channel.c

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/*
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/**
 * $Id: d6f3e31b83f774bebcfa7d3d2cb46109cc6bb828 $
 *
 * @brief Two-way thread-safe channels.
 * @file io/channel.c
 *
 * @copyright 2016 Alan DeKok (aland@freeradius.org)
 */
RCSID("$Id: d6f3e31b83f774bebcfa7d3d2cb46109cc6bb828 $")
 
#include <freeradius-devel/io/channel.h>
#include <freeradius-devel/util/debug.h>
 
#ifdef HAVE_STDATOMIC_H
#  include <stdatomic.h>
#else
#  include <freeradius-devel/util/stdatomic.h>
#endif
 
/*
 *      Debugging, mainly for channel_test
 */
#ifdef DEBUG_CHANNEL
#define MPRINT(...) fprintf(stdout, __VA_ARGS__)
#else
#define MPRINT(...)
#endif
 
/*
 *      We disable this until we fix all of the signaling issues...
 */
#define ENABLE_SKIPS (0)
 
typedef enum {
        TO_RESPONDER = 0,
        TO_REQUESTOR = 1
} fr_channel_direction_t;
 
#ifdef DEBUG_CHANNEL
static fr_table_num_sorted_t const channel_direction[] = {
        { L("to responder"),    TO_RESPONDER },
        { L("to requestor"),    TO_REQUESTOR },
};
size_t channel_direction_len = NUM_ELEMENTS(channel_direction);
#endif
 
#if 0
#define SIGNAL_INTERVAL (1000000)       //!< The minimum interval between responder signals.
#endif
 
/** Size of the atomic queues
 *
 * The queue reader MUST service the queue occasionally,
 * otherwise the writer will not be able to write.  If it's too
 * low, the writer will fail.  If it's too high, it will
 * unnecessarily use memory.  So we're better off putting it on
 * the high side.
 *
 * The reader SHOULD service the queues at inter-packet latency.
 * i.e. at 1M pps, the queue will get serviced every microsecond.
 */
#define ATOMIC_QUEUE_SIZE (1024)
 
typedef enum fr_channel_signal_t {
        FR_CHANNEL_SIGNAL_ERROR                 = FR_CHANNEL_ERROR,
        FR_CHANNEL_SIGNAL_DATA_TO_RESPONDER     = FR_CHANNEL_DATA_READY_RESPONDER,
        FR_CHANNEL_SIGNAL_DATA_TO_REQUESTOR     = FR_CHANNEL_DATA_READY_REQUESTOR,
        FR_CHANNEL_SIGNAL_OPEN                  = FR_CHANNEL_OPEN,
        FR_CHANNEL_SIGNAL_CLOSE                 = FR_CHANNEL_CLOSE,
 
        /*
         *      The preceding MUST be in the same order as fr_channel_event_t
         */
 
        FR_CHANNEL_SIGNAL_DATA_DONE_RESPONDER,
        FR_CHANNEL_SIGNAL_RESPONDER_SLEEPING,
} fr_channel_signal_t;
 
typedef struct {
        fr_channel_signal_t     signal;         //!< the signal to send
        uint64_t                ack;            //!< or the endpoint..
        fr_channel_t            *ch;            //!< the channel
} fr_channel_control_t;
 
/** One end of a channel
 *
 * Consists of a kqueue descriptor, and an atomic queue.
 * The atomic queue is there to get bulk data through, because it's more efficient
 * than pushing 1M+ events per second through a kqueue.
 */
typedef struct {
        fr_channel_direction_t  direction;      //!< Use for debug messages.
 
        fr_control_t            *control;       //!< The control plane, consisting of an atomic queue and kqueue.
 
        fr_ring_buffer_t        *rb;            //!< Ring buffer for control-plane messages.
 
        void                    *uctx;          //!< Worker context.
 
        fr_channel_recv_callback_t recv;        //!< callback for receiving messages
        void                    *recv_uctx;     //!< context for receiving messages
 
        bool                    must_signal;    //!< we need to signal the other end
 
 
        uint64_t                sequence;       //!< Sequence number for this channel.
        uint64_t                ack;            //!< Sequence number of the other end.
        uint64_t                their_view_of_my_sequence;      //!< Should be clear.
 
        uint64_t                sequence_at_last_signal;        //!< When we last signaled.
 
        fr_atomic_queue_t       *aq;            //!< The queue of messages - visible only to this channel.
 
        atomic_bool             active;         //!< Whether the channel is active.
 
        fr_channel_stats_t      stats;          //!< channel statistics
} fr_channel_end_t;
 
typedef struct fr_channel_s fr_channel_t;
 
