hw/net/vmxnet_tx_pkt.c

   1 /*
   2  * QEMU VMWARE VMXNET* paravirtual NICs - TX packets abstractions
   3  *
   4  * Copyright (c) 2012 Ravello Systems LTD (http://ravellosystems.com)
   5  *
   6  * Developed by Daynix Computing LTD (http://www.daynix.com)
   7  *
   8  * Authors:
   9  * Dmitry Fleytman <dmitry@daynix.com>
  10  * Tamir Shomer <tamirs@daynix.com>
  11  * Yan Vugenfirer <yan@daynix.com>
  12  *
  13  * This work is licensed under the terms of the GNU GPL, version 2 or later.
  14  * See the COPYING file in the top-level directory.
  15  *
  16  */
  17
  18 #include "qemu/osdep.h"
  19 #include "hw/hw.h"
  20 #include "vmxnet_tx_pkt.h"
  21 #include "net/eth.h"
  22 #include "qemu-common.h"
  23 #include "qemu/iov.h"
  24 #include "net/checksum.h"
  25 #include "net/tap.h"
  26 #include "net/net.h"
  27
  28 enum {
  29     VMXNET_TX_PKT_VHDR_FRAG = 0,
  30     VMXNET_TX_PKT_L2HDR_FRAG,
  31     VMXNET_TX_PKT_L3HDR_FRAG,
  32     VMXNET_TX_PKT_PL_START_FRAG
  33 };
  34
  35 /* TX packet private context */
  36 struct VmxnetTxPkt {
  37     struct virtio_net_hdr virt_hdr;
  38     bool has_virt_hdr;
  39
  40     struct iovec *raw;
  41     uint32_t raw_frags;
  42     uint32_t max_raw_frags;
  43
  44     struct iovec *vec;
  45
  46     uint8_t l2_hdr[ETH_MAX_L2_HDR_LEN];
  47
  48     uint32_t payload_len;
  49
  50     uint32_t payload_frags;
  51     uint32_t max_payload_frags;
  52
  53     uint16_t hdr_len;
  54     eth_pkt_types_e packet_type;
  55     uint8_t l4proto;
  56 };
  57
  58 void vmxnet_tx_pkt_init(struct VmxnetTxPkt **pkt, uint32_t max_frags,
  59     bool has_virt_hdr)
  60 {
  61     struct VmxnetTxPkt *p = g_malloc0(sizeof *p);
  62
  63     p->vec = g_malloc((sizeof *p->vec) *
  64         (max_frags + VMXNET_TX_PKT_PL_START_FRAG));
  65
  66     p->raw = g_malloc((sizeof *p->raw) * max_frags);
  67
  68     p->max_payload_frags = max_frags;
  69     p->max_raw_frags = max_frags;
  70     p->has_virt_hdr = has_virt_hdr;
  71     p->vec[VMXNET_TX_PKT_VHDR_FRAG].iov_base = &p->virt_hdr;
  72     p->vec[VMXNET_TX_PKT_VHDR_FRAG].iov_len =
  73         p->has_virt_hdr ? sizeof p->virt_hdr : 0;
  74     p->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_base = &p->l2_hdr;
  75     p->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_base = NULL;
  76     p->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_len = 0;
  77
  78     *pkt = p;
  79 }
  80
  81 void vmxnet_tx_pkt_uninit(struct VmxnetTxPkt *pkt)
  82 {
  83     if (pkt) {
  84         g_free(pkt->vec);
  85         g_free(pkt->raw);
  86         g_free(pkt);
  87     }
  88 }
  89
  90 void vmxnet_tx_pkt_update_ip_checksums(struct VmxnetTxPkt *pkt)
  91 {
  92     uint16_t csum;
  93     uint32_t ph_raw_csum;
  94     assert(pkt);
  95     uint8_t gso_type = pkt->virt_hdr.gso_type & ~VIRTIO_NET_HDR_GSO_ECN;
  96     struct ip_header *ip_hdr;
  97
  98     if (VIRTIO_NET_HDR_GSO_TCPV4 != gso_type &&
  99         VIRTIO_NET_HDR_GSO_UDP != gso_type) {
 100         return;
 101     }
 102
 103     ip_hdr = pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_base;
 104
 105     if (pkt->payload_len + pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_len >
 106         ETH_MAX_IP_DGRAM_LEN) {
 107         return;
 108     }
 109
