/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (C) 2013-2016 Vincenzo Maffione
 * Copyright (C) 2013-2016 Luigi Rizzo
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *   2. Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in the
 *      documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * This module implements netmap support on top of standard,
 * unmodified device drivers.
 *
 * A NIOCREGIF request is handled here if the device does not
 * have native support. TX and RX rings are emulated as follows:
 *
 * NIOCREGIF
 *      We preallocate a block of TX mbufs (roughly as many as
 *      tx descriptors; the number is not critical) to speed up
 *      operation during transmissions. The refcount on most of
 *      these buffers is artificially bumped up so we can recycle
 *      them more easily. Also, the destructor is intercepted
 *      so we use it as an interrupt notification to wake up
 *      processes blocked on a poll().
 *
 *      For each receive ring we allocate one "struct mbq"
 *      (an mbuf tailq plus a spinlock). We intercept packets
 *      (through if_input)
 *      on the receive path and put them in the mbq from which
 *      netmap receive routines can grab them.
 *
 * TX:
 *      in the generic_txsync() routine, netmap buffers are copied
 *      (or linked, in a future) to the preallocated mbufs
 *      and pushed to the transmit queue. Some of these mbufs
 *      (those with NS_REPORT, or otherwise every half ring)
 *      have the refcount=1, others have refcount=2.
 *      When the destructor is invoked, we take that as
 *      a notification that all mbufs up to that one in
 *      the specific ring have been completed, and generate
 *      the equivalent of a transmit interrupt.
 *
 * RX:
 *
 */

#ifdef __FreeBSD__

#include <sys/cdefs.h> /* prerequisite */
#include <sys/types.h>
#include <sys/errno.h>
#include <sys/malloc.h>
#include <sys/lock.h>   /* PROT_EXEC */
#include <sys/rwlock.h>
#include <sys/socket.h> /* sockaddrs */
#include <sys/selinfo.h>
#include <net/if.h>
#include <net/if_types.h>
#include <net/if_var.h>
#include <machine/bus.h>        /* bus_dmamap_* in netmap_kern.h */

#include <net/netmap.h>
#include <dev/netmap/netmap_kern.h>
#include <dev/netmap/netmap_mem2.h>

#define MBUF_RXQ(m)     ((m)->m_pkthdr.flowid)
#define smp_mb()

#elif defined _WIN32

#include "win_glue.h"

#define MBUF_TXQ(m)     0//((m)->m_pkthdr.flowid)
#define MBUF_RXQ(m)         0//((m)->m_pkthdr.flowid)
#define smp_mb()                //XXX: to be correctly defined

#else /* linux */

#include "bsd_glue.h"

#include <linux/ethtool.h>      /* struct ethtool_ops, get_ringparam */
#include <linux/hrtimer.h>

static inline struct mbuf *
nm_os_get_mbuf(struct ifnet *ifp, int len)
{
        return alloc_skb(LL_RESERVED_SPACE(ifp) + len +
                         ifp->needed_tailroom, GFP_ATOMIC);
}

#endif /* linux */


/* Common headers. */
#include <net/netmap.h>
#include <dev/netmap/netmap_kern.h>
#include <dev/netmap/netmap_mem2.h>


#define for_each_kring_n(_i, _k, _karr, _n) \
        for ((_k)=*(_karr), (_i) = 0; (_i) < (_n); (_i)++, (_k) = (_karr)[(_i)])

#define for_each_tx_kring(_i, _k, _na) \
                for_each_kring_n(_i, _k, (_na)->tx_rings, (_na)->num_tx_rings)
#define for_each_tx_kring_h(_i, _k, _na) \
                for_each_kring_n(_i, _k, (_na)->tx_rings, (_na)->num_tx_rings + 1)

#define for_each_rx_kring(_i, _k, _na) \
                for_each_kring_n(_i, _k, (_na)->rx_rings, (_na)->num_rx_rings)
#define for_each_rx_kring_h(_i, _k, _na) \
                for_each_kring_n(_i, _k, (_na)->rx_rings, (_na)->num_rx_rings + 1)


/* ======================== PERFORMANCE STATISTICS =========================== */

#ifdef RATE_GENERIC
#define IFRATE(x) x
struct rate_stats {
        unsigned long txpkt;
        unsigned long txsync;
        unsigned long txirq;
        unsigned long txrepl;
        unsigned long txdrop;
        unsigned long rxpkt;
        unsigned long rxirq;
        unsigned long rxsync;
};

struct rate_context {
        unsigned refcount;
        struct timer_list timer;
        struct rate_stats new;
        struct rate_stats old;
};

#define RATE_PRINTK(_NAME_) \
        printk( #_NAME_ " = %lu Hz\n", (cur._NAME_ - ctx->old._NAME_)/RATE_PERIOD);
#define RATE_PERIOD  2
static void rate_callback(unsigned long arg)
{
        struct rate_context * ctx = (struct rate_context *)arg;
        struct rate_stats cur = ctx->new;
        int r;

