xpc_channel.c

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/*
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (c) 2004-2009 Silicon Graphics, Inc.  All Rights Reserved.
 */

/*
 * Cross Partition Communication (XPC) channel support.
 *
 *  This is the part of XPC that manages the channels and
 *  sends/receives messages across them to/from other partitions.
 *
 */

#include <linux/device.h>
#include "xpc.h"

/*
 * Process a connect message from a remote partition.
 *
 * Note: xpc_process_connect() is expecting to be called with the
 * spin_lock_irqsave held and will leave it locked upon return.
 */
static void
xpc_process_connect(struct xpc_channel *ch, unsigned long *irq_flags)
{
    enum xp_retval ret;

    DBUG_ON(!spin_is_locked(&ch->lock));

    if (!(ch->flags & XPC_C_OPENREQUEST) ||
        !(ch->flags & XPC_C_ROPENREQUEST)) {
        /* nothing more to do for now */
        return;
    }
    DBUG_ON(!(ch->flags & XPC_C_CONNECTING));

    if (!(ch->flags & XPC_C_SETUP)) {
        spin_unlock_irqrestore(&ch->lock, *irq_flags);
        ret = xpc_arch_ops.setup_msg_structures(ch);
        spin_lock_irqsave(&ch->lock, *irq_flags);

        if (ret != xpSuccess)
            XPC_DISCONNECT_CHANNEL(ch, ret, irq_flags);
        else
            ch->flags |= XPC_C_SETUP;

        if (ch->flags & XPC_C_DISCONNECTING)
            return;
    }

    if (!(ch->flags & XPC_C_OPENREPLY)) {
        ch->flags |= XPC_C_OPENREPLY;
        xpc_arch_ops.send_chctl_openreply(ch, irq_flags);
    }

    if (!(ch->flags & XPC_C_ROPENREPLY))
        return;

    if (!(ch->flags & XPC_C_OPENCOMPLETE)) {
        ch->flags |= (XPC_C_OPENCOMPLETE | XPC_C_CONNECTED);
        xpc_arch_ops.send_chctl_opencomplete(ch, irq_flags);
    }

    if (!(ch->flags & XPC_C_ROPENCOMPLETE))
        return;

    dev_info(xpc_chan, "channel %d to partition %d connected\n",
         ch->number, ch->partid);

    ch->flags = (XPC_C_CONNECTED | XPC_C_SETUP);    /* clear all else */
}

/*
 * spin_lock_irqsave() is expected to be held on entry.
 */
static void
xpc_process_disconnect(struct xpc_channel *ch, unsigned long *irq_flags)
{
    struct xpc_partition *part = &xpc_partitions[ch->partid];
    u32 channel_was_connected = (ch->flags & XPC_C_WASCONNECTED);

    DBUG_ON(!spin_is_locked(&ch->lock));

    if (!(ch->flags & XPC_C_DISCONNECTING))
        return;

    DBUG_ON(!(ch->flags & XPC_C_CLOSEREQUEST));

    /* make sure all activity has settled down first */

    if (atomic_read(&ch->kthreads_assigned) > 0 ||
        atomic_read(&ch->references) > 0) {
        return;
    }
    DBUG_ON((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
        !(ch->flags & XPC_C_DISCONNECTINGCALLOUT_MADE));

    if (part->act_state == XPC_P_AS_DEACTIVATING) {
        /* can't proceed until the other side disengages from us */
        if (xpc_arch_ops.partition_engaged(ch->partid))
            return;

    } else {

        /* as long as the other side is up do the full protocol */

        if (!(ch->flags & XPC_C_RCLOSEREQUEST))
            return;

        if (!(ch->flags & XPC_C_CLOSEREPLY)) {
            ch->flags |= XPC_C_CLOSEREPLY;
            xpc_arch_ops.send_chctl_closereply(ch, irq_flags);
        }

        if (!(ch->flags & XPC_C_RCLOSEREPLY))
            return;
    }

    /* wake those waiting for notify completion */
    if (atomic_read(&ch->n_to_notify) > 0) {
        /* we do callout while holding ch->lock, callout can't block */
        xpc_arch_ops.notify_senders_of_disconnect(ch);
    }

