/*
 * Copyright (C) 2014-2016 Giuseppe Lettieri
 * 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.
 */

/*
 *
 * Monitors
 *
 * netmap monitors can be used to do monitoring of network traffic
 * on another adapter, when the latter adapter is working in netmap mode.
 *
 * Monitors offer to userspace the same interface as any other netmap port,
 * with as many pairs of netmap rings as the monitored adapter.
 * However, only the rx rings are actually used. Each monitor rx ring receives
 * the traffic transiting on both the tx and rx corresponding rings in the
 * monitored adapter. During registration, the user can choose if she wants
 * to intercept tx only, rx only, or both tx and rx traffic.
 * The slots containing traffic intercepted in the tx direction will have
 * the NS_TXMON flag set.
 *
 * If the monitor is not able to cope with the stream of frames, excess traffic
 * will be dropped.
 *
 * If the monitored adapter leaves netmap mode, the monitor has to be restarted.
 *
 * Monitors can be either zero-copy or copy-based.
 *
 * Copy monitors see the frames before they are consumed:
 *
 *  - For tx traffic, this is when the application sends them, before they are
 *    passed down to the adapter.
 *
 *  - For rx traffic, this is when they are received by the adapter, before
 *    they are sent up to the application, if any (note that, if no
 *    application is reading from a monitored ring, the ring will eventually
 *    fill up and traffic will stop).
 *
 * Zero-copy monitors only see the frames after they have been consumed:
 *
 *  - For tx traffic, this is after the slots containing the frames have been
 *    marked as free. Note that this may happen at a considerably delay after
 *    frame transmission, since freeing of slots is often done lazily.
 *
 *  - For rx traffic, this is after the consumer on the monitored adapter
 *    has released them. In most cases, the consumer is a userspace
 *    application which may have modified the frame contents.
 *
 * Several copy or zero-copy monitors may be active on any ring.
 *
 */


#if defined(__FreeBSD__)
#include <sys/cdefs.h> /* prerequisite */

#include <sys/types.h>
#include <sys/errno.h>
#include <sys/param.h>  /* defines used in kernel.h */
#include <sys/kernel.h> /* types used in module initialization */
#include <sys/malloc.h>
#include <sys/poll.h>
#include <sys/lock.h>
#include <sys/rwlock.h>
#include <sys/selinfo.h>
#include <sys/sysctl.h>
#include <sys/socket.h> /* sockaddrs */
#include <net/if.h>
#include <net/if_var.h>
#include <machine/bus.h>        /* bus_dmamap_* */
#include <sys/refcount.h>


#elif defined(linux)

#include "bsd_glue.h"

#elif defined(__APPLE__)

#warning OSX support is only partial
#include "osx_glue.h"

#elif defined(_WIN32)
#include "win_glue.h"
#else

#error  Unsupported platform

#endif /* unsupported */

/*
 * common headers
 */

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

#ifdef WITH_MONITOR

#define NM_MONITOR_MAXSLOTS 4096

/*
 ********************************************************************
 * functions common to both kind of monitors
 ********************************************************************
 */

static int netmap_zmon_reg(struct netmap_adapter *, int);
static int
nm_is_zmon(struct netmap_adapter *na)
{
        return na->nm_register == netmap_zmon_reg;
}

/* nm_sync callback for the monitor's own tx rings.
 * This makes no sense and always returns error
 */
static int
netmap_monitor_txsync(struct netmap_kring *kring, int flags)
{
        nm_prlim(1, "%s %x", kring->name, flags);
        return EIO;
}

/* nm_sync callback for the monitor's own rx rings.
 * Note that the lock in netmap_zmon_parent_sync only protects
 * writers among themselves. Synchronization between writers
 * (i.e., netmap_zmon_parent_txsync and netmap_zmon_parent_rxsync)
 * and readers (i.e., netmap_zmon_rxsync) relies on memory barriers.
 */
static int
netmap_monitor_rxsync(struct netmap_kring *kring, int flags)
{
        struct netmap_monitor_adapter *mna =
                (struct netmap_monitor_adapter *)kring->na;
        if (unlikely(mna->priv.np_na == NULL)) {
                /* parent left netmap mode */
                return EIO;
        }
        nm_prdis("%s %x", kring->name, flags);
        kring->nr_hwcur = kring->rhead;
        mb();
        return 0;
}