        RATE_PRINTK(txpkt);
        RATE_PRINTK(txsync);
        RATE_PRINTK(txirq);
        RATE_PRINTK(txrepl);
        RATE_PRINTK(txdrop);
        RATE_PRINTK(rxpkt);
        RATE_PRINTK(rxsync);
        RATE_PRINTK(rxirq);
        printk("\n");

        ctx->old = cur;
        r = mod_timer(&ctx->timer, jiffies +
                        msecs_to_jiffies(RATE_PERIOD * 1000));
        if (unlikely(r))
                nm_prerr("mod_timer() failed");
}

static struct rate_context rate_ctx;

void generic_rate(int txp, int txs, int txi, int rxp, int rxs, int rxi)
{
        if (txp) rate_ctx.new.txpkt++;
        if (txs) rate_ctx.new.txsync++;
        if (txi) rate_ctx.new.txirq++;
        if (rxp) rate_ctx.new.rxpkt++;
        if (rxs) rate_ctx.new.rxsync++;
        if (rxi) rate_ctx.new.rxirq++;
}

#else /* !RATE */
#define IFRATE(x)
#endif /* !RATE */


/* ========== GENERIC (EMULATED) NETMAP ADAPTER SUPPORT ============= */

/*
 * Wrapper used by the generic adapter layer to notify
 * the poller threads. Differently from netmap_rx_irq(), we check
 * only NAF_NETMAP_ON instead of NAF_NATIVE_ON to enable the irq.
 */
void
netmap_generic_irq(struct netmap_adapter *na, u_int q, u_int *work_done)
{
        if (unlikely(!nm_netmap_on(na)))
                return;

        netmap_common_irq(na, q, work_done);
#ifdef RATE_GENERIC
        if (work_done)
                rate_ctx.new.rxirq++;
        else
                rate_ctx.new.txirq++;
#endif  /* RATE_GENERIC */
}

static int
generic_netmap_unregister(struct netmap_adapter *na)
{
        struct netmap_generic_adapter *gna = (struct netmap_generic_adapter *)na;
        struct netmap_kring *kring = NULL;
        int i, r;

        if (na->active_fds == 0) {
                na->na_flags &= ~NAF_NETMAP_ON;

                /* Stop intercepting packets on the RX path. */
                nm_os_catch_rx(gna, 0);

                /* Release packet steering control. */
                nm_os_catch_tx(gna, 0);
        }

        netmap_krings_mode_commit(na, /*onoff=*/0);

        for_each_rx_kring(r, kring, na) {
                /* Free the mbufs still pending in the RX queues,
                 * that did not end up into the corresponding netmap
                 * RX rings. */
                mbq_safe_purge(&kring->rx_queue);
                nm_os_mitigation_cleanup(&gna->mit[r]);
        }

        /* Decrement reference counter for the mbufs in the
         * TX pools. These mbufs can be still pending in drivers,
         * (e.g. this happens with virtio-net driver, which
         * does lazy reclaiming of transmitted mbufs). */
        for_each_tx_kring(r, kring, na) {
                /* We must remove the destructor on the TX event,
                 * because the destructor invokes netmap code, and
                 * the netmap module may disappear before the
                 * TX event is consumed. */
                mtx_lock_spin(&kring->tx_event_lock);
                if (kring->tx_event) {
                        SET_MBUF_DESTRUCTOR(kring->tx_event, NULL, NULL);
                }
                kring->tx_event = NULL;
                mtx_unlock_spin(&kring->tx_event_lock);
        }

        if (na->active_fds == 0) {
                nm_os_free(gna->mit);

                for_each_rx_kring(r, kring, na) {
                        mbq_safe_fini(&kring->rx_queue);
                }

                for_each_tx_kring(r, kring, na) {
                        callout_drain(&kring->tx_event_callout);

                        if (kring->tx_pool == NULL) {
                                continue;
                        }

                        for (i=0; i<na->num_tx_desc; i++) {
                                if (kring->tx_pool[i]) {
                                        m_free(kring->tx_pool[i]);
                                        kring->tx_pool[i] = NULL;
                                }
                        }
                        mtx_destroy(&kring->tx_event_lock);
                        nm_os_free(kring->tx_pool);
                        kring->tx_pool = NULL;
                }

#ifdef RATE_GENERIC
                if (--rate_ctx.refcount == 0) {
                        nm_prinf("del_timer()");
                        del_timer(&rate_ctx.timer);
                }
#endif
                nm_prinf("Emulated adapter for %s deactivated", na->name);
        }

        return 0;
}

/* Enable/disable netmap mode for a generic network interface. */
static int
generic_netmap_register(struct netmap_adapter *na, int enable)
{
        struct netmap_generic_adapter *gna = (struct netmap_generic_adapter *)na;
        struct netmap_kring *kring = NULL;
        int error;
        int i, r;

        if (!na) {
                return EINVAL;
        }

        if (!enable) {
                /* This is actually an unregif. */
                return generic_netmap_unregister(na);
        }

        if (na->active_fds == 0) {
                nm_prinf("Emulated adapter for %s activated", na->name);
                /* Do all memory allocations when (na->active_fds == 0), to
                 * simplify error management. */