    /* both sides are disconnected now */

    if (ch->flags & XPC_C_DISCONNECTINGCALLOUT_MADE) {
        spin_unlock_irqrestore(&ch->lock, *irq_flags);
        xpc_disconnect_callout(ch, xpDisconnected);
        spin_lock_irqsave(&ch->lock, *irq_flags);
    }

    DBUG_ON(atomic_read(&ch->n_to_notify) != 0);

    /* it's now safe to free the channel's message queues */
    xpc_arch_ops.teardown_msg_structures(ch);

    ch->func = NULL;
    ch->key = NULL;
    ch->entry_size = 0;
    ch->local_nentries = 0;
    ch->remote_nentries = 0;
    ch->kthreads_assigned_limit = 0;
    ch->kthreads_idle_limit = 0;

    /*
     * Mark the channel disconnected and clear all other flags, including
     * XPC_C_SETUP (because of call to
     * xpc_arch_ops.teardown_msg_structures()) but not including
     * XPC_C_WDISCONNECT (if it was set).
     */
    ch->flags = (XPC_C_DISCONNECTED | (ch->flags & XPC_C_WDISCONNECT));

    atomic_dec(&part->nchannels_active);

    if (channel_was_connected) {
        dev_info(xpc_chan, "channel %d to partition %d disconnected, "
             "reason=%d\n", ch->number, ch->partid, ch->reason);
    }

    if (ch->flags & XPC_C_WDISCONNECT) {
        /* we won't lose the CPU since we're holding ch->lock */
        complete(&ch->wdisconnect_wait);
    } else if (ch->delayed_chctl_flags) {
        if (part->act_state != XPC_P_AS_DEACTIVATING) {
            /* time to take action on any delayed chctl flags */
            spin_lock(&part->chctl_lock);
            part->chctl.flags[ch->number] |=
                ch->delayed_chctl_flags;
            spin_unlock(&part->chctl_lock);
        }
        ch->delayed_chctl_flags = 0;
    }
}

/*
 * Process a change in the channel's remote connection state.
 */
static void
xpc_process_openclose_chctl_flags(struct xpc_partition *part, int ch_number,
                  u8 chctl_flags)
{
    unsigned long irq_flags;
    struct xpc_openclose_args *args =
        &part->remote_openclose_args[ch_number];
    struct xpc_channel *ch = &part->channels[ch_number];
    enum xp_retval reason;
    enum xp_retval ret;
    int create_kthread = 0;

    spin_lock_irqsave(&ch->lock, irq_flags);

again:

    if ((ch->flags & XPC_C_DISCONNECTED) &&
        (ch->flags & XPC_C_WDISCONNECT)) {
        /*
         * Delay processing chctl flags until thread waiting disconnect
         * has had a chance to see that the channel is disconnected.
         */
        ch->delayed_chctl_flags |= chctl_flags;
        goto out;
    }

    if (chctl_flags & XPC_CHCTL_CLOSEREQUEST) {

        dev_dbg(xpc_chan, "XPC_CHCTL_CLOSEREQUEST (reason=%d) received "
            "from partid=%d, channel=%d\n", args->reason,
            ch->partid, ch->number);

        /*
         * If RCLOSEREQUEST is set, we're probably waiting for
         * RCLOSEREPLY. We should find it and a ROPENREQUEST packed
         * with this RCLOSEREQUEST in the chctl_flags.
         */

        if (ch->flags & XPC_C_RCLOSEREQUEST) {
            DBUG_ON(!(ch->flags & XPC_C_DISCONNECTING));
            DBUG_ON(!(ch->flags & XPC_C_CLOSEREQUEST));
            DBUG_ON(!(ch->flags & XPC_C_CLOSEREPLY));
            DBUG_ON(ch->flags & XPC_C_RCLOSEREPLY);

            DBUG_ON(!(chctl_flags & XPC_CHCTL_CLOSEREPLY));
            chctl_flags &= ~XPC_CHCTL_CLOSEREPLY;
            ch->flags |= XPC_C_RCLOSEREPLY;