/* nm_krings_create callbacks for monitors.
 */
static int
netmap_monitor_krings_create(struct netmap_adapter *na)
{
        int error = netmap_krings_create(na, 0);
        enum txrx t;

        if (error)
                return error;
        /* override the host rings callbacks */
        for_rx_tx(t) {
                int i;
                u_int first = nma_get_nrings(na, t);
                for (i = 0; i < nma_get_host_nrings(na, t); i++) {
                        struct netmap_kring *kring = NMR(na, t)[first + i];
                        kring->nm_sync = t == NR_TX ? netmap_monitor_txsync :
                                                      netmap_monitor_rxsync;
                }
        }
        return 0;
}

/* nm_krings_delete callback for monitors */
static void
netmap_monitor_krings_delete(struct netmap_adapter *na)
{
        netmap_krings_delete(na);
}


static u_int
nm_txrx2flag(enum txrx t)
{
        return (t == NR_RX ? NR_MONITOR_RX : NR_MONITOR_TX);
}

/* allocate the monitors array in the monitored kring */
static int
nm_monitor_alloc(struct netmap_kring *kring, u_int n)
{
        size_t old_len, len;
        struct netmap_kring **nm;

        if (n <= kring->max_monitors)
                /* we already have more entries that requested */
                return 0;

        old_len = sizeof(struct netmap_kring *)*kring->max_monitors;
        len = sizeof(struct netmap_kring *) * n;
        nm = nm_os_realloc(kring->monitors, len, old_len);
        if (nm == NULL)
                return ENOMEM;

        kring->monitors = nm;
        kring->max_monitors = n;

        return 0;
}

/* deallocate the parent array in the parent adapter */
static void
nm_monitor_dealloc(struct netmap_kring *kring)
{
        if (kring->monitors) {
                if (kring->n_monitors > 0) {
                        nm_prerr("freeing not empty monitor array for %s (%d dangling monitors)!",
                            kring->name, kring->n_monitors);
                }
                nm_os_free(kring->monitors);
                kring->monitors = NULL;
                kring->max_monitors = 0;
                kring->n_monitors = 0;
        }
}

/* returns 1 iff kring has no monitors */
static inline int
nm_monitor_none(struct netmap_kring *kring)
{
        return kring->n_monitors == 0 &&
                kring->zmon_list[NR_TX].next == NULL &&
                kring->zmon_list[NR_RX].next == NULL;
}

/*
 * monitors work by replacing the nm_sync() and possibly the
 * nm_notify() callbacks in the monitored rings.
 */
static int netmap_zmon_parent_txsync(struct netmap_kring *, int);
static int netmap_zmon_parent_rxsync(struct netmap_kring *, int);
static int netmap_monitor_parent_txsync(struct netmap_kring *, int);
static int netmap_monitor_parent_rxsync(struct netmap_kring *, int);
static int netmap_monitor_parent_notify(struct netmap_kring *, int);

static int
nm_monitor_dummycb(struct netmap_kring *kring, int flags)
{
        (void)kring;
        (void)flags;
        return 0;
}

static void
nm_monitor_intercept_callbacks(struct netmap_kring *kring)
{
        nm_prdis("intercept callbacks on %s", kring->name);
        kring->mon_sync = kring->nm_sync != NULL ?
                kring->nm_sync : nm_monitor_dummycb;
        kring->mon_notify = kring->nm_notify;
        if (kring->tx == NR_TX) {
                kring->nm_sync = netmap_monitor_parent_txsync;
        } else {
                kring->nm_sync = netmap_monitor_parent_rxsync;
                kring->nm_notify = netmap_monitor_parent_notify;
                kring->mon_tail = kring->nr_hwtail;
        }
}

static void
nm_monitor_restore_callbacks(struct netmap_kring *kring)
{
        nm_prdis("restoring callbacks on %s", kring->name);
        kring->nm_sync = kring->mon_sync;
        kring->mon_sync = NULL;
        if (kring->tx == NR_RX) {
                kring->nm_notify = kring->mon_notify;
        }
        kring->mon_notify = NULL;
}

static struct netmap_kring *
nm_zmon_list_head(struct netmap_kring *mkring, enum txrx t)
{
        struct netmap_adapter *na = mkring->na;
        struct netmap_kring *kring = mkring;
        struct netmap_zmon_list *z = &kring->zmon_list[t];
        /* reach the head of the list */
        while (nm_is_zmon(na) && z->prev != NULL) {
                kring = z->prev;
                na = kring->na;
                z = &kring->zmon_list[t];
        }
        return nm_is_zmon(na) ? NULL : kring;
}

