syncache: Simplify port calculation by reusing ACK's hash for IPv4.

[dragonfly.git] / sys / kern / kern_dmsg.c

/*-
 * Copyright (c) 2012 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 *
 * 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.
 * 3. Neither the name of The DragonFly Project nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific, prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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.
 */
/*
 * TODO: txcmd CREATE state is deferred by tx msgq, need to calculate
 *       a streaming response.  See subr_diskiocom()'s diskiodone().
 */
#include <sys/param.h>
#include <sys/types.h>
#include <sys/kernel.h>
#include <sys/conf.h>
#include <sys/systm.h>
#include <sys/queue.h>
#include <sys/tree.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/socket.h>
#include <sys/vnode.h>
#include <sys/sysctl.h>
#include <sys/file.h>
#include <sys/proc.h>
#include <sys/priv.h>
#include <sys/thread.h>
#include <sys/globaldata.h>
#include <sys/limits.h>

#include <sys/dmsg.h>

RB_GENERATE(kdmsg_state_tree, kdmsg_state, rbnode, kdmsg_state_cmp);

SYSCTL_NODE(, OID_AUTO, kdmsg, CTLFLAG_RW, 0, "kdmsg");
static int kdmsg_debug = 1;
SYSCTL_INT(_kdmsg, OID_AUTO, debug, CTLFLAG_RW, &kdmsg_debug, 0,
           "Set debug level for kernel dmsg layer");

#define kd_printf(level, ctl, ...)              \
        if (kdmsg_debug >= (level)) kprintf("kdmsg: " ctl, __VA_ARGS__)

#define kdio_printf(iocom, level, ctl, ...)      \
        if (kdmsg_debug >= (level)) kprintf("kdmsg: " ctl, __VA_ARGS__)

static int kdmsg_msg_receive_handling(kdmsg_msg_t *msg);
static int kdmsg_state_msgrx(kdmsg_msg_t *msg);
static int kdmsg_state_msgtx(kdmsg_msg_t *msg);
static void kdmsg_msg_write_locked(kdmsg_iocom_t *iocom, kdmsg_msg_t *msg);
static void kdmsg_state_cleanuprx(kdmsg_msg_t *msg);
static void kdmsg_state_cleanuptx(kdmsg_msg_t *msg);
static void kdmsg_subq_delete(kdmsg_state_t *state);
static void kdmsg_simulate_failure(kdmsg_state_t *state, int meto, int error);
static void kdmsg_state_abort(kdmsg_state_t *state);
static void kdmsg_state_dying(kdmsg_state_t *state);
static void kdmsg_state_free(kdmsg_state_t *state);

#ifdef KDMSG_DEBUG
#define KDMSG_DEBUG_ARGS        , const char *file, int line
#define kdmsg_state_hold(state) _kdmsg_state_hold(state, __FILE__, __LINE__)
#define kdmsg_state_drop(state) _kdmsg_state_drop(state, __FILE__, __LINE__)
#else
#define KDMSG_DEBUG_ARGS
#define kdmsg_state_hold(state) _kdmsg_state_hold(state)
#define kdmsg_state_drop(state) _kdmsg_state_drop(state)
#endif
static void _kdmsg_state_hold(kdmsg_state_t *state KDMSG_DEBUG_ARGS);
static void _kdmsg_state_drop(kdmsg_state_t *state KDMSG_DEBUG_ARGS);

static void kdmsg_iocom_thread_rd(void *arg);
static void kdmsg_iocom_thread_wr(void *arg);
static int kdmsg_autorxmsg(kdmsg_msg_t *msg);

/*static struct lwkt_token kdmsg_token = LWKT_TOKEN_INITIALIZER(kdmsg_token);*/

/*
 * Initialize the roll-up communications structure for a network
 * messaging session.  This function does not install the socket.
 */
void
kdmsg_iocom_init(kdmsg_iocom_t *iocom, void *handle, uint32_t flags,
                 struct malloc_type *mmsg,
                 int (*rcvmsg)(kdmsg_msg_t *msg))
{
        bzero(iocom, sizeof(*iocom));
        iocom->handle = handle;
        iocom->mmsg = mmsg;
        iocom->rcvmsg = rcvmsg;
        iocom->flags = flags;
        lockinit(&iocom->msglk, "h2msg", 0, 0);
        TAILQ_INIT(&iocom->msgq);
        RB_INIT(&iocom->staterd_tree);
        RB_INIT(&iocom->statewr_tree);

        iocom->state0.iocom = iocom;
        iocom->state0.parent = &iocom->state0;
        TAILQ_INIT(&iocom->state0.subq);
}

/*
 * [Re]connect using the passed file pointer.  The caller must ref the
 * fp for us.  We own that ref now.
 */
void
kdmsg_iocom_reconnect(kdmsg_iocom_t *iocom, struct file *fp,
                      const char *subsysname)
{
        /*
         * Destroy the current connection
         */
        lockmgr(&iocom->msglk, LK_EXCLUSIVE);
        atomic_set_int(&iocom->msg_ctl, KDMSG_CLUSTERCTL_KILLRX);
        while (iocom->msgrd_td || iocom->msgwr_td) {
                wakeup(&iocom->msg_ctl);
                lksleep(iocom, &iocom->msglk, 0, "clstrkl", hz);
        }

        /*
         * Drop communications descriptor
         */
        if (iocom->msg_fp) {
                fdrop(iocom->msg_fp);
                iocom->msg_fp = NULL;
        }

        /*
         * Setup new communications descriptor
         */
        iocom->msg_ctl = 0;
        iocom->msg_fp = fp;
        iocom->msg_seq = 0;
        iocom->flags &= ~KDMSG_IOCOMF_EXITNOACC;

        lwkt_create(kdmsg_iocom_thread_rd, iocom, &iocom->msgrd_td,
                    NULL, 0, -1, "%s-msgrd", subsysname);
        lwkt_create(kdmsg_iocom_thread_wr, iocom, &iocom->msgwr_td,
                    NULL, 0, -1, "%s-msgwr", subsysname);
        lockmgr(&iocom->msglk, LK_RELEASE);
}

/*
 * Caller sets up iocom->auto_lnk_conn and iocom->auto_lnk_span, then calls
 * this function to handle the state machine for LNK_CONN and LNK_SPAN.
 */
static int kdmsg_lnk_conn_reply(kdmsg_state_t *state, kdmsg_msg_t *msg);
static int kdmsg_lnk_span_reply(kdmsg_state_t *state, kdmsg_msg_t *msg);

void
kdmsg_iocom_autoinitiate(kdmsg_iocom_t *iocom,
                         void (*auto_callback)(kdmsg_msg_t *msg))
{
        kdmsg_msg_t *msg;

        iocom->auto_callback = auto_callback;

        msg = kdmsg_msg_alloc(&iocom->state0,
                              DMSG_LNK_CONN | DMSGF_CREATE,
                              kdmsg_lnk_conn_reply, NULL);
        iocom->auto_lnk_conn.head = msg->any.head;
        msg->any.lnk_conn = iocom->auto_lnk_conn;
        iocom->conn_state = msg->state;
        kdmsg_state_hold(msg->state);   /* iocom->conn_state */
        kdmsg_msg_write(msg);
}

static
int
kdmsg_lnk_conn_reply(kdmsg_state_t *state, kdmsg_msg_t *msg)
{
        kdmsg_iocom_t *iocom = state->iocom;
        kdmsg_msg_t *rmsg;

        /*
         * Upon receipt of the LNK_CONN acknowledgement initiate an
         * automatic SPAN if we were asked to.  Used by e.g. xdisk, but
         * not used by HAMMER2 which must manage more than one transmitted
         * SPAN.
         */
        if ((msg->any.head.cmd & DMSGF_CREATE) &&
            (iocom->flags & KDMSG_IOCOMF_AUTOTXSPAN)) {
                rmsg = kdmsg_msg_alloc(&iocom->state0,
                                       DMSG_LNK_SPAN | DMSGF_CREATE,
                                       kdmsg_lnk_span_reply, NULL);
                iocom->auto_lnk_span.head = rmsg->any.head;
                rmsg->any.lnk_span = iocom->auto_lnk_span;
                kdmsg_msg_write(rmsg);
        }

        /*
         * Process shim after the CONN is acknowledged and before the CONN
         * transaction is deleted.  For deletions this gives device drivers
         * the ability to interlock new operations on the circuit before
         * it becomes illegal and panics.
         */
        if (iocom->auto_callback)
                iocom->auto_callback(msg);

        if ((state->txcmd & DMSGF_DELETE) == 0 &&
            (msg->any.head.cmd & DMSGF_DELETE)) {
                /*
                 * iocom->conn_state has a state ref, drop it when clearing.
                 */
                if (iocom->conn_state)
                        kdmsg_state_drop(iocom->conn_state);
                iocom->conn_state = NULL;
                kdmsg_msg_reply(msg, 0);
        }

        return (0);
}

static
int
kdmsg_lnk_span_reply(kdmsg_state_t *state, kdmsg_msg_t *msg)
{
        /*
         * Be sure to process shim before terminating the SPAN
         * transaction.  Gives device drivers the ability to
         * interlock new operations on the circuit before it
         * becomes illegal and panics.
         */
        if (state->iocom->auto_callback)
                state->iocom->auto_callback(msg);

        if ((state->txcmd & DMSGF_DELETE) == 0 &&
            (msg->any.head.cmd & DMSGF_DELETE)) {
                kdmsg_msg_reply(msg, 0);
        }
        return (0);
}

