VBoxNetFlt/linux/VBoxNetFlt-linux.c

	VBoxNetFlt-linux.c revision 0280e4ae13799a3136778dc90efa5841a3f40cf2
/* $Id$ */
/** @file
 * VBoxNetFlt - Network Filter Driver (Host), Linux Specific Code.
 */

/*
 * Copyright (C) 2006-2008 Sun Microsystems, Inc.
 *
 * This file is part of VirtualBox Open Source Edition (OSE), as
 * available from http://www.virtualbox.org. This file is free software;
 * you can redistribute it and/or modify it under the terms of the GNU
 * General Public License (GPL) as published by the Free Software
 * Foundation, in version 2 as it comes in the "COPYING" file of the
 * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
 * Clara, CA 95054 USA or visit http://www.sun.com if you need
 * additional information or have any questions.
 */

/*******************************************************************************
*   Header Files                                                               *
*******************************************************************************/
#include "the-linux-kernel.h"
#include "version-generated.h"
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/rtnetlink.h>
#include <linux/miscdevice.h>
#include <linux/ip.h>

#define LOG_GROUP LOG_GROUP_NET_FLT_DRV
#include <VBox/log.h>
#include <VBox/err.h>
#include <VBox/intnetinline.h>
#include <VBox/pdmnetinline.h>
#include <VBox/param.h>
#include <iprt/alloca.h>
#include <iprt/assert.h>
#include <iprt/spinlock.h>
#include <iprt/semaphore.h>
#include <iprt/initterm.h>
#include <iprt/process.h>
#include <iprt/mem.h>
#include <iprt/net.h>
#include <iprt/log.h>
#include <iprt/mp.h>
#include <iprt/mem.h>
#include <iprt/time.h>

#define VBOXNETFLT_OS_SPECFIC 1
#include "../VBoxNetFltInternal.h"


/*******************************************************************************
*   Defined Constants And Macros                                               *
*******************************************************************************/
#define VBOX_FLT_NB_TO_INST(pNB) ((PVBOXNETFLTINS)((uint8_t *)pNB - RT_OFFSETOF(VBOXNETFLTINS, u.s.Notifier)))
#define VBOX_FLT_PT_TO_INST(pPT) ((PVBOXNETFLTINS)((uint8_t *)pPT - RT_OFFSETOF(VBOXNETFLTINS, u.s.PacketType)))
#define VBOX_FLT_XT_TO_INST(pXT) ((PVBOXNETFLTINS)((uint8_t *)pXT - RT_OFFSETOF(VBOXNETFLTINS, u.s.XmitTask)))

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 22)
# define VBOX_SKB_RESET_NETWORK_HDR(skb)    skb_reset_network_header(skb)
# define VBOX_SKB_RESET_MAC_HDR(skb)        skb_reset_mac_header(skb)
#else
# define VBOX_SKB_RESET_NETWORK_HDR(skb)    skb->nh.raw = skb->data
# define VBOX_SKB_RESET_MAC_HDR(skb)        skb->mac.raw = skb->data
#endif

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 19)
# define VBOX_SKB_CHECKSUM_HELP(skb)        skb_checksum_help(skb)
#else
# define CHECKSUM_PARTIAL                   CHECKSUM_HW
# if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 10)
#  define VBOX_SKB_CHECKSUM_HELP(skb)       skb_checksum_help(skb, 0)
# else
#  if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 7)
#   define VBOX_SKB_CHECKSUM_HELP(skb)      skb_checksum_help(&skb, 0)
#  else
#   define VBOX_SKB_CHECKSUM_HELP(skb)      (!skb_checksum_help(skb))
#  endif
# endif
#endif

#ifndef NET_IP_ALIGN
# define NET_IP_ALIGN 2
#endif

#if 0
/** Create scatter / gather segments for fragments. When not used, we will
 *  linearize the socket buffer before creating the internal networking SG. */
# define VBOXNETFLT_SG_SUPPORT 1
#endif

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 18)
/** Indicates that the linux kernel may send us GSO frames. */
# define VBOXNETFLT_WITH_GSO  1

/** This enables or disables the transmitting of GSO frame from the internal
 *  network and to the host.  */
# define VBOXNETFLT_WITH_GSO_XMIT_HOST    1

# if 0 /** @todo This is currently disable because it causes performance loss of 5-10%.  */
/** This enables or disables the transmitting of GSO frame from the internal
 *  network and to the wire. */
#  define VBOXNETFLT_WITH_GSO_XMIT_WIRE   1
# endif

#endif


/*******************************************************************************
*   Internal Functions                                                         *
*******************************************************************************/
static int      VBoxNetFltLinuxInit(void);
static void     VBoxNetFltLinuxUnload(void);


/*******************************************************************************
*   Global Variables                                                           *
*******************************************************************************/
/**
 * The (common) global data.
 */
static VBOXNETFLTGLOBALS g_VBoxNetFltGlobals;

module_init(VBoxNetFltLinuxInit);
module_exit(VBoxNetFltLinuxUnload);

MODULE_AUTHOR("Sun Microsystems, Inc.");
MODULE_DESCRIPTION("VirtualBox Network Filter Driver");
MODULE_LICENSE("GPL");
#ifdef MODULE_VERSION
MODULE_VERSION(VBOX_VERSION_STRING " (" RT_XSTR(INTNETTRUNKIFPORT_VERSION) ")");
#endif


#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 12) && defined(LOG_ENABLED)
unsigned dev_get_flags(const struct net_device *dev)
{
    unsigned flags;

    flags = (dev->flags & ~(IFF_PROMISC |
                            IFF_ALLMULTI |
                            IFF_RUNNING)) |
            (dev->gflags & (IFF_PROMISC |
                            IFF_ALLMULTI));

    if (netif_running(dev) && netif_carrier_ok(dev))
        flags |= IFF_RUNNING;

    return flags;
}
#endif /* LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 12) */


/**
 * Initialize module.
 *
 * @returns appropriate status code.
 */
static int __init VBoxNetFltLinuxInit(void)
{
    int rc;
    /*
     * Initialize IPRT.
     */
    rc = RTR0Init(0);
    if (RT_SUCCESS(rc))
    {
        Log(("VBoxNetFltLinuxInit\n"));

        /*
         * Initialize the globals and connect to the support driver.
         *
         * This will call back vboxNetFltOsOpenSupDrv (and maybe vboxNetFltOsCloseSupDrv)
         * for establishing the connect to the support driver.
         */
        memset(&g_VBoxNetFltGlobals, 0, sizeof(g_VBoxNetFltGlobals));
        rc = vboxNetFltInitGlobalsAndIdc(&g_VBoxNetFltGlobals);
        if (RT_SUCCESS(rc))
        {
            LogRel(("VBoxNetFlt: Successfully started.\n"));
            return 0;
        }

        LogRel(("VBoxNetFlt: failed to initialize device extension (rc=%d)\n", rc));
        RTR0Term();
    }
    else
        LogRel(("VBoxNetFlt: failed to initialize IPRT (rc=%d)\n", rc));

    memset(&g_VBoxNetFltGlobals, 0, sizeof(g_VBoxNetFltGlobals));
    return -RTErrConvertToErrno(rc);
}


/**
 * Unload the module.
 *
 * @todo We have to prevent this if we're busy!
 */
static void __exit VBoxNetFltLinuxUnload(void)
{
    int rc;
    Log(("VBoxNetFltLinuxUnload\n"));
    Assert(vboxNetFltCanUnload(&g_VBoxNetFltGlobals));

    /*
     * Undo the work done during start (in reverse order).
     */
    rc = vboxNetFltTryDeleteIdcAndGlobals(&g_VBoxNetFltGlobals);
    AssertRC(rc); NOREF(rc);

    RTR0Term();

    memset(&g_VBoxNetFltGlobals, 0, sizeof(g_VBoxNetFltGlobals));

    Log(("VBoxNetFltLinuxUnload - done\n"));
}


/**
 * Reads and retains the host interface handle.
 *
 * @returns The handle, NULL if detached.
 * @param   pThis
 */
DECLINLINE(struct net_device *) vboxNetFltLinuxRetainNetDev(PVBOXNETFLTINS pThis)
{
#if 0
    RTSPINLOCKTMP Tmp = RTSPINLOCKTMP_INITIALIZER;
    struct net_device *pDev = NULL;

    Log(("vboxNetFltLinuxRetainNetDev\n"));
    /*
     * Be careful here to avoid problems racing the detached callback.
     */
    RTSpinlockAcquire(pThis->hSpinlock, &Tmp);
    if (!ASMAtomicUoReadBool(&pThis->fDisconnectedFromHost))
    {
        pDev = (struct net_device *)ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev);
        if (pDev)
        {
            dev_hold(pDev);
            Log(("vboxNetFltLinuxRetainNetDev: Device %p(%s) retained. ref=%d\n", pDev, pDev->name, atomic_read(&pDev->refcnt)));
        }
    }
    RTSpinlockRelease(pThis->hSpinlock, &Tmp);