            /* both sides have finished disconnecting */
            xpc_process_disconnect(ch, &irq_flags);
            DBUG_ON(!(ch->flags & XPC_C_DISCONNECTED));
            goto again;
        }

        if (ch->flags & XPC_C_DISCONNECTED) {
            if (!(chctl_flags & XPC_CHCTL_OPENREQUEST)) {
                if (part->chctl.flags[ch_number] &
                    XPC_CHCTL_OPENREQUEST) {

                    DBUG_ON(ch->delayed_chctl_flags != 0);
                    spin_lock(&part->chctl_lock);
                    part->chctl.flags[ch_number] |=
                        XPC_CHCTL_CLOSEREQUEST;
                    spin_unlock(&part->chctl_lock);
                }
                goto out;
            }

            XPC_SET_REASON(ch, 0, 0);
            ch->flags &= ~XPC_C_DISCONNECTED;

            atomic_inc(&part->nchannels_active);
            ch->flags |= (XPC_C_CONNECTING | XPC_C_ROPENREQUEST);
        }

        chctl_flags &= ~(XPC_CHCTL_OPENREQUEST | XPC_CHCTL_OPENREPLY |
            XPC_CHCTL_OPENCOMPLETE);

        /*
         * The meaningful CLOSEREQUEST connection state fields are:
         *      reason = reason connection is to be closed
         */

        ch->flags |= XPC_C_RCLOSEREQUEST;

        if (!(ch->flags & XPC_C_DISCONNECTING)) {
            reason = args->reason;
            if (reason <= xpSuccess || reason > xpUnknownReason)
                reason = xpUnknownReason;
            else if (reason == xpUnregistering)
                reason = xpOtherUnregistering;

            XPC_DISCONNECT_CHANNEL(ch, reason, &irq_flags);

            DBUG_ON(chctl_flags & XPC_CHCTL_CLOSEREPLY);
            goto out;
        }

        xpc_process_disconnect(ch, &irq_flags);
    }

    if (chctl_flags & XPC_CHCTL_CLOSEREPLY) {

        dev_dbg(xpc_chan, "XPC_CHCTL_CLOSEREPLY received from partid="
            "%d, channel=%d\n", ch->partid, ch->number);

        if (ch->flags & XPC_C_DISCONNECTED) {
            DBUG_ON(part->act_state != XPC_P_AS_DEACTIVATING);
            goto out;
        }

        DBUG_ON(!(ch->flags & XPC_C_CLOSEREQUEST));

        if (!(ch->flags & XPC_C_RCLOSEREQUEST)) {
            if (part->chctl.flags[ch_number] &
                XPC_CHCTL_CLOSEREQUEST) {

                DBUG_ON(ch->delayed_chctl_flags != 0);
                spin_lock(&part->chctl_lock);
                part->chctl.flags[ch_number] |=
                    XPC_CHCTL_CLOSEREPLY;
                spin_unlock(&part->chctl_lock);
            }
            goto out;
        }

        ch->flags |= XPC_C_RCLOSEREPLY;

        if (ch->flags & XPC_C_CLOSEREPLY) {
            /* both sides have finished disconnecting */
            xpc_process_disconnect(ch, &irq_flags);
        }
    }

    if (chctl_flags & XPC_CHCTL_OPENREQUEST) {

        dev_dbg(xpc_chan, "XPC_CHCTL_OPENREQUEST (entry_size=%d, "
            "local_nentries=%d) received from partid=%d, "
            "channel=%d\n", args->entry_size, args->local_nentries,
            ch->partid, ch->number);

        if (part->act_state == XPC_P_AS_DEACTIVATING ||
            (ch->flags & XPC_C_ROPENREQUEST)) {
            goto out;
        }

        if (ch->flags & (XPC_C_DISCONNECTING | XPC_C_WDISCONNECT)) {
            ch->delayed_chctl_flags |= XPC_CHCTL_OPENREQUEST;
            goto out;
        }
        DBUG_ON(!(ch->flags & (XPC_C_DISCONNECTED |
                       XPC_C_OPENREQUEST)));
        DBUG_ON(ch->flags & (XPC_C_ROPENREQUEST | XPC_C_ROPENREPLY |
                     XPC_C_OPENREPLY | XPC_C_CONNECTED));