/*
 * Disconnect and clean up
 */
void
kdmsg_iocom_uninit(kdmsg_iocom_t *iocom)
{
        kdmsg_state_t *state;
        kdmsg_msg_t *msg;
        int retries;

        /*
         * Ask the cluster controller to go away by setting
         * KILLRX.  Send a PING to get a response to unstick reading
         * from the pipe.
         *
         * After 10 seconds shitcan the pipe and do an unclean shutdown.
         */
        lockmgr(&iocom->msglk, LK_EXCLUSIVE);

        atomic_set_int(&iocom->msg_ctl, KDMSG_CLUSTERCTL_KILLRX);
        msg = kdmsg_msg_alloc(&iocom->state0, DMSG_LNK_PING, NULL, NULL);
        kdmsg_msg_write_locked(iocom, msg);

        retries = 10;
        while (iocom->msgrd_td || iocom->msgwr_td) {
                wakeup(&iocom->msg_ctl);
                lksleep(iocom, &iocom->msglk, 0, "clstrkl", hz);
                if (--retries == 0 && iocom->msg_fp) {
                        kdio_printf(iocom, 0, "%s\n",
                                    "iocom_uninit: "
                                    "shitcanning unresponsive pipe");
                        fp_shutdown(iocom->msg_fp, SHUT_RDWR);
                        /* retries allowed to go negative, keep looping */
                }
        }

        /*
         * Cleanup caches
         */
        if ((state = iocom->freerd_state) != NULL) {
                iocom->freerd_state = NULL;
                kdmsg_state_drop(state);
        }

        if ((state = iocom->freewr_state) != NULL) {
                iocom->freewr_state = NULL;
                kdmsg_state_drop(state);
        }

        /*
         * Drop communications descriptor
         */
        if (iocom->msg_fp) {
                fdrop(iocom->msg_fp);
                iocom->msg_fp = NULL;
        }
        lockmgr(&iocom->msglk, LK_RELEASE);
}

/*
 * Cluster controller thread.  Perform messaging functions.  We have one
 * thread for the reader and one for the writer.  The writer handles
 * shutdown requests (which should break the reader thread).
 */
static
void
kdmsg_iocom_thread_rd(void *arg)
{
        kdmsg_iocom_t *iocom = arg;
        dmsg_hdr_t hdr;
        kdmsg_msg_t *msg = NULL;
        size_t hbytes;
        size_t abytes;
        int error = 0;

        while ((iocom->msg_ctl & KDMSG_CLUSTERCTL_KILLRX) == 0) {
                /*
                 * Retrieve the message from the pipe or socket.
                 */
                error = fp_read(iocom->msg_fp, &hdr, sizeof(hdr),
                                NULL, 1, UIO_SYSSPACE);
                if (error)
                        break;
                if (hdr.magic != DMSG_HDR_MAGIC) {
                        kdio_printf(iocom, 1, "bad magic: %04x\n", hdr.magic);
                        error = EINVAL;
                        break;
                }
                hbytes = (hdr.cmd & DMSGF_SIZE) * DMSG_ALIGN;
                if (hbytes < sizeof(hdr) || hbytes > DMSG_HDR_MAX) {
                        kdio_printf(iocom, 1, "bad header size %zd\n", hbytes);
                        error = EINVAL;
                        break;
                }

                /* XXX messy: mask cmd to avoid allocating state */
                msg = kdmsg_msg_alloc(&iocom->state0,
                                      hdr.cmd & DMSGF_BASECMDMASK,
                                      NULL, NULL);
                msg->any.head = hdr;
                msg->hdr_size = hbytes;
                if (hbytes > sizeof(hdr)) {
                        error = fp_read(iocom->msg_fp, &msg->any.head + 1,
                                        hbytes - sizeof(hdr),
                                        NULL, 1, UIO_SYSSPACE);
                        if (error) {
                                kdio_printf(iocom, 1, "%s\n",
                                            "short msg received");
                                error = EINVAL;
                                break;
                        }
                }
                msg->aux_size = hdr.aux_bytes;
                if (msg->aux_size > DMSG_AUX_MAX) {
                        kdio_printf(iocom, 1,
                                    "illegal msg payload size %zd\n",
                                    msg->aux_size);
                        error = EINVAL;
                        break;
                }
                if (msg->aux_size) {
                        abytes = DMSG_DOALIGN(msg->aux_size);
                        msg->aux_data = kmalloc(abytes, iocom->mmsg, M_WAITOK);
                        msg->flags |= KDMSG_FLAG_AUXALLOC;
                        error = fp_read(iocom->msg_fp, msg->aux_data,
                                        abytes, NULL, 1, UIO_SYSSPACE);
                        if (error) {
                                kdio_printf(iocom, 1, "%s\n",
                                            "short msg payload received");
                                break;
                        }
                }

                error = kdmsg_msg_receive_handling(msg);
                msg = NULL;
        }

        kdio_printf(iocom, 1, "read thread terminating error=%d\n", error);

        lockmgr(&iocom->msglk, LK_EXCLUSIVE);
        if (msg)
                kdmsg_msg_free(msg);

        /*
         * Shutdown the socket and set KILLRX for consistency in case the
         * shutdown was not commanded.  Signal the transmit side to shutdown
         * by setting KILLTX and waking it up.
         */
        fp_shutdown(iocom->msg_fp, SHUT_RDWR);
        atomic_set_int(&iocom->msg_ctl, KDMSG_CLUSTERCTL_KILLRX |
                                        KDMSG_CLUSTERCTL_KILLTX);
        iocom->msgrd_td = NULL;
        lockmgr(&iocom->msglk, LK_RELEASE);
        wakeup(&iocom->msg_ctl);

        /*
         * iocom can be ripped out at any time once the lock is
         * released with msgrd_td set to NULL.  The wakeup()s are safe but
         * that is all.
         */
        wakeup(iocom);
        lwkt_exit();
}

static
void
kdmsg_iocom_thread_wr(void *arg)
{
        kdmsg_iocom_t *iocom = arg;
        kdmsg_msg_t *msg;
        ssize_t res;
        size_t abytes;
        int error = 0;
        int save_ticks;
        int didwarn;

        /*
         * Transmit loop
         */
        msg = NULL;
        lockmgr(&iocom->msglk, LK_EXCLUSIVE);

        while ((iocom->msg_ctl & KDMSG_CLUSTERCTL_KILLTX) == 0 && error == 0) {
                /*
                 * Sleep if no messages pending.  Interlock with flag while
                 * holding msglk.
                 */
                if (TAILQ_EMPTY(&iocom->msgq)) {
                        atomic_set_int(&iocom->msg_ctl,
                                       KDMSG_CLUSTERCTL_SLEEPING);
                        lksleep(&iocom->msg_ctl, &iocom->msglk, 0, "msgwr", hz);
                        atomic_clear_int(&iocom->msg_ctl,
                                         KDMSG_CLUSTERCTL_SLEEPING);
                }

                while ((msg = TAILQ_FIRST(&iocom->msgq)) != NULL) {
                        /*
                         * Remove msg from the transmit queue and do
                         * persist and half-closed state handling.
                         */
                        TAILQ_REMOVE(&iocom->msgq, msg, qentry);

                        error = kdmsg_state_msgtx(msg);
                        if (error == EALREADY) {
                                error = 0;
                                kdmsg_msg_free(msg);
                                continue;
                        }
                        if (error) {
                                kdmsg_msg_free(msg);
                                break;
                        }

                        /*
                         * Dump the message to the pipe or socket.
                         *
                         * We have to clean up the message as if the transmit
                         * succeeded even if it failed.
                         */
                        lockmgr(&iocom->msglk, LK_RELEASE);
                        error = fp_write(iocom->msg_fp, &msg->any,
                                         msg->hdr_size, &res, UIO_SYSSPACE);
                        if (error || res != msg->hdr_size) {
                                if (error == 0)
                                        error = EINVAL;
                                lockmgr(&iocom->msglk, LK_EXCLUSIVE);
                                kdmsg_state_cleanuptx(msg);
                                break;
                        }
                        if (msg->aux_size) {
                                abytes = DMSG_DOALIGN(msg->aux_size);
                                error = fp_write(iocom->msg_fp,
                                                 msg->aux_data, abytes,
                                                 &res, UIO_SYSSPACE);
                                if (error || res != abytes) {
                                        if (error == 0)
                                                error = EINVAL;
                                        lockmgr(&iocom->msglk, LK_EXCLUSIVE);
                                        kdmsg_state_cleanuptx(msg);
                                        break;
                                }
                        }
                        lockmgr(&iocom->msglk, LK_EXCLUSIVE);
                        kdmsg_state_cleanuptx(msg);
                }
        }

        kdio_printf(iocom, 1, "write thread terminating error=%d\n", error);

        /*
         * Shutdown the socket and set KILLTX for consistency in case the
         * shutdown was not commanded.  Signal the receive side to shutdown
         * by setting KILLRX and waking it up.
         */
        fp_shutdown(iocom->msg_fp, SHUT_RDWR);
        atomic_set_int(&iocom->msg_ctl, KDMSG_CLUSTERCTL_KILLRX |
                                        KDMSG_CLUSTERCTL_KILLTX);
        wakeup(&iocom->msg_ctl);