    Log(("vboxNetFltLinuxRetainNetDev - done\n"));
    return pDev;
#else
    return (struct net_device *)ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev);
#endif
}


/**
 * Release the host interface handle previously retained
 * by vboxNetFltLinuxRetainNetDev.
 *
 * @param   pThis           The instance.
 * @param   pDev            The vboxNetFltLinuxRetainNetDev
 *                          return value, NULL is fine.
 */
DECLINLINE(void) vboxNetFltLinuxReleaseNetDev(PVBOXNETFLTINS pThis, struct net_device *pDev)
{
#if 0
    Log(("vboxNetFltLinuxReleaseNetDev\n"));
    NOREF(pThis);
    if (pDev)
    {
        dev_put(pDev);
        Log(("vboxNetFltLinuxReleaseNetDev: Device %p(%s) released. ref=%d\n", pDev, pDev->name, atomic_read(&pDev->refcnt)));
    }
    Log(("vboxNetFltLinuxReleaseNetDev - done\n"));
#endif
}

#define VBOXNETFLT_CB_TAG(skb) (0xA1C90000 | (skb->dev->ifindex & 0xFFFF))
#define VBOXNETFLT_SKB_TAG(skb) (*(uint32_t*)&((skb)->cb[sizeof((skb)->cb)-sizeof(uint32_t)]))

/**
 * Checks whether this is an mbuf created by vboxNetFltLinuxMBufFromSG,
 * i.e. a buffer which we're pushing and should be ignored by the filter callbacks.
 *
 * @returns true / false accordingly.
 * @param   pBuf            The sk_buff.
 */
DECLINLINE(bool) vboxNetFltLinuxSkBufIsOur(struct sk_buff *pBuf)
{
    return VBOXNETFLT_SKB_TAG(pBuf) == VBOXNETFLT_CB_TAG(pBuf);
}


/**
 * Internal worker that create a linux sk_buff for a
 * (scatter/)gather list.
 *
 * @returns Pointer to the sk_buff.
 * @param   pThis           The instance.
 * @param   pSG             The (scatter/)gather list.
 * @param   fDstWire        Set if the destination is the wire.
 */
static struct sk_buff *vboxNetFltLinuxSkBufFromSG(PVBOXNETFLTINS pThis, PINTNETSG pSG, bool fDstWire)
{
    struct sk_buff *pPkt;
    struct net_device *pDev;
    unsigned fGsoType = 0;

    if (pSG->cbTotal == 0)
    {
        LogRel(("VBoxNetFlt: Dropped empty packet coming from internal network.\n"));
        return NULL;
    }

    /** @todo We should use fragments mapping the SG buffers with large packets.
     *        256 bytes seems to be the a threshold used a lot for this.  It
     *        requires some nasty work on the intnet side though...  */
    /*
     * Allocate a packet and copy over the data.
     */
    pDev = (struct net_device *)ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev);
#if 0 /* trying to figure out why submitting GSOs is so darn slow. */
    if (   pSG->GsoCtx.u8Type != PDMNETWORKGSOTYPE_INVALID
        && pSG->cbTotal > 4096
        && fDstWire
        && pDev
        && (pDev->features & NETIF_F_SG)
        )
    {
        uint32_t off    = 0;
        uint32_t cbLeft = pSG->cbTotal;
        uint32_t iFrag  = 0;

        pPkt = dev_alloc_skb(pSG->GsoCtx.cbHdrs + NET_IP_ALIGN + 64);
        if (RT_UNLIKELY(!pPkt))
        {
            Log(("vboxNetFltLinuxSkBufFromSG: Failed to allocate sk_buff(%u).\n", pSG->cbTotal));
            pSG->pvUserData = NULL;
            return NULL;
        }
        pPkt->dev       = pDev;
        pPkt->ip_summed = CHECKSUM_NONE;

        /* Align IP header on 16-byte boundary: 2 + 14 (ethernet hdr size). */
        skb_reserve(pPkt, NET_IP_ALIGN);

        /* Copy the headers. */
        skb_put(pPkt, pSG->GsoCtx.cbHdrs);
        INTNETSgReadEx(pSG, off, pSG->GsoCtx.cbHdrs, pPkt->data);
        off    += pSG->GsoCtx.cbHdrs;
        cbLeft -= off;

        /* Copy the payload into fragments. */
        while (cbLeft)
        {
            void           *pvPage;
            uint32_t        cbUsed = RT_MIN(cbLeft, PAGE_SIZE);
            struct page    *pPage  = alloc_page(GFP_ATOMIC);
            if (!pPage)
            {
                dev_kfree_skb(pPkt);
                return NULL;
            }

            skb_fill_page_desc(pPkt, iFrag, pPage, 0, cbUsed);

            pvPage = kmap(pPage);
            INTNETSgReadEx(pSG, off, cbUsed, pvPage);
            kunmap(pPage);

            /* advance */
            iFrag          += 1;
            pPkt->len      += cbUsed;
            pPkt->data_len += cbUsed;
            pPkt->truesize += cbUsed;
            off            += cbUsed;
            cbLeft         -= cbUsed;
        }
    }
    else
#endif
    {
        pPkt = dev_alloc_skb(pSG->cbTotal + NET_IP_ALIGN);
        if (RT_UNLIKELY(!pPkt))
        {
            Log(("vboxNetFltLinuxSkBufFromSG: Failed to allocate sk_buff(%u).\n", pSG->cbTotal));
            pSG->pvUserData = NULL;
            return NULL;
        }
        pPkt->dev       = pDev;
        pPkt->ip_summed = CHECKSUM_NONE;

        /* Align IP header on 16-byte boundary: 2 + 14 (ethernet hdr size). */
        skb_reserve(pPkt, NET_IP_ALIGN);

        /* Copy the segments. */
        skb_put(pPkt, pSG->cbTotal);
        INTNETSgRead(pSG, pPkt->data);
    }

#if defined(VBOXNETFLT_WITH_GSO_XMIT_WIRE) || defined(VBOXNETFLT_WITH_GSO_XMIT_HOST)
    /*
     * Setup GSO if used by this packet.
     */
    switch ((PDMNETWORKGSOTYPE)pSG->GsoCtx.u8Type)
    {
        default:
            AssertMsgFailed(("%u (%s)\n", pSG->GsoCtx.u8Type, PDMNetGsoTypeName((PDMNETWORKGSOTYPE)pSG->GsoCtx.u8Type) ));
            /* fall thru */
        case PDMNETWORKGSOTYPE_INVALID:
            fGsoType = 0;
            break;
        case PDMNETWORKGSOTYPE_IPV4_TCP:
            fGsoType = SKB_GSO_TCPV4;
            break;
        case PDMNETWORKGSOTYPE_IPV4_UDP:
            fGsoType = SKB_GSO_UDP;
            break;
        case PDMNETWORKGSOTYPE_IPV6_TCP:
            fGsoType = SKB_GSO_TCPV6;
            break;
    }
    if (fGsoType)
    {
        struct skb_shared_info *pShInfo = skb_shinfo(pPkt);

        if (!fDstWire)
            fGsoType |= SKB_GSO_DODGY;
        pShInfo->gso_type = fGsoType;
        pShInfo->gso_size = pSG->GsoCtx.cbMaxSeg;
        pShInfo->gso_segs = PDMNetGsoCalcSegmentCount(&pSG->GsoCtx, pSG->cbTotal);

        /** @todo figure out the checksum bit... We're checksumming way too much here
         *        I hope.  */
        if (fDstWire)
        {
            /** @todo check skb_partial_csum_set status code.  */
            if (fGsoType & (SKB_GSO_TCPV4 | SKB_GSO_TCPV6))
                skb_partial_csum_set(pPkt, pSG->GsoCtx.offHdr2, RT_OFFSETOF(RTNETTCP, th_sum));
            else
                skb_partial_csum_set(pPkt, pSG->GsoCtx.offHdr2, RT_OFFSETOF(RTNETUDP, uh_sum));
        }
        else
        {
            pPkt->ip_summed = CHECKSUM_UNNECESSARY;
            PDMNetGsoPrepForDirectUse(&pSG->GsoCtx, pPkt->data, pSG->cbTotal, false /*fPayloadChecksum*/);
        }
    }
#endif /* VBOXNETFLT_WITH_GSO_XMIT_WIRE || VBOXNETFLT_WITH_GSO_XMIT_HOST */

    /*
     * Finish up the socket buffer.
     */
    pPkt->protocol = eth_type_trans(pPkt, pDev);
    if (fDstWire)
    {
        VBOX_SKB_RESET_NETWORK_HDR(pPkt);