        /*
         * The meaningful OPENREQUEST connection state fields are:
         *      entry_size = size of channel's messages in bytes
         *      local_nentries = remote partition's local_nentries
         */
        if (args->entry_size == 0 || args->local_nentries == 0) {
            /* assume OPENREQUEST was delayed by mistake */
            goto out;
        }

        ch->flags |= (XPC_C_ROPENREQUEST | XPC_C_CONNECTING);
        ch->remote_nentries = args->local_nentries;

        if (ch->flags & XPC_C_OPENREQUEST) {
            if (args->entry_size != ch->entry_size) {
                XPC_DISCONNECT_CHANNEL(ch, xpUnequalMsgSizes,
                               &irq_flags);
                goto out;
            }
        } else {
            ch->entry_size = args->entry_size;

            XPC_SET_REASON(ch, 0, 0);
            ch->flags &= ~XPC_C_DISCONNECTED;

            atomic_inc(&part->nchannels_active);
        }

        xpc_process_connect(ch, &irq_flags);
    }

    if (chctl_flags & XPC_CHCTL_OPENREPLY) {

        dev_dbg(xpc_chan, "XPC_CHCTL_OPENREPLY (local_msgqueue_pa="
            "0x%lx, local_nentries=%d, remote_nentries=%d) "
            "received from partid=%d, channel=%d\n",
            args->local_msgqueue_pa, args->local_nentries,
            args->remote_nentries, ch->partid, ch->number);

        if (ch->flags & (XPC_C_DISCONNECTING | XPC_C_DISCONNECTED))
            goto out;

        if (!(ch->flags & XPC_C_OPENREQUEST)) {
            XPC_DISCONNECT_CHANNEL(ch, xpOpenCloseError,
                           &irq_flags);
            goto out;
        }

        DBUG_ON(!(ch->flags & XPC_C_ROPENREQUEST));
        DBUG_ON(ch->flags & XPC_C_CONNECTED);

        /*
         * The meaningful OPENREPLY connection state fields are:
         *      local_msgqueue_pa = physical address of remote
         *                          partition's local_msgqueue
         *      local_nentries = remote partition's local_nentries
         *      remote_nentries = remote partition's remote_nentries
         */
        DBUG_ON(args->local_msgqueue_pa == 0);
        DBUG_ON(args->local_nentries == 0);
        DBUG_ON(args->remote_nentries == 0);

        ret = xpc_arch_ops.save_remote_msgqueue_pa(ch,
                              args->local_msgqueue_pa);
        if (ret != xpSuccess) {
            XPC_DISCONNECT_CHANNEL(ch, ret, &irq_flags);
            goto out;
        }
        ch->flags |= XPC_C_ROPENREPLY;

        if (args->local_nentries < ch->remote_nentries) {
            dev_dbg(xpc_chan, "XPC_CHCTL_OPENREPLY: new "
                "remote_nentries=%d, old remote_nentries=%d, "
                "partid=%d, channel=%d\n",
                args->local_nentries, ch->remote_nentries,
                ch->partid, ch->number);

            ch->remote_nentries = args->local_nentries;
        }
        if (args->remote_nentries < ch->local_nentries) {
            dev_dbg(xpc_chan, "XPC_CHCTL_OPENREPLY: new "
                "local_nentries=%d, old local_nentries=%d, "
                "partid=%d, channel=%d\n",
                args->remote_nentries, ch->local_nentries,
                ch->partid, ch->number);

            ch->local_nentries = args->remote_nentries;
        }

        xpc_process_connect(ch, &irq_flags);
    }

    if (chctl_flags & XPC_CHCTL_OPENCOMPLETE) {

        dev_dbg(xpc_chan, "XPC_CHCTL_OPENCOMPLETE received from "
            "partid=%d, channel=%d\n", ch->partid, ch->number);

        if (ch->flags & (XPC_C_DISCONNECTING | XPC_C_DISCONNECTED))
            goto out;

        if (!(ch->flags & XPC_C_OPENREQUEST) ||
            !(ch->flags & XPC_C_OPENREPLY)) {
            XPC_DISCONNECT_CHANNEL(ch, xpOpenCloseError,
                           &irq_flags);
            goto out;
        }