        /*
         * The transmit thread is responsible for final cleanups, wait
         * for the receive side to terminate to prevent new received
         * states from interfering with our cleanup.
         *
         * Do not set msgwr_td to NULL until we actually exit.
         */
        while (iocom->msgrd_td) {
                wakeup(&iocom->msg_ctl);
                lksleep(iocom, &iocom->msglk, 0, "clstrkt", hz);
        }

        /*
         * We can no longer receive new messages.  We must drain the transmit
         * message queue and simulate received messages to close anay remaining
         * states.
         *
         * Loop until all the states are gone and there are no messages
         * pending transmit.
         */
        save_ticks = ticks;
        didwarn = 0;

        while (TAILQ_FIRST(&iocom->msgq) ||
               RB_ROOT(&iocom->staterd_tree) ||
               RB_ROOT(&iocom->statewr_tree)) {
                /*
                 * Simulate failure for all sub-states of state0.
                 */
                kdmsg_drain_msgq(iocom);
                kdio_printf(iocom, 2, "%s\n",
                            "simulate failure for all substates of state0");
                kdmsg_simulate_failure(&iocom->state0, 0, DMSG_ERR_LOSTLINK);

                lksleep(iocom, &iocom->msglk, 0, "clstrtk", hz / 2);

                if ((int)(ticks - save_ticks) > hz*2 && didwarn == 0) {
                        didwarn = 1;
                        kdio_printf(iocom, 0,
                                    "Warning, write thread on %p "
                                    "still terminating\n",
                                    iocom);
                }
                if ((int)(ticks - save_ticks) > hz*15 && didwarn == 1) {
                        didwarn = 2;
                        kdio_printf(iocom, 0,
                                    "Warning, write thread on %p "
                                    "still terminating\n",
                                    iocom);
                }
                if ((int)(ticks - save_ticks) > hz*60) {
                        kdio_printf(iocom, 0,
                                    "Can't terminate: msgq %p "
                                    "rd_tree %p wr_tree %p\n",
                                    TAILQ_FIRST(&iocom->msgq),
                                    RB_ROOT(&iocom->staterd_tree),
                                    RB_ROOT(&iocom->statewr_tree));
                        lksleep(iocom, &iocom->msglk, 0, "clstrtk", hz * 10);
                }
        }

        /*
         * Exit handling is done by the write thread.
         */
        iocom->flags |= KDMSG_IOCOMF_EXITNOACC;
        lockmgr(&iocom->msglk, LK_RELEASE);

        /*
         * The state trees had better be empty now
         */
        KKASSERT(RB_EMPTY(&iocom->staterd_tree));
        KKASSERT(RB_EMPTY(&iocom->statewr_tree));
        KKASSERT(iocom->conn_state == NULL);

        if (iocom->exit_func) {
                /*
                 * iocom is invalid after we call the exit function.
                 */
                iocom->msgwr_td = NULL;
                iocom->exit_func(iocom);
        } else {
                /*
                 * iocom can be ripped out from under us once msgwr_td is
                 * set to NULL.  The wakeup is safe.
                 */
                iocom->msgwr_td = NULL;
                wakeup(iocom);
        }
        lwkt_exit();
}

/*
 * This cleans out the pending transmit message queue, adjusting any
 * persistent states properly in the process.
 *
 * Called with iocom locked.
 */
void
kdmsg_drain_msgq(kdmsg_iocom_t *iocom)
{
        kdmsg_msg_t *msg;

        /*
         * Clean out our pending transmit queue, executing the
         * appropriate state adjustments.  If this tries to open
         * any new outgoing transactions we have to loop up and
         * clean them out.
         */
        while ((msg = TAILQ_FIRST(&iocom->msgq)) != NULL) {
                TAILQ_REMOVE(&iocom->msgq, msg, qentry);
                if (kdmsg_state_msgtx(msg))
                        kdmsg_msg_free(msg);
                else
                        kdmsg_state_cleanuptx(msg);
        }
}

/*
 * Do all processing required to handle a freshly received message
 * after its low level header has been validated.
 *
 * iocom is not locked.
 */
static
int
kdmsg_msg_receive_handling(kdmsg_msg_t *msg)
{
        kdmsg_iocom_t *iocom = msg->state->iocom;
        int error;

        /*
         * State machine tracking, state assignment for msg,
         * returns error and discard status.  Errors are fatal
         * to the connection except for EALREADY which forces
         * a discard without execution.
         */
        error = kdmsg_state_msgrx(msg);
        if (msg->state->flags & KDMSG_STATE_ABORTING) {
                kdio_printf(iocom, 5,
                            "kdmsg_state_abort(b): state %p rxcmd=%08x "
                            "txcmd=%08x msgrx error %d\n",
                            msg->state, msg->state->rxcmd,
                            msg->state->txcmd, error);
        }
        if (error) {
                /*
                 * Raw protocol or connection error
                 */
                if (msg->state->flags & KDMSG_STATE_ABORTING)
                        kdio_printf(iocom, 5,
                                    "X1 state %p error %d\n",
                                    msg->state, error);
                kdmsg_msg_free(msg);
                if (error == EALREADY)
                        error = 0;
        } else if (msg->state && msg->state->func) {
                /*
                 * Message related to state which already has a
                 * handling function installed for it.
                 */
                if (msg->state->flags & KDMSG_STATE_ABORTING)
                        kdio_printf(iocom, 5,
                                    "X2 state %p func %p\n",
                                    msg->state, msg->state->func);
                error = msg->state->func(msg->state, msg);
                kdmsg_state_cleanuprx(msg);
        } else if (iocom->flags & KDMSG_IOCOMF_AUTOANY) {
                if (msg->state->flags & KDMSG_STATE_ABORTING)
                        kdio_printf(iocom, 5,
                                    "X3 state %p\n", msg->state);
                error = kdmsg_autorxmsg(msg);
                kdmsg_state_cleanuprx(msg);
        } else {
                if (msg->state->flags & KDMSG_STATE_ABORTING)
                        kdio_printf(iocom, 5,
                                    "X4 state %p\n", msg->state);
                error = iocom->rcvmsg(msg);
                kdmsg_state_cleanuprx(msg);
        }
        return error;
}

/*
 * Process state tracking for a message after reception and dequeueing,
 * prior to execution of the state callback.  The state is updated and
 * will be removed from the RBTREE if completely closed, but the state->parent
 * and subq linkage is not cleaned up until after the callback (see
 * cleanuprx()).
 *
 * msglk is not held.
 *
 * NOTE: A message transaction can consist of several messages in either
 *       direction.
 *
 * NOTE: The msgid is unique to the initiator, not necessarily unique for
 *       us or for any relay or for the return direction for that matter.
 *       That is, two sides sending a new message can use the same msgid
 *       without colliding.
 *
 * --
 *
 * ABORT sequences work by setting the ABORT flag along with normal message
 * state.  However, ABORTs can also be sent on half-closed messages, that is
 * even if the command or reply side has already sent a DELETE, as long as
 * the message has not been fully closed it can still send an ABORT+DELETE
 * to terminate the half-closed message state.
 *
 * Since ABORT+DELETEs can race we silently discard ABORT's for message
 * state which has already been fully closed.  REPLY+ABORT+DELETEs can
 * also race, and in this situation the other side might have already
 * initiated a new unrelated command with the same message id.  Since
 * the abort has not set the CREATE flag the situation can be detected
  * and the message will also be discarded.
 *
 * Non-blocking requests can be initiated with ABORT+CREATE[+DELETE].
 * The ABORT request is essentially integrated into the command instead
 * of being sent later on.  In this situation the command implementation
 * detects that CREATE and ABORT are both set (vs ABORT alone) and can
 * special-case non-blocking operation for the command.
 *
 * NOTE!  Messages with ABORT set without CREATE or DELETE are considered
 *        to be mid-stream aborts for command/reply sequences.  ABORTs on
 *        one-way messages are not supported.
 *
 * NOTE!  If a command sequence does not support aborts the ABORT flag is
 *        simply ignored.
 *
 * --
 *
 * One-off messages (no reply expected) are sent with neither CREATE or DELETE
 * set.  One-off messages cannot be aborted and typically aren't processed
 * by these routines.  The REPLY bit can be used to distinguish whether a
 * one-off message is a command or reply.  For example, one-off replies
 * will typically just contain status updates.
 */
static
int
kdmsg_state_msgrx(kdmsg_msg_t *msg)
{
        kdmsg_iocom_t *iocom = msg->state->iocom;
        kdmsg_state_t *state;
        kdmsg_state_t *pstate;
        kdmsg_state_t sdummy;
        int error;

        bzero(&sdummy, sizeof(sdummy)); /* avoid gcc warnings */

        /*
         * Make sure a state structure is ready to go in case we need a new
         * one.  This is the only routine which uses freerd_state so no
         * races are possible.
         */
        if ((state = iocom->freerd_state) == NULL) {
                state = kmalloc(sizeof(*state), iocom->mmsg, M_WAITOK | M_ZERO);
                state->flags = KDMSG_STATE_DYNAMIC;
                state->iocom = iocom;
                state->refs = 1;
                TAILQ_INIT(&state->subq);
                iocom->freerd_state = state;
        }
        state = NULL;   /* safety */

        /*
         * Lock RB tree and locate existing persistent state, if any.
         *
         * If received msg is a command state is on staterd_tree.
         * If received msg is a reply state is on statewr_tree.
         */
        lockmgr(&iocom->msglk, LK_EXCLUSIVE);

again:
        if (msg->state == &iocom->state0) {
                sdummy.msgid = msg->any.head.msgid;
                sdummy.iocom = iocom;
                if (msg->any.head.cmd & DMSGF_REVTRANS) {
                        state = RB_FIND(kdmsg_state_tree, &iocom->statewr_tree,
                                        &sdummy);
                } else {
                        state = RB_FIND(kdmsg_state_tree, &iocom->staterd_tree,
                                        &sdummy);
                }