        /* Restore ethernet header back. */
        skb_push(pPkt, ETH_HLEN); /** @todo VLAN: +4 if VLAN? */
        VBOX_SKB_RESET_MAC_HDR(pPkt);
    }
    VBOXNETFLT_SKB_TAG(pPkt) = VBOXNETFLT_CB_TAG(pPkt);

    return pPkt;
}


/**
 * Initializes a SG list from an sk_buff.
 *
 * @returns Number of segments.
 * @param   pThis               The instance.
 * @param   pBuf                The sk_buff.
 * @param   pSG                 The SG.
 * @param   pvFrame             The frame pointer, optional.
 * @param   cSegs               The number of segments allocated for the SG.
 *                              This should match the number in the mbuf exactly!
 * @param   fSrc                The source of the frame.
 * @param   pGso                Pointer to the GSO context if it's a GSO
 *                              internal network frame.  NULL if regular frame.
 */
DECLINLINE(void) vboxNetFltLinuxSkBufToSG(PVBOXNETFLTINS pThis, struct sk_buff *pBuf, PINTNETSG pSG,
                                          unsigned cSegs, uint32_t fSrc, PCPDMNETWORKGSO pGsoCtx)
{
    int i;
    NOREF(pThis);

    Assert(!skb_shinfo(pBuf)->frag_list);

    if (fSrc & INTNETTRUNKDIR_WIRE)
    {
        /*
         * The packet came from wire, ethernet header was removed by device driver.
         * Restore it.
         */
        skb_push(pBuf, ETH_HLEN);
    }

    if (!pGsoCtx)
        INTNETSgInitTempSegs(pSG, pBuf->len, cSegs, 0 /*cSegsUsed*/);
    else
        INTNETSgInitTempSegsGso(pSG, pBuf->len, cSegs, 0 /*cSegsUsed*/, pGsoCtx);

#ifdef VBOXNETFLT_SG_SUPPORT
    pSG->aSegs[0].cb = skb_headlen(pBuf);
    pSG->aSegs[0].pv = pBuf->data;
    pSG->aSegs[0].Phys = NIL_RTHCPHYS;

    for (i = 0; i < skb_shinfo(pBuf)->nr_frags; i++)
    {
        skb_frag_t *pFrag = &skb_shinfo(pBuf)->frags[i];
        pSG->aSegs[i+1].cb = pFrag->size;
        pSG->aSegs[i+1].pv = kmap(pFrag->page);
        printk("%p = kmap()\n", pSG->aSegs[i+1].pv);
        pSG->aSegs[i+1].Phys = NIL_RTHCPHYS;
    }
    ++i;

#else
    pSG->aSegs[0].cb = pBuf->len;
    pSG->aSegs[0].pv = pBuf->data;
    pSG->aSegs[0].Phys = NIL_RTHCPHYS;
    i = 1;
#endif

    pSG->cSegsUsed = i;

#ifdef PADD_RUNT_FRAMES_FROM_HOST
    /*
     * Add a trailer if the frame is too small.
     *
     * Since we're getting to the packet before it is framed, it has not
     * yet been padded. The current solution is to add a segment pointing
     * to a buffer containing all zeros and pray that works for all frames...
     */
    if (pSG->cbTotal < 60 && (fSrc & INTNETTRUNKDIR_HOST))
    {
        static uint8_t const s_abZero[128] = {0};

        AssertReturnVoid(i < cSegs);

        pSG->aSegs[i].Phys = NIL_RTHCPHYS;
        pSG->aSegs[i].pv = (void *)&s_abZero[0];
        pSG->aSegs[i].cb = 60 - pSG->cbTotal;
        pSG->cbTotal = 60;
        pSG->cSegsUsed++;
        Assert(i + 1 <= pSG->cSegsAlloc)
    }
#endif

    Log4(("vboxNetFltLinuxSkBufToSG: allocated=%d, segments=%d frags=%d next=%p frag_list=%p pkt_type=%x fSrc=%x\n",
          pSG->cSegsAlloc, pSG->cSegsUsed, skb_shinfo(pBuf)->nr_frags, pBuf->next, skb_shinfo(pBuf)->frag_list, pBuf->pkt_type, fSrc));
    for (i = 0; i < pSG->cSegsUsed; i++)
        Log4(("vboxNetFltLinuxSkBufToSG:   #%d: cb=%d pv=%p\n",
              i, pSG->aSegs[i].cb, pSG->aSegs[i].pv));
}

/**
 * Packet handler,
 *
 * @returns 0 or EJUSTRETURN.
 * @param   pThis           The instance.
 * @param   pMBuf           The mbuf.
 * @param   pvFrame         The start of the frame, optional.
 * @param   fSrc            Where the packet (allegedly) comes from, one INTNETTRUNKDIR_* value.
 * @param   eProtocol       The protocol.
 */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 14)
static int vboxNetFltLinuxPacketHandler(struct sk_buff *pBuf,
                                        struct net_device *pSkbDev,
                                        struct packet_type *pPacketType,
                                        struct net_device *pOrigDev)
#else
static int vboxNetFltLinuxPacketHandler(struct sk_buff *pBuf,
                                        struct net_device *pSkbDev,
                                        struct packet_type *pPacketType)
#endif
{
    PVBOXNETFLTINS pThis;
    struct net_device *pDev;
    LogFlow(("vboxNetFltLinuxPacketHandler: pBuf=%p pSkbDev=%p pPacketType=%p\n",
             pBuf, pSkbDev, pPacketType));
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 18)
    Log3(("vboxNetFltLinuxPacketHandler: skb len=%u data_len=%u truesize=%u next=%p nr_frags=%u gso_size=%u gso_seqs=%u gso_type=%x frag_list=%p pkt_type=%x\n",
          pBuf->len, pBuf->data_len, pBuf->truesize, pBuf->next, skb_shinfo(pBuf)->nr_frags, skb_shinfo(pBuf)->gso_size, skb_shinfo(pBuf)->gso_segs, skb_shinfo(pBuf)->gso_type, skb_shinfo(pBuf)->frag_list, pBuf->pkt_type));
#else
    Log3(("vboxNetFltLinuxPacketHandler: skb len=%u data_len=%u truesize=%u next=%p nr_frags=%u tso_size=%u tso_seqs=%u frag_list=%p pkt_type=%x\n",
          pBuf->len, pBuf->data_len, pBuf->truesize, pBuf->next, skb_shinfo(pBuf)->nr_frags, skb_shinfo(pBuf)->tso_size, skb_shinfo(pBuf)->tso_segs, skb_shinfo(pBuf)->frag_list, pBuf->pkt_type));
#endif
    /*
     * Drop it immediately?
     */
    if (!pBuf)
        return 0;

    pThis = VBOX_FLT_PT_TO_INST(pPacketType);
    pDev = (struct net_device *)ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev);
    if (pThis->u.s.pDev != pSkbDev)
    {
        Log(("vboxNetFltLinuxPacketHandler: Devices do not match, pThis may be wrong! pThis=%p\n", pThis));
        return 0;
    }

    Log4(("vboxNetFltLinuxPacketHandler: pBuf->cb dump:\n%.*Rhxd\n", sizeof(pBuf->cb), pBuf->cb));
    if (vboxNetFltLinuxSkBufIsOur(pBuf))
    {
        Log2(("vboxNetFltLinuxPacketHandler: got our own sk_buff, drop it.\n"));
        dev_kfree_skb(pBuf);
        return 0;
    }

#ifndef VBOXNETFLT_SG_SUPPORT
    {
        /*
         * Get rid of fragmented packets, they cause too much trouble.
         */
        struct sk_buff *pCopy = skb_copy(pBuf, GFP_ATOMIC);
        kfree_skb(pBuf);
        if (!pCopy)
        {
            LogRel(("VBoxNetFlt: Failed to allocate packet buffer, dropping the packet.\n"));
            return 0;
        }
        pBuf = pCopy;
# if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 18)
        Log3(("vboxNetFltLinuxPacketHandler: skb copy len=%u data_len=%u truesize=%u next=%p nr_frags=%u gso_size=%u gso_seqs=%u gso_type=%x frag_list=%p pkt_type=%x\n",
              pBuf->len, pBuf->data_len, pBuf->truesize, pBuf->next, skb_shinfo(pBuf)->nr_frags, skb_shinfo(pBuf)->gso_size, skb_shinfo(pBuf)->gso_segs, skb_shinfo(pBuf)->gso_type, skb_shinfo(pBuf)->frag_list, pBuf->pkt_type));
# else
        Log3(("vboxNetFltLinuxPacketHandler: skb copy len=%u data_len=%u truesize=%u next=%p nr_frags=%u tso_size=%u tso_seqs=%u frag_list=%p pkt_type=%x\n",
              pBuf->len, pBuf->data_len, pBuf->truesize, pBuf->next, skb_shinfo(pBuf)->nr_frags, skb_shinfo(pBuf)->tso_size, skb_shinfo(pBuf)->tso_segs, skb_shinfo(pBuf)->frag_list, pBuf->pkt_type));
# endif
    }
#endif