/** A full channel, which consists of two ends
 *
 * A channel consists of an I/O identifier that can be placed in kequeue
 * and an atomic queue in each direction to allow for bidirectional communication.
 */
struct fr_channel_s {
        fr_time_delta_t         cpu_time;       //!< Total time used by the responder for this channel.
        fr_time_delta_t         processing_time; //!< Time spent by the responder processing requests.
 
        bool                    same_thread;    //!< are both ends in the same thread?
 
        fr_channel_end_t        end[2];         //!< Two ends of the channel.
};
 
fr_table_num_sorted_t const channel_signals[] = {
        { L("error"),                   FR_CHANNEL_ERROR                        },
        { L("data-to-responder"),       FR_CHANNEL_SIGNAL_DATA_TO_RESPONDER     },
        { L("data-to-requestor"),       FR_CHANNEL_DATA_READY_REQUESTOR         },
        { L("open"),                    FR_CHANNEL_OPEN                         },
        { L("close"),                   FR_CHANNEL_CLOSE                        },
        { L("data-done-responder"),     FR_CHANNEL_SIGNAL_DATA_DONE_RESPONDER   },
        { L("responder-sleeping"),      FR_CHANNEL_SIGNAL_RESPONDER_SLEEPING    },
};
size_t channel_signals_len = NUM_ELEMENTS(channel_signals);
 
fr_table_num_sorted_t const channel_packet_priority[] = {
        { L("high"),    PRIORITY_HIGH           },
        { L("low"),     PRIORITY_LOW            },
        { L("normal"),  PRIORITY_NORMAL         },
        { L("now"),     PRIORITY_NOW            }
};
size_t channel_packet_priority_len = NUM_ELEMENTS(channel_packet_priority);
 
 
/** Create a new channel
 *
 * @param[in] ctx       The talloc_ctx to allocate channel data in.
 * @param[in] requestor control plane.
 * @param[in] responder control plane.
 * @param[in] same      whether or not the channel is for the same thread
 * @return
 *      - NULL on error
 *      - channel on success
 */
fr_channel_t *fr_channel_create(TALLOC_CTX *ctx, fr_control_t *requestor, fr_control_t *responder, bool same)
{
        fr_time_t now;
        fr_channel_t *ch;
 
        ch = talloc_zero(ctx, fr_channel_t);
        if (!ch) {
        nomem:
                fr_strerror_const("Failed allocating memory");
                return NULL;
        }
 
        ch->same_thread = same;
 
        ch->end[TO_RESPONDER].direction = TO_RESPONDER;
        ch->end[TO_REQUESTOR].direction = TO_REQUESTOR;
 
        ch->end[TO_RESPONDER].aq = fr_atomic_queue_alloc(ch, ATOMIC_QUEUE_SIZE);
        if (!ch->end[TO_RESPONDER].aq) {
                talloc_free(ch);
                goto nomem;
        }
 
        ch->end[TO_REQUESTOR].aq = fr_atomic_queue_alloc(ch, ATOMIC_QUEUE_SIZE);
        if (!ch->end[TO_REQUESTOR].aq) {
                talloc_free(ch);
                goto nomem;
        }
 
        ch->end[TO_RESPONDER].control = responder;
        ch->end[TO_REQUESTOR].control = requestor;
 
        /*
         *      Create the ring buffer for the requestor to send
         *      control-plane messages to the responder, and vice-versa.
         */
        ch->end[TO_RESPONDER].rb = fr_ring_buffer_create(ch, FR_CONTROL_MAX_MESSAGES * FR_CONTROL_MAX_SIZE);
        if (!ch->end[TO_RESPONDER].rb) {
        rb_nomem:
                fr_strerror_const_push("Failed allocating ring buffer");
                talloc_free(ch);
                return NULL;
        }
 
        ch->end[TO_REQUESTOR].rb = fr_ring_buffer_create(ch, FR_CONTROL_MAX_MESSAGES * FR_CONTROL_MAX_SIZE);
        if (!ch->end[TO_REQUESTOR].rb) {
                talloc_free(ch);
                goto rb_nomem;
        }
 
        /*
         *      Initialize all of the timers to now.
         */
        now = fr_time();
 
        ch->end[TO_RESPONDER].stats.last_write = now;
        ch->end[TO_RESPONDER].stats.last_read_other = now;
        ch->end[TO_RESPONDER].stats.last_sent_signal = now;
        atomic_store(&ch->end[TO_RESPONDER].active, true);
 
        ch->end[TO_REQUESTOR].stats.last_write = now;
        ch->end[TO_REQUESTOR].stats.last_read_other = now;
        ch->end[TO_REQUESTOR].stats.last_sent_signal = now;
        atomic_store(&ch->end[TO_REQUESTOR].active, true);
 