                /*
                 * Set message state unconditionally.  If this is a CREATE
                 * message this state will become the parent state and new
                 * state will be allocated for the message state.
                 */
                if (state == NULL)
                        state = &iocom->state0;
                if (state->flags & KDMSG_STATE_INTERLOCK) {
                        state->flags |= KDMSG_STATE_SIGNAL;
                        lksleep(state, &iocom->msglk, 0, "dmrace", hz);
                        goto again;
                }
                kdmsg_state_hold(state);
                kdmsg_state_drop(msg->state);   /* iocom->state0 */
                msg->state = state;
        } else {
                state = msg->state;
        }

        /*
         * Short-cut one-off or mid-stream messages.
         */
        if ((msg->any.head.cmd & (DMSGF_CREATE | DMSGF_DELETE |
                                  DMSGF_ABORT)) == 0) {
                error = 0;
                goto done;
        }

        /*
         * Switch on CREATE, DELETE, REPLY, and also handle ABORT from
         * inside the case statements.
         */
        switch(msg->any.head.cmd & (DMSGF_CREATE|DMSGF_DELETE|DMSGF_REPLY)) {
        case DMSGF_CREATE:
        case DMSGF_CREATE | DMSGF_DELETE:
                /*
                 * New persistant command received.
                 */
                if (state != &iocom->state0) {
                        kdio_printf(iocom, 1, "%s\n",
                                    "duplicate transaction");
                        error = EINVAL;
                        break;
                }

                /*
                 * Lookup the circuit.  The circuit is an open transaction.
                 * the REVCIRC bit in the message tells us which side
                 * initiated the transaction representing the circuit.
                 */
                if (msg->any.head.circuit) {
                        sdummy.msgid = msg->any.head.circuit;

                        if (msg->any.head.cmd & DMSGF_REVCIRC) {
                                pstate = RB_FIND(kdmsg_state_tree,
                                                 &iocom->statewr_tree,
                                                 &sdummy);
                        } else {
                                pstate = RB_FIND(kdmsg_state_tree,
                                                 &iocom->staterd_tree,
                                                 &sdummy);
                        }
                        if (pstate == NULL) {
                                kdio_printf(iocom, 1, "%s\n",
                                            "missing parent in "
                                            "stacked trans");
                                error = EINVAL;
                                break;
                        }
                } else {
                        pstate = &iocom->state0;
                }

                /*
                 * Allocate new state.
                 *
                 * msg->state becomes the owner of the ref we inherit from
                 * freerd_stae.
                 */
                kdmsg_state_drop(state);
                state = iocom->freerd_state;
                iocom->freerd_state = NULL;

                msg->state = state;             /* inherits freerd ref */
                state->parent = pstate;
                KKASSERT(state->iocom == iocom);
                state->flags |= KDMSG_STATE_RBINSERTED |
                                KDMSG_STATE_SUBINSERTED |
                                KDMSG_STATE_OPPOSITE;
                if (TAILQ_EMPTY(&pstate->subq))
                        kdmsg_state_hold(pstate);/* states on pstate->subq */
                kdmsg_state_hold(state);        /* state on pstate->subq */
                kdmsg_state_hold(state);        /* state on rbtree */
                state->icmd = msg->any.head.cmd & DMSGF_BASECMDMASK;
                state->rxcmd = msg->any.head.cmd & ~DMSGF_DELETE;
                state->txcmd = DMSGF_REPLY;
                state->msgid = msg->any.head.msgid;
                state->flags &= ~KDMSG_STATE_NEW;
                RB_INSERT(kdmsg_state_tree, &iocom->staterd_tree, state);
                TAILQ_INSERT_TAIL(&pstate->subq, state, entry);
                error = 0;
                break;
        case DMSGF_DELETE:
                /*
                 * Persistent state is expected but might not exist if an
                 * ABORT+DELETE races the close.
                 */
                if (state == &iocom->state0) {
                        if (msg->any.head.cmd & DMSGF_ABORT) {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgrx: "
                                            "state already A");
                                error = EALREADY;
                        } else {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgrx: no state for DELETE");
                                error = EINVAL;
                        }
                        break;
                }

                /*
                 * Handle another ABORT+DELETE case if the msgid has already
                 * been reused.
                 */
                if ((state->rxcmd & DMSGF_CREATE) == 0) {
                        if (msg->any.head.cmd & DMSGF_ABORT) {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgrx: state already B");
                                error = EALREADY;
                        } else {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgrx: state reused for DELETE");
                                error = EINVAL;
                        }
                        break;
                }
                error = 0;
                break;
        default:
                /*
                 * Check for mid-stream ABORT command received, otherwise
                 * allow.
                 */
                if (msg->any.head.cmd & DMSGF_ABORT) {
                        if (state == &iocom->state0 ||
                            (state->rxcmd & DMSGF_CREATE) == 0) {
                                error = EALREADY;
                                break;
                        }
                }
                error = 0;
                break;
        case DMSGF_REPLY | DMSGF_CREATE:
        case DMSGF_REPLY | DMSGF_CREATE | DMSGF_DELETE:
                /*
                 * When receiving a reply with CREATE set the original
                 * persistent state message should already exist.
                 */
                if (state == &iocom->state0) {
                        kdio_printf(iocom, 1,
                                    "msgrx: no state match for "
                                    "REPLY cmd=%08x msgid=%016jx\n",
                                    msg->any.head.cmd,
                                    (intmax_t)msg->any.head.msgid);
                        error = EINVAL;
                        break;
                }
                state->rxcmd = msg->any.head.cmd & ~DMSGF_DELETE;
                error = 0;
                break;
        case DMSGF_REPLY | DMSGF_DELETE:
                /*
                 * Received REPLY+ABORT+DELETE in case where msgid has
                 * already been fully closed, ignore the message.
                 */
                if (state == &iocom->state0) {
                        if (msg->any.head.cmd & DMSGF_ABORT) {
                                error = EALREADY;
                        } else {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgrx: no state match "
                                            "for REPLY|DELETE");
                                error = EINVAL;
                        }
                        break;
                }

                /*
                 * Received REPLY+ABORT+DELETE in case where msgid has
                 * already been reused for an unrelated message,
                 * ignore the message.
                 */
                if ((state->rxcmd & DMSGF_CREATE) == 0) {
                        if (msg->any.head.cmd & DMSGF_ABORT) {
                                error = EALREADY;
                        } else {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgrx: state reused "
                                            "for REPLY|DELETE");
                                error = EINVAL;
                        }
                        break;
                }
                error = 0;
                break;
        case DMSGF_REPLY:
                /*
                 * Check for mid-stream ABORT reply received to sent command.
                 */
                if (msg->any.head.cmd & DMSGF_ABORT) {
                        if (state == &iocom->state0 ||
                            (state->rxcmd & DMSGF_CREATE) == 0) {
                                error = EALREADY;
                                break;
                        }
                }
                error = 0;
                break;
        }

        /*
         * Calculate the easy-switch() transactional command.  Represents
         * the outer-transaction command for any transaction-create or
         * transaction-delete, and the inner message command for any
         * non-transaction or inside-transaction command.  tcmd will be
         * set to 0 if the message state is illegal.
         *
         * The two can be told apart because outer-transaction commands
         * always have a DMSGF_CREATE and/or DMSGF_DELETE flag.
         */
done:
        if (msg->any.head.cmd & (DMSGF_CREATE | DMSGF_DELETE)) {
                if (state != &iocom->state0) {
                        msg->tcmd = (msg->state->icmd & DMSGF_BASECMDMASK) |
                                    (msg->any.head.cmd & (DMSGF_CREATE |
                                                          DMSGF_DELETE |
                                                          DMSGF_REPLY));
                } else {
                        msg->tcmd = 0;
                }
        } else {
                msg->tcmd = msg->any.head.cmd & DMSGF_CMDSWMASK;
        }

        /*
         * Adjust the state for DELETE handling now, before making the
         * callback so we are atomic with other state updates.
         *
         * Subq/parent linkages are cleaned up after the callback.
         * If an error occurred the message is ignored and state is not
         * updated.
         */
        if ((state = msg->state) == NULL || error != 0) {
                kdio_printf(iocom, 1,
                            "msgrx: state=%p error %d\n",
                            state, error);
        } else if (msg->any.head.cmd & DMSGF_DELETE) {
                KKASSERT((state->rxcmd & DMSGF_DELETE) == 0);
                state->rxcmd |= DMSGF_DELETE;
                if (state->txcmd & DMSGF_DELETE) {
                        KKASSERT(state->flags & KDMSG_STATE_RBINSERTED);
                        if (state->rxcmd & DMSGF_REPLY) {
                                KKASSERT(msg->any.head.cmd &
                                         DMSGF_REPLY);
                                RB_REMOVE(kdmsg_state_tree,
                                          &iocom->statewr_tree, state);
                        } else {
                                KKASSERT((msg->any.head.cmd &
                                          DMSGF_REPLY) == 0);
                                RB_REMOVE(kdmsg_state_tree,
                                          &iocom->staterd_tree, state);
                        }
                        state->flags &= ~KDMSG_STATE_RBINSERTED;
                        kdmsg_state_drop(state);        /* state on rbtree */
                }
        }
        lockmgr(&iocom->msglk, LK_RELEASE);

        return (error);
}

/*
 * Called instead of iocom->rcvmsg() if any of the AUTO flags are set.
 * This routine must call iocom->rcvmsg() for anything not automatically
 * handled.
 */
static int
kdmsg_autorxmsg(kdmsg_msg_t *msg)
{
        kdmsg_iocom_t *iocom = msg->state->iocom;
        kdmsg_msg_t *rep;
        int error = 0;
        uint32_t cmd;