    /* Add the packet to transmit queue and schedule the bottom half. */
    skb_queue_tail(&pThis->u.s.XmitQueue, pBuf);
    schedule_work(&pThis->u.s.XmitTask);
    Log4(("vboxNetFltLinuxPacketHandler: scheduled work %p for sk_buff %p\n",
          &pThis->u.s.XmitTask, pBuf));

    /* It does not really matter what we return, it is ignored by the kernel. */
    return 0;
}

/**
 * Calculate the number of INTNETSEG segments the socket buffer will need.
 *
 * @returns Segment count.
 * @param   pBuf                The socket buffer.
 */
DECLINLINE(unsigned) vboxNetFltLinuxCalcSGSegments(struct sk_buff *pBuf)
{
#ifdef VBOXNETFLT_SG_SUPPORT
    unsigned cSegs = 1 + skb_shinfo(pBuf)->nr_frags;
#else
    unsigned cSegs = 1;
#endif
#ifdef PADD_RUNT_FRAMES_FROM_HOST
    /* vboxNetFltLinuxSkBufToSG adds a padding segment if it's a runt. */
    if (pBuf->len < 60)
        cSegs++;
#endif
    return cSegs;
}

/**
 * Destroy the intnet scatter / gather buffer created by
 * vboxNetFltLinuxSkBufToSG.
 */
static void vboxNetFltLinuxDestroySG(PINTNETSG pSG)
{
#ifdef VBOXNETFLT_SG_SUPPORT
    int i;

    for (i = 0; i < skb_shinfo(pBuf)->nr_frags; i++)
    {
        printk("kunmap(%p)\n", pSG->aSegs[i+1].pv);
        kunmap(pSG->aSegs[i+1].pv);
    }
#endif
    NOREF(pSG);
}

#ifdef LOG_ENABLED
/**
 * Logging helper.
 */
static void vboxNetFltDumpPacket(PINTNETSG pSG, bool fEgress, const char *pszWhere, int iIncrement)
{
    uint8_t *pInt, *pExt;
    static int iPacketNo = 1;
    iPacketNo += iIncrement;
    if (fEgress)
    {
        pExt = pSG->aSegs[0].pv;
        pInt = pExt + 6;
    }
    else
    {
        pInt = pSG->aSegs[0].pv;
        pExt = pInt + 6;
    }
    Log(("VBoxNetFlt: (int)%02x:%02x:%02x:%02x:%02x:%02x"
         " %s (%s)%02x:%02x:%02x:%02x:%02x:%02x (%u bytes) packet #%u\n",
         pInt[0], pInt[1], pInt[2], pInt[3], pInt[4], pInt[5],
         fEgress ? "-->" : "<--", pszWhere,
         pExt[0], pExt[1], pExt[2], pExt[3], pExt[4], pExt[5],
         pSG->cbTotal, iPacketNo));
    Log3(("%.*Rhxd\n", pSG->aSegs[0].cb, pSG->aSegs[0].pv));
}
#else
# define vboxNetFltDumpPacket(a, b, c, d) do {} while (0)
#endif

#ifdef VBOXNETFLT_WITH_GSO

/**
 * Worker for vboxNetFltLinuxForwardToIntNet that checks if we can forwards a
 * GSO socket buffer without having to segment it.
 *
 * @returns true on success, false if needs segmenting.
 * @param   pThis               The net filter instance.
 * @param   pSkb                The GSO socket buffer.
 * @param   fSrc                The source.
 * @param   pGsoCtx             Where to return the GSO context on success.
 */
static bool vboxNetFltLinuxCanForwardAsGso(PVBOXNETFLTINS pThis, struct sk_buff *pSkb, uint32_t fSrc,
                                           PPDMNETWORKGSO pGsoCtx)
{
    PDMNETWORKGSOTYPE   enmGsoType;
    uint16_t            uEtherType;
    unsigned int        cbTransport;
    unsigned int        offTransport;
    unsigned int        cbTransportHdr;
    unsigned            uProtocol;
    union
    {
        RTNETIPV4           IPv4;
        RTNETIPV6           IPv6;
        RTNETTCP            Tcp;
        uint8_t             ab[40];
        uint16_t            au16[40/2];
        uint32_t            au32[40/4];
    }                   Buf;

    /*
     * Check the GSO properties of the socket buffer and make sure it fits.
     */
    /** @todo Figure out how to handle SKB_GSO_TCP_ECN! */
    if (RT_UNLIKELY( skb_shinfo(pSkb)->gso_type & ~(SKB_GSO_UDP | SKB_GSO_DODGY | SKB_GSO_TCPV6 | SKB_GSO_TCPV4) ))
    {
        Log5(("vboxNetFltLinuxCanForwardAsGso: gso_type=%#x\n", skb_shinfo(pSkb)->gso_type));
        return false;
    }
    if (RT_UNLIKELY(   skb_shinfo(pSkb)->gso_size < 1
                    || pSkb->len > VBOX_MAX_GSO_SIZE ))
    {
        Log5(("vboxNetFltLinuxCanForwardAsGso: gso_size=%#x skb_len=%#x (max=%#x)\n", skb_shinfo(pSkb)->gso_size, pSkb->len, VBOX_MAX_GSO_SIZE));
        return false;
    }
    if (RT_UNLIKELY(fSrc & INTNETTRUNKDIR_WIRE))
    {
        Log5(("vboxNetFltLinuxCanForwardAsGso: fSrc=wire\n"));
        return false;
    }

    /*
     * skb_gso_segment does the following. Do we need to do it as well?
     */
    skb_reset_mac_header(pSkb);
    pSkb->mac_len = pSkb->network_header - pSkb->mac_header;

    /*
     * Switch on the ethertype.
     */
    uEtherType = pSkb->protocol;
    if (   uEtherType    == RT_H2N_U16_C(RTNET_ETHERTYPE_VLAN)
        && pSkb->mac_len == sizeof(RTNETETHERHDR) + sizeof(uint32_t))
    {
        uint16_t const *puEtherType = skb_header_pointer(pSkb, sizeof(RTNETETHERHDR) + sizeof(uint16_t), sizeof(uint16_t), &Buf);
        if (puEtherType)
            uEtherType = *puEtherType;
    }
    switch (uEtherType)
    {
        case RT_H2N_U16_C(RTNET_ETHERTYPE_IPV4):
        {
            unsigned int cbHdr;
            PCRTNETIPV4  pIPv4 = (PCRTNETIPV4)skb_header_pointer(pSkb, pSkb->mac_len, sizeof(Buf.IPv4), &Buf);
            if (RT_UNLIKELY(!pIPv4))
            {
                Log5(("vboxNetFltLinuxCanForwardAsGso: failed to access IPv4 hdr\n"));
                return false;
            }

            cbHdr       = pIPv4->ip_hl * 4;
            cbTransport = RT_N2H_U16(pIPv4->ip_len);
            if (RT_UNLIKELY(   cbHdr < RTNETIPV4_MIN_LEN
                            || cbHdr > cbTransport ))
            {
                Log5(("vboxNetFltLinuxCanForwardAsGso: invalid IPv4 lengths: ip_hl=%u ip_len=%u\n", pIPv4->ip_hl, RT_N2H_U16(pIPv4->ip_len)));
                return false;
            }
            cbTransport -= cbHdr;
            offTransport = pSkb->mac_len + cbHdr;
            uProtocol    = pIPv4->ip_p;
            if (uProtocol == RTNETIPV4_PROT_TCP)
                enmGsoType = PDMNETWORKGSOTYPE_IPV4_TCP;
            else if (uProtocol == RTNETIPV4_PROT_UDP)
                enmGsoType = PDMNETWORKGSOTYPE_IPV4_UDP;
            else /** @todo IPv6: 4to6 tunneling */
                enmGsoType = PDMNETWORKGSOTYPE_INVALID;
            break;
        }

        case RT_H2N_U16_C(RTNET_ETHERTYPE_IPV6):
        {
            PCRTNETIPV6 pIPv6 = (PCRTNETIPV6)skb_header_pointer(pSkb, pSkb->mac_len, sizeof(Buf.IPv6), &Buf);
            if (RT_UNLIKELY(!pIPv6))
            {
                Log5(("vboxNetFltLinuxCanForwardAsGso: failed to access IPv6 hdr\n"));
                return false;
            }

