx_pkt.c
@@ -589,10 +589,11 @@ static bool net_tx_pkt_do_sw_fragmentation(struct NetTxPkt *pkt,
 
         more_frags = (fragment_offset + fragment_len < pkt->payload_len);
 
-        eth_setup_ip4_fragmentation(l2_iov_base, l2_iov_len, l3_iov_base,
-            l3_iov_len, fragment_len, fragment_offset, more_frags);
+        eth_setup_ip_fragmentation(l2_iov_base, l2_iov_len, l3_iov_base,
+            &l3_iov_len, ETH_MAX_IP_DGRAM_LEN,
+            fragment_len, fragment_offset, more_frags);
 
-        eth_fix_ip4_checksum(l3_iov_base, l3_iov_len);
+        fragment[NET_TX_PKT_FRAGMENT_L3_HDR_POS].iov_len = l3_iov_len;
 
         net_tx_pkt_sendv(pkt, nc, fragment, dst_idx);
 
@@ -626,6 +627,7 @@ bool net_tx_pkt_send(struct NetTxPkt *pkt, NetClientState *nc)
 
     if (pkt->has_virt_hdr ||
         pkt->virt_hdr.gso_type == VIRTIO_NET_HDR_GSO_NONE) {
+        net_tx_pkt_fix_ip6_payload_len(pkt);
         net_tx_pkt_sendv(pkt, nc, pkt->vec,
             pkt->payload_frags + NET_TX_PKT_PL_START_FRAG);
         return true;
@@ -644,3 +646,25 @@ bool net_tx_pkt_send_loopback(struct NetTxPkt *pkt, NetClientState *nc)
 
     return res;
 }
+
+void net_tx_pkt_fix_ip6_payload_len(struct NetTxPkt *pkt)
+{
+    struct iovec *l2 = &pkt->vec[NET_TX_PKT_L2HDR_FRAG];
+    if (eth_get_l3_proto(l2, 1, l2->iov_len) == ETH_P_IPV6) {
+        struct ip6_header *ip6 = (struct ip6_header *) pkt->l3_hdr;
+        /*
+         * TODO: if qemu would support >64K packets - add jumbo option check
+         * something like that:
+         * 'if (ip6->ip6_plen == 0 && !has_jumbo_option(ip6)) {'
+         */
+        if (ip6->ip6_plen == 0) {
+            if (pkt->payload_len <= ETH_MAX_IP_DGRAM_LEN) {
+                ip6->ip6_plen = htons(pkt->payload_len);
+            }
+            /*
+             * TODO: if qemu would support >64K packets
+             * add jumbo option for packets greater then 65,535 bytes
+             */
+        }
+    }
+}
diff --git a/hw/net/net_tx_pkt.h b/hw/net/net_tx_pkt.h
index 212ecc62fc..4ec8bbe9bd 100644
--- a/hw/net/net_tx_pkt.h
+++ b/hw/net/net_tx_pkt.h
@@ -187,4 +187,18 @@ bool net_tx_pkt_parse(struct NetTxPkt *pkt);
 */
 bool net_tx_pkt_has_fragments(struct NetTxPkt *pkt);
 
+/**
+ * Fix IPv6 'plen' field.
+ * If ipv6 payload length field is 0 - then there should be Hop-by-Hop
+ * option for packets greater than 65,535.
+ * For packets with a payload less than 65,535: fix 'plen' field.
+ * For backends with vheader, we need just one packet with proper
+ * payload size. For now, qemu drops every packet with size greater 64K
+ * (see net_tx_pkt_send()) so, there is no reason to add jumbo option to ip6
+ * hop-by-hop extension if it's missed
+ *
+ * @pkt            packet
+ */
+void net_tx_pkt_fix_ip6_payload_len(struct NetTxPkt *pkt);
+
 #endif
diff --git a/include/net/eth.h b/include/net/eth.h
index 7f45c678e7..05c75ac9fc 100644
--- a/include/net/eth.h
+++ b/include/net/eth.h
@@ -139,6 +139,14 @@ struct ip6_ext_hdr_routing {
     uint8_t     rsvd[4];
 };
 