        /*
         * Main switch processes transaction create/delete sequences only.
         * Use icmd (DELETEs use DMSG_LNK_ERROR
         *
         * NOTE: If processing in-transaction messages you generally want
         *       an inner switch on msg->any.head.cmd.
         */
        if (msg->state) {
                cmd = (msg->state->icmd & DMSGF_BASECMDMASK) |
                      (msg->any.head.cmd & (DMSGF_CREATE |
                                            DMSGF_DELETE |
                                            DMSGF_REPLY));
        } else {
                cmd = 0;
        }

        switch(cmd) {
        case DMSG_LNK_PING:
                /*
                 * Received ping, send reply
                 */
                rep = kdmsg_msg_alloc(msg->state, DMSG_LNK_PING | DMSGF_REPLY,
                                      NULL, NULL);
                kdmsg_msg_write(rep);
                break;
        case DMSG_LNK_PING | DMSGF_REPLY:
                /* ignore replies */
                break;
        case DMSG_LNK_CONN | DMSGF_CREATE:
        case DMSG_LNK_CONN | DMSGF_CREATE | DMSGF_DELETE:
                /*
                 * Received LNK_CONN transaction.  Transmit response and
                 * leave transaction open, which allows the other end to
                 * start to the SPAN protocol.
                 *
                 * Handle shim after acknowledging the CONN.
                 */
                if ((msg->any.head.cmd & DMSGF_DELETE) == 0) {
                        if (iocom->flags & KDMSG_IOCOMF_AUTOCONN) {
                                kdmsg_msg_result(msg, 0);
                                if (iocom->auto_callback)
                                        iocom->auto_callback(msg);
                        } else {
                                error = iocom->rcvmsg(msg);
                        }
                        break;
                }
                /* fall through */
        case DMSG_LNK_CONN | DMSGF_DELETE:
                /*
                 * This message is usually simulated after a link is lost
                 * to clean up the transaction.
                 */
                if (iocom->flags & KDMSG_IOCOMF_AUTOCONN) {
                        if (iocom->auto_callback)
                                iocom->auto_callback(msg);
                        kdmsg_msg_reply(msg, 0);
                } else {
                        error = iocom->rcvmsg(msg);
                }
                break;
        case DMSG_LNK_SPAN | DMSGF_CREATE:
        case DMSG_LNK_SPAN | DMSGF_CREATE | DMSGF_DELETE:
                /*
                 * Received LNK_SPAN transaction.  We do not have to respond
                 * (except on termination), but we must leave the transaction
                 * open.
                 *
                 * Handle shim after acknowledging the SPAN.
                 */
                if (iocom->flags & KDMSG_IOCOMF_AUTORXSPAN) {
                        if ((msg->any.head.cmd & DMSGF_DELETE) == 0) {
                                if (iocom->auto_callback)
                                        iocom->auto_callback(msg);
                                break;
                        }
                        /* fall through */
                } else {
                        error = iocom->rcvmsg(msg);
                        break;
                }
                /* fall through */
        case DMSG_LNK_SPAN | DMSGF_DELETE:
                /*
                 * Process shims (auto_callback) before cleaning up the
                 * circuit structure and closing the transactions.  Device
                 * driver should ensure that the circuit is not used after
                 * the auto_callback() returns.
                 *
                 * Handle shim before closing the SPAN transaction.
                 */
                if (iocom->flags & KDMSG_IOCOMF_AUTORXSPAN) {
                        if (iocom->auto_callback)
                                iocom->auto_callback(msg);
                        kdmsg_msg_reply(msg, 0);
                } else {
                        error = iocom->rcvmsg(msg);
                }
                break;
        default:
                /*
                 * Anything unhandled goes into rcvmsg.
                 *
                 * NOTE: Replies to link-level messages initiated by our side
                 *       are handled by the state callback, they are NOT
                 *       handled here.
                 */
                error = iocom->rcvmsg(msg);
                break;
        }
        return (error);
}

/*
 * Post-receive-handling message and state cleanup.  This routine is called
 * after the state function handling/callback to properly dispose of the
 * message and unlink the state's parent/subq linkage if the state is
 * completely closed.
 *
 * msglk is not held.
 */
static
void
kdmsg_state_cleanuprx(kdmsg_msg_t *msg)
{
        kdmsg_state_t *state = msg->state;
        kdmsg_iocom_t *iocom = state->iocom;

        lockmgr(&iocom->msglk, LK_EXCLUSIVE);
        if (state != &iocom->state0) {
                /*
                 * When terminating a transaction (in either direction), all
                 * sub-states are aborted.
                 */
                if ((msg->any.head.cmd & DMSGF_DELETE) &&
                    TAILQ_FIRST(&msg->state->subq)) {
                        kdio_printf(iocom, 2,
                                    "simulate failure for substates of "
                                    "state %p cmd %08x/%08x\n",
                                    msg->state,
                                    msg->state->rxcmd,
                                    msg->state->txcmd);
                        kdmsg_simulate_failure(msg->state,
                                               0, DMSG_ERR_LOSTLINK);
                }

                /*
                 * Once the state is fully closed we can (try to) remove it
                 * from the subq topology.
                 */
                if ((state->flags & KDMSG_STATE_SUBINSERTED) &&
                    (state->rxcmd & DMSGF_DELETE) &&
                    (state->txcmd & DMSGF_DELETE)) {
                        /* 
                         * Remove parent linkage if state is completely closed.
                         */
                        kdmsg_subq_delete(state);
                }
        }
        kdmsg_msg_free(msg);

        lockmgr(&iocom->msglk, LK_RELEASE);
}

/*
 * Remove state from its parent's subq.  This can wind up recursively
 * dropping the parent upward.
 *
 * NOTE: Once we drop the parent, our pstate pointer may become invalid.
 */
static
void
kdmsg_subq_delete(kdmsg_state_t *state)
{
        kdmsg_state_t *pstate;

        if (state->flags & KDMSG_STATE_SUBINSERTED) {
                pstate = state->parent;
                KKASSERT(pstate);
                if (pstate->scan == state)
                        pstate->scan = NULL;
                TAILQ_REMOVE(&pstate->subq, state, entry);
                state->flags &= ~KDMSG_STATE_SUBINSERTED;
                state->parent = NULL;
                if (TAILQ_EMPTY(&pstate->subq)) {
                        kdmsg_state_drop(pstate);/* pstate->subq */
                }
                pstate = NULL;                   /* safety */
                kdmsg_state_drop(state);         /* pstate->subq */
        } else {
                KKASSERT(state->parent == NULL);
        }
}

/*
 * Simulate receiving a message which terminates an active transaction
 * state.  Our simulated received message must set DELETE and may also
 * have to set CREATE.  It must also ensure that all fields are set such
 * that the receive handling code can find the state (kdmsg_state_msgrx())
 * or an endless loop will ensue.
 *
 * This is used when the other end of the link is dead so the device driver
 * gets a completed transaction for all pending states.
 *
 * Called with iocom locked.
 */
static
void
kdmsg_simulate_failure(kdmsg_state_t *state, int meto, int error)
{
        kdmsg_state_t *substate;

        kdmsg_state_hold(state);                /* aborting */

        /*
         * Abort parent state first. Parent will not actually disappear
         * until children are gone.  Device drivers must handle the situation.
         * The advantage of this is that device drivers can flag the situation
         * as an interlock against new operations on dying states.  And since
         * device operations are often asynchronous anyway, this sequence of
         * events works out better.
         */
        if (meto)
                kdmsg_state_abort(state);

        /*
         * Recurse through any children.
         */
again:
        TAILQ_FOREACH(substate, &state->subq, entry) {
                if (substate->flags & KDMSG_STATE_ABORTING)
                        continue;
                state->scan = substate;
                kdmsg_simulate_failure(substate, 1, error);
                if (state->scan != substate)
                        goto again;
        }
        kdmsg_state_drop(state);                /* aborting */
}

static
void
kdmsg_state_abort(kdmsg_state_t *state)
{
        kdmsg_msg_t *msg;

        /*
         * Set ABORTING and DYING, return if already set.  If the state was
         * just allocated we defer the abort operation until the related
         * message is processed.
         */
        KKASSERT((state->flags & KDMSG_STATE_ABORTING) == 0);
        if (state->flags & KDMSG_STATE_ABORTING)
                return;
        state->flags |= KDMSG_STATE_ABORTING;
        kdmsg_state_dying(state);
        if (state->flags & KDMSG_STATE_NEW) {
                kdio_printf(iocom, 5,
                            "kdmsg_state_abort(0): state %p rxcmd %08x "
                            "txcmd %08x flags %08x - in NEW state\n",
                            state, state->rxcmd,
                            state->txcmd, state->flags);
                return;
        }