 110     ip_hdr->ip_len = cpu_to_be16(pkt->payload_len +
 111         pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_len);
 112
 113     /* Calculate IP header checksum                    */
 114     ip_hdr->ip_sum = 0;
 115     csum = net_raw_checksum((uint8_t *)ip_hdr,
 116         pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_len);
 117     ip_hdr->ip_sum = cpu_to_be16(csum);
 118
 119     /* Calculate IP pseudo header checksum             */
 120     ph_raw_csum = eth_calc_pseudo_hdr_csum(ip_hdr, pkt->payload_len);
 121     csum = cpu_to_be16(~net_checksum_finish(ph_raw_csum));
 122     iov_from_buf(&pkt->vec[VMXNET_TX_PKT_PL_START_FRAG], pkt->payload_frags,
 123                  pkt->virt_hdr.csum_offset, &csum, sizeof(csum));
 124 }
 125
 126 static void vmxnet_tx_pkt_calculate_hdr_len(struct VmxnetTxPkt *pkt)
 127 {
 128     pkt->hdr_len = pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_len +
 129         pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_len;
 130 }
 131
 132 static bool vmxnet_tx_pkt_parse_headers(struct VmxnetTxPkt *pkt)
 133 {
 134     struct iovec *l2_hdr, *l3_hdr;
 135     size_t bytes_read;
 136     size_t full_ip6hdr_len;
 137     uint16_t l3_proto;
 138
 139     assert(pkt);
 140
 141     l2_hdr = &pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG];
 142     l3_hdr = &pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG];
 143
 144     bytes_read = iov_to_buf(pkt->raw, pkt->raw_frags, 0, l2_hdr->iov_base,
 145                             ETH_MAX_L2_HDR_LEN);
 146     if (bytes_read < sizeof(struct eth_header)) {
 147         l2_hdr->iov_len = 0;
 148         return false;
 149     }
 150
 151     l2_hdr->iov_len = sizeof(struct eth_header);
 152     switch (be16_to_cpu(PKT_GET_ETH_HDR(l2_hdr->iov_base)->h_proto)) {
 153     case ETH_P_VLAN:
 154         l2_hdr->iov_len += sizeof(struct vlan_header);
 155         break;
 156     case ETH_P_DVLAN:
 157         l2_hdr->iov_len += 2 * sizeof(struct vlan_header);
 158         break;
 159     }
 160
 161     if (bytes_read < l2_hdr->iov_len) {
 162         l2_hdr->iov_len = 0;
 163         return false;
 164     }
 165
 166     l3_proto = eth_get_l3_proto(l2_hdr->iov_base, l2_hdr->iov_len);
 167
 168     switch (l3_proto) {
 169     case ETH_P_IP:
 170         l3_hdr->iov_base = g_malloc(ETH_MAX_IP4_HDR_LEN);
 171
 172         bytes_read = iov_to_buf(pkt->raw, pkt->raw_frags, l2_hdr->iov_len,
 173                                 l3_hdr->iov_base, sizeof(struct ip_header));
 174
 175         if (bytes_read < sizeof(struct ip_header)) {
 176             l3_hdr->iov_len = 0;
 177             return false;
 178         }
 179
 180         l3_hdr->iov_len = IP_HDR_GET_LEN(l3_hdr->iov_base);
 181         pkt->l4proto = ((struct ip_header *) l3_hdr->iov_base)->ip_p;
 182
 183         /* copy optional IPv4 header data */
 184         bytes_read = iov_to_buf(pkt->raw, pkt->raw_frags,
 185                                 l2_hdr->iov_len + sizeof(struct ip_header),
 186                                 l3_hdr->iov_base + sizeof(struct ip_header),
 187                                 l3_hdr->iov_len - sizeof(struct ip_header));
 188         if (bytes_read < l3_hdr->iov_len - sizeof(struct ip_header)) {
 189             l3_hdr->iov_len = 0;
 190             return false;