+struct ip6_ext_hdr_fragment {
+    uint8_t     nxt;
+    uint8_t     res0;
+    uint16_t    off;
+    uint32_t    id;
+};
+
+
 struct ip6_option_hdr {
 #define IP6_OPT_PAD1   (0x00)
 #define IP6_OPT_HOME   (0xC9)
@@ -186,6 +194,7 @@ struct tcp_hdr {
 
 #define ip6_nxt      ip6_ctlun.ip6_un1.ip6_un1_nxt
 #define ip6_ecn_acc  ip6_ctlun.ip6_un3.ip6_un3_ecn
+#define ip6_plen     ip6_ctlun.ip6_un1.ip6_un1_plen
 
 #define PKT_GET_ETH_HDR(p)        \
     ((struct eth_header *)(p))
@@ -398,9 +407,9 @@ void eth_get_protocols(const struct iovec *iov, int iovcnt,
                        eth_ip4_hdr_info *ip4hdr_info,
                        eth_l4_hdr_info  *l4hdr_info);
 
-void eth_setup_ip4_fragmentation(const void *l2hdr, size_t l2hdr_len,
-                                 void *l3hdr, size_t l3hdr_len,
-                                 size_t l3payload_len,
+void eth_setup_ip_fragmentation(const void *l2hdr, size_t l2hdr_len,
+                                 void *l3hdr, size_t *l3hdr_len,
+                                 size_t l3hdr_max_len, size_t l3payload_len,
                                  size_t frag_offset, bool more_frags);
 
 void
diff --git a/net/eth.c b/net/eth.c
index 0c1d413ee2..067111526d 100644
--- a/net/eth.c
+++ b/net/eth.c
@@ -314,10 +314,65 @@ eth_strip_vlan_ex(const struct iovec *iov, int iovcnt, size_t iovoff,
     return 0;
 }
 
+static bool eth_is_ip6_extension_header_type(uint8_t hdr_type);
+
+static void *eth_ip6_find_ext(struct ip6_header *ip6, uint8_t ext_type)
+{
+    uint8_t curr_ext_hdr_type = ip6->ip6_nxt;
+    struct ip6_ext_hdr *ext_hdr = (struct ip6_ext_hdr *)(ip6 + 1);
+    for (; eth_is_ip6_extension_header_type(curr_ext_hdr_type);) {
+        if (curr_ext_hdr_type == ext_type) {
+            return ext_hdr;
+        }
+        curr_ext_hdr_type = ext_hdr->ip6r_nxt;
+        ext_hdr = (struct ip6_ext_hdr *)(((uint8_t *)ext_hdr)
+                + (ext_hdr->ip6r_len + 1) * IP6_EXT_GRANULARITY);
+    }
+
+    return NULL;
+}
+
+/*
+ * To add an extension - there is should be
+ * enough memory 'behind' the ip6 header.
+ */
+static void *eth_ip6_add_ext_nonsafe(struct ip6_header *ip6, uint8_t ext_type)
+{
+    uint8_t curr_ext_hdr_type = ip6->ip6_nxt;
+    struct ip6_ext_hdr *ext_hdr = (struct ip6_ext_hdr *)(ip6 + 1);
+    struct ip6_ext_hdr *ext_hdr_prev = NULL;
+
+    if (!eth_is_ip6_extension_header_type(curr_ext_hdr_type)) {
+        ext_hdr->ip6r_nxt = ip6->ip6_nxt;
+        ip6->ip6_nxt = ext_type;
+        return ext_hdr;
+    }
+
+    ext_hdr_prev = ext_hdr;
+    curr_ext_hdr_type = ext_hdr->ip6r_nxt;
+    ext_hdr = (struct ip6_ext_hdr *)(((uint8_t *)ext_hdr)
+            + (ext_hdr->ip6r_len + 1) * IP6_EXT_GRANULARITY);
+
+    for (; eth_is_ip6_extension_header_type(curr_ext_hdr_type);) {
+        ext_hdr_prev = ext_hdr;
+        curr_ext_hdr_type = ext_hdr->ip6r_nxt;
+        ext_hdr = (struct ip6_ext_hdr *)(((uint8_t *)ext_hdr)
+                + (ext_hdr->ip6r_len + 1) * IP6_EXT_GRANULARITY);
+    }
+
+    ext_hdr->ip6r_nxt = ext_hdr_prev->ip6r_nxt;
+    ext_hdr_prev->ip6r_nxt = ext_type;
+
+    return ext_hdr;
+}
+
+/* When IP6_FRAGMENT added, first 'id' would be 0x71656d75 */
+static const uint32_t s_first_fragment_identificator = 0x71656d75; /* 'qemu' */
+
 void
-eth_setup_ip4_fragmentation(const void *l2hdr, size_t l2hdr_len,
-                            void *l3hdr, size_t l3hdr_len,
-                            size_t l3payload_len,
+eth_setup_ip_fragmentation(const void *l2hdr, size_t l2hdr_len,
+                            void *l3hdr, size_t *l3hdr_len,
+                            size_t l3hdr_max_len, size_t l3payload_len,
                             size_t frag_offset, bool more_frags)
 {
     const struct iovec l2vec = {
@@ -325,7 +380,9 @@ eth_setup_ip4_fragmentation(const void *l2hdr, size_t l2hdr_len,
         .iov_len = l2hdr_len
     };
 