        /*
         * NOTE: The DELETE flag might already be set due to an early
         *       termination.
         *
         * NOTE: Args to kdmsg_msg_alloc() to avoid dynamic state allocation.
         *
         * NOTE: We are simulating a received message using our state
         *       (vs a message generated by the other side using its state),
         *       so we must invert DMSGF_REVTRANS and DMSGF_REVCIRC.
         */
        kdio_printf(iocom, 5, 
                    "kdmsg_state_abort(1): state %p rxcmd %08x txcmd %08x\n",
                    state, state->rxcmd, state->txcmd);
        if ((state->rxcmd & DMSGF_DELETE) == 0) {
                msg = kdmsg_msg_alloc(state, DMSG_LNK_ERROR, NULL, NULL);
                if ((state->rxcmd & DMSGF_CREATE) == 0)
                        msg->any.head.cmd |= DMSGF_CREATE;
                msg->any.head.cmd |= DMSGF_DELETE |
                                     (state->rxcmd & DMSGF_REPLY);
                msg->any.head.cmd ^= (DMSGF_REVTRANS | DMSGF_REVCIRC);
                msg->any.head.error = DMSG_ERR_LOSTLINK;
                kdio_printf(iocom, 5,
                            "kdmsg_state_abort(a): state %p msgcmd %08x\n",
                            state, msg->any.head.cmd);
                /* circuit not initialized */
                lockmgr(&state->iocom->msglk, LK_RELEASE);
                kdmsg_msg_receive_handling(msg);
                lockmgr(&state->iocom->msglk, LK_EXCLUSIVE);
                msg = NULL;
        }
        kdio_printf(iocom, 5,
                    "kdmsg_state_abort(2): state %p rxcmd %08x txcmd %08x\n",
                    state, state->rxcmd, state->txcmd);
}

/*
 * Recursively sets KDMSG_STATE_DYING on state and all sub-states, preventing
 * the transmission of any new messages on these states.  This is done
 * atomically when parent state is terminating, whereas setting ABORTING is
 * not atomic and can leak races.
 */
static
void
kdmsg_state_dying(kdmsg_state_t *state)
{
        kdmsg_state_t *scan;

        if ((state->flags & KDMSG_STATE_DYING) == 0) {
                state->flags |= KDMSG_STATE_DYING;
                TAILQ_FOREACH(scan, &state->subq, entry)
                        kdmsg_state_dying(scan);
        }
}

/*
 * Process state tracking for a message prior to transmission.
 *
 * Called with msglk held and the msg dequeued.  Returns non-zero if
 * the message is bad and should be deleted by the caller.
 *
 * One-off messages are usually with dummy state and msg->state may be NULL
 * in this situation.
 *
 * New transactions (when CREATE is set) will insert the state.
 *
 * May request that caller discard the message by setting *discardp to 1.
 * A NULL state may be returned in this case.
 */
static
int
kdmsg_state_msgtx(kdmsg_msg_t *msg)
{
        kdmsg_iocom_t *iocom = msg->state->iocom;
        kdmsg_state_t *state;
        int error;

        /*
         * Make sure a state structure is ready to go in case we need a new
         * one.  This is the only routine which uses freewr_state so no
         * races are possible.
         */
        if ((state = iocom->freewr_state) == NULL) {
                state = kmalloc(sizeof(*state), iocom->mmsg, M_WAITOK | M_ZERO);
                state->flags = KDMSG_STATE_DYNAMIC;
                state->iocom = iocom;
                state->refs = 1;
                TAILQ_INIT(&state->subq);
                iocom->freewr_state = state;
        }

        /*
         * Lock RB tree.  If persistent state is present it will have already
         * been assigned to msg.
         */
        state = msg->state;

        /*
         * Short-cut one-off or mid-stream messages (state may be NULL).
         */
        if ((msg->any.head.cmd & (DMSGF_CREATE | DMSGF_DELETE |
                                  DMSGF_ABORT)) == 0) {
                return(0);
        }


        /*
         * Switch on CREATE, DELETE, REPLY, and also handle ABORT from
         * inside the case statements.
         */
        switch(msg->any.head.cmd & (DMSGF_CREATE | DMSGF_DELETE |
                                    DMSGF_REPLY)) {
        case DMSGF_CREATE:
        case DMSGF_CREATE | DMSGF_DELETE:
                /*
                 * Insert the new persistent message state and mark
                 * half-closed if DELETE is set.  Since this is a new
                 * message it isn't possible to transition into the fully
                 * closed state here.
                 *
                 * XXX state must be assigned and inserted by
                 *     kdmsg_msg_write().  txcmd is assigned by us
                 *     on-transmit.
                 */
                KKASSERT(state != NULL);
                state->icmd = msg->any.head.cmd & DMSGF_BASECMDMASK;
                state->txcmd = msg->any.head.cmd & ~DMSGF_DELETE;
                state->rxcmd = DMSGF_REPLY;
                state->flags &= ~KDMSG_STATE_NEW;
                error = 0;
                break;
        case DMSGF_DELETE:
                /*
                 * Sent ABORT+DELETE in case where msgid has already
                 * been fully closed, ignore the message.
                 */
                if (state == &iocom->state0) {
                        if (msg->any.head.cmd & DMSGF_ABORT) {
                                error = EALREADY;
                        } else {
                                kdio_printf(iocom, 1,
                                        "msgtx: no state match "
                                        "for DELETE cmd=%08x msgid=%016jx\n",
                                        msg->any.head.cmd,
                                        (intmax_t)msg->any.head.msgid);
                                error = EINVAL;
                        }
                        break;
                }

                /*
                 * Sent ABORT+DELETE in case where msgid has
                 * already been reused for an unrelated message,
                 * ignore the message.
                 */
                if ((state->txcmd & DMSGF_CREATE) == 0) {
                        if (msg->any.head.cmd & DMSGF_ABORT) {
                                error = EALREADY;
                        } else {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgtx: state reused "
                                            "for DELETE");
                                error = EINVAL;
                        }
                        break;
                }
                error = 0;
                break;
        default:
                /*
                 * Check for mid-stream ABORT command sent
                 */
                if (msg->any.head.cmd & DMSGF_ABORT) {
                        if (state == &state->iocom->state0 ||
                            (state->txcmd & DMSGF_CREATE) == 0) {
                                error = EALREADY;
                                break;
                        }
                }
                error = 0;
                break;
        case DMSGF_REPLY | DMSGF_CREATE:
        case DMSGF_REPLY | DMSGF_CREATE | DMSGF_DELETE:
                /*
                 * When transmitting a reply with CREATE set the original
                 * persistent state message should already exist.
                 */
                if (state == &state->iocom->state0) {
                        kdio_printf(iocom, 1, "%s\n",
                                    "msgtx: no state match "
                                    "for REPLY | CREATE");
                        error = EINVAL;
                        break;
                }
                state->txcmd = msg->any.head.cmd & ~DMSGF_DELETE;
                error = 0;
                break;
        case DMSGF_REPLY | DMSGF_DELETE:
                /*
                 * When transmitting a reply with DELETE set the original
                 * persistent state message should already exist.
                 *
                 * This is very similar to the REPLY|CREATE|* case except
                 * txcmd is already stored, so we just add the DELETE flag.
                 *
                 * Sent REPLY+ABORT+DELETE in case where msgid has
                 * already been fully closed, ignore the message.
                 */
                if (state == &state->iocom->state0) {
                        if (msg->any.head.cmd & DMSGF_ABORT) {
                                error = EALREADY;
                        } else {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgtx: no state match "
                                            "for REPLY | DELETE");
                                error = EINVAL;
                        }
                        break;
                }

                /*
                 * Sent REPLY+ABORT+DELETE in case where msgid has already
                 * been reused for an unrelated message, ignore the message.
                 */
                if ((state->txcmd & DMSGF_CREATE) == 0) {
                        if (msg->any.head.cmd & DMSGF_ABORT) {
                                error = EALREADY;
                        } else {
                                kdio_printf(iocom, 1, "%s\n",
                                            "msgtx: state reused "
                                            "for REPLY | DELETE");
                                error = EINVAL;
                        }
                        break;
                }
                error = 0;
                break;
        case DMSGF_REPLY:
                /*
                 * Check for mid-stream ABORT reply sent.
                 *
                 * One-off REPLY messages are allowed for e.g. status updates.
                 */
                if (msg->any.head.cmd & DMSGF_ABORT) {
                        if (state == &state->iocom->state0 ||
                            (state->txcmd & DMSGF_CREATE) == 0) {
                                error = EALREADY;
                                break;
                        }
                }
                error = 0;
                break;
        }

        /*
         * Set interlock (XXX hack) in case the send side blocks and a
         * response is returned before kdmsg_state_cleanuptx() can be
         * run.
         */
        if (state && error == 0)
                state->flags |= KDMSG_STATE_INTERLOCK;

        return (error);
}

/*
 * Called with iocom locked.
 */
static
void
kdmsg_state_cleanuptx(kdmsg_msg_t *msg)
{
        kdmsg_iocom_t *iocom = msg->state->iocom;
        kdmsg_state_t *state;

        if ((state = msg->state) == NULL) {
                kdmsg_msg_free(msg);
                return;
        }