/* add the monitor mkring to the list of monitors of kring.
 * If this is the first monitor, intercept the callbacks
 */
static int
netmap_monitor_add(struct netmap_kring *mkring, struct netmap_kring *kring, int zmon)
{
        int error = NM_IRQ_COMPLETED;
        enum txrx t = kring->tx;
        struct netmap_zmon_list *z = &kring->zmon_list[t];
        struct netmap_zmon_list *mz = &mkring->zmon_list[t];
        struct netmap_kring *ikring = kring;

        /* a zero-copy monitor which is not the first in the list
         * must monitor the previous monitor
         */
        if (zmon && z->prev != NULL)
                ikring = z->prev; /* tail of the list */

        /* synchronize with concurrently running nm_sync()s */
        nm_kr_stop(kring, NM_KR_LOCKED);

        if (nm_monitor_none(ikring)) {
                /* this is the first monitor, intercept the callbacks */
                nm_prdis("%s: intercept callbacks on %s", mkring->name, ikring->name);
                nm_monitor_intercept_callbacks(ikring);
        }

        if (zmon) {
                /* append the zmon to the list */
                ikring->zmon_list[t].next = mkring;
                z->prev = mkring; /* new tail */
                mz->prev = ikring;
                mz->next = NULL;
                /* grab a reference to the previous netmap adapter
                 * in the chain (this may be the monitored port
                 * or another zero-copy monitor)
                 */
                netmap_adapter_get(ikring->na);
        } else {
                /* make sure the monitor array exists and is big enough */
                error = nm_monitor_alloc(kring, kring->n_monitors + 1);
                if (error)
                        goto out;
                kring->monitors[kring->n_monitors] = mkring;
                mkring->mon_pos[kring->tx] = kring->n_monitors;
                kring->n_monitors++;
        }

out:
        nm_kr_start(kring);
        return error;
}

/* remove the monitor mkring from the list of monitors of kring.
 * If this is the last monitor, restore the original callbacks
 */
static void
netmap_monitor_del(struct netmap_kring *mkring, struct netmap_kring *kring, enum txrx t)
{
        int zmon = nm_is_zmon(mkring->na);
        struct netmap_zmon_list *mz = &mkring->zmon_list[t];
        struct netmap_kring *ikring = kring;


        if (zmon) {
                /* get to the head of the list */
                kring = nm_zmon_list_head(mkring, t);
                ikring = mz->prev;
        }

        /* synchronize with concurrently running nm_sync()s
         * if kring is NULL (orphaned list) the monitored port
         * has exited netmap mode, so there is nothing to stop
         */
        if (kring != NULL)
                nm_kr_stop(kring, NM_KR_LOCKED);

        if (zmon) {
                /* remove the monitor from the list */
                if (mz->next != NULL) {
                        mz->next->zmon_list[t].prev = mz->prev;
                        /* we also need to let the next monitor drop the
                         * reference to us and grab the reference to the
                         * previous ring owner, instead
                         */
                        if (mz->prev != NULL)
                                netmap_adapter_get(mz->prev->na);
                        netmap_adapter_put(mkring->na);
                } else if (kring != NULL) {
                        /* in the monitored kring, prev is actually the
                         * pointer to the tail of the list
                         */
                        kring->zmon_list[t].prev =
                                (mz->prev != kring ? mz->prev : NULL);
                }
                if (mz->prev != NULL) {
                        netmap_adapter_put(mz->prev->na);
                        mz->prev->zmon_list[t].next = mz->next;
                }
                mz->prev = NULL;
                mz->next = NULL;
        } else {
                /* this is a copy monitor */
                uint32_t mon_pos = mkring->mon_pos[kring->tx];
                kring->n_monitors--;
                if (mon_pos != kring->n_monitors) {
                        kring->monitors[mon_pos] =
                                kring->monitors[kring->n_monitors];
                        kring->monitors[mon_pos]->mon_pos[kring->tx] = mon_pos;
                }
                kring->monitors[kring->n_monitors] = NULL;
                if (kring->n_monitors == 0) {
                        nm_monitor_dealloc(kring);
                }
        }