        DBUG_ON(!(ch->flags & XPC_C_ROPENREQUEST));
        DBUG_ON(!(ch->flags & XPC_C_ROPENREPLY));
        DBUG_ON(!(ch->flags & XPC_C_CONNECTED));

        ch->flags |= XPC_C_ROPENCOMPLETE;

        xpc_process_connect(ch, &irq_flags);
        create_kthread = 1;
    }

out:
    spin_unlock_irqrestore(&ch->lock, irq_flags);

    if (create_kthread)
        xpc_create_kthreads(ch, 1, 0);
}

/*
 * Attempt to establish a channel connection to a remote partition.
 */
static enum xp_retval
xpc_connect_channel(struct xpc_channel *ch)
{
    unsigned long irq_flags;
    struct xpc_registration *registration = &xpc_registrations[ch->number];

    if (mutex_trylock(&registration->mutex) == 0)
        return xpRetry;

    if (!XPC_CHANNEL_REGISTERED(ch->number)) {
        mutex_unlock(&registration->mutex);
        return xpUnregistered;
    }

    spin_lock_irqsave(&ch->lock, irq_flags);

    DBUG_ON(ch->flags & XPC_C_CONNECTED);
    DBUG_ON(ch->flags & XPC_C_OPENREQUEST);

    if (ch->flags & XPC_C_DISCONNECTING) {
        spin_unlock_irqrestore(&ch->lock, irq_flags);
        mutex_unlock(&registration->mutex);
        return ch->reason;
    }

    /* add info from the channel connect registration to the channel */

    ch->kthreads_assigned_limit = registration->assigned_limit;
    ch->kthreads_idle_limit = registration->idle_limit;
    DBUG_ON(atomic_read(&ch->kthreads_assigned) != 0);
    DBUG_ON(atomic_read(&ch->kthreads_idle) != 0);
    DBUG_ON(atomic_read(&ch->kthreads_active) != 0);

    ch->func = registration->func;
    DBUG_ON(registration->func == NULL);
    ch->key = registration->key;

    ch->local_nentries = registration->nentries;

    if (ch->flags & XPC_C_ROPENREQUEST) {
        if (registration->entry_size != ch->entry_size) {
            /* the local and remote sides aren't the same */

            /*
             * Because XPC_DISCONNECT_CHANNEL() can block we're
             * forced to up the registration sema before we unlock
             * the channel lock. But that's okay here because we're
             * done with the part that required the registration
             * sema. XPC_DISCONNECT_CHANNEL() requires that the
             * channel lock be locked and will unlock and relock
             * the channel lock as needed.
             */
            mutex_unlock(&registration->mutex);
            XPC_DISCONNECT_CHANNEL(ch, xpUnequalMsgSizes,
                           &irq_flags);
            spin_unlock_irqrestore(&ch->lock, irq_flags);
            return xpUnequalMsgSizes;
        }
    } else {
        ch->entry_size = registration->entry_size;

        XPC_SET_REASON(ch, 0, 0);
        ch->flags &= ~XPC_C_DISCONNECTED;

        atomic_inc(&xpc_partitions[ch->partid].nchannels_active);
    }

    mutex_unlock(&registration->mutex);

    /* initiate the connection */

    ch->flags |= (XPC_C_OPENREQUEST | XPC_C_CONNECTING);
    xpc_arch_ops.send_chctl_openrequest(ch, &irq_flags);

    xpc_process_connect(ch, &irq_flags);

    spin_unlock_irqrestore(&ch->lock, irq_flags);

    return xpSuccess;
}

void
xpc_process_sent_chctl_flags(struct xpc_partition *part)
{
    unsigned long irq_flags;
    union xpc_channel_ctl_flags chctl;
    struct xpc_channel *ch;
    int ch_number;
    u32 ch_flags;

    chctl.all_flags = xpc_arch_ops.get_chctl_all_flags(part);

    /*
     * Initiate channel connections for registered channels.
     *
     * For each connected channel that has pending messages activate idle
     * kthreads and/or create new kthreads as needed.
     */

    for (ch_number = 0; ch_number < part->nchannels; ch_number++) {
        ch = &part->channels[ch_number];