        return ch;
}
 
 
/** Send a message via a kq user signal
 *
 * Note that the caller doesn't care about data in the event, that is
 * sent via the atomic queue.  The kevent code takes care of
 * delivering the signal once, even if it's sent by multiple requestor
 * threads.
 *
 * The thread watching the KQ knows which end it is.  So when it gets
 * the signal (and the channel pointer) it knows to look at end[0] or
 * end[1].  We also send which end in 'which' (0, 1) to further help
 * the recipient.
 *
 * @param[in] ch        the channel.
 * @param[in] when      the data was ready.  Typically taken from the message.
 * @param[in] end       of the channel that the message was written to.
 * @param[in] which     end of the channel (0/1).
 * @return
 *      - <0 on error
 *      - 0 on success
 */
static int fr_channel_data_ready(fr_channel_t *ch, fr_time_t when, fr_channel_end_t *end, fr_channel_signal_t which)
{
        fr_channel_control_t cc;
 
        end->stats.last_sent_signal = when;
        end->stats.signals++;
        end->must_signal = false;
 
        cc.signal = which;
        cc.ack = end->ack;
        cc.ch = ch;
 
        MPRINT("Signalling %s, with %s\n",
               fr_table_str_by_value(channel_direction, end->direction, "<INVALID>"),
               fr_table_str_by_value(channel_signals, which, "<INVALID>"));
 
        return fr_control_message_send(end->control, end->rb, FR_CONTROL_ID_CHANNEL, &cc, sizeof(cc));
}
 
#define IALPHA (8)
#define RTT(_old, _new) fr_time_delta_wrap((fr_time_delta_unwrap(_new) + (fr_time_delta_unwrap(_old) * (IALPHA - 1))) / IALPHA)
 
/** Send a request message into the channel
 *
 * The message should be initialized, other than "sequence" and "ack".
 *
 * This function automatically calls the recv_reply callback if there is a reply.
 *
 * @param[in] ch        the channel to send the request on.
 * @param[in] cd        the message to send.
 * @return
 *      - <0 on error
 *      - 0 on success
 */
int fr_channel_send_request(fr_channel_t *ch, fr_channel_data_t *cd)
{
        uint64_t sequence;
        fr_time_t when;
        fr_time_delta_t message_interval;
        fr_channel_end_t *requestor;
 
        if (!fr_cond_assert_msg(atomic_load(&ch->end[TO_RESPONDER].active), "Channel not active")) return -1;
 
        /*
         *      Same thread?  Just call the "recv" function directly.
         */
        if (ch->same_thread) {
                ch->end[TO_REQUESTOR].recv(ch->end[TO_REQUESTOR].recv_uctx, ch, cd);
                return 0;
        }
 
        requestor = &(ch->end[TO_RESPONDER]);
        when = cd->m.when;
 
        sequence = requestor->sequence + 1;
        cd->live.sequence = sequence;
        cd->live.ack = requestor->ack;
 
        /*
         *      Push the message onto the queue for the other end.  If
         *      the push fails, the caller should try another queue.
         */
        if (!fr_atomic_queue_push(requestor->aq, cd)) {
                fr_strerror_printf("Failed pushing to atomic queue - full.  Queue contains %zu items",
                                   fr_atomic_queue_size(requestor->aq));
                while (fr_channel_recv_reply(ch));
                return -1;
        }
 
        requestor->sequence = sequence;
        message_interval = fr_time_sub(when, requestor->stats.last_write);
 
        if (!fr_time_delta_ispos(requestor->stats.message_interval)) {
                requestor->stats.message_interval = message_interval;
        } else {
                requestor->stats.message_interval = RTT(requestor->stats.message_interval, message_interval);
        }
 
        fr_assert_msg(fr_time_lteq(requestor->stats.last_write, when),
                      "Channel data timestamp (%" PRId64") older than last channel data sent (%" PRId64 ")",
                      fr_time_unwrap(when), fr_time_unwrap(requestor->stats.last_write));
        requestor->stats.last_write = when;
 
        requestor->stats.outstanding++;
        requestor->stats.packets++;
 
        MPRINT("REQUESTOR requests %"PRIu64", num_outstanding %"PRIu64"\n", requestor->stats.packets, requestor->stats.outstanding);
 
#if ENABLE_SKIPS
        /*
         *      We just sent the first packet.  There can't possibly be a reply, so don't bother looking.
         */
        if (requestor->stats.outstanding == 1) {
 
                /*
                 *      There is at least one old packet which is
                 *      outstanding, look for a reply.
                 */
        } else if (requestor->stats.outstanding > 1) {
                bool has_reply;
 
                has_reply = fr_channel_recv_reply(ch);
 
                if (has_reply) while (fr_channel_recv_reply(ch));
 