            cbTransport  = RT_N2H_U16(pIPv6->ip6_plen);
            offTransport = pSkb->mac_len + sizeof(RTNETIPV6);
            uProtocol    = pIPv6->ip6_nxt;
            /** @todo IPv6: Dig our way out of the other headers. */
            if (uProtocol == RTNETIPV4_PROT_TCP)
                enmGsoType = PDMNETWORKGSOTYPE_IPV6_TCP;
            else if (uProtocol == RTNETIPV4_PROT_UDP)
                enmGsoType = PDMNETWORKGSOTYPE_IPV4_UDP;
            else
                enmGsoType = PDMNETWORKGSOTYPE_INVALID;
            break;
        }

        default:
            Log5(("vboxNetFltLinuxCanForwardAsGso: uEtherType=%#x\n", RT_H2N_U16(uEtherType)));
            return false;
    }

    if (enmGsoType == PDMNETWORKGSOTYPE_INVALID)
    {
        Log5(("vboxNetFltLinuxCanForwardAsGso: Unsupported protocol %d\n", uProtocol));
        return false;
    }

    if (RT_UNLIKELY(   offTransport + cbTransport <= offTransport
                    || offTransport + cbTransport > pSkb->len
                    || cbTransport < (uProtocol == RTNETIPV4_PROT_TCP ? RTNETTCP_MIN_LEN : RTNETUDP_MIN_LEN)) )
    {
        Log5(("vboxNetFltLinuxCanForwardAsGso: Bad transport length; off=%#x + cb=%#x => %#x; skb_len=%#x (%s)\n",
              offTransport, cbTransport, offTransport + cbTransport, pSkb->len, PDMNetGsoTypeName(enmGsoType) ));
        return false;
    }

    /*
     * Check the TCP/UDP bits.
     */
    if (uProtocol == RTNETIPV4_PROT_TCP)
    {
        PCRTNETTCP pTcp = (PCRTNETTCP)skb_header_pointer(pSkb, offTransport, sizeof(Buf.Tcp), &Buf);
        if (RT_UNLIKELY(!pTcp))
        {
            Log5(("vboxNetFltLinuxCanForwardAsGso: failed to access TCP hdr\n"));
            return false;
        }

        cbTransportHdr = pTcp->th_off * 4;
        if (RT_UNLIKELY(   cbTransportHdr < RTNETTCP_MIN_LEN
                        || cbTransportHdr > cbTransport
                        || offTransport + cbTransportHdr >= UINT8_MAX
                        || offTransport + cbTransportHdr >= pSkb->len ))
        {
            Log5(("vboxNetFltLinuxCanForwardAsGso: No space for TCP header; off=%#x cb=%#x skb_len=%#x\n", offTransport, cbTransportHdr, pSkb->len));
            return false;
        }

    }
    else
    {
        Assert(uProtocol == RTNETIPV4_PROT_UDP);
        cbTransportHdr = sizeof(RTNETUDP);
        if (RT_UNLIKELY(   offTransport + cbTransportHdr >= UINT8_MAX
                        || offTransport + cbTransportHdr >= pSkb->len ))
        {
            Log5(("vboxNetFltLinuxCanForwardAsGso: No space for UDP header; off=%#x skb_len=%#x\n", offTransport, pSkb->len));
            return false;
        }
    }

    /*
     * We're good, init the GSO context.
     */
    pGsoCtx->u8Type       = enmGsoType;
    pGsoCtx->cbHdrs       = offTransport + cbTransportHdr;
    pGsoCtx->cbMaxSeg     = skb_shinfo(pSkb)->gso_size;
    pGsoCtx->offHdr1      = pSkb->mac_len;
    pGsoCtx->offHdr2      = offTransport;
    pGsoCtx->au8Unused[0] = 0;
    pGsoCtx->au8Unused[1] = 0;

    return true;
}

/**
 * Forward the socket buffer as a GSO internal network frame.
 *
 * @returns IPRT status code.
 * @param   pThis               The net filter instance.
 * @param   pSkb                The GSO socket buffer.
 * @param   fSrc                The source.
 * @param   pGsoCtx             Where to return the GSO context on success.
 */
static int vboxNetFltLinuxForwardAsGso(PVBOXNETFLTINS pThis, struct sk_buff *pSkb, uint32_t fSrc, PCPDMNETWORKGSO pGsoCtx)
{
    int         rc;
    unsigned    cSegs = vboxNetFltLinuxCalcSGSegments(pSkb);
    if (RT_LIKELY(cSegs <= MAX_SKB_FRAGS + 1))
    {
        PINTNETSG pSG = (PINTNETSG)alloca(RT_OFFSETOF(INTNETSG, aSegs[cSegs]));
        if (RT_LIKELY(pSG))
        {
            vboxNetFltLinuxSkBufToSG(pThis, pSkb, pSG, cSegs, fSrc, pGsoCtx);

            vboxNetFltDumpPacket(pSG, false, (fSrc & INTNETTRUNKDIR_HOST) ? "host" : "wire", 1);
            pThis->pSwitchPort->pfnRecv(pThis->pSwitchPort, pSG, fSrc);

            vboxNetFltLinuxDestroySG(pSG);
            rc = VINF_SUCCESS;
        }
        else
        {
            Log(("VBoxNetFlt: Dropping the sk_buff (failure case).\n"));
            rc = VERR_NO_MEMORY;
        }
    }
    else
    {
        Log(("VBoxNetFlt: Bad sk_buff? cSegs=%#x.\n", cSegs));
        rc = VERR_INTERNAL_ERROR_3;
    }

    Log4(("VBoxNetFlt: Dropping the sk_buff.\n"));
    dev_kfree_skb(pSkb);
    return rc;
}

#endif /* VBOXNETFLT_WITH_GSO */

/**
 * Worker for vboxNetFltLinuxForwardToIntNet.
 *
 * @returns VINF_SUCCESS or VERR_NO_MEMORY.
 * @param   pThis               The net filter instance.
 * @param   pBuf                The socket buffer.
 * @param   fSrc                The source.
 */
static int vboxNetFltLinuxForwardSegment(PVBOXNETFLTINS pThis, struct sk_buff *pBuf, uint32_t fSrc)
{
    int         rc;
    unsigned    cSegs = vboxNetFltLinuxCalcSGSegments(pBuf);
    if (cSegs <= MAX_SKB_FRAGS + 1)
    {
        PINTNETSG pSG = (PINTNETSG)alloca(RT_OFFSETOF(INTNETSG, aSegs[cSegs]));
        if (RT_LIKELY(pSG))
        {
            vboxNetFltLinuxSkBufToSG(pThis, pBuf, pSG, cSegs, fSrc, NULL /*pGsoCtx*/);

            vboxNetFltDumpPacket(pSG, false, (fSrc & INTNETTRUNKDIR_HOST) ? "host" : "wire", 1);
            pThis->pSwitchPort->pfnRecv(pThis->pSwitchPort, pSG, fSrc);

            vboxNetFltLinuxDestroySG(pSG);
            rc = VINF_SUCCESS;
        }
        else
        {
            Log(("VBoxNetFlt: Failed to allocate SG buffer.\n"));
            rc = VERR_NO_MEMORY;
        }
    }
    else
    {
        Log(("VBoxNetFlt: Bad sk_buff? cSegs=%#x.\n", cSegs));
        rc = VERR_INTERNAL_ERROR_3;
    }

    Log4(("VBoxNetFlt: Dropping the sk_buff.\n"));
    dev_kfree_skb(pBuf);
    return rc;
}

static void vboxNetFltLinuxForwardToIntNet(PVBOXNETFLTINS pThis, struct sk_buff *pBuf)
{
    uint32_t fSrc = pBuf->pkt_type == PACKET_OUTGOING ? INTNETTRUNKDIR_HOST : INTNETTRUNKDIR_WIRE;