                /* Allocate memory for mitigation support on all the rx queues. */
                gna->mit = nm_os_malloc(na->num_rx_rings * sizeof(struct nm_generic_mit));
                if (!gna->mit) {
                        nm_prerr("mitigation allocation failed");
                        error = ENOMEM;
                        goto out;
                }

                for_each_rx_kring(r, kring, na) {
                        /* Init mitigation support. */
                        nm_os_mitigation_init(&gna->mit[r], r, na);

                        /* Initialize the rx queue, as generic_rx_handler() can
                         * be called as soon as nm_os_catch_rx() returns.
                         */
                        mbq_safe_init(&kring->rx_queue);
                }

                /*
                 * Prepare mbuf pools (parallel to the tx rings), for packet
                 * transmission. Don't preallocate the mbufs here, it's simpler
                 * to leave this task to txsync.
                 */
                for_each_tx_kring(r, kring, na) {
                        kring->tx_pool = NULL;
                }
                for_each_tx_kring(r, kring, na) {
                        kring->tx_pool =
                                nm_os_malloc(na->num_tx_desc * sizeof(struct mbuf *));
                        if (!kring->tx_pool) {
                                nm_prerr("tx_pool allocation failed");
                                error = ENOMEM;
                                goto free_tx_pools;
                        }
                        mtx_init(&kring->tx_event_lock, "tx_event_lock",
                                 NULL, MTX_SPIN);
                        callout_init_mtx(&kring->tx_event_callout,
                                         &kring->tx_event_lock,
                                         CALLOUT_RETURNUNLOCKED);
                }
        }

        netmap_krings_mode_commit(na, /*onoff=*/1);

        for_each_tx_kring(r, kring, na) {
                /* Initialize tx_pool and tx_event. */
                for (i=0; i<na->num_tx_desc; i++) {
                        kring->tx_pool[i] = NULL;
                }

                kring->tx_event = NULL;
        }

        if (na->active_fds == 0) {
                /* Prepare to intercept incoming traffic. */
                error = nm_os_catch_rx(gna, 1);
                if (error) {
                        nm_prerr("nm_os_catch_rx(1) failed (%d)", error);
                        goto free_tx_pools;
                }

                /* Let netmap control the packet steering. */
                error = nm_os_catch_tx(gna, 1);
                if (error) {
                        nm_prerr("nm_os_catch_tx(1) failed (%d)", error);
                        goto catch_rx;
                }

                na->na_flags |= NAF_NETMAP_ON;

#ifdef RATE_GENERIC
                if (rate_ctx.refcount == 0) {
                        nm_prinf("setup_timer()");
                        memset(&rate_ctx, 0, sizeof(rate_ctx));
                        setup_timer(&rate_ctx.timer, &rate_callback, (unsigned long)&rate_ctx);
                        if (mod_timer(&rate_ctx.timer, jiffies + msecs_to_jiffies(1500))) {
                                nm_prerr("Error: mod_timer()");
                        }
                }
                rate_ctx.refcount++;
#endif /* RATE */
        }

        return 0;

        /* Here (na->active_fds == 0) holds. */
catch_rx:
        nm_os_catch_rx(gna, 0);
free_tx_pools:
        for_each_tx_kring(r, kring, na) {
                mtx_destroy(&kring->tx_event_lock);
                if (kring->tx_pool == NULL) {
                        continue;
                }
                nm_os_free(kring->tx_pool);
                kring->tx_pool = NULL;
        }
        for_each_rx_kring(r, kring, na) {
                mbq_safe_fini(&kring->rx_queue);
        }
        nm_os_free(gna->mit);
out:

        return error;
}

/*
 * Callback invoked when the device driver frees an mbuf used
 * by netmap to transmit a packet. This usually happens when
 * the NIC notifies the driver that transmission is completed.
 */
static void
generic_mbuf_dtor(struct mbuf *m)
{
        struct netmap_adapter *na = GEN_TX_MBUF_NA(m);
        struct netmap_kring *kring;
        unsigned int r = MBUF_TXQ(m);
        unsigned int r_orig = r;

        if (unlikely(!nm_netmap_on(na) || r >= na->num_tx_rings)) {
                nm_prerr("Error: no netmap adapter on device %p",
                  GEN_TX_MBUF_IFP(m));
                return;
        }

        /*
         * First, clear the event mbuf.
         * In principle, the event 'm' should match the one stored
         * on ring 'r'. However we check it explicitly to stay
         * safe against lower layers (qdisc, driver, etc.) changing
         * MBUF_TXQ(m) under our feet. If the match is not found
         * on 'r', we try to see if it belongs to some other ring.
         */
        for (;;) {
                bool match = false;

                kring = na->tx_rings[r];
                mtx_lock_spin(&kring->tx_event_lock);