        /*
         * Clear interlock (XXX hack) in case the send side blocks and a
         * response is returned in the other thread before
         * kdmsg_state_cleanuptx() can be run.  We maintain our hold on
         * iocom->msglk so we can do this before completing our task.
         */
        if (state->flags & KDMSG_STATE_SIGNAL) {
                kdio_printf(iocom, 1, "state %p interlock!\n", state);
                wakeup(state);
        }
        state->flags &= ~(KDMSG_STATE_INTERLOCK | KDMSG_STATE_SIGNAL);
        kdmsg_state_hold(state);

        if (msg->any.head.cmd & DMSGF_DELETE) {
                KKASSERT((state->txcmd & DMSGF_DELETE) == 0);
                state->txcmd |= DMSGF_DELETE;
                if (state->rxcmd & DMSGF_DELETE) {
                        KKASSERT(state->flags & KDMSG_STATE_RBINSERTED);
                        if (state->txcmd & DMSGF_REPLY) {
                                KKASSERT(msg->any.head.cmd &
                                         DMSGF_REPLY);
                                RB_REMOVE(kdmsg_state_tree,
                                          &iocom->staterd_tree, state);
                        } else {
                                KKASSERT((msg->any.head.cmd &
                                          DMSGF_REPLY) == 0);
                                RB_REMOVE(kdmsg_state_tree,
                                          &iocom->statewr_tree, state);
                        }
                        state->flags &= ~KDMSG_STATE_RBINSERTED;

                        /*
                         * The subq recursion is used for parent linking and
                         * scanning the topology for aborts, we can only
                         * remove leafs.  The circuit is effectively dead now,
                         * but topology won't be torn down until all of its
                         * children have finished/aborted.
                         *
                         * This is particularly important for end-point
                         * devices which might need to access private data
                         * in parent states.  Out of order disconnects can
                         * occur if an end-point device is processing a
                         * message transaction asynchronously because abort
                         * requests are basically synchronous and it probably
                         * isn't convenient (or possible) for the end-point
                         * to abort an asynchronous operation.
                         */
                        if (TAILQ_EMPTY(&state->subq))
                                kdmsg_subq_delete(state);
                        kdmsg_msg_free(msg);
                        kdmsg_state_drop(state);   /* state on rbtree */
                } else {
                        kdmsg_msg_free(msg);
                }
        } else {
                kdmsg_msg_free(msg);
        }

        /*
         * Deferred abort after transmission.
         */
        if ((state->flags & (KDMSG_STATE_ABORTING | KDMSG_STATE_DYING)) &&
            (state->rxcmd & DMSGF_DELETE) == 0) {
                kdio_printf(iocom, 5,
                            "kdmsg_state_cleanuptx: state=%p "
                            "executing deferred abort\n",
                            state);
                state->flags &= ~KDMSG_STATE_ABORTING;
                kdmsg_state_abort(state);
        }
        kdmsg_state_drop(state);
}

static
void
_kdmsg_state_hold(kdmsg_state_t *state KDMSG_DEBUG_ARGS)
{
        atomic_add_int(&state->refs, 1);
#if KDMSG_DEBUG
        kd_printf(4, "state %p +%d\t%s:%d\n", state, state->refs, file, line);
#endif
}

static
void
_kdmsg_state_drop(kdmsg_state_t *state KDMSG_DEBUG_ARGS)
{
        KKASSERT(state->refs > 0);
#if KDMSG_DEBUG
        kd_printf(4, "state %p -%d\t%s:%d\n", state, state->refs, file, line);
#endif
        if (atomic_fetchadd_int(&state->refs, -1) == 1)
                kdmsg_state_free(state);
}

static
void
kdmsg_state_free(kdmsg_state_t *state)
{
        kdmsg_iocom_t *iocom = state->iocom;

        KKASSERT((state->flags & KDMSG_STATE_RBINSERTED) == 0);
        KKASSERT((state->flags & KDMSG_STATE_SUBINSERTED) == 0);
        KKASSERT(TAILQ_EMPTY(&state->subq));

        if (state != &state->iocom->state0)
                kfree(state, iocom->mmsg);
}

kdmsg_msg_t *
kdmsg_msg_alloc(kdmsg_state_t *state, uint32_t cmd,
                int (*func)(kdmsg_state_t *, kdmsg_msg_t *), void *data)
{
        kdmsg_iocom_t *iocom = state->iocom;
        kdmsg_state_t *pstate;
        kdmsg_msg_t *msg;
        size_t hbytes;

        KKASSERT(iocom != NULL);
        hbytes = (cmd & DMSGF_SIZE) * DMSG_ALIGN;
        msg = kmalloc(offsetof(struct kdmsg_msg, any) + hbytes,
                      iocom->mmsg, M_WAITOK | M_ZERO);
        msg->hdr_size = hbytes;

        if ((cmd & (DMSGF_CREATE | DMSGF_REPLY)) == DMSGF_CREATE) {
                /*
                 * New transaction, requires tracking state and a unique
                 * msgid to be allocated.
                 *
                 * It is possible to race a circuit failure, inherit the
                 * parent's STATE_DYING flag to trigger an abort sequence
                 * in the transmit path.  By not inheriting ABORTING the
                 * abort sequence can recurse.
                 *
                 * NOTE: The transactions has not yet been initiated so we
                 *       cannot set DMSGF_CREATE/DELETE bits in txcmd or rxcmd.
                 *       We have to properly setup DMSGF_REPLY, however.
                 */
                pstate = state;
                state = kmalloc(sizeof(*state), iocom->mmsg, M_WAITOK | M_ZERO);
                TAILQ_INIT(&state->subq);
                state->iocom = iocom;
                state->parent = pstate;
                state->flags = KDMSG_STATE_DYNAMIC |
                               KDMSG_STATE_NEW;
                state->func = func;
                state->any.any = data;
                state->msgid = (uint64_t)(uintptr_t)state;
                /*msg->any.head.msgid = state->msgid;XXX*/

                lockmgr(&iocom->msglk, LK_EXCLUSIVE);
                if (RB_INSERT(kdmsg_state_tree, &iocom->statewr_tree, state))
                        panic("duplicate msgid allocated");
                if (TAILQ_EMPTY(&pstate->subq))
                        kdmsg_state_hold(pstate);/* pstate->subq */
                TAILQ_INSERT_TAIL(&pstate->subq, state, entry);
                state->flags |= KDMSG_STATE_RBINSERTED |
                                KDMSG_STATE_SUBINSERTED;
                state->flags |= pstate->flags & KDMSG_STATE_DYING;
                kdmsg_state_hold(state);        /* pstate->subq */
                kdmsg_state_hold(state);        /* state on rbtree */
                kdmsg_state_hold(state);        /* msg->state */
                lockmgr(&iocom->msglk, LK_RELEASE);
        } else {
                pstate = state->parent;
                KKASSERT(pstate != NULL);
                kdmsg_state_hold(state);        /* msg->state */
        }

        if (state->flags & KDMSG_STATE_OPPOSITE)
                cmd |= DMSGF_REVTRANS;
        if (pstate->flags & KDMSG_STATE_OPPOSITE)
                cmd |= DMSGF_REVCIRC;

        msg->any.head.magic = DMSG_HDR_MAGIC;
        msg->any.head.cmd = cmd;
        msg->any.head.msgid = state->msgid;
        msg->any.head.circuit = pstate->msgid;
        msg->state = state;

        return (msg);
}

void
kdmsg_msg_free(kdmsg_msg_t *msg)
{
        kdmsg_iocom_t *iocom = msg->state->iocom;
        kdmsg_state_t *state;

        if ((msg->flags & KDMSG_FLAG_AUXALLOC) &&
            msg->aux_data && msg->aux_size) {
                kfree(msg->aux_data, iocom->mmsg);
                msg->flags &= ~KDMSG_FLAG_AUXALLOC;
        }
        if ((state = msg->state) != NULL) {
                msg->state = NULL;
                kdmsg_state_drop(state);        /* msg->state */
        }
        msg->aux_data = NULL;
        msg->aux_size = 0;

        kfree(msg, iocom->mmsg);
}

void
kdmsg_detach_aux_data(kdmsg_msg_t *msg, kdmsg_data_t *data)
{
        if (msg->flags & KDMSG_FLAG_AUXALLOC) {
                data->aux_data = msg->aux_data;
                data->aux_size = msg->aux_size;
                data->iocom = msg->state->iocom;
                msg->flags &= ~KDMSG_FLAG_AUXALLOC;
        } else {
                data->aux_data = NULL;
                data->aux_size = 0;
                data->iocom = msg->state->iocom;
        }
}

void
kdmsg_free_aux_data(kdmsg_data_t *data)
{
        if (data->aux_data)
                kfree(data->aux_data, data->iocom->mmsg);
}

/*
 * Indexed messages are stored in a red-black tree indexed by their
 * msgid.  Only persistent messages are indexed.
 */
int
kdmsg_state_cmp(kdmsg_state_t *state1, kdmsg_state_t *state2)
{
        if (state1->iocom < state2->iocom)
                return(-1);
        if (state1->iocom > state2->iocom)
                return(1);
        if (state1->msgid < state2->msgid)
                return(-1);
        if (state1->msgid > state2->msgid)
                return(1);
        return(0);
}