                /*
                 *      There's no reply yet, so we still have packets outstanding.
                 *      Or, there is a reply, and there are more packets outstanding.
                 *      Skip the signal.
                 */
                if (!requestor->must_signal && (!has_reply || (has_reply && (requestor->stats.outstanding > 1)))) {
                        MPRINT("REQUESTOR SKIPS signal\n");
                        return 0;
                }
        }
#endif
 
        /*
         *      Tell the other end that there is new data ready.
         *
         *      Ignore errors on signalling.  The responder already has
         *      the packet in its inbound queue, so at some point, it
         *      will pick up the message.
         */
        MPRINT("REQUESTOR SIGNALS\n");
        (void) fr_channel_data_ready(ch, when, requestor, FR_CHANNEL_SIGNAL_DATA_TO_RESPONDER);
        return 0;
}
 
/** Receive a reply message from the channel
 *
 * @param[in] ch        the channel to read data from.
 * @return
 *      - true if there was a message received
 *      - false if there are no more messages
 */
bool fr_channel_recv_reply(fr_channel_t *ch)
{
        fr_channel_data_t *cd;
        fr_channel_end_t *requestor;
        fr_atomic_queue_t *aq;
 
        fr_assert(ch->end[TO_RESPONDER].recv != NULL);
 
        aq = ch->end[TO_REQUESTOR].aq;
        requestor = &(ch->end[TO_RESPONDER]);
 
        /*
         *      It's OK for the queue to be empty.
         */
        if (!fr_atomic_queue_pop(aq, (void **) &cd)) return false;
 
        /*
         *      We want an exponential moving average for round trip
         *      time, where "alpha" is a number between [0,1)
         *
         *      RTT_new = alpha * RTT_old + (1 - alpha) * RTT_sample
         *
         *      BUT we use fixed-point arithmetic, so we need to use inverse alpha,
         *      which works out to the following equation:
         *
         *      RTT_new = (RTT_sample + (ialpha - 1) * RTT_old) / ialpha
         *
         *      NAKs have zero processing time, so we ignore them for
         *      the purpose of RTT.
         */
        if (fr_time_delta_ispos(cd->reply.processing_time)) {
                ch->processing_time = RTT(ch->processing_time, cd->reply.processing_time);
        }
        ch->cpu_time = cd->reply.cpu_time;
 
        /*
         *      Update the outbound channel with the knowledge that
         *      we've received one more reply, and with the responders
         *      ACK.
         */
        fr_assert(requestor->stats.outstanding > 0);
        fr_assert(cd->live.sequence > requestor->ack);
        fr_assert(cd->live.sequence <= requestor->sequence); /* must have fewer replies than requests */
 
        requestor->stats.outstanding--;
        requestor->ack = cd->live.sequence;
        requestor->their_view_of_my_sequence = cd->live.ack;
 
        fr_assert(fr_time_lteq(requestor->stats.last_read_other, cd->m.when));
        requestor->stats.last_read_other = cd->m.when;
 
        ch->end[TO_RESPONDER].recv(ch->end[TO_RESPONDER].recv_uctx, ch, cd);
 
        return true;
}
 
 
/** Receive a request message from the channel
 *
 * @param[in] ch the channel
 * @return
 *      - true if there was a message received
 *      - false if there are no more messages
 */
bool fr_channel_recv_request(fr_channel_t *ch)
{
        fr_channel_data_t *cd;
        fr_channel_end_t *responder;
        fr_atomic_queue_t *aq;
 
        aq = ch->end[TO_RESPONDER].aq;
        responder = &(ch->end[TO_REQUESTOR]);
 
        /*
         *      It's OK for the queue to be empty.
         */
        if (!fr_atomic_queue_pop(aq, (void **) &cd)) return false;
 
        fr_assert(cd->live.sequence > responder->ack);
        fr_assert(cd->live.sequence >= responder->sequence); /* must have more requests than replies */
 
        responder->stats.outstanding++;
        responder->ack = cd->live.sequence;
        responder->their_view_of_my_sequence = cd->live.ack;
 
        fr_assert(fr_time_lteq(responder->stats.last_read_other, cd->m.when));
        responder->stats.last_read_other = cd->m.when;
 
        ch->end[TO_REQUESTOR].recv(ch->end[TO_REQUESTOR].recv_uctx, ch, cd);
 
        return true;
}
 
/** Send a reply message into the channel
 *
 * The message should be initialized, other than "sequence" and "ack".
 *
 * @param[in] ch                the channel to send the reply on.
 * @param[in] cd                the message to send
 * @return
 *      - <0 on error
 *      - 0 on success
 */
int fr_channel_send_reply(fr_channel_t *ch, fr_channel_data_t *cd)
{
        uint64_t                sequence;
        fr_time_t               when;
        fr_time_delta_t         message_interval;
        fr_channel_end_t        *responder;
 
        if (!fr_cond_assert_msg(atomic_load(&ch->end[TO_REQUESTOR].active), "Channel not active")) return -1;
 