                /*
                 * The netmap destructor can be called between us getting the
                 * reference and taking the lock, in that case the ring
                 * reference won't be valid. The destructor will free this mbuf
                 * so we can stop here.
                 */
                if (GEN_TX_MBUF_NA(m) == NULL) {
                        mtx_unlock_spin(&kring->tx_event_lock);
                        return;
                }

                if (kring->tx_event == m) {
                        kring->tx_event = NULL;
                        match = true;
                }
                mtx_unlock_spin(&kring->tx_event_lock);

                if (match) {
                        if (r != r_orig) {
                                nm_prlim(1, "event %p migrated: ring %u --> %u",
                                      m, r_orig, r);
                        }
                        break;
                }

                if (++r == na->num_tx_rings) r = 0;

                if (r == r_orig) {
#ifndef __FreeBSD__
                        /*
                         * On FreeBSD this situation can arise if the tx_event
                         * callout handler cleared a stuck packet.
                         */
                        nm_prlim(1, "Cannot match event %p", m);
#endif
                        nm_generic_mbuf_dtor(m);
                        return;
                }
        }

        /* Second, wake up clients. They will reclaim the event through
         * txsync. */
        netmap_generic_irq(na, r, NULL);
        nm_generic_mbuf_dtor(m);
}

/* Record completed transmissions and update hwtail.
 *
 * The oldest tx buffer not yet completed is at nr_hwtail + 1,
 * nr_hwcur is the first unsent buffer.
 */
static u_int
generic_netmap_tx_clean(struct netmap_kring *kring, int txqdisc)
{
        u_int const lim = kring->nkr_num_slots - 1;
        u_int nm_i = nm_next(kring->nr_hwtail, lim);
        u_int hwcur = kring->nr_hwcur;
        u_int n = 0;
        struct mbuf **tx_pool = kring->tx_pool;

        nm_prdis("hwcur = %d, hwtail = %d", kring->nr_hwcur, kring->nr_hwtail);

        while (nm_i != hwcur) { /* buffers not completed */
                struct mbuf *m = tx_pool[nm_i];

                if (txqdisc) {
                        if (m == NULL) {
                                /* Nothing to do, this is going
                                 * to be replenished. */
                                nm_prlim(3, "Is this happening?");

                        } else if (MBUF_QUEUED(m)) {
                                break; /* Not dequeued yet. */

                        } else if (MBUF_REFCNT(m) != 1) {
                                /* This mbuf has been dequeued but is still busy
                                 * (refcount is 2).
                                 * Leave it to the driver and replenish. */
                                m_free(m);
                                tx_pool[nm_i] = NULL;
                        }

                } else {
                        if (unlikely(m == NULL)) {
                                int event_consumed;

                                /* This slot was used to place an event. */
                                mtx_lock_spin(&kring->tx_event_lock);
                                event_consumed = (kring->tx_event == NULL);
                                mtx_unlock_spin(&kring->tx_event_lock);
                                if (!event_consumed) {
                                        /* The event has not been consumed yet,
                                         * still busy in the driver. */
                                        break;
                                }
                                /* The event has been consumed, we can go
                                 * ahead. */
                        } else if (MBUF_REFCNT(m) != 1) {
                                /* This mbuf is still busy: its refcnt is 2. */
                                break;
                        }
                }

                n++;
                nm_i = nm_next(nm_i, lim);
        }
        kring->nr_hwtail = nm_prev(nm_i, lim);
        nm_prdis("tx completed [%d] -> hwtail %d", n, kring->nr_hwtail);

        return n;
}

/* Compute a slot index in the middle between inf and sup. */
static inline u_int
ring_middle(u_int inf, u_int sup, u_int lim)
{
        u_int n = lim + 1;
        u_int e;

        if (sup >= inf) {
                e = (sup + inf) / 2;
        } else { /* wrap around */
                e = (sup + n + inf) / 2;
                if (e >= n) {
                        e -= n;
                }
        }

        if (unlikely(e >= n)) {
                nm_prerr("This cannot happen");
                e = 0;
        }

        return e;
}

#ifdef __FreeBSD__
static void
generic_tx_callout(void *arg)
{
        struct netmap_kring *kring = arg;

        kring->tx_event = NULL;
        mtx_unlock_spin(&kring->tx_event_lock);
        netmap_generic_irq(kring->na, kring->ring_id, NULL);
}
#endif

static void
generic_set_tx_event(struct netmap_kring *kring, u_int hwcur)
{
        u_int lim = kring->nkr_num_slots - 1;
        struct mbuf *m;
        u_int e;
        u_int ntc = nm_next(kring->nr_hwtail, lim); /* next to clean */