 191         }
 192         break;
 193
 194     case ETH_P_IPV6:
 195         if (!eth_parse_ipv6_hdr(pkt->raw, pkt->raw_frags, l2_hdr->iov_len,
 196                                &pkt->l4proto, &full_ip6hdr_len)) {
 197             l3_hdr->iov_len = 0;
 198             return false;
 199         }
 200
 201         l3_hdr->iov_base = g_malloc(full_ip6hdr_len);
 202
 203         bytes_read = iov_to_buf(pkt->raw, pkt->raw_frags, l2_hdr->iov_len,
 204                                 l3_hdr->iov_base, full_ip6hdr_len);
 205
 206         if (bytes_read < full_ip6hdr_len) {
 207             l3_hdr->iov_len = 0;
 208             return false;
 209         } else {
 210             l3_hdr->iov_len = full_ip6hdr_len;
 211         }
 212         break;
 213
 214     default:
 215         l3_hdr->iov_len = 0;
 216         break;
 217     }
 218
 219     vmxnet_tx_pkt_calculate_hdr_len(pkt);
 220     pkt->packet_type = get_eth_packet_type(l2_hdr->iov_base);
 221     return true;
 222 }
 223
 224 static bool vmxnet_tx_pkt_rebuild_payload(struct VmxnetTxPkt *pkt)
 225 {
 226     size_t payload_len = iov_size(pkt->raw, pkt->raw_frags) - pkt->hdr_len;
 227
 228     pkt->payload_frags = iov_copy(&pkt->vec[VMXNET_TX_PKT_PL_START_FRAG],
 229                                 pkt->max_payload_frags,
 230                                 pkt->raw, pkt->raw_frags,
 231                                 pkt->hdr_len, payload_len);
 232
 233     if (pkt->payload_frags != (uint32_t) -1) {
 234         pkt->payload_len = payload_len;
 235         return true;
 236     } else {
 237         return false;
 238     }
 239 }
 240
 241 bool vmxnet_tx_pkt_parse(struct VmxnetTxPkt *pkt)
 242 {
 243     return vmxnet_tx_pkt_parse_headers(pkt) &&
 244            vmxnet_tx_pkt_rebuild_payload(pkt);
 245 }
 246
 247 struct virtio_net_hdr *vmxnet_tx_pkt_get_vhdr(struct VmxnetTxPkt *pkt)
 248 {
 249     assert(pkt);
 250     return &pkt->virt_hdr;
 251 }
 252
 253 static uint8_t vmxnet_tx_pkt_get_gso_type(struct VmxnetTxPkt *pkt,
 254                                           bool tso_enable)
 255 {
 256     uint8_t rc = VIRTIO_NET_HDR_GSO_NONE;
 257     uint16_t l3_proto;
 258
 259     l3_proto = eth_get_l3_proto(pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_base,
 260         pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_len);
 261
 262     if (!tso_enable) {
 263         goto func_exit;
 264     }
 265
 266     rc = eth_get_gso_type(l3_proto, pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_base,
 267                           pkt->l4proto);
 268
 269 func_exit:
 270     return rc;
 271 }
 272
 273 void vmxnet_tx_pkt_build_vheader(struct VmxnetTxPkt *pkt, bool tso_enable,
 274     bool csum_enable, uint32_t gso_size)
 275 {
 276     struct tcp_hdr l4hdr;
 277     assert(pkt);
 278
 279     /* csum has to be enabled if tso is. */
 280     assert(csum_enable || !tso_enable);
 281
 282     pkt->virt_hdr.gso_type = vmxnet_tx_pkt_get_gso_type(pkt, tso_enable);
 283
 284     switch (pkt->virt_hdr.gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
 285     case VIRTIO_NET_HDR_GSO_NONE:
 286         pkt->virt_hdr.hdr_len = 0;
 287         pkt->virt_hdr.gso_size = 0;
 288         break;
 289
 290     case VIRTIO_NET_HDR_GSO_UDP:
 291         pkt->virt_hdr.gso_size = IP_FRAG_ALIGN_SIZE(gso_size);