-    if (eth_get_l3_proto(&l2vec, 1, l2hdr_len) == ETH_P_IP) {
+    uint16_t l3_proto = eth_get_l3_proto(&l2vec, 1, l2hdr_len);
+
+    if (l3_proto == ETH_P_IP) {
         uint16_t orig_flags;
         struct ip_header *iphdr = (struct ip_header *) l3hdr;
         uint16_t frag_off_units = frag_offset / IP_FRAG_UNIT_SIZE;
@@ -337,7 +394,39 @@ eth_setup_ip4_fragmentation(const void *l2hdr, size_t l2hdr_len,
         orig_flags = be16_to_cpu(iphdr->ip_off) & ~(IP_OFFMASK|IP_MF);
         new_ip_off = frag_off_units | orig_flags  | (more_frags ? IP_MF : 0);
         iphdr->ip_off = cpu_to_be16(new_ip_off);
-        iphdr->ip_len = cpu_to_be16(l3payload_len + l3hdr_len);
+        iphdr->ip_len = cpu_to_be16(l3payload_len + *l3hdr_len);
+
+        eth_fix_ip4_checksum(l3hdr, *l3hdr_len);
+    } else if (l3_proto == ETH_P_IPV6) {
+        struct ip6_header *ip6 = (struct ip6_header *) l3hdr;
+
+        struct ip6_ext_hdr_fragment *frag_ext = NULL;
+
+        /* Find frag extension */
+        frag_ext = eth_ip6_find_ext(ip6, IP6_FRAGMENT);
+        if (frag_ext == NULL) {
+            /* No frag extension? Add one */
+            if (*l3hdr_len + sizeof(*frag_ext) > l3hdr_max_len) {
+                /*
+                 * TODO:
+                 * For now, qemu's L3 buffer allocated with NetTxPkt
+                 * and have enough memory(buffer allocated with 65K bytes
+                 * ETH_MAX_IP_DGRAM_LEN = 0xFFFF)
+                 * for additional extensions.
+                 */
+                return; /* TODO: request to reallocate l3hdr */
+            }
+            frag_ext = eth_ip6_add_ext_nonsafe(ip6, IP6_FRAGMENT);
+            *l3hdr_len += sizeof(*frag_ext);
+            static uint32_t s_id = s_first_fragment_identificator;
+            frag_ext->id = cpu_to_be32(s_id);
+            ++s_id;
+        }
+
+        frag_ext->off = cpu_to_be16((frag_offset / IP_FRAG_UNIT_SIZE) << 3
+                | (uint16_t)!!more_frags);
+
+        ip6->ip6_plen = cpu_to_be16(l3payload_len + *l3hdr_len - sizeof(*ip6));
     }
 }
 
-- 
2.27.0