        if (ntc == hwcur) {
                return; /* all buffers are free */
        }

        /*
         * We have pending packets in the driver between hwtail+1
         * and hwcur, and we have to chose one of these slot to
         * generate a notification.
         * There is a race but this is only called within txsync which
         * does a double check.
         */
#if 0
        /* Choose a slot in the middle, so that we don't risk ending
         * up in a situation where the client continuously wake up,
         * fills one or a few TX slots and go to sleep again. */
        e = ring_middle(ntc, hwcur, lim);
#else
        /* Choose the first pending slot, to be safe against driver
         * reordering mbuf transmissions. */
        e = ntc;
#endif

        m = kring->tx_pool[e];
        if (m == NULL) {
                /* An event is already in place. */
                return;
        }

        mtx_lock_spin(&kring->tx_event_lock);
        if (kring->tx_event) {
                /* An event is already in place. */
                mtx_unlock_spin(&kring->tx_event_lock);
                return;
        }

        SET_MBUF_DESTRUCTOR(m, generic_mbuf_dtor, kring->na);

        kring->tx_event = m;
#ifdef __FreeBSD__
        /*
         * Handle the possibility that the transmitted buffer isn't reclaimed
         * within a bounded period of time.  This can arise when transmitting
         * out of multiple ports via a lagg or bridge interface, since the
         * member ports may legitimately only free transmitted buffers in
         * batches.
         *
         * The callout handler clears the stuck packet from the ring, allowing
         * transmission to proceed.  In the common case we let
         * generic_mbuf_dtor() unstick the ring, allowing mbufs to be
         * reused most of the time.
         */
        callout_reset_sbt_curcpu(&kring->tx_event_callout, SBT_1MS, 0,
            generic_tx_callout, kring, 0);
#endif
        mtx_unlock_spin(&kring->tx_event_lock);

        kring->tx_pool[e] = NULL;

        nm_prdis("Request Event at %d mbuf %p refcnt %d", e, m, m ? MBUF_REFCNT(m) : -2 );

        /* Decrement the refcount. This will free it if we lose the race
         * with the driver. */
        m_free(m);
}

/*
 * generic_netmap_txsync() transforms netmap buffers into mbufs
 * and passes them to the standard device driver
 * (ndo_start_xmit() or ifp->if_transmit() ).
 * On linux this is not done directly, but using dev_queue_xmit(),
 * since it implements the TX flow control (and takes some locks).
 */
static int
generic_netmap_txsync(struct netmap_kring *kring, int flags)
{
        struct netmap_adapter *na = kring->na;
        struct netmap_generic_adapter *gna = (struct netmap_generic_adapter *)na;
        if_t ifp = na->ifp;
        struct netmap_ring *ring = kring->ring;
        u_int nm_i;     /* index into the netmap ring */ // j
        u_int const lim = kring->nkr_num_slots - 1;
        u_int const head = kring->rhead;
        u_int ring_nr = kring->ring_id;

        IFRATE(rate_ctx.new.txsync++);

        rmb();

        /*
         * First part: process new packets to send.
         */
        nm_i = kring->nr_hwcur;
        if (nm_i != head) {     /* we have new packets to send */
                struct nm_os_gen_arg a;
                u_int event = -1;
#ifdef __FreeBSD__
                struct epoch_tracker et;

                NET_EPOCH_ENTER(et);
#endif

                if (gna->txqdisc && nm_kr_txempty(kring)) {
                        /* In txqdisc mode, we ask for a delayed notification,
                         * but only when cur == hwtail, which means that the
                         * client is going to block. */
                        event = ring_middle(nm_i, head, lim);
                        nm_prdis("Place txqdisc event (hwcur=%u,event=%u,"
                              "head=%u,hwtail=%u)", nm_i, event, head,
                              kring->nr_hwtail);
                }

                a.ifp = ifp;
                a.ring_nr = ring_nr;
                a.head = a.tail = NULL;

                while (nm_i != head) {
                        struct netmap_slot *slot = &ring->slot[nm_i];
                        u_int len = slot->len;
                        void *addr = NMB(na, slot);
                        /* device-specific */
                        struct mbuf *m;
                        int tx_ret;

                        NM_CHECK_ADDR_LEN(na, addr, len);

                        /* Tale a mbuf from the tx pool (replenishing the pool
                         * entry if necessary) and copy in the user packet. */
                        m = kring->tx_pool[nm_i];
                        if (unlikely(m == NULL)) {
                                kring->tx_pool[nm_i] = m =
                                        nm_os_get_mbuf(ifp, NETMAP_BUF_SIZE(na));
                                if (m == NULL) {
                                        nm_prlim(2, "Failed to replenish mbuf");
                                        /* Here we could schedule a timer which
                                         * retries to replenish after a while,
                                         * and notifies the client when it
                                         * manages to replenish some slots. In
                                         * any case we break early to avoid
                                         * crashes. */
                                        break;
                                }
                                IFRATE(rate_ctx.new.txrepl++);
                        } else {
                                nm_os_mbuf_reinit(m);
                        }