 292         pkt->virt_hdr.hdr_len = pkt->hdr_len + sizeof(struct udp_header);
 293         break;
 294
 295     case VIRTIO_NET_HDR_GSO_TCPV4:
 296     case VIRTIO_NET_HDR_GSO_TCPV6:
 297         iov_to_buf(&pkt->vec[VMXNET_TX_PKT_PL_START_FRAG], pkt->payload_frags,
 298                    0, &l4hdr, sizeof(l4hdr));
 299         pkt->virt_hdr.hdr_len = pkt->hdr_len + l4hdr.th_off * sizeof(uint32_t);
 300         pkt->virt_hdr.gso_size = IP_FRAG_ALIGN_SIZE(gso_size);
 301         break;
 302
 303     default:
 304         g_assert_not_reached();
 305     }
 306
 307     if (csum_enable) {
 308         switch (pkt->l4proto) {
 309         case IP_PROTO_TCP:
 310             pkt->virt_hdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
 311             pkt->virt_hdr.csum_start = pkt->hdr_len;
 312             pkt->virt_hdr.csum_offset = offsetof(struct tcp_hdr, th_sum);
 313             break;
 314         case IP_PROTO_UDP:
 315             pkt->virt_hdr.flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
 316             pkt->virt_hdr.csum_start = pkt->hdr_len;
 317             pkt->virt_hdr.csum_offset = offsetof(struct udp_hdr, uh_sum);
 318             break;
 319         default:
 320             break;
 321         }
 322     }
 323 }
 324
 325 void vmxnet_tx_pkt_setup_vlan_header(struct VmxnetTxPkt *pkt, uint16_t vlan)
 326 {
 327     bool is_new;
 328     assert(pkt);
 329
 330     eth_setup_vlan_headers(pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_base,
 331         vlan, &is_new);
 332
 333     /* update l2hdrlen */
 334     if (is_new) {
 335         pkt->hdr_len += sizeof(struct vlan_header);
 336         pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_len +=
 337             sizeof(struct vlan_header);
 338     }
 339 }
 340
 341 bool vmxnet_tx_pkt_add_raw_fragment(struct VmxnetTxPkt *pkt, hwaddr pa,
 342     size_t len)
 343 {
 344     hwaddr mapped_len = 0;
 345     struct iovec *ventry;
 346     assert(pkt);
 347     assert(pkt->max_raw_frags > pkt->raw_frags);
 348
 349     if (!len) {
 350         return true;
 351      }
 352
 353     ventry = &pkt->raw[pkt->raw_frags];
 354     mapped_len = len;
 355
 356     ventry->iov_base = cpu_physical_memory_map(pa, &mapped_len, false);
 357     ventry->iov_len = mapped_len;
 358     pkt->raw_frags += !!ventry->iov_base;
 359
 360     if ((ventry->iov_base == NULL) || (len != mapped_len)) {
 361         return false;
 362     }
 363
 364     return true;
 365 }
 366
 367 eth_pkt_types_e vmxnet_tx_pkt_get_packet_type(struct VmxnetTxPkt *pkt)
 368 {
 369     assert(pkt);
 370
 371     return pkt->packet_type;
 372 }
 373
 374 size_t vmxnet_tx_pkt_get_total_len(struct VmxnetTxPkt *pkt)
 375 {
 376     assert(pkt);
 377
 378     return pkt->hdr_len + pkt->payload_len;
 379 }
 380
 381 void vmxnet_tx_pkt_dump(struct VmxnetTxPkt *pkt)
 382 {
 383 #ifdef VMXNET_TX_PKT_DEBUG
 384     assert(pkt);
 385
 386     printf("TX PKT: hdr_len: %d, pkt_type: 0x%X, l2hdr_len: %lu, "
 387         "l3hdr_len: %lu, payload_len: %u\n", pkt->hdr_len, pkt->packet_type,
 388         pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_len,
 389         pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_len, pkt->payload_len);
 390 #endif
 391 }
 392