        if (ikring != NULL && nm_monitor_none(ikring)) {
                /* this was the last monitor, restore the callbacks */
                nm_monitor_restore_callbacks(ikring);
        }

        if (kring != NULL)
                nm_kr_start(kring);
}


/* This is called when the monitored adapter leaves netmap mode
 * (see netmap_do_unregif).
 * We need to notify the monitors that the monitored rings are gone.
 * We do this by setting their mna->priv.np_na to NULL.
 * Note that the rings are already stopped when this happens, so
 * no monitor ring callback can be active.
 */
void
netmap_monitor_stop(struct netmap_adapter *na)
{
        enum txrx t;

        for_rx_tx(t) {
                u_int i;

                for (i = 0; i < netmap_all_rings(na, t); i++) {
                        struct netmap_kring *kring = NMR(na, t)[i];
                        struct netmap_zmon_list *z = &kring->zmon_list[t];
                        u_int j;

                        if (nm_monitor_none(kring))
                                continue;

                        for (j = 0; j < kring->n_monitors; j++) {
                                struct netmap_kring *mkring =
                                        kring->monitors[j];
                                struct netmap_monitor_adapter *mna =
                                        (struct netmap_monitor_adapter *)mkring->na;
                                /* forget about this adapter */
                                if (mna->priv.np_na != NULL) {
                                        netmap_adapter_put(mna->priv.np_na);
                                        mna->priv.np_na = NULL;
                                }
                                kring->monitors[j] = NULL;
                        }
                        kring->n_monitors = 0;
                        nm_monitor_dealloc(kring);

                        if (!nm_is_zmon(na)) {
                                /* we are the head of at most one list */
                                struct netmap_kring *zkring;
                                for (zkring = z->next; zkring != NULL;
                                                zkring = zkring->zmon_list[t].next)
                                {
                                        struct netmap_monitor_adapter *next =
                                                (struct netmap_monitor_adapter *)zkring->na;
                                        /* let the monitor forget about us */
                                        netmap_adapter_put(next->priv.np_na); /* nop if null */
                                        next->priv.np_na = NULL;
                                        /* drop the additional ref taken in netmap_monitor_add() */
                                        netmap_adapter_put(zkring->zmon_list[t].prev->na);
                                }
                                /* orphan the zmon list */
                                if (z->next != NULL)
                                        z->next->zmon_list[t].prev = NULL;
                                z->next = NULL;
                                z->prev = NULL;
                        }

                        nm_monitor_restore_callbacks(kring);
                }
        }
}


/* common functions for the nm_register() callbacks of both kind of
 * monitors.
 */
static int
netmap_monitor_reg_common(struct netmap_adapter *na, int onoff, int zmon)
{
        struct netmap_monitor_adapter *mna =
                (struct netmap_monitor_adapter *)na;
        struct netmap_priv_d *priv = &mna->priv;
        struct netmap_adapter *pna = priv->np_na;
        struct netmap_kring *kring, *mkring;
        int i;
        enum txrx t, s;

        nm_prdis("%p: onoff %d", na, onoff);
        if (onoff) {
                if (pna == NULL) {
                        /* parent left netmap mode, fatal */
                        nm_prerr("%s: parent left netmap mode", na->name);
                        return ENXIO;
                }
                for_rx_tx(t) {
                        for (i = 0; i < netmap_all_rings(na, t); i++) {
                                mkring = NMR(na, t)[i];
                                if (!nm_kring_pending_on(mkring))
                                        continue;
                                mkring->nr_mode = NKR_NETMAP_ON;
                                if (t == NR_TX)
                                        continue;
                                for_rx_tx(s) {
                                        if (i > nma_get_nrings(pna, s))
                                                continue;
                                        if (mna->flags & nm_txrx2flag(s)) {
                                                kring = NMR(pna, s)[i];
                                                netmap_monitor_add(mkring, kring, zmon);
                                        }
                                }
                        }
                }
                na->na_flags |= NAF_NETMAP_ON;
        } else {
                if (na->active_fds == 0)
                        na->na_flags &= ~NAF_NETMAP_ON;
                for_rx_tx(t) {
                        for (i = 0; i < netmap_all_rings(na, t); i++) {
                                mkring = NMR(na, t)[i];
                                if (!nm_kring_pending_off(mkring))
                                        continue;
                                mkring->nr_mode = NKR_NETMAP_OFF;
                                if (t == NR_TX)
                                        continue;
                                /* we cannot access the parent krings if the parent
                                 * has left netmap mode. This is signaled by a NULL
                                 * pna pointer
                                 */
                                if (pna == NULL)
                                        continue;
                                for_rx_tx(s) {
                                        if (i > nma_get_nrings(pna, s))
                                                continue;
                                        if (mna->flags & nm_txrx2flag(s)) {
                                                kring = NMR(pna, s)[i];
                                                netmap_monitor_del(mkring, kring, s);
                                        }
                                }
                        }
                }
        }
        return 0;
}