                        a.m = m;
                        a.addr = addr;
                        a.len = len;
                        a.qevent = (nm_i == event);
                        /* When not in txqdisc mode, we should ask
                         * notifications when NS_REPORT is set, or roughly
                         * every half ring. To optimize this, we set a
                         * notification event when the client runs out of
                         * TX ring space, or when transmission fails. In
                         * the latter case we also break early.
                         */
                        tx_ret = nm_os_generic_xmit_frame(&a);
                        if (unlikely(tx_ret)) {
                                if (!gna->txqdisc) {
                                        /*
                                         * No room for this mbuf in the device driver.
                                         * Request a notification FOR A PREVIOUS MBUF,
                                         * then call generic_netmap_tx_clean(kring) to do the
                                         * double check and see if we can free more buffers.
                                         * If there is space continue, else break;
                                         * NOTE: the double check is necessary if the problem
                                         * occurs in the txsync call after selrecord().
                                         * Also, we need some way to tell the caller that not
                                         * all buffers were queued onto the device (this was
                                         * not a problem with native netmap driver where space
                                         * is preallocated). The bridge has a similar problem
                                         * and we solve it there by dropping the excess packets.
                                         */
                                        generic_set_tx_event(kring, nm_i);
                                        if (generic_netmap_tx_clean(kring, gna->txqdisc)) {
                                                /* space now available */
                                                continue;
                                        } else {
                                                break;
                                        }
                                }

                                /* In txqdisc mode, the netmap-aware qdisc
                                 * queue has the same length as the number of
                                 * netmap slots (N). Since tail is advanced
                                 * only when packets are dequeued, qdisc
                                 * queue overrun cannot happen, so
                                 * nm_os_generic_xmit_frame() did not fail
                                 * because of that.
                                 * However, packets can be dropped because
                                 * carrier is off, or because our qdisc is
                                 * being deactivated, or possibly for other
                                 * reasons. In these cases, we just let the
                                 * packet to be dropped. */
                                IFRATE(rate_ctx.new.txdrop++);
                        }

                        slot->flags &= ~(NS_REPORT | NS_BUF_CHANGED);
                        nm_i = nm_next(nm_i, lim);
                        IFRATE(rate_ctx.new.txpkt++);
                }
                if (a.head != NULL) {
                        a.addr = NULL;
                        nm_os_generic_xmit_frame(&a);
                }
                /* Update hwcur to the next slot to transmit. Here nm_i
                 * is not necessarily head, we could break early. */
                kring->nr_hwcur = nm_i;

#ifdef __FreeBSD__
                NET_EPOCH_EXIT(et);
#endif
        }

        if (!gna->txqdisc && (flags & NAF_FORCE_RECLAIM || nm_kr_txempty(kring))) {
                /* No more available slots? Set a notification event
                 * on a netmap slot that will be cleaned in the future.
                 * No doublecheck is performed, since txsync() will be
                 * called twice by netmap_poll().
                 */
                generic_set_tx_event(kring, nm_i);
        }

        /*
         * Second, reclaim completed buffers
         */
        generic_netmap_tx_clean(kring, gna->txqdisc);

        return 0;
}


/*
 * This handler is registered (through nm_os_catch_rx())
 * within the attached network interface
 * in the RX subsystem, so that every mbuf passed up by
 * the driver can be stolen to the network stack.
 * Stolen packets are put in a queue where the
 * generic_netmap_rxsync() callback can extract them.
 * Returns 1 if the packet was stolen, 0 otherwise.
 */
int
generic_rx_handler(if_t ifp, struct mbuf *m)
{
        struct netmap_adapter *na = NA(ifp);
        struct netmap_generic_adapter *gna = (struct netmap_generic_adapter *)na;
        struct netmap_kring *kring;
        u_int work_done;
        u_int r = MBUF_RXQ(m); /* receive ring number */

        if (r >= na->num_rx_rings) {
                r = r % na->num_rx_rings;
        }

        kring = na->rx_rings[r];

        if (kring->nr_mode == NKR_NETMAP_OFF) {
                /* We must not intercept this mbuf. */
                return 0;
        }

        /* limit the size of the queue */
        if (unlikely(!gna->rxsg && MBUF_LEN(m) > NETMAP_BUF_SIZE(na))) {
                /* This may happen when GRO/LRO features are enabled for
                 * the NIC driver when the generic adapter does not
                 * support RX scatter-gather. */
                nm_prlim(2, "Warning: driver pushed up big packet "
                                "(size=%d)", (int)MBUF_LEN(m));
                if_inc_counter(ifp, IFCOUNTER_IQDROPS, 1);
                m_freem(m);
        } else if (unlikely(mbq_len(&kring->rx_queue) > na->num_rx_desc)) {
                if_inc_counter(ifp, IFCOUNTER_IQDROPS, 1);
                m_freem(m);
        } else {
                mbq_safe_enqueue(&kring->rx_queue, m);
        }

        if (netmap_generic_mit < 32768) {
                /* no rx mitigation, pass notification up */
                netmap_generic_irq(na, r, &work_done);
        } else {
                /* same as send combining, filter notification if there is a
                 * pending timer, otherwise pass it up and start a timer.
                 */
                if (likely(nm_os_mitigation_active(&gna->mit[r]))) {
                        /* Record that there is some pending work. */
                        gna->mit[r].mit_pending = 1;
                } else {
                        netmap_generic_irq(na, r, &work_done);
                        nm_os_mitigation_start(&gna->mit[r]);
                }
        }