        /*
         * Process any open or close related chctl flags, and then deal
         * with connecting or disconnecting the channel as required.
         */

        if (chctl.flags[ch_number] & XPC_OPENCLOSE_CHCTL_FLAGS) {
            xpc_process_openclose_chctl_flags(part, ch_number,
                            chctl.flags[ch_number]);
        }

        ch_flags = ch->flags;   /* need an atomic snapshot of flags */

        if (ch_flags & XPC_C_DISCONNECTING) {
            spin_lock_irqsave(&ch->lock, irq_flags);
            xpc_process_disconnect(ch, &irq_flags);
            spin_unlock_irqrestore(&ch->lock, irq_flags);
            continue;
        }

        if (part->act_state == XPC_P_AS_DEACTIVATING)
            continue;

        if (!(ch_flags & XPC_C_CONNECTED)) {
            if (!(ch_flags & XPC_C_OPENREQUEST)) {
                DBUG_ON(ch_flags & XPC_C_SETUP);
                (void)xpc_connect_channel(ch);
            }
            continue;
        }

        /*
         * Process any message related chctl flags, this may involve
         * the activation of kthreads to deliver any pending messages
         * sent from the other partition.
         */

        if (chctl.flags[ch_number] & XPC_MSG_CHCTL_FLAGS)
            xpc_arch_ops.process_msg_chctl_flags(part, ch_number);
    }
}

/*
 * XPC's heartbeat code calls this function to inform XPC that a partition is
 * going down.  XPC responds by tearing down the XPartition Communication
 * infrastructure used for the just downed partition.
 *
 * XPC's heartbeat code will never call this function and xpc_partition_up()
 * at the same time. Nor will it ever make multiple calls to either function
 * at the same time.
 */
void
xpc_partition_going_down(struct xpc_partition *part, enum xp_retval reason)
{
    unsigned long irq_flags;
    int ch_number;
    struct xpc_channel *ch;

    dev_dbg(xpc_chan, "deactivating partition %d, reason=%d\n",
        XPC_PARTID(part), reason);

    if (!xpc_part_ref(part)) {
        /* infrastructure for this partition isn't currently set up */
        return;
    }

    /* disconnect channels associated with the partition going down */

    for (ch_number = 0; ch_number < part->nchannels; ch_number++) {
        ch = &part->channels[ch_number];

        xpc_msgqueue_ref(ch);
        spin_lock_irqsave(&ch->lock, irq_flags);

        XPC_DISCONNECT_CHANNEL(ch, reason, &irq_flags);

        spin_unlock_irqrestore(&ch->lock, irq_flags);
        xpc_msgqueue_deref(ch);
    }

    xpc_wakeup_channel_mgr(part);

    xpc_part_deref(part);
}

/*
 * Called by XP at the time of channel connection registration to cause
 * XPC to establish connections to all currently active partitions.
 */
void
xpc_initiate_connect(int ch_number)
{
    short partid;
    struct xpc_partition *part;
    struct xpc_channel *ch;

    DBUG_ON(ch_number < 0 || ch_number >= XPC_MAX_NCHANNELS);

    for (partid = 0; partid < xp_max_npartitions; partid++) {
        part = &xpc_partitions[partid];

        if (xpc_part_ref(part)) {
            ch = &part->channels[ch_number];

            /*
             * Initiate the establishment of a connection on the
             * newly registered channel to the remote partition.
             */
            xpc_wakeup_channel_mgr(part);
            xpc_part_deref(part);
        }
    }
}

void
xpc_connected_callout(struct xpc_channel *ch)
{
    /* let the registerer know that a connection has been established */

    if (ch->func != NULL) {
        dev_dbg(xpc_chan, "ch->func() called, reason=xpConnected, "
            "partid=%d, channel=%d\n", ch->partid, ch->number);

        ch->func(xpConnected, ch->partid, ch->number,
             (void *)(u64)ch->local_nentries, ch->key);

        dev_dbg(xpc_chan, "ch->func() returned, reason=xpConnected, "
            "partid=%d, channel=%d\n", ch->partid, ch->number);
    }
}