 393 void vmxnet_tx_pkt_reset(struct VmxnetTxPkt *pkt)
 394 {
 395     int i;
 396
 397     /* no assert, as reset can be called before tx_pkt_init */
 398     if (!pkt) {
 399         return;
 400     }
 401
 402     memset(&pkt->virt_hdr, 0, sizeof(pkt->virt_hdr));
 403
 404     g_free(pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_base);
 405     pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_base = NULL;
 406
 407     assert(pkt->vec);
 408     for (i = VMXNET_TX_PKT_L2HDR_FRAG;
 409          i < pkt->payload_frags + VMXNET_TX_PKT_PL_START_FRAG; i++) {
 410         pkt->vec[i].iov_len = 0;
 411     }
 412     pkt->payload_len = 0;
 413     pkt->payload_frags = 0;
 414
 415     assert(pkt->raw);
 416     for (i = 0; i < pkt->raw_frags; i++) {
 417         assert(pkt->raw[i].iov_base);
 418         cpu_physical_memory_unmap(pkt->raw[i].iov_base, pkt->raw[i].iov_len,
 419                                   false, pkt->raw[i].iov_len);
 420         pkt->raw[i].iov_len = 0;
 421     }
 422     pkt->raw_frags = 0;
 423
 424     pkt->hdr_len = 0;
 425     pkt->packet_type = 0;
 426     pkt->l4proto = 0;
 427 }
 428
 429 static void vmxnet_tx_pkt_do_sw_csum(struct VmxnetTxPkt *pkt)
 430 {
 431     struct iovec *iov = &pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG];
 432     uint32_t csum_cntr;
 433     uint16_t csum = 0;
 434     /* num of iovec without vhdr */
 435     uint32_t iov_len = pkt->payload_frags + VMXNET_TX_PKT_PL_START_FRAG - 1;
 436     uint16_t csl;
 437     struct ip_header *iphdr;
 438     size_t csum_offset = pkt->virt_hdr.csum_start + pkt->virt_hdr.csum_offset;
 439
 440     /* Put zero to checksum field */
 441     iov_from_buf(iov, iov_len, csum_offset, &csum, sizeof csum);
 442
 443     /* Calculate L4 TCP/UDP checksum */
 444     csl = pkt->payload_len;
 445
 446     /* data checksum */
 447     csum_cntr =
 448         net_checksum_add_iov(iov, iov_len, pkt->virt_hdr.csum_start, csl);
 449     /* add pseudo header to csum */
 450     iphdr = pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_base;
 451     csum_cntr += eth_calc_pseudo_hdr_csum(iphdr, csl);
 452
 453     /* Put the checksum obtained into the packet */
 454     csum = cpu_to_be16(net_checksum_finish(csum_cntr));
 455     iov_from_buf(iov, iov_len, csum_offset, &csum, sizeof csum);
 456 }
 457
 458 enum {
 459     VMXNET_TX_PKT_FRAGMENT_L2_HDR_POS = 0,
 460     VMXNET_TX_PKT_FRAGMENT_L3_HDR_POS,
 461     VMXNET_TX_PKT_FRAGMENT_HEADER_NUM
 462 };
 463
 464 #define VMXNET_MAX_FRAG_SG_LIST (64)
 465
 466 static size_t vmxnet_tx_pkt_fetch_fragment(struct VmxnetTxPkt *pkt,
 467     int *src_idx, size_t *src_offset, struct iovec *dst, int *dst_idx)
 468 {
 469     size_t fetched = 0;
 470     struct iovec *src = pkt->vec;
 471
 472     *dst_idx = VMXNET_TX_PKT_FRAGMENT_HEADER_NUM;
 473
 474     while (fetched < pkt->virt_hdr.gso_size) {
 475
 476         /* no more place in fragment iov */
 477         if (*dst_idx == VMXNET_MAX_FRAG_SG_LIST) {
 478             break;
 479         }
 480
 481         /* no more data in iovec */
 482         if (*src_idx == (pkt->payload_frags + VMXNET_TX_PKT_PL_START_FRAG)) {
 483             break;
 484         }
 485
 486
 487         dst[*dst_idx].iov_base = src[*src_idx].iov_base + *src_offset;
 488         dst[*dst_idx].iov_len = MIN(src[*src_idx].iov_len - *src_offset,