        /* We have intercepted the mbuf. */
        return 1;
}

/*
 * generic_netmap_rxsync() extracts mbufs from the queue filled by
 * generic_netmap_rx_handler() and puts their content in the netmap
 * receive ring.
 * Access must be protected because the rx handler is asynchronous,
 */
static int
generic_netmap_rxsync(struct netmap_kring *kring, int flags)
{
        struct netmap_ring *ring = kring->ring;
        struct netmap_adapter *na = kring->na;
        u_int nm_i;     /* index into the netmap ring */ //j,
        u_int n;
        u_int const lim = kring->nkr_num_slots - 1;
        u_int const head = kring->rhead;
        int force_update = (flags & NAF_FORCE_READ) || kring->nr_kflags & NKR_PENDINTR;

        /* Adapter-specific variables. */
        u_int nm_buf_len = NETMAP_BUF_SIZE(na);
        struct mbq tmpq;
        struct mbuf *m;
        int avail; /* in bytes */
        int mlen;
        int copy;

        if (head > lim)
                return netmap_ring_reinit(kring);

        IFRATE(rate_ctx.new.rxsync++);

        /*
         * First part: skip past packets that userspace has released.
         * This can possibly make room for the second part.
         */
        nm_i = kring->nr_hwcur;
        if (nm_i != head) {
                /* Userspace has released some packets. */
                for (n = 0; nm_i != head; n++) {
                        struct netmap_slot *slot = &ring->slot[nm_i];

                        slot->flags &= ~NS_BUF_CHANGED;
                        nm_i = nm_next(nm_i, lim);
                }
                kring->nr_hwcur = head;
        }

        /*
         * Second part: import newly received packets.
         */
        if (!netmap_no_pendintr && !force_update) {
                return 0;
        }

        nm_i = kring->nr_hwtail; /* First empty slot in the receive ring. */

        /* Compute the available space (in bytes) in this netmap ring.
         * The first slot that is not considered in is the one before
         * nr_hwcur. */

        avail = nm_prev(kring->nr_hwcur, lim) - nm_i;
        if (avail < 0)
                avail += lim + 1;
        avail *= nm_buf_len;

        /* First pass: While holding the lock on the RX mbuf queue,
         * extract as many mbufs as they fit the available space,
         * and put them in a temporary queue.
         * To avoid performing a per-mbuf division (mlen / nm_buf_len) to
         * to update avail, we do the update in a while loop that we
         * also use to set the RX slots, but without performing the copy. */
        mbq_init(&tmpq);
        mbq_lock(&kring->rx_queue);
        for (n = 0;; n++) {
                m = mbq_peek(&kring->rx_queue);
                if (!m) {
                        /* No more packets from the driver. */
                        break;
                }

                mlen = MBUF_LEN(m);
                if (mlen > avail) {
                        /* No more space in the ring. */
                        break;
                }

                mbq_dequeue(&kring->rx_queue);

                while (mlen) {
                        copy = nm_buf_len;
                        if (mlen < copy) {
                                copy = mlen;
                        }
                        mlen -= copy;
                        avail -= nm_buf_len;

                        ring->slot[nm_i].len = copy;
                        ring->slot[nm_i].flags = (mlen ? NS_MOREFRAG : 0);
                        nm_i = nm_next(nm_i, lim);
                }

                mbq_enqueue(&tmpq, m);
        }
        mbq_unlock(&kring->rx_queue);

        /* Second pass: Drain the temporary queue, going over the used RX slots,
         * and perform the copy out of the RX queue lock. */
        nm_i = kring->nr_hwtail;

        for (;;) {
                void *nmaddr;
                int ofs = 0;
                int morefrag;

                m = mbq_dequeue(&tmpq);
                if (!m) {
                        break;
                }

                do {
                        nmaddr = NMB(na, &ring->slot[nm_i]);
                        /* We only check the address here on generic rx rings. */
                        if (nmaddr == NETMAP_BUF_BASE(na)) { /* Bad buffer */
                                m_freem(m);
                                mbq_purge(&tmpq);
                                mbq_fini(&tmpq);
                                return netmap_ring_reinit(kring);
                        }