/*
 * Called by XP at the time of channel connection unregistration to cause
 * XPC to teardown all current connections for the specified channel.
 *
 * Before returning xpc_initiate_disconnect() will wait until all connections
 * on the specified channel have been closed/torndown. So the caller can be
 * assured that they will not be receiving any more callouts from XPC to the
 * function they registered via xpc_connect().
 *
 * Arguments:
 *
 *  ch_number - channel # to unregister.
 */
void
xpc_initiate_disconnect(int ch_number)
{
    unsigned long irq_flags;
    short partid;
    struct xpc_partition *part;
    struct xpc_channel *ch;

    DBUG_ON(ch_number < 0 || ch_number >= XPC_MAX_NCHANNELS);

    /* initiate the channel disconnect for every active partition */
    for (partid = 0; partid < xp_max_npartitions; partid++) {
        part = &xpc_partitions[partid];

        if (xpc_part_ref(part)) {
            ch = &part->channels[ch_number];
            xpc_msgqueue_ref(ch);

            spin_lock_irqsave(&ch->lock, irq_flags);

            if (!(ch->flags & XPC_C_DISCONNECTED)) {
                ch->flags |= XPC_C_WDISCONNECT;

                XPC_DISCONNECT_CHANNEL(ch, xpUnregistering,
                               &irq_flags);
            }

            spin_unlock_irqrestore(&ch->lock, irq_flags);

            xpc_msgqueue_deref(ch);
            xpc_part_deref(part);
        }
    }

    xpc_disconnect_wait(ch_number);
}

/*
 * To disconnect a channel, and reflect it back to all who may be waiting.
 *
 * An OPEN is not allowed until XPC_C_DISCONNECTING is cleared by
 * xpc_process_disconnect(), and if set, XPC_C_WDISCONNECT is cleared by
 * xpc_disconnect_wait().
 *
 * THE CHANNEL IS TO BE LOCKED BY THE CALLER AND WILL REMAIN LOCKED UPON RETURN.
 */
void
xpc_disconnect_channel(const int line, struct xpc_channel *ch,
               enum xp_retval reason, unsigned long *irq_flags)
{
    u32 channel_was_connected = (ch->flags & XPC_C_CONNECTED);

    DBUG_ON(!spin_is_locked(&ch->lock));

    if (ch->flags & (XPC_C_DISCONNECTING | XPC_C_DISCONNECTED))
        return;

    DBUG_ON(!(ch->flags & (XPC_C_CONNECTING | XPC_C_CONNECTED)));

    dev_dbg(xpc_chan, "reason=%d, line=%d, partid=%d, channel=%d\n",
        reason, line, ch->partid, ch->number);

    XPC_SET_REASON(ch, reason, line);

    ch->flags |= (XPC_C_CLOSEREQUEST | XPC_C_DISCONNECTING);
    /* some of these may not have been set */
    ch->flags &= ~(XPC_C_OPENREQUEST | XPC_C_OPENREPLY |
               XPC_C_ROPENREQUEST | XPC_C_ROPENREPLY |
               XPC_C_CONNECTING | XPC_C_CONNECTED);

    xpc_arch_ops.send_chctl_closerequest(ch, irq_flags);

    if (channel_was_connected)
        ch->flags |= XPC_C_WASCONNECTED;

    spin_unlock_irqrestore(&ch->lock, *irq_flags);

    /* wake all idle kthreads so they can exit */
    if (atomic_read(&ch->kthreads_idle) > 0) {
        wake_up_all(&ch->idle_wq);

    } else if ((ch->flags & XPC_C_CONNECTEDCALLOUT_MADE) &&
           !(ch->flags & XPC_C_DISCONNECTINGCALLOUT)) {
        /* start a kthread that will do the xpDisconnecting callout */
        xpc_create_kthreads(ch, 1, 1);
    }