#ifdef VBOXNETFLT_WITH_GSO
    if (skb_is_gso(pBuf))
    {
        PDMNETWORKGSO GsoCtx;
        Log3(("vboxNetFltLinuxForwardToIntNet: skb len=%u data_len=%u truesize=%u next=%p nr_frags=%u gso_size=%u gso_seqs=%u gso_type=%x frag_list=%p pkt_type=%x ip_summed=%d\n",
              pBuf->len, pBuf->data_len, pBuf->truesize, pBuf->next, skb_shinfo(pBuf)->nr_frags, skb_shinfo(pBuf)->gso_size, skb_shinfo(pBuf)->gso_segs, skb_shinfo(pBuf)->gso_type, skb_shinfo(pBuf)->frag_list, pBuf->pkt_type, pBuf->ip_summed));
        if (   (skb_shinfo(pBuf)->gso_type & (SKB_GSO_UDP | SKB_GSO_TCPV6 | SKB_GSO_TCPV4))
            && vboxNetFltLinuxCanForwardAsGso(pThis, pBuf, fSrc, &GsoCtx) )
            vboxNetFltLinuxForwardAsGso(pThis, pBuf, fSrc, &GsoCtx);
        else
        {
            /* Need to segment the packet */
            struct sk_buff *pNext;
            struct sk_buff *pSegment = skb_gso_segment(pBuf, 0 /*supported features*/);
            if (IS_ERR(pSegment))
            {
                dev_kfree_skb(pBuf);
                LogRel(("VBoxNetFlt: Failed to segment a packet (%d).\n", PTR_ERR(pSegment)));
                return;
            }

            for (; pSegment; pSegment = pNext)
            {
                Log3(("vboxNetFltLinuxForwardToIntNet: segment len=%u data_len=%u truesize=%u next=%p nr_frags=%u gso_size=%u gso_seqs=%u gso_type=%x frag_list=%p pkt_type=%x\n",
                      pSegment->len, pSegment->data_len, pSegment->truesize, pSegment->next, skb_shinfo(pSegment)->nr_frags, skb_shinfo(pSegment)->gso_size, skb_shinfo(pSegment)->gso_segs, skb_shinfo(pSegment)->gso_type, skb_shinfo(pSegment)->frag_list, pSegment->pkt_type));
                pNext = pSegment->next;
                pSegment->next = 0;
                vboxNetFltLinuxForwardSegment(pThis, pSegment, fSrc);
            }
            dev_kfree_skb(pBuf);
        }
    }
    else
#endif /* VBOXNETFLT_WITH_GSO */
    {
        if (pBuf->ip_summed == CHECKSUM_PARTIAL && pBuf->pkt_type == PACKET_OUTGOING)
        {
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 18)
            /*
             * Try to work around the problem with CentOS 4.7 and 5.2 (2.6.9
             * and 2.6.18 kernels), they pass wrong 'h' pointer down. We take IP
             * header length from the header itself and reconstruct 'h' pointer
             * to TCP (or whatever) header.
             */
            unsigned char *tmp = pBuf->h.raw;
            if (pBuf->h.raw == pBuf->nh.raw && pBuf->protocol == htons(ETH_P_IP))
                pBuf->h.raw = pBuf->nh.raw + pBuf->nh.iph->ihl * 4;
#endif /* LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 18) */
            if (VBOX_SKB_CHECKSUM_HELP(pBuf))
            {
                LogRel(("VBoxNetFlt: Failed to compute checksum, dropping the packet.\n"));
                dev_kfree_skb(pBuf);
                return;
            }
#if LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 18)
            /* Restore the original (wrong) pointer. */
            pBuf->h.raw = tmp;
#endif /* LINUX_VERSION_CODE <= KERNEL_VERSION(2, 6, 18) */
        }
        vboxNetFltLinuxForwardSegment(pThis, pBuf, fSrc);
    }
}

/**
 * Work queue handler that forwards the socket buffers queued by
 * vboxNetFltLinuxPacketHandler to the internal network.
 *
 * @param   pWork               The work queue.
 */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 20)
static void vboxNetFltLinuxXmitTask(struct work_struct *pWork)
#else
static void vboxNetFltLinuxXmitTask(void *pWork)
#endif
{
    PVBOXNETFLTINS  pThis   = VBOX_FLT_XT_TO_INST(pWork);
    RTSPINLOCKTMP   Tmp     = RTSPINLOCKTMP_INITIALIZER;
    struct sk_buff *pBuf;

    Log4(("vboxNetFltLinuxXmitTask: Got work %p.\n", pWork));

    /*
     * Active? Retain the instance and increment the busy counter.
     */
    RTSpinlockAcquire(pThis->hSpinlock, &Tmp);
    if (ASMAtomicUoReadBool(&pThis->fActive))
    {
        vboxNetFltRetain(pThis, true /* fBusy */);
        RTSpinlockRelease(pThis->hSpinlock, &Tmp);

        while ((pBuf = skb_dequeue(&pThis->u.s.XmitQueue)) != NULL)
            vboxNetFltLinuxForwardToIntNet(pThis, pBuf);

        vboxNetFltRelease(pThis, true /* fBusy */);
    }
    else
    {
        RTSpinlockRelease(pThis->hSpinlock, &Tmp);
        /** @todo Shouldn't we just drop the packets here? There is little point in
         *        making them accumulate when the VM is paused and it'll only waste
         *        kernel memory anyway... Hmm. maybe wait a short while (2-5 secs)
         *        before start draining the packets (goes for the intnet ring buf
         *        too)? */
    }
}

/**
 * Reports the GSO capabilites of the hardware NIC.
 *
 * @param   pThis               The net filter instance.  The caller hold a
 *                              reference to this.
 */
static void vboxNetFltLinuxReportNicGsoCapabilities(PVBOXNETFLTINS pThis)
{
#ifdef VBOXNETFLT_WITH_GSO_XMIT_WIRE
    struct net_device  *pDev;
    PINTNETTRUNKSWPORT  pSwitchPort;
    unsigned int        fFeatures;
    RTSPINLOCKTMP       Tmp = RTSPINLOCKTMP_INITIALIZER;

    RTSpinlockAcquire(pThis->hSpinlock, &Tmp);

    pSwitchPort = pThis->pSwitchPort; /* this doesn't need to be here, but it doesn't harm. */
    pDev = (struct net_device *)ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev);
    if (pDev)
        fFeatures = pDev->features;
    else
        fFeatures = 0;

    RTSpinlockRelease(pThis->hSpinlock, &Tmp);

    if (pThis->pSwitchPort)
    {
        /* Set/update the GSO capabilities of the NIC. */
        uint32_t fGsoCapabilites = 0;
        if (fFeatures & NETIF_F_TSO)
            fGsoCapabilites |= RT_BIT_32(PDMNETWORKGSOTYPE_IPV4_TCP);
        if (fFeatures & NETIF_F_TSO6)
            fGsoCapabilites |= RT_BIT_32(PDMNETWORKGSOTYPE_IPV6_TCP);
# if 0 /** @todo GSO: Test UDP offloading (UFO) on linux. */
        if (fFeatures & NETIF_F_UFO)
            fGsoCapabilites |= RT_BIT_32(PDMNETWORKGSOTYPE_IPV4_UDP);
        if (fFeatures & NETIF_F_UFO)
            fGsoCapabilites |= RT_BIT_32(PDMNETWORKGSOTYPE_IPV6_UDP);
# endif
        pThis->pSwitchPort->pfnReportGsoCapabilities(pThis->pSwitchPort, fGsoCapabilites, INTNETTRUNKDIR_WIRE);
    }
#endif /* VBOXNETFLT_WITH_GSO_XMIT_WIRE */
}

/**
 * Internal worker for vboxNetFltLinuxNotifierCallback.
 *
 * @returns VBox status code.
 * @param   pThis           The instance.
 * @param   fRediscovery    If set we're doing a rediscovery attempt, so, don't
 *                          flood the release log.
 */
static int vboxNetFltLinuxAttachToInterface(PVBOXNETFLTINS pThis, struct net_device *pDev)
{
    RTSPINLOCKTMP Tmp = RTSPINLOCKTMP_INITIALIZER;
    LogFlow(("vboxNetFltLinuxAttachToInterface: pThis=%p (%s)\n", pThis, pThis->szName));

    /*
     * Retain and store the device.
     */
    dev_hold(pDev);

    RTSpinlockAcquire(pThis->hSpinlock, &Tmp);
    ASMAtomicUoWritePtr((void * volatile *)&pThis->u.s.pDev, pDev);
    RTSpinlockRelease(pThis->hSpinlock, &Tmp);

    Log(("vboxNetFltLinuxAttachToInterface: Device %p(%s) retained. ref=%d\n", pDev, pDev->name, atomic_read(&pDev->refcnt)));
    Log(("vboxNetFltLinuxAttachToInterface: Got pDev=%p pThis=%p pThis->u.s.pDev=%p\n", pDev, pThis, ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev)));

    /* Get the mac address while we still have a valid net_device reference. */
    memcpy(&pThis->u.s.Mac, pDev->dev_addr, sizeof(pThis->u.s.Mac));

    /*
     * Install a packet filter for this device with a protocol wildcard (ETH_P_ALL).
     */
    pThis->u.s.PacketType.type = __constant_htons(ETH_P_ALL);
    pThis->u.s.PacketType.dev  = pDev;
    pThis->u.s.PacketType.func = vboxNetFltLinuxPacketHandler;
    dev_add_pack(&pThis->u.s.PacketType);

    /*
     * Set indicators that require the spinlock. Be abit paranoid about racing
     * the device notification handle.
     */
    RTSpinlockAcquire(pThis->hSpinlock, &Tmp);
    pDev = (struct net_device *)ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev);
    if (pDev)
    {
        ASMAtomicUoWriteBool(&pThis->fDisconnectedFromHost, false);
        ASMAtomicUoWriteBool(&pThis->u.s.fRegistered, true);
        pDev = NULL; /* don't dereference it */
    }
    RTSpinlockRelease(pThis->hSpinlock, &Tmp);
    Log(("vboxNetFltLinuxAttachToInterface: this=%p: Packet handler installed.\n", pThis));