        /*
         *      Same thread?  Just call the "recv" function directly.
         */
        if (ch->same_thread) {
                ch->end[TO_RESPONDER].recv(ch->end[TO_RESPONDER].recv_uctx, ch, cd);
                return 0;
        }
 
        responder = &(ch->end[TO_REQUESTOR]);
 
        when = cd->m.when;
 
        sequence = responder->sequence + 1;
        cd->live.sequence = sequence;
        cd->live.ack = responder->ack;
 
        if (!fr_atomic_queue_push(responder->aq, cd)) {
                fr_strerror_printf("Failed pushing to atomic queue - full.  Queue contains %zu items",
                                   fr_atomic_queue_size(responder->aq));
                while (fr_channel_recv_request(ch));
                return -1;
        }
 
        fr_assert(responder->stats.outstanding > 0);
        responder->stats.outstanding--;
        responder->stats.packets++;
 
        MPRINT("\tRESPONDER replies %"PRIu64", num_outstanding %"PRIu64"\n", responder->stats.packets, responder->stats.outstanding);
 
        responder->sequence = sequence;
        message_interval = fr_time_sub(when, responder->stats.last_write);
        responder->stats.message_interval = RTT(responder->stats.message_interval, message_interval);
 
        fr_assert_msg(fr_time_lteq(responder->stats.last_write, when),
                      "Channel data timestamp (%" PRId64") older than last channel data sent (%" PRId64 ")",
                      fr_time_unwrap(when), fr_time_unwrap(responder->stats.last_write));
        responder->stats.last_write = when;
 
        /*
         *      Even if we think we have no more packets to process,
         *      the caller may have sent us one.  Go check the input
         *      channel.
         */
        while (fr_channel_recv_request(ch));
 
        /*
         *      No packets outstanding, we HAVE to signal the requestor
         *      thread.
         */
        if (responder->stats.outstanding == 0) {
                (void) fr_channel_data_ready(ch, when, responder, FR_CHANNEL_SIGNAL_DATA_DONE_RESPONDER);
                return 0;
        }
 
        MPRINT("\twhen - last_read_other = %"PRIu64" - %"PRIu64" = %"PRIu64"\n", when, responder->stats.last_read_other, when - responder->stats.last_read_other);
        MPRINT("\twhen - last signal = %"PRIu64" - %"PRIu64" = %"PRIu64"\n", when, responder->stats.last_sent_signal, when - responder->stats.last_sent_signal);
        MPRINT("\tsequence - ack = %"PRIu64" - %"PRIu64" = %"PRIu64"\n", responder->sequence, responder->their_view_of_my_sequence, responder->sequence - responder->their_view_of_my_sequence);
 
#ifdef __APPLE__
        /*
         *      If we've sent them a signal since the last ACK, they
         *      will receive it, and process the packets.  So we don't
         *      need to signal them again.
         *
         *      But... this doesn't appear to work on the Linux
         *      libkqueue implementation.
         */
        if (responder->sequence_at_last_signal > responder->their_view_of_my_sequence) return 0;
#endif
 
        /*
         *      If we've received a new packet in the last while, OR
         *      we've sent a signal in the last while, then we don't
         *      need to send a new signal.  But we DO send a signal if
         *      we haven't seen an ACK for a few packets.
         *
         *      FIXME: make these limits configurable, or include
         *      predictions about packet processing time?
         */
        fr_assert(responder->their_view_of_my_sequence <= responder->sequence);
#if 0
        if (((responder->sequence - their_view_of_my_sequence) <= 1000) &&
            ((when - responder->stats.last_read_other < SIGNAL_INTERVAL) ||
             ((when - responder->stats.last_sent_signal) < SIGNAL_INTERVAL))) {
                MPRINT("\tRESPONDER SKIPS signal\n");
                return 0;
        }
#endif
 
        MPRINT("\tRESPONDER SIGNALS num_outstanding %"PRIu64"\n", responder->stats.outstanding);
        (void) fr_channel_data_ready(ch, when, responder, FR_CHANNEL_SIGNAL_DATA_TO_REQUESTOR);
        return 0;
}
 
 
/** Don't send a reply message into the channel
 *
 * The message should be the one we received from the network.
 *
 * @param[in] ch                the channel on which we're dropping a packet
 * @return
 *      - <0 on error
 *      - 0 on success
 */
int fr_channel_null_reply(fr_channel_t *ch)
{
        fr_channel_end_t *responder;
 
        responder = &(ch->end[TO_REQUESTOR]);
 
        responder->sequence++;
        return 0;
}
 
 
 