 489             pkt->virt_hdr.gso_size - fetched);
 490
 491         *src_offset += dst[*dst_idx].iov_len;
 492         fetched += dst[*dst_idx].iov_len;
 493
 494         if (*src_offset == src[*src_idx].iov_len) {
 495             *src_offset = 0;
 496             (*src_idx)++;
 497         }
 498
 499         (*dst_idx)++;
 500     }
 501
 502     return fetched;
 503 }
 504
 505 static bool vmxnet_tx_pkt_do_sw_fragmentation(struct VmxnetTxPkt *pkt,
 506     NetClientState *nc)
 507 {
 508     struct iovec fragment[VMXNET_MAX_FRAG_SG_LIST];
 509     size_t fragment_len = 0;
 510     bool more_frags = false;
 511
 512     /* some pointers for shorter code */
 513     void *l2_iov_base, *l3_iov_base;
 514     size_t l2_iov_len, l3_iov_len;
 515     int src_idx =  VMXNET_TX_PKT_PL_START_FRAG, dst_idx;
 516     size_t src_offset = 0;
 517     size_t fragment_offset = 0;
 518
 519     l2_iov_base = pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_base;
 520     l2_iov_len = pkt->vec[VMXNET_TX_PKT_L2HDR_FRAG].iov_len;
 521     l3_iov_base = pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_base;
 522     l3_iov_len = pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_len;
 523
 524     /* Copy headers */
 525     fragment[VMXNET_TX_PKT_FRAGMENT_L2_HDR_POS].iov_base = l2_iov_base;
 526     fragment[VMXNET_TX_PKT_FRAGMENT_L2_HDR_POS].iov_len = l2_iov_len;
 527     fragment[VMXNET_TX_PKT_FRAGMENT_L3_HDR_POS].iov_base = l3_iov_base;
 528     fragment[VMXNET_TX_PKT_FRAGMENT_L3_HDR_POS].iov_len = l3_iov_len;
 529
 530
 531     /* Put as much data as possible and send */
 532     do {
 533         fragment_len = vmxnet_tx_pkt_fetch_fragment(pkt, &src_idx, &src_offset,
 534             fragment, &dst_idx);
 535
 536         more_frags = (fragment_offset + fragment_len < pkt->payload_len);
 537
 538         eth_setup_ip4_fragmentation(l2_iov_base, l2_iov_len, l3_iov_base,
 539             l3_iov_len, fragment_len, fragment_offset, more_frags);
 540
 541         eth_fix_ip4_checksum(l3_iov_base, l3_iov_len);
 542
 543         qemu_sendv_packet(nc, fragment, dst_idx);
 544
 545         fragment_offset += fragment_len;
 546
 547     } while (more_frags);
 548
 549     return true;
 550 }
 551
 552 bool vmxnet_tx_pkt_send(struct VmxnetTxPkt *pkt, NetClientState *nc)
 553 {
 554     assert(pkt);
 555
 556     if (!pkt->has_virt_hdr &&
 557         pkt->virt_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
 558         vmxnet_tx_pkt_do_sw_csum(pkt);
 559     }
 560
 561     /*
 562      * Since underlying infrastructure does not support IP datagrams longer
 563      * than 64K we should drop such packets and don't even try to send
 564      */
 565     if (VIRTIO_NET_HDR_GSO_NONE != pkt->virt_hdr.gso_type) {
 566         if (pkt->payload_len >
 567             ETH_MAX_IP_DGRAM_LEN -
 568             pkt->vec[VMXNET_TX_PKT_L3HDR_FRAG].iov_len) {
 569             return false;
 570         }
 571     }
 572
 573     if (pkt->has_virt_hdr ||
 574         pkt->virt_hdr.gso_type == VIRTIO_NET_HDR_GSO_NONE) {
 575         qemu_sendv_packet(nc, pkt->vec,
 576             pkt->payload_frags + VMXNET_TX_PKT_PL_START_FRAG);
 577         return true;
 578     }
 579
 580     return vmxnet_tx_pkt_do_sw_fragmentation(pkt, nc);
 581 }