/*
 ****************************************************************
 * functions specific for zero-copy monitors
 ****************************************************************
 */

/*
 * Common function for both zero-copy tx and rx nm_sync()
 * callbacks
 */
static int
netmap_zmon_parent_sync(struct netmap_kring *kring, int flags, enum txrx tx)
{
        struct netmap_kring *mkring = kring->zmon_list[tx].next;
        struct netmap_ring *ring = kring->ring, *mring;
        int error = 0;
        int rel_slots, free_slots, busy, sent = 0;
        u_int beg, end, i;
        u_int lim = kring->nkr_num_slots - 1,
              mlim; // = mkring->nkr_num_slots - 1;
        uint16_t txmon = kring->tx == NR_TX ? NS_TXMON : 0;

        if (mkring == NULL) {
                nm_prlim(5, "NULL monitor on %s", kring->name);
                return 0;
        }
        mring = mkring->ring;
        mlim = mkring->nkr_num_slots - 1;

        /* get the released slots (rel_slots) */
        if (tx == NR_TX) {
                beg = kring->nr_hwtail + 1;
                error = kring->mon_sync(kring, flags);
                if (error)
                        return error;
                end = kring->nr_hwtail + 1;
        } else { /* NR_RX */
                beg = kring->nr_hwcur;
                end = kring->rhead;
        }

        rel_slots = end - beg;
        if (rel_slots < 0)
                rel_slots += kring->nkr_num_slots;

        if (!rel_slots) {
                /* no released slots, but we still need
                 * to call rxsync if this is a rx ring
                 */
                goto out_rxsync;
        }

        /* we need to lock the monitor receive ring, since it
         * is the target of bot tx and rx traffic from the monitored
         * adapter
         */
        mtx_lock(&mkring->q_lock);
        /* get the free slots available on the monitor ring */
        i = mkring->nr_hwtail;
        busy = i - mkring->nr_hwcur;
        if (busy < 0)
                busy += mkring->nkr_num_slots;
        free_slots = mlim - busy;

        if (!free_slots)
                goto out;

        /* swap min(free_slots, rel_slots) slots */
        if (free_slots < rel_slots) {
                beg += (rel_slots - free_slots);
                rel_slots = free_slots;
        }
        if (unlikely(beg >= kring->nkr_num_slots))
                beg -= kring->nkr_num_slots;

        sent = rel_slots;
        for ( ; rel_slots; rel_slots--) {
                struct netmap_slot *s = &ring->slot[beg];
                struct netmap_slot *ms = &mring->slot[i];
                uint32_t tmp;

                tmp = ms->buf_idx;
                ms->buf_idx = s->buf_idx;
                s->buf_idx = tmp;
                nm_prdis(5, "beg %d buf_idx %d", beg, tmp);

                tmp = ms->len;
                ms->len = s->len;
                s->len = tmp;

                ms->flags = (s->flags & ~NS_TXMON) | txmon;
                s->flags |= NS_BUF_CHANGED;

                beg = nm_next(beg, lim);
                i = nm_next(i, mlim);

        }
        mb();
        mkring->nr_hwtail = i;

out:
        mtx_unlock(&mkring->q_lock);

        if (sent) {
                /* notify the new frames to the monitor */
                mkring->nm_notify(mkring, 0);
        }

out_rxsync:
        if (tx == NR_RX)
                error = kring->mon_sync(kring, flags);

        return error;
}

/* callback used to replace the nm_sync callback in the monitored tx rings */
static int
netmap_zmon_parent_txsync(struct netmap_kring *kring, int flags)
{
        return netmap_zmon_parent_sync(kring, flags, NR_TX);
}