/*
 * Write a message.  All requisit command flags have been set.
 *
 * If msg->state is non-NULL the message is written to the existing
 * transaction.  msgid will be set accordingly.
 *
 * If msg->state is NULL and CREATE is set new state is allocated and
 * (func, data) is installed.  A msgid is assigned.
 *
 * If msg->state is NULL and CREATE is not set the message is assumed
 * to be a one-way message.  The originator must assign the msgid
 * (or leave it 0, which is typical.
 *
 * This function merely queues the message to the management thread, it
 * does not write to the message socket/pipe.
 */
void
kdmsg_msg_write(kdmsg_msg_t *msg)
{
        kdmsg_iocom_t *iocom = msg->state->iocom;

        lockmgr(&iocom->msglk, LK_EXCLUSIVE);
        kdmsg_msg_write_locked(iocom, msg);
        lockmgr(&iocom->msglk, LK_RELEASE);
}

static void
kdmsg_msg_write_locked(kdmsg_iocom_t *iocom, kdmsg_msg_t *msg)
{
        kdmsg_state_t *state;

        if (msg->state) {
                /*
                 * Continuance or termination of existing transaction.
                 * The transaction could have been initiated by either end.
                 *
                 * (Function callback and aux data for the receive side can
                 * be replaced or left alone).
                 */
                state = msg->state;
                msg->any.head.msgid = state->msgid;
        } else {
                /*
                 * One-off message (always uses msgid 0 to distinguish
                 * between a possibly lost in-transaction message due to
                 * competing aborts and a real one-off message?)
                 */
                state = NULL;
                msg->any.head.msgid = 0;
        }

#if 0
        /*
         * XXX removed - don't make this a panic, allow the state checks
         *     below to catch the situation.
         *
         * This flag is not set until after the tx thread has drained
         * the tx msgq and simulated responses.  After that point the
         * txthread is dead and can no longer simulate responses.
         *
         * Device drivers should never try to send a message once this
         * flag is set.  They should have detected (through the state
         * closures) that the link is in trouble.
         */
        if (iocom->flags & KDMSG_IOCOMF_EXITNOACC) {
                lockmgr(&iocom->msglk, LK_RELEASE);
                panic("kdmsg_msg_write: Attempt to write message to "
                      "terminated iocom\n");
        }
#endif

        /*
         * For stateful messages, if the circuit is dead or dying we have
         * to abort the potentially newly-created state and discard the
         * message.
         *
         * - We must discard the message because the other end will not
         *   be expecting any more messages over the dead or dying circuit
         *   and might not be able to receive them.
         *
         * - We abort the state by simulating a failure to generate a fake
         *   incoming DELETE.  This will trigger the state callback and allow
         *   the device to clean things up and reply, closing the outgoing
         *   direction and allowing the state to be freed.
         *
         * This situation occurs quite often, particularly as SPANs stabilize.
         * End-points must do the right thing.
         */
        if (state) {
                KKASSERT((state->txcmd & DMSGF_DELETE) == 0);
                if (state->flags & KDMSG_STATE_DYING) {
#if 0
                if ((state->flags & KDMSG_STATE_DYING) ||
                    (state->parent->txcmd & DMSGF_DELETE) ||
                    (state->parent->flags & KDMSG_STATE_DYING)) {
#endif
                        kdio_printf(iocom, 4,
                                    "kdmsg_msg_write: Write to dying circuit "
                                    "state=%p "
                                    "ptxcmd=%08x prxcmd=%08x flags=%08x\n",
                                    state,
                                    state->parent->rxcmd,
                                    state->parent->txcmd,
                                    state->parent->flags);
                        kdmsg_state_hold(state);
                        kdmsg_state_msgtx(msg);
                        kdmsg_state_cleanuptx(msg);
                        kdmsg_state_drop(state);
                        return;
                }
        }

        /*
         * Finish up the msg fields.  Note that msg->aux_size and the
         * aux_bytes stored in the message header represent the unaligned
         * (actual) bytes of data, but the buffer is sized to an aligned
         * size and the CRC is generated over the aligned length.
         */
        msg->any.head.salt = /* (random << 8) | */ (iocom->msg_seq & 255);
        ++iocom->msg_seq;

        if (msg->aux_data && msg->aux_size) {
                uint32_t abytes = DMSG_DOALIGN(msg->aux_size);

                msg->any.head.aux_bytes = msg->aux_size;
                msg->any.head.aux_crc = iscsi_crc32(msg->aux_data, abytes);
        }
        msg->any.head.hdr_crc = 0;
        msg->any.head.hdr_crc = iscsi_crc32(msg->any.buf, msg->hdr_size);

        TAILQ_INSERT_TAIL(&iocom->msgq, msg, qentry);

        if (iocom->msg_ctl & KDMSG_CLUSTERCTL_SLEEPING) {
                atomic_clear_int(&iocom->msg_ctl,
                                 KDMSG_CLUSTERCTL_SLEEPING);
                wakeup(&iocom->msg_ctl);
        }
}

/*
 * Reply to a message and terminate our side of the transaction.
 *
 * If msg->state is non-NULL we are replying to a one-way message.
 */
void
kdmsg_msg_reply(kdmsg_msg_t *msg, uint32_t error)
{
        kdmsg_state_t *state = msg->state;
        kdmsg_msg_t *nmsg;
        uint32_t cmd;

        /*
         * Reply with a simple error code and terminate the transaction.
         */
        cmd = DMSG_LNK_ERROR;

        /*
         * Check if our direction has even been initiated yet, set CREATE.
         *
         * Check what direction this is (command or reply direction).  Note
         * that txcmd might not have been initiated yet.
         *
         * If our direction has already been closed we just return without
         * doing anything.
         */
        if (state != &state->iocom->state0) {
                if (state->txcmd & DMSGF_DELETE)
                        return;
                if ((state->txcmd & DMSGF_CREATE) == 0)
                        cmd |= DMSGF_CREATE;
                if (state->txcmd & DMSGF_REPLY)
                        cmd |= DMSGF_REPLY;
                cmd |= DMSGF_DELETE;
        } else {
                if ((msg->any.head.cmd & DMSGF_REPLY) == 0)
                        cmd |= DMSGF_REPLY;
        }

        nmsg = kdmsg_msg_alloc(state, cmd, NULL, NULL);
        nmsg->any.head.error = error;
        kdmsg_msg_write(nmsg);
}

/*
 * Reply to a message and continue our side of the transaction.
 *
 * If msg->state is non-NULL we are replying to a one-way message and this
 * function degenerates into the same as kdmsg_msg_reply().
 */
void
kdmsg_msg_result(kdmsg_msg_t *msg, uint32_t error)
{
        kdmsg_state_t *state = msg->state;
        kdmsg_msg_t *nmsg;
        uint32_t cmd;

        /*
         * Return a simple result code, do NOT terminate the transaction.
         */
        cmd = DMSG_LNK_ERROR;

        /*
         * Check if our direction has even been initiated yet, set CREATE.
         *
         * Check what direction this is (command or reply direction).  Note
         * that txcmd might not have been initiated yet.
         *
         * If our direction has already been closed we just return without
         * doing anything.
         */
        if (state != &state->iocom->state0) {
                if (state->txcmd & DMSGF_DELETE)
                        return;
                if ((state->txcmd & DMSGF_CREATE) == 0)
                        cmd |= DMSGF_CREATE;
                if (state->txcmd & DMSGF_REPLY)
                        cmd |= DMSGF_REPLY;
                /* continuing transaction, do not set MSGF_DELETE */
        } else {
                if ((msg->any.head.cmd & DMSGF_REPLY) == 0)
                        cmd |= DMSGF_REPLY;
        }

        nmsg = kdmsg_msg_alloc(state, cmd, NULL, NULL);
        nmsg->any.head.error = error;
        kdmsg_msg_write(nmsg);
}

/*
 * Reply to a message and terminate our side of the transaction.
 *
 * If msg->state is non-NULL we are replying to a one-way message.
 */
void
kdmsg_state_reply(kdmsg_state_t *state, uint32_t error)
{
        kdmsg_msg_t *nmsg;
        uint32_t cmd;

        /*
         * Reply with a simple error code and terminate the transaction.
         */
        cmd = DMSG_LNK_ERROR;

        /*
         * Check if our direction has even been initiated yet, set CREATE.
         *
         * Check what direction this is (command or reply direction).  Note
         * that txcmd might not have been initiated yet.
         *
         * If our direction has already been closed we just return without
         * doing anything.
         */
        KKASSERT(state);
        if (state->txcmd & DMSGF_DELETE)
                return;
        if ((state->txcmd & DMSGF_CREATE) == 0)
                cmd |= DMSGF_CREATE;
        if (state->txcmd & DMSGF_REPLY)
                cmd |= DMSGF_REPLY;
        cmd |= DMSGF_DELETE;

        nmsg = kdmsg_msg_alloc(state, cmd, NULL, NULL);
        nmsg->any.head.error = error;
        kdmsg_msg_write(nmsg);
}

/*
 * Reply to a message and continue our side of the transaction.
 *
 * If msg->state is non-NULL we are replying to a one-way message and this
 * function degenerates into the same as kdmsg_msg_reply().
 */
void
kdmsg_state_result(kdmsg_state_t *state, uint32_t error)
{
        kdmsg_msg_t *nmsg;
        uint32_t cmd;

        /*
         * Return a simple result code, do NOT terminate the transaction.
         */
        cmd = DMSG_LNK_ERROR;

        /*
         * Check if our direction has even been initiated yet, set CREATE.
         *
         * Check what direction this is (command or reply direction).  Note
         * that txcmd might not have been initiated yet.
         *
         * If our direction has already been closed we just return without
         * doing anything.
         */
        KKASSERT(state);
        if (state->txcmd & DMSGF_DELETE)
                return;
        if ((state->txcmd & DMSGF_CREATE) == 0)
                cmd |= DMSGF_CREATE;
        if (state->txcmd & DMSGF_REPLY)
                cmd |= DMSGF_REPLY;
        /* continuing transaction, do not set MSGF_DELETE */

        nmsg = kdmsg_msg_alloc(state, cmd, NULL, NULL);
        nmsg->any.head.error = error;
        kdmsg_msg_write(nmsg);
}