/** Signal a channel that the responder is sleeping
 *
 * This function should be called from the responders idle loop.
 * i.e. only when it has nothing else to do.
 *
 * @param[in] ch        the channel to signal we're no longer listening on.
 * @return
 *      - <0 on error
 *      - 0 on success
 */
int fr_channel_responder_sleeping(fr_channel_t *ch)
{
        fr_channel_end_t *responder;
        fr_channel_control_t cc;
 
        responder = &(ch->end[TO_REQUESTOR]);
 
        /*
         *      We don't have any outstanding requests to process for
         *      this channel, don't signal the network thread that
         *      we're sleeping.  It already knows.
         */
        if (responder->stats.outstanding == 0) return 0;
 
        responder->stats.signals++;
 
        cc.signal = FR_CHANNEL_SIGNAL_RESPONDER_SLEEPING;
        cc.ack = responder->ack;
        cc.ch = ch;
 
        MPRINT("\tRESPONDER SLEEPING num_outstanding %"PRIu64", packets in %"PRIu64", packets out %"PRIu64"\n", responder->stats.outstanding,
               ch->end[TO_RESPONDER].stats.packets, responder->stats.packets);
        return fr_control_message_send(responder->control, responder->rb, FR_CONTROL_ID_CHANNEL, &cc, sizeof(cc));
}
 
 
/** Service a control-plane message
 *
 * @param[in] when              The current time.
 * @param[out] p_channel        The channel which should be serviced.
 * @param[in] data              The control message.
 * @param[in] data_size         The size of the control message.
 * @return
 *      - FR_CHANNEL_ERROR on error
 *      - FR_CHANNEL_NOOP, on do nothing
 *      - FR_CHANNEL_DATA_READY on data ready
 *      - FR_CHANNEL_OPEN when a channel has been opened and sent to us
 *      - FR_CHANNEL_CLOSE when a channel should be closed
 */
fr_channel_event_t fr_channel_service_message(fr_time_t when, fr_channel_t **p_channel, void const *data, size_t data_size)
{
        int rcode;
#if ENABLE_SKIPS
        uint64_t ack;
#endif
        fr_channel_control_t cc;
        fr_channel_signal_t cs;
        fr_channel_event_t ce = FR_CHANNEL_ERROR;
        fr_channel_end_t *requestor;
        fr_channel_t *ch;
 
        fr_assert(data_size == sizeof(cc));
        memcpy(&cc, data, data_size);
 
        cs = cc.signal;
#if ENABLE_SKIPS
        ack = cc.ack;
#endif
        *p_channel = ch = cc.ch;
 
        switch (cs) {
        /*
         *      These all have the same numbers as the channel
         *      events, and have no extra processing.  We just
         *      return them as-is.
         */
        case FR_CHANNEL_SIGNAL_ERROR:
        case FR_CHANNEL_SIGNAL_DATA_TO_RESPONDER:
        case FR_CHANNEL_SIGNAL_DATA_TO_REQUESTOR:
        case FR_CHANNEL_SIGNAL_OPEN:
        case FR_CHANNEL_SIGNAL_CLOSE:
                MPRINT("channel got %d\n", cs);
                return (fr_channel_event_t) cs;
 
        /*
         *      Only sent by the responder.  Both of these
         *      situations are largely the same, except for
         *      return codes.
         */
        case FR_CHANNEL_SIGNAL_DATA_DONE_RESPONDER:
                MPRINT("channel got data_done_responder\n");
                ce = FR_CHANNEL_DATA_READY_REQUESTOR;
                ch->end[TO_RESPONDER].must_signal = true;
                break;
 
        case FR_CHANNEL_SIGNAL_RESPONDER_SLEEPING:
                MPRINT("channel got responder_sleeping\n");
                ce = FR_CHANNEL_NOOP;
                ch->end[TO_RESPONDER].must_signal = true;
                break;
        }
 
        /*
         *      Compare their ACK to the last sequence we
         *      sent.  If it's different, we signal the responder
         *      to wake up.
         */
        requestor = &ch->end[TO_RESPONDER];
#if ENABLE_SKIPS
        if (!requestor->must_signal && (ack == requestor->sequence)) {
                MPRINT("REQUESTOR SKIPS signal AFTER CE %d num_outstanding %"PRIu64"\n", cs, requestor->stats.outstanding);
                MPRINT("REQUESTOR has ack %"PRIu64", my seq %"PRIu64" my_view %"PRIu64"\n", ack, requestor->sequence, requestor->their_view_of_my_sequence);
                return ce;
        }
 
        /*
         *      The responder is sleeping or done.  There are more
         *      packets available, so we signal it to wake up again.
         */
        fr_assert(ack <= requestor->sequence);
#endif
 