                        copy = ring->slot[nm_i].len;
                        m_copydata(m, ofs, copy, nmaddr);
                        ofs += copy;
                        morefrag = ring->slot[nm_i].flags & NS_MOREFRAG;
                        nm_i = nm_next(nm_i, lim);
                } while (morefrag);

                m_freem(m);
        }

        mbq_fini(&tmpq);

        if (n) {
                kring->nr_hwtail = nm_i;
                IFRATE(rate_ctx.new.rxpkt += n);
        }
        kring->nr_kflags &= ~NKR_PENDINTR;

        return 0;
}

static void
generic_netmap_dtor(struct netmap_adapter *na)
{
        struct netmap_generic_adapter *gna = (struct netmap_generic_adapter*)na;
        if_t ifp = netmap_generic_getifp(gna);
        struct netmap_adapter *prev_na = gna->prev;

        if (prev_na != NULL) {
                netmap_adapter_put(prev_na);
                if (nm_iszombie(na)) {
                        /*
                         * The driver has been removed without releasing
                         * the reference so we need to do it here.
                         */
                        netmap_adapter_put(prev_na);
                }
                nm_prinf("Native netmap adapter for %s restored", prev_na->name);
        }
        NM_RESTORE_NA(ifp, prev_na);
        na->ifp = NULL;
        nm_prinf("Emulated netmap adapter for %s destroyed", na->name);
}

int
na_is_generic(struct netmap_adapter *na)
{
        return na->nm_register == generic_netmap_register;
}

/*
 * generic_netmap_attach() makes it possible to use netmap on
 * a device without native netmap support.
 * This is less performant than native support but potentially
 * faster than raw sockets or similar schemes.
 *
 * In this "emulated" mode, netmap rings do not necessarily
 * have the same size as those in the NIC. We use a default
 * value and possibly override it if the OS has ways to fetch the
 * actual configuration.
 */
int
generic_netmap_attach(if_t ifp)
{
        struct netmap_adapter *na;
        struct netmap_generic_adapter *gna;
        int retval;
        u_int num_tx_desc, num_rx_desc;

#ifdef __FreeBSD__
        if (if_gettype(ifp) == IFT_LOOP) {
                nm_prerr("if_loop is not supported by %s", __func__);
                return EINVAL;
        }
#endif

        if (NM_NA_CLASH(ifp)) {
                /* If NA(ifp) is not null but there is no valid netmap
                 * adapter it means that someone else is using the same
                 * pointer (e.g. ax25_ptr on linux). This happens for
                 * instance when also PF_RING is in use. */
                nm_prerr("Error: netmap adapter hook is busy");
                return EBUSY;
        }

        num_tx_desc = num_rx_desc = netmap_generic_ringsize; /* starting point */

        nm_os_generic_find_num_desc(ifp, &num_tx_desc, &num_rx_desc); /* ignore errors */
        if (num_tx_desc == 0 || num_rx_desc == 0) {
                nm_prerr("Device has no hw slots (tx %u, rx %u)", num_tx_desc, num_rx_desc);
                return EINVAL;
        }

        gna = nm_os_malloc(sizeof(*gna));
        if (gna == NULL) {
                nm_prerr("no memory on attach, give up");
                return ENOMEM;
        }
        na = (struct netmap_adapter *)gna;
        strlcpy(na->name, if_name(ifp), sizeof(na->name));
        na->ifp = ifp;
        na->num_tx_desc = num_tx_desc;
        na->num_rx_desc = num_rx_desc;
        na->rx_buf_maxsize = 32768;
        na->nm_register = &generic_netmap_register;
        na->nm_txsync = &generic_netmap_txsync;
        na->nm_rxsync = &generic_netmap_rxsync;
        na->nm_dtor = &generic_netmap_dtor;
        /* when using generic, NAF_NETMAP_ON is set so we force
         * NAF_SKIP_INTR to use the regular interrupt handler
         */
        na->na_flags = NAF_SKIP_INTR | NAF_HOST_RINGS;

        nm_prdis("[GNA] num_tx_queues(%d), real_num_tx_queues(%d), len(%lu)",
                        ifp->num_tx_queues, ifp->real_num_tx_queues,
                        ifp->tx_queue_len);
        nm_prdis("[GNA] num_rx_queues(%d), real_num_rx_queues(%d)",
                        ifp->num_rx_queues, ifp->real_num_rx_queues);

        nm_os_generic_find_num_queues(ifp, &na->num_tx_rings, &na->num_rx_rings);

        retval = netmap_attach_common(na);
        if (retval) {
                nm_os_free(gna);
                return retval;
        }

        if (NM_NA_VALID(ifp)) {
                gna->prev = NA(ifp); /* save old na */
                netmap_adapter_get(gna->prev);
        }
        NM_ATTACH_NA(ifp, na);

        nm_os_generic_set_features(gna);

        nm_prinf("Emulated adapter for %s created (prev was %s)", na->name,
            gna->prev ? gna->prev->name : "NULL");

        return retval;
}