/* callback used to replace the nm_sync callback in the monitored rx rings */
static int
netmap_zmon_parent_rxsync(struct netmap_kring *kring, int flags)
{
        return netmap_zmon_parent_sync(kring, flags, NR_RX);
}

static int
netmap_zmon_reg(struct netmap_adapter *na, int onoff)
{
        return netmap_monitor_reg_common(na, onoff, 1 /* zcopy */);
}

/* nm_dtor callback for monitors */
static void
netmap_zmon_dtor(struct netmap_adapter *na)
{
        struct netmap_monitor_adapter *mna =
                (struct netmap_monitor_adapter *)na;
        struct netmap_priv_d *priv = &mna->priv;
        struct netmap_adapter *pna = priv->np_na;

        netmap_adapter_put(pna);
}

/*
 ****************************************************************
 * functions specific for copy monitors
 ****************************************************************
 */

static void
netmap_monitor_parent_sync(struct netmap_kring *kring, u_int first_new, int new_slots)
{
        u_int j;
        uint16_t txmon = kring->tx == NR_TX ? NS_TXMON : 0;

        for (j = 0; j < kring->n_monitors; j++) {
                struct netmap_kring *mkring = kring->monitors[j];
                u_int i, mlim, beg;
                int free_slots, busy, sent = 0, m;
                u_int lim = kring->nkr_num_slots - 1;
                struct netmap_ring *ring = kring->ring, *mring = mkring->ring;
                u_int max_len;
                mlim = mkring->nkr_num_slots - 1;

                /* we need to lock the monitor receive ring, since it
                 * is the target of bot tx and rx traffic from the monitored
                 * adapter
                 */
                mtx_lock(&mkring->q_lock);
                /* get the free slots available on the monitor ring */
                i = mkring->nr_hwtail;
                busy = i - mkring->nr_hwcur;
                if (busy < 0)
                        busy += mkring->nkr_num_slots;
                free_slots = mlim - busy;

                if (!free_slots)
                        goto out;

                /* copy min(free_slots, new_slots) slots */
                m = new_slots;
                beg = first_new;
                if (free_slots < m) {
                        beg += (m - free_slots);
                        if (beg >= kring->nkr_num_slots)
                                beg -= kring->nkr_num_slots;
                        m = free_slots;
                }

                for ( ; m; m--) {
                        struct netmap_slot *s = &ring->slot[beg];
                        struct netmap_slot *ms = &mring->slot[i];
                        u_int copy_len = s->len;
                        char *src = NMB_O(kring, s),
                             *dst = NMB_O(mkring, ms);

                        max_len = NETMAP_BUF_SIZE(mkring->na) - nm_get_offset(mkring, ms);
                        if (unlikely(copy_len > max_len)) {
                                nm_prlim(5, "%s->%s: truncating %d to %d", kring->name,
                                                mkring->name, copy_len, max_len);
                                copy_len = max_len;
                        }

                        memcpy(dst, src, copy_len);
                        ms->len = copy_len;
                        ms->flags = (s->flags & ~NS_TXMON) | txmon;
                        sent++;

                        beg = nm_next(beg, lim);
                        i = nm_next(i, mlim);
                }
                mb();
                mkring->nr_hwtail = i;
        out:
                mtx_unlock(&mkring->q_lock);

                if (sent) {
                        /* notify the new frames to the monitor */
                        mkring->nm_notify(mkring, 0);
                }
        }
}

/* callback used to replace the nm_sync callback in the monitored tx rings */
static int
netmap_monitor_parent_txsync(struct netmap_kring *kring, int flags)
{
        u_int first_new;
        int new_slots;

        /* get the new slots */
        if (kring->n_monitors > 0) {
                first_new = kring->nr_hwcur;
                new_slots = kring->rhead - first_new;
                if (new_slots < 0)
                        new_slots += kring->nkr_num_slots;
                if (new_slots)
                        netmap_monitor_parent_sync(kring, first_new, new_slots);
        }
        if (kring->zmon_list[NR_TX].next != NULL) {
                return netmap_zmon_parent_txsync(kring, flags);
        }
        return kring->mon_sync(kring, flags);
}