    /*
     * If the above succeeded report GSO capabilites,  if not undo and
     * release the device.
     */
    if (!pDev)
        vboxNetFltLinuxReportNicGsoCapabilities(pThis);
    else
    {
        RTSpinlockAcquire(pThis->hSpinlock, &Tmp);
        ASMAtomicUoWritePtr((void * volatile *)&pThis->u.s.pDev, NULL);
        RTSpinlockRelease(pThis->hSpinlock, &Tmp);
        dev_put(pDev);
        Log(("vboxNetFltLinuxAttachToInterface: Device %p(%s) released. ref=%d\n", pDev, pDev->name, atomic_read(&pDev->refcnt)));
    }

    LogRel(("VBoxNetFlt: attached to '%s' / %.*Rhxs\n", pThis->szName, sizeof(pThis->u.s.Mac), &pThis->u.s.Mac));
    return VINF_SUCCESS;
}


static int vboxNetFltLinuxUnregisterDevice(PVBOXNETFLTINS pThis, struct net_device *pDev)
{
    RTSPINLOCKTMP Tmp = RTSPINLOCKTMP_INITIALIZER;

    Assert(!pThis->fDisconnectedFromHost);
    RTSpinlockAcquire(pThis->hSpinlock, &Tmp);
    ASMAtomicWriteBool(&pThis->u.s.fRegistered, false);
    ASMAtomicWriteBool(&pThis->fDisconnectedFromHost, true);
    ASMAtomicUoWritePtr((void * volatile *)&pThis->u.s.pDev, NULL);
    RTSpinlockRelease(pThis->hSpinlock, &Tmp);

    dev_remove_pack(&pThis->u.s.PacketType);
    skb_queue_purge(&pThis->u.s.XmitQueue);
    Log(("vboxNetFltLinuxUnregisterDevice: this=%p: Packet handler removed, xmit queue purged.\n", pThis));
    Log(("vboxNetFltLinuxUnregisterDevice: Device %p(%s) released. ref=%d\n", pDev, pDev->name, atomic_read(&pDev->refcnt)));
    dev_put(pDev);

    return NOTIFY_OK;
}

static int vboxNetFltLinuxDeviceIsUp(PVBOXNETFLTINS pThis, struct net_device *pDev)
{
    /* Check if we are not suspended and promiscuous mode has not been set. */
    if (ASMAtomicUoReadBool(&pThis->fActive) && !ASMAtomicUoReadBool(&pThis->u.s.fPromiscuousSet))
    {
        /* Note that there is no need for locking as the kernel got hold of the lock already. */
        dev_set_promiscuity(pDev, 1);
        ASMAtomicWriteBool(&pThis->u.s.fPromiscuousSet, true);
        Log(("vboxNetFltLinuxDeviceIsUp: enabled promiscuous mode on %s (%d)\n", pThis->szName, pDev->promiscuity));
    }
    else
        Log(("vboxNetFltLinuxDeviceIsUp: no need to enable promiscuous mode on %s (%d)\n", pThis->szName, pDev->promiscuity));
    return NOTIFY_OK;
}

static int vboxNetFltLinuxDeviceGoingDown(PVBOXNETFLTINS pThis, struct net_device *pDev)
{
    /* Undo promiscuous mode if we has set it. */
    if (ASMAtomicUoReadBool(&pThis->u.s.fPromiscuousSet))
    {
        /* Note that there is no need for locking as the kernel got hold of the lock already. */
        dev_set_promiscuity(pDev, -1);
        ASMAtomicWriteBool(&pThis->u.s.fPromiscuousSet, false);
        Log(("vboxNetFltLinuxDeviceGoingDown: disabled promiscuous mode on %s (%d)\n", pThis->szName, pDev->promiscuity));
    }
    else
        Log(("vboxNetFltLinuxDeviceGoingDown: no need to disable promiscuous mode on %s (%d)\n", pThis->szName, pDev->promiscuity));
    return NOTIFY_OK;
}

#ifdef LOG_ENABLED
/** Stringify the NETDEV_XXX constants. */
static const char *vboxNetFltLinuxGetNetDevEventName(unsigned long ulEventType)
{
    const char *pszEvent = "NETDRV_<unknown>";
    switch (ulEventType)
    {
        case NETDEV_REGISTER: pszEvent = "NETDEV_REGISTER"; break;
        case NETDEV_UNREGISTER: pszEvent = "NETDEV_UNREGISTER"; break;
        case NETDEV_UP: pszEvent = "NETDEV_UP"; break;
        case NETDEV_DOWN: pszEvent = "NETDEV_DOWN"; break;
        case NETDEV_REBOOT: pszEvent = "NETDEV_REBOOT"; break;
        case NETDEV_CHANGENAME: pszEvent = "NETDEV_CHANGENAME"; break;
        case NETDEV_CHANGE: pszEvent = "NETDEV_CHANGE"; break;
        case NETDEV_CHANGEMTU: pszEvent = "NETDEV_CHANGEMTU"; break;
        case NETDEV_CHANGEADDR: pszEvent = "NETDEV_CHANGEADDR"; break;
        case NETDEV_GOING_DOWN: pszEvent = "NETDEV_GOING_DOWN"; break;
# ifdef NETDEV_FEAT_CHANGE
        case NETDEV_FEAT_CHANGE: pszEvent = "NETDEV_FEAT_CHANGE"; break;
# endif
    }
    return pszEvent;
}
#endif /* LOG_ENABLED */

/**
 * Callback for listening to netdevice events.
 *
 * This works the rediscovery, clean up on unregistration, promiscuity on
 * up/down, and GSO feature changes from ethtool.
 *
 * @returns NOTIFY_OK
 * @param   self                Pointer to our notifier registration block.
 * @param   ulEventType         The event.
 * @param   ptr                 Event specific, but it is usually the device it
 *                              relates to.
 */
static int vboxNetFltLinuxNotifierCallback(struct notifier_block *self, unsigned long ulEventType, void *ptr)

{
    PVBOXNETFLTINS      pThis = VBOX_FLT_NB_TO_INST(self);
    struct net_device  *pDev  = (struct net_device *)ptr;
    int                 rc    = NOTIFY_OK;

    Log(("VBoxNetFlt: got event %s(0x%lx) on %s, pDev=%p pThis=%p pThis->u.s.pDev=%p\n",
         vboxNetFltLinuxGetNetDevEventName(ulEventType), ulEventType, pDev->name, pDev, pThis, ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev)));
    if (    ulEventType == NETDEV_REGISTER
        && !strcmp(pDev->name, pThis->szName))
    {
        vboxNetFltLinuxAttachToInterface(pThis, pDev);
    }
    else
    {
        pDev = (struct net_device *)ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev);
        if (pDev == ptr)
        {
            switch (ulEventType)
            {
                case NETDEV_UNREGISTER:
                    rc = vboxNetFltLinuxUnregisterDevice(pThis, pDev);
                    break;
                case NETDEV_UP:
                    rc = vboxNetFltLinuxDeviceIsUp(pThis, pDev);
                    break;
                case NETDEV_GOING_DOWN:
                    rc = vboxNetFltLinuxDeviceGoingDown(pThis, pDev);
                    break;
                case NETDEV_CHANGENAME:
                    break;
#ifdef NETDEV_FEAT_CHANGE
                case NETDEV_FEAT_CHANGE:
                    vboxNetFltLinuxReportNicGsoCapabilities(pThis);
                    break;
#endif
            }
        }
    }

    return rc;
}

bool vboxNetFltOsMaybeRediscovered(PVBOXNETFLTINS pThis)
{
    return !ASMAtomicUoReadBool(&pThis->fDisconnectedFromHost);
}

int  vboxNetFltPortOsXmit(PVBOXNETFLTINS pThis, PINTNETSG pSG, uint32_t fDst)
{
    struct net_device * pDev;
    int err;
    int rc = VINF_SUCCESS;

    LogFlow(("vboxNetFltPortOsXmit: pThis=%p (%s)\n", pThis, pThis->szName));

    pDev = vboxNetFltLinuxRetainNetDev(pThis);
    if (pDev)
    {
        /*
         * Create a sk_buff for the gather list and push it onto the wire.
         */
        if (fDst & INTNETTRUNKDIR_WIRE)
        {
            struct sk_buff *pBuf = vboxNetFltLinuxSkBufFromSG(pThis, pSG, true);
            if (pBuf)
            {
                vboxNetFltDumpPacket(pSG, true, "wire", 1);
                Log4(("vboxNetFltPortOsXmit: pBuf->cb dump:\n%.*Rhxd\n", sizeof(pBuf->cb), pBuf->cb));
                Log4(("vboxNetFltPortOsXmit: dev_queue_xmit(%p)\n", pBuf));
                err = dev_queue_xmit(pBuf);
                if (err)
                    rc = RTErrConvertFromErrno(err);
            }
            else
                rc = VERR_NO_MEMORY;
        }