        /*
         *      We're signaling it again...
         */
        requestor->stats.resignals++;
 
        /*
         *      The responder hasn't seen our last few packets.  Signal
         *      that there is data ready.
         */
        MPRINT("REQUESTOR SIGNALS AFTER CE %d\n", cs);
        rcode = fr_channel_data_ready(ch, when, requestor, FR_CHANNEL_SIGNAL_DATA_TO_RESPONDER);
        if (rcode < 0) return FR_CHANNEL_ERROR;
 
        return ce;
}
 
 
/** Service a control-plane event.
 *
 * The channels use control planes for internal signaling.  Note that
 * the caller does NOT pass the channel into this function.  Instead,
 * the channel is taken from the kevent.
 *
 * @param[in] ch        The channel to service.
 * @param[in] c         The control plane on which we received the kev.
 * @param[in] kev       The kevent data, should get passed to the control plane.
 * @return
 *      - <0 on error
 *      - 0 on success
 */
int fr_channel_service_kevent(fr_channel_t *ch, fr_control_t *c, UNUSED struct kevent const *kev)
{
        (void) talloc_get_type_abort(ch, fr_channel_t);
 
        if (c == ch->end[TO_RESPONDER].control) {
                ch->end[TO_RESPONDER].stats.kevents++;
        } else {
                ch->end[TO_REQUESTOR].stats.kevents++;
        }
 
        return 0;
}
 
 
/** Check if a channel is active.
 *
 * A channel may be closed by either end.  If so, it stays alive (but
 * inactive) until both ends acknowledge the close.
 *
 * @param[in] ch the channel
 * @return
 *      - false the channel is closing.
 *      - true the channel is active
 */
bool fr_channel_active(fr_channel_t *ch)
{
        return atomic_load(&ch->end[TO_REQUESTOR].active) && atomic_load(&ch->end[TO_RESPONDER].active);
}
 
/** Signal a responder that the channel is closing
 *
 * @param[in] ch        The channel.
 * @return
 *      - <0 on error
 *      - 0 on success
 */
int fr_channel_signal_responder_close(fr_channel_t *ch)
{
        int ret;
        bool active;
        fr_channel_control_t cc;
 
        active = atomic_load(&ch->end[TO_RESPONDER].active);
        if (!active) return 0;                                  /* Already signalled to close */
 
        atomic_store(&ch->end[TO_RESPONDER].active, false);     /* Prevent further requests */
 
        (void) talloc_get_type_abort(ch, fr_channel_t);
 
        cc.signal = FR_CHANNEL_SIGNAL_CLOSE;
        cc.ack = TO_RESPONDER;
        cc.ch = ch;
 
        ret = fr_control_message_send(ch->end[TO_RESPONDER].control,
                                      ch->end[TO_RESPONDER].rb, FR_CONTROL_ID_CHANNEL, &cc, sizeof(cc));
 
        return ret;
}
 
/** Acknowledge that the channel is closing
 *
 * @param[in] ch        The channel.
 * @return
 *      - <0 on error
 *      - 0 on success
 */
int fr_channel_responder_ack_close(fr_channel_t *ch)
{
        int ret;
        bool active;
 
        fr_channel_control_t cc;
 
        active = atomic_load(&ch->end[TO_REQUESTOR].active);
        if (!active) return 0;                                  /* Already signalled to close */
 
        atomic_store(&ch->end[TO_REQUESTOR].active, false);     /* Prevent further responses */
 
        (void) talloc_get_type_abort(ch, fr_channel_t);
 
        cc.signal = FR_CHANNEL_SIGNAL_CLOSE;
        cc.ack = TO_REQUESTOR;
        cc.ch = ch;
 
        ret = fr_control_message_send(ch->end[TO_REQUESTOR].control,
                                      ch->end[TO_REQUESTOR].rb, FR_CONTROL_ID_CHANNEL, &cc, sizeof(cc));
 
        return ret;
}
 
/** Add responder-specific data to a channel
 *
 * @param[in] ch        The channel.
 * @param[in] uctx      The context to add.
 */
void fr_channel_responder_uctx_add(fr_channel_t *ch, void *uctx)
{
        (void) talloc_get_type_abort(ch, fr_channel_t);
 
        ch->end[TO_REQUESTOR].uctx = uctx;
}
 
 
/** Get responder-specific data from a channel
 *
 * @param[in] ch        The channel.
 */
void *fr_channel_responder_uctx_get(fr_channel_t *ch)
{
        (void) talloc_get_type_abort(ch, fr_channel_t);
 
        return ch->end[TO_REQUESTOR].uctx;
}
 
 
/** Add network-specific data to a channel
 *
 * @param[in] ch        The channel.
 * @param[in] uctx      The context to add.
 */
void fr_channel_requestor_uctx_add(fr_channel_t *ch, void *uctx)
{
        (void) talloc_get_type_abort(ch, fr_channel_t);
 