/* callback used to replace the nm_sync callback in the monitored rx rings */
static int
netmap_monitor_parent_rxsync(struct netmap_kring *kring, int flags)
{
        u_int first_new;
        int new_slots, error;

        /* get the new slots */
        if (kring->zmon_list[NR_RX].next != NULL) {
                error = netmap_zmon_parent_rxsync(kring, flags);
        } else {
                error =  kring->mon_sync(kring, flags);
        }
        if (error)
                return error;
        if (kring->n_monitors > 0) {
                first_new = kring->mon_tail;
                new_slots = kring->nr_hwtail - first_new;
                if (new_slots < 0)
                        new_slots += kring->nkr_num_slots;
                if (new_slots)
                        netmap_monitor_parent_sync(kring, first_new, new_slots);
                kring->mon_tail = kring->nr_hwtail;
        }
        return 0;
}

/* callback used to replace the nm_notify() callback in the monitored rx rings */
static int
netmap_monitor_parent_notify(struct netmap_kring *kring, int flags)
{
        int (*notify)(struct netmap_kring*, int);
        nm_prdis(5, "%s %x", kring->name, flags);
        /* ?xsync callbacks have tryget called by their callers
         * (NIOCREGIF and poll()), but here we have to call it
         * by ourself
         */
        if (nm_kr_tryget(kring, 0, NULL)) {
                /* in all cases, just skip the sync */
                return NM_IRQ_COMPLETED;
        }
        if (kring->n_monitors > 0) {
                netmap_monitor_parent_rxsync(kring, NAF_FORCE_READ);
        }
        if (nm_monitor_none(kring)) {
                /* we are no longer monitoring this ring, so both
                 * mon_sync and mon_notify are NULL
                 */
                notify = kring->nm_notify;
        } else {
                notify = kring->mon_notify;
        }
        nm_kr_put(kring);
        return notify(kring, flags);
}


static int
netmap_monitor_reg(struct netmap_adapter *na, int onoff)
{
        return netmap_monitor_reg_common(na, onoff, 0 /* no zcopy */);
}

static void
netmap_monitor_dtor(struct netmap_adapter *na)
{
        struct netmap_monitor_adapter *mna =
                (struct netmap_monitor_adapter *)na;
        struct netmap_priv_d *priv = &mna->priv;
        struct netmap_adapter *pna = priv->np_na;

        netmap_adapter_put(pna);
}


/* check if req is a request for a monitor adapter that we can satisfy */
int
netmap_get_monitor_na(struct nmreq_header *hdr, struct netmap_adapter **na,
                        struct netmap_mem_d *nmd, int create)
{
        struct nmreq_register *req = (struct nmreq_register *)(uintptr_t)hdr->nr_body;
        struct nmreq_register preq;
        struct netmap_adapter *pna; /* parent adapter */
        struct netmap_monitor_adapter *mna;
        if_t ifp = NULL;
        int  error;
        int zcopy = (req->nr_flags & NR_ZCOPY_MON);

        if (zcopy) {
                req->nr_flags |= (NR_MONITOR_TX | NR_MONITOR_RX);
        }
        if ((req->nr_flags & (NR_MONITOR_TX | NR_MONITOR_RX)) == 0) {
                nm_prdis("not a monitor");
                return 0;
        }
        /* this is a request for a monitor adapter */

        nm_prdis("flags %lx", req->nr_flags);

        /* First, try to find the adapter that we want to monitor.
         * We use the same req, after we have turned off the monitor flags.
         * In this way we can potentially monitor everything netmap understands,
         * except other monitors.
         */
        memcpy(&preq, req, sizeof(preq));
        preq.nr_flags &= ~(NR_MONITOR_TX | NR_MONITOR_RX | NR_ZCOPY_MON);
        hdr->nr_body = (uintptr_t)&preq;
        error = netmap_get_na(hdr, &pna, &ifp, nmd, create);
        hdr->nr_body = (uintptr_t)req;
        if (error) {
                nm_prerr("parent lookup failed: %d", error);
                return error;
        }
        nm_prdis("found parent: %s", pna->name);

        if (!nm_netmap_on(pna)) {
                /* parent not in netmap mode */
                /* XXX we can wait for the parent to enter netmap mode,
                 * by intercepting its nm_register callback (2014-03-16)
                 */
                nm_prerr("%s not in netmap mode", pna->name);
                error = EINVAL;
                goto put_out;
        }

        mna = nm_os_malloc(sizeof(*mna));
        if (mna == NULL) {
                error = ENOMEM;
                goto put_out;
        }
        mna->priv.np_na = pna;