        /*
         * Create a sk_buff for the gather list and push it onto the host stack.
         */
        if (fDst & INTNETTRUNKDIR_HOST)
        {
            struct sk_buff *pBuf = vboxNetFltLinuxSkBufFromSG(pThis, pSG, false);
            if (pBuf)
            {
                vboxNetFltDumpPacket(pSG, true, "host", (fDst & INTNETTRUNKDIR_WIRE) ? 0 : 1);
                Log4(("vboxNetFltPortOsXmit: pBuf->cb dump:\n%.*Rhxd\n", sizeof(pBuf->cb), pBuf->cb));
                Log4(("vboxNetFltPortOsXmit: netif_rx_ni(%p)\n", pBuf));
                err = netif_rx_ni(pBuf);
                if (err)
                    rc = RTErrConvertFromErrno(err);
            }
            else
                rc = VERR_NO_MEMORY;
        }

        vboxNetFltLinuxReleaseNetDev(pThis, pDev);
    }

    return rc;
}


bool vboxNetFltPortOsIsPromiscuous(PVBOXNETFLTINS pThis)
{
    bool fRc = false;
    struct net_device * pDev = vboxNetFltLinuxRetainNetDev(pThis);
    if (pDev)
    {
        fRc = !!(pDev->promiscuity - (ASMAtomicUoReadBool(&pThis->u.s.fPromiscuousSet) & 1));
        LogFlow(("vboxNetFltPortOsIsPromiscuous: returns %d, pDev->promiscuity=%d, fPromiscuousSet=%d\n",
                 fRc, pDev->promiscuity, pThis->u.s.fPromiscuousSet));
        vboxNetFltLinuxReleaseNetDev(pThis, pDev);
    }
    return fRc;
}


void vboxNetFltPortOsGetMacAddress(PVBOXNETFLTINS pThis, PRTMAC pMac)
{
    *pMac = pThis->u.s.Mac;
}


bool vboxNetFltPortOsIsHostMac(PVBOXNETFLTINS pThis, PCRTMAC pMac)
{
    /* ASSUMES that the MAC address never changes. */
    return pThis->u.s.Mac.au16[0] == pMac->au16[0]
        && pThis->u.s.Mac.au16[1] == pMac->au16[1]
        && pThis->u.s.Mac.au16[2] == pMac->au16[2];
}


void vboxNetFltPortOsSetActive(PVBOXNETFLTINS pThis, bool fActive)
{
    struct net_device * pDev;

    LogFlow(("vboxNetFltPortOsSetActive: pThis=%p (%s), fActive=%s, fDisablePromiscuous=%s\n",
             pThis, pThis->szName, fActive?"true":"false",
             pThis->fDisablePromiscuous?"true":"false"));

    if (pThis->fDisablePromiscuous)
        return;

    pDev = vboxNetFltLinuxRetainNetDev(pThis);
    if (pDev)
    {
        /*
         * This api is a bit weird, the best reference is the code.
         *
         * Also, we have a bit or race conditions wrt the maintance of
         * host the interface promiscuity for vboxNetFltPortOsIsPromiscuous.
         */
#ifdef LOG_ENABLED
        u_int16_t fIf;
        unsigned const cPromiscBefore = pDev->promiscuity;
#endif
        if (fActive)
        {
            Assert(!pThis->u.s.fPromiscuousSet);

            rtnl_lock();
            dev_set_promiscuity(pDev, 1);
            rtnl_unlock();
            pThis->u.s.fPromiscuousSet = true;
            Log(("vboxNetFltPortOsSetActive: enabled promiscuous mode on %s (%d)\n", pThis->szName, pDev->promiscuity));
        }
        else
        {
            if (pThis->u.s.fPromiscuousSet)
            {
                rtnl_lock();
                dev_set_promiscuity(pDev, -1);
                rtnl_unlock();
                Log(("vboxNetFltPortOsSetActive: disabled promiscuous mode on %s (%d)\n", pThis->szName, pDev->promiscuity));
            }
            pThis->u.s.fPromiscuousSet = false;

#ifdef LOG_ENABLED
            fIf = dev_get_flags(pDev);
            Log(("VBoxNetFlt: fIf=%#x; %d->%d\n", fIf, cPromiscBefore, pDev->promiscuity));
#endif
        }

        vboxNetFltLinuxReleaseNetDev(pThis, pDev);
    }
}


int vboxNetFltOsDisconnectIt(PVBOXNETFLTINS pThis)
{
    /* Nothing to do here. */
    return VINF_SUCCESS;
}


int  vboxNetFltOsConnectIt(PVBOXNETFLTINS pThis)
{
    /*
     * Report the GSO capabilities of the host and device (if connected).
     */
#if defined(VBOXNETFLT_WITH_GSO_XMIT_HOST)
    pThis->pSwitchPort->pfnReportGsoCapabilities(pThis->pSwitchPort,
                                                 0
                                                 | RT_BIT_32(PDMNETWORKGSOTYPE_IPV4_TCP)
                                                 | RT_BIT_32(PDMNETWORKGSOTYPE_IPV6_TCP)
# if 0 /** @todo GSO: Test UDP offloading (UFO) on linux. */
                                                 | RT_BIT_32(PDMNETWORKGSOTYPE_IPV4_UDP)
                                                 | RT_BIT_32(PDMNETWORKGSOTYPE_IPV6_UDP)
# endif
                                                 , INTNETTRUNKDIR_HOST);

#endif
    vboxNetFltLinuxReportNicGsoCapabilities(pThis);

    return VINF_SUCCESS;
}


void vboxNetFltOsDeleteInstance(PVBOXNETFLTINS pThis)
{
    struct net_device *pDev;
    bool fRegistered;
    RTSPINLOCKTMP Tmp = RTSPINLOCKTMP_INITIALIZER;

    RTSpinlockAcquire(pThis->hSpinlock, &Tmp);
    pDev = (struct net_device *)ASMAtomicUoReadPtr((void * volatile *)&pThis->u.s.pDev);
    fRegistered = ASMAtomicUoReadBool(&pThis->u.s.fRegistered);
    RTSpinlockRelease(pThis->hSpinlock, &Tmp);
    if (fRegistered)
    {
        dev_remove_pack(&pThis->u.s.PacketType);
        skb_queue_purge(&pThis->u.s.XmitQueue);
        Log(("vboxNetFltOsDeleteInstance: this=%p: Packet handler removed, xmit queue purged.\n", pThis));
        Log(("vboxNetFltOsDeleteInstance: Device %p(%s) released. ref=%d\n", pDev, pDev->name, atomic_read(&pDev->refcnt)));
        dev_put(pDev);
    }
    Log(("vboxNetFltOsDeleteInstance: this=%p: Notifier removed.\n", pThis));
    unregister_netdevice_notifier(&pThis->u.s.Notifier);
    module_put(THIS_MODULE);
}


int  vboxNetFltOsInitInstance(PVBOXNETFLTINS pThis, void *pvContext)
{
    int err;
    NOREF(pvContext);

    pThis->u.s.Notifier.notifier_call = vboxNetFltLinuxNotifierCallback;
    err = register_netdevice_notifier(&pThis->u.s.Notifier);
    if (err)
        return VERR_INTNET_FLT_IF_FAILED;
    if (!pThis->u.s.fRegistered)
    {
        unregister_netdevice_notifier(&pThis->u.s.Notifier);
        LogRel(("VBoxNetFlt: failed to find %s.\n", pThis->szName));
        return VERR_INTNET_FLT_IF_NOT_FOUND;
    }

    Log(("vboxNetFltOsInitInstance: this=%p: Notifier installed.\n", pThis));
    if (   pThis->fDisconnectedFromHost
        || !try_module_get(THIS_MODULE))
        return VERR_INTNET_FLT_IF_FAILED;

    return VINF_SUCCESS;
}

int  vboxNetFltOsPreInitInstance(PVBOXNETFLTINS pThis)
{
    /*
     * Init the linux specific members.
     */
    pThis->u.s.pDev = NULL;
    pThis->u.s.fRegistered = false;
    pThis->u.s.fPromiscuousSet = false;
    memset(&pThis->u.s.PacketType, 0, sizeof(pThis->u.s.PacketType));
    skb_queue_head_init(&pThis->u.s.XmitQueue);
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 20)
    INIT_WORK(&pThis->u.s.XmitTask, vboxNetFltLinuxXmitTask);
#else
    INIT_WORK(&pThis->u.s.XmitTask, vboxNetFltLinuxXmitTask, &pThis->u.s.XmitTask);
#endif

    return VINF_SUCCESS;
}