        ch->end[TO_RESPONDER].uctx = uctx;
}
 
 
/** Get network-specific data from a channel
 *
 * @param[in] ch        The channel.
 */
void *fr_channel_requestor_uctx_get(fr_channel_t *ch)
{
        (void) talloc_get_type_abort(ch, fr_channel_t);
 
        return ch->end[TO_RESPONDER].uctx;
}
 
 
int fr_channel_set_recv_reply(fr_channel_t *ch, void *uctx, fr_channel_recv_callback_t recv_reply)
{
        ch->end[TO_RESPONDER].recv = recv_reply;
        ch->end[TO_RESPONDER].recv_uctx = uctx;
 
        return 0;
}
 
int fr_channel_set_recv_request(fr_channel_t *ch, void *uctx, fr_channel_recv_callback_t recv_request)
{
        ch->end[TO_REQUESTOR].recv = recv_request;
        ch->end[TO_REQUESTOR].recv_uctx = uctx;
        return 0;
}
 
/** Send a channel to a responder
 *
 * @param[in] ch        The channel.
 * @return
 *      - <0 on error
 *      - 0 on success
 */
int fr_channel_signal_open(fr_channel_t *ch)
{
        fr_channel_control_t cc;
 
        cc.signal = FR_CHANNEL_SIGNAL_OPEN;
        cc.ack = 0;
        cc.ch = ch;
 
        return fr_control_message_send(ch->end[TO_RESPONDER].control, ch->end[TO_RESPONDER].rb, FR_CONTROL_ID_CHANNEL, &cc, sizeof(cc));
}
 
void fr_channel_stats_log(fr_channel_t const *ch, fr_log_t const *log, char const *file, int line)
{
        fr_log(log, L_INFO, file, line, "requestor\n");
        fr_log(log, L_INFO, file, line, "\tsignals sent = %" PRIu64 "\n", ch->end[TO_RESPONDER].stats.signals);
        fr_log(log, L_INFO, file, line, "\tsignals re-sent = %" PRIu64 "\n", ch->end[TO_RESPONDER].stats.resignals);
        fr_log(log, L_INFO, file, line, "\tkevents checked = %" PRIu64 "\n", ch->end[TO_RESPONDER].stats.kevents);
        fr_log(log, L_INFO, file, line, "\toutstanding = %" PRIu64 "\n", ch->end[TO_RESPONDER].stats.outstanding);
        fr_log(log, L_INFO, file, line, "\tpackets processed = %" PRIu64 "\n", ch->end[TO_RESPONDER].stats.packets);
        fr_log(log, L_INFO, file, line, "\tmessage interval (RTT) = %" PRIu64 "\n", fr_time_delta_unwrap(ch->end[TO_RESPONDER].stats.message_interval));
        fr_log(log, L_INFO, file, line, "\tlast write = %" PRIu64 "\n", fr_time_unwrap(ch->end[TO_RESPONDER].stats.last_write));
        fr_log(log, L_INFO, file, line, "\tlast read other end = %" PRIu64 "\n", fr_time_unwrap(ch->end[TO_RESPONDER].stats.last_read_other));
        fr_log(log, L_INFO, file, line, "\tlast signal other = %" PRIu64 "\n", fr_time_unwrap(ch->end[TO_RESPONDER].stats.last_sent_signal));
 
        fr_log(log, L_INFO, file, line, "responder\n");
        fr_log(log, L_INFO, file, line, "\tsignals sent = %" PRIu64"\n", ch->end[TO_REQUESTOR].stats.signals);
        fr_log(log, L_INFO, file, line, "\tkevents checked = %" PRIu64 "\n", ch->end[TO_REQUESTOR].stats.kevents);
        fr_log(log, L_INFO, file, line, "\tpackets processed = %" PRIu64 "\n", ch->end[TO_REQUESTOR].stats.packets);
        fr_log(log, L_INFO, file, line, "\tmessage interval (RTT) = %" PRIu64 "\n", fr_time_delta_unwrap(ch->end[TO_REQUESTOR].stats.message_interval));
        fr_log(log, L_INFO, file, line, "\tlast write = %" PRIu64 "\n", fr_time_unwrap(ch->end[TO_REQUESTOR].stats.last_write));
        fr_log(log, L_INFO, file, line, "\tlast read other end = %" PRIu64 "\n", fr_time_unwrap(ch->end[TO_REQUESTOR].stats.last_read_other));
        fr_log(log, L_INFO, file, line, "\tlast signal other = %" PRIu64 "\n", fr_time_unwrap(ch->end[TO_REQUESTOR].stats.last_sent_signal));
}