        /* grab all the rings we need in the parent */
        error = netmap_interp_ringid(&mna->priv, hdr);
        if (error) {
                nm_prerr("ringid error");
                goto free_out;
        }
        snprintf(mna->up.name, sizeof(mna->up.name), "%s/%s%s%s#%lu", pna->name,
                        zcopy ? "z" : "",
                        (req->nr_flags & NR_MONITOR_RX) ? "r" : "",
                        (req->nr_flags & NR_MONITOR_TX) ? "t" : "",
                        pna->monitor_id++);

        /* the monitor supports the host rings iff the parent does */
        mna->up.na_flags |= (pna->na_flags & NAF_HOST_RINGS) & ~NAF_OFFSETS;
        if (!zcopy)
                mna->up.na_flags |= NAF_OFFSETS;
        /* a do-nothing txsync: monitors cannot be used to inject packets */
        mna->up.nm_txsync = netmap_monitor_txsync;
        mna->up.nm_rxsync = netmap_monitor_rxsync;
        mna->up.nm_krings_create = netmap_monitor_krings_create;
        mna->up.nm_krings_delete = netmap_monitor_krings_delete;
        mna->up.num_tx_rings = 1; // XXX what should we do here with chained zmons?
        /* we set the number of our rx_rings to be max(num_rx_rings, num_rx_rings)
         * in the parent
         */
        mna->up.num_rx_rings = pna->num_rx_rings;
        if (pna->num_tx_rings > pna->num_rx_rings)
                mna->up.num_rx_rings = pna->num_tx_rings;
        /* by default, the number of slots is the same as in
         * the parent rings, but the user may ask for a different
         * number
         */
        mna->up.num_tx_desc = req->nr_tx_slots;
        nm_bound_var(&mna->up.num_tx_desc, pna->num_tx_desc,
                        1, NM_MONITOR_MAXSLOTS, NULL);
        mna->up.num_rx_desc = req->nr_rx_slots;
        nm_bound_var(&mna->up.num_rx_desc, pna->num_rx_desc,
                        1, NM_MONITOR_MAXSLOTS, NULL);
        if (zcopy) {
                mna->up.nm_register = netmap_zmon_reg;
                mna->up.nm_dtor = netmap_zmon_dtor;
                /* to have zero copy, we need to use the same memory allocator
                 * as the monitored port
                 */
                mna->up.nm_mem = netmap_mem_get(pna->nm_mem);
                /* and the allocator cannot be changed */
                mna->up.na_flags |= NAF_MEM_OWNER;
        } else {
                mna->up.nm_register = netmap_monitor_reg;
                mna->up.nm_dtor = netmap_monitor_dtor;
                mna->up.nm_mem = netmap_mem_private_new(
                                mna->up.num_tx_rings,
                                mna->up.num_tx_desc,
                                mna->up.num_rx_rings,
                                mna->up.num_rx_desc,
                                0, /* extra bufs */
                                0, /* pipes */
                                &error);
                if (mna->up.nm_mem == NULL)
                        goto put_out;
        }

        error = netmap_attach_common(&mna->up);
        if (error) {
                nm_prerr("netmap_attach_common failed");
                goto mem_put_out;
        }

        /* remember the traffic directions we have to monitor */
        mna->flags = (req->nr_flags & (NR_MONITOR_TX | NR_MONITOR_RX | NR_ZCOPY_MON));

        *na = &mna->up;
        netmap_adapter_get(*na);

        /* keep the reference to the parent */
        nm_prdis("monitor ok");

        /* drop the reference to the ifp, if any */
        if (ifp)
                if_rele(ifp);

        return 0;

mem_put_out:
        netmap_mem_put(mna->up.nm_mem);
free_out:
        nm_os_free(mna);
put_out:
        netmap_unget_na(pna, ifp);
        return error;
}


#endif /* WITH_MONITOR */