    /* wake those waiting to allocate an entry from the local msg queue */
    if (atomic_read(&ch->n_on_msg_allocate_wq) > 0)
        wake_up(&ch->msg_allocate_wq);

    spin_lock_irqsave(&ch->lock, *irq_flags);
}

void
xpc_disconnect_callout(struct xpc_channel *ch, enum xp_retval reason)
{
    /*
     * Let the channel's registerer know that the channel is being
     * disconnected. We don't want to do this if the registerer was never
     * informed of a connection being made.
     */

    if (ch->func != NULL) {
        dev_dbg(xpc_chan, "ch->func() called, reason=%d, partid=%d, "
            "channel=%d\n", reason, ch->partid, ch->number);

        ch->func(reason, ch->partid, ch->number, NULL, ch->key);

        dev_dbg(xpc_chan, "ch->func() returned, reason=%d, partid=%d, "
            "channel=%d\n", reason, ch->partid, ch->number);
    }
}

/*
 * Wait for a message entry to become available for the specified channel,
 * but don't wait any longer than 1 jiffy.
 */
enum xp_retval
xpc_allocate_msg_wait(struct xpc_channel *ch)
{
    enum xp_retval ret;

    if (ch->flags & XPC_C_DISCONNECTING) {
        DBUG_ON(ch->reason == xpInterrupted);
        return ch->reason;
    }

    atomic_inc(&ch->n_on_msg_allocate_wq);
    ret = interruptible_sleep_on_timeout(&ch->msg_allocate_wq, 1);
    atomic_dec(&ch->n_on_msg_allocate_wq);

    if (ch->flags & XPC_C_DISCONNECTING) {
        ret = ch->reason;
        DBUG_ON(ch->reason == xpInterrupted);
    } else if (ret == 0) {
        ret = xpTimeout;
    } else {
        ret = xpInterrupted;
    }

    return ret;
}

/*
 * Send a message that contains the user's payload on the specified channel
 * connected to the specified partition.
 *
 * NOTE that this routine can sleep waiting for a message entry to become
 * available. To not sleep, pass in the XPC_NOWAIT flag.
 *
 * Once sent, this routine will not wait for the message to be received, nor
 * will notification be given when it does happen.
 *
 * Arguments:
 *
 *  partid - ID of partition to which the channel is connected.
 *  ch_number - channel # to send message on.
 *  flags - see xp.h for valid flags.
 *  payload - pointer to the payload which is to be sent.
 *  payload_size - size of the payload in bytes.
 */
enum xp_retval
xpc_initiate_send(short partid, int ch_number, u32 flags, void *payload,
          u16 payload_size)
{
    struct xpc_partition *part = &xpc_partitions[partid];
    enum xp_retval ret = xpUnknownReason;

    dev_dbg(xpc_chan, "payload=0x%p, partid=%d, channel=%d\n", payload,
        partid, ch_number);

    DBUG_ON(partid < 0 || partid >= xp_max_npartitions);
    DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);
    DBUG_ON(payload == NULL);

    if (xpc_part_ref(part)) {
        ret = xpc_arch_ops.send_payload(&part->channels[ch_number],
                  flags, payload, payload_size, 0, NULL, NULL);
        xpc_part_deref(part);
    }

    return ret;
}

/*
 * Send a message that contains the user's payload on the specified channel
 * connected to the specified partition.
 *
 * NOTE that this routine can sleep waiting for a message entry to become
 * available. To not sleep, pass in the XPC_NOWAIT flag.
 *
 * This routine will not wait for the message to be sent or received.
 *
 * Once the remote end of the channel has received the message, the function
 * passed as an argument to xpc_initiate_send_notify() will be called. This
 * allows the sender to free up or re-use any buffers referenced by the
 * message, but does NOT mean the message has been processed at the remote
 * end by a receiver.
 *
 * If this routine returns an error, the caller's function will NOT be called.
 *
 * Arguments:
 *
 *  partid - ID of partition to which the channel is connected.
 *  ch_number - channel # to send message on.
 *  flags - see xp.h for valid flags.
 *  payload - pointer to the payload which is to be sent.
 *  payload_size - size of the payload in bytes.
 *  func - function to call with asynchronous notification of message
 *        receipt. THIS FUNCTION MUST BE NON-BLOCKING.
 *  key - user-defined key to be passed to the function when it's called.
 */
enum xp_retval
xpc_initiate_send_notify(short partid, int ch_number, u32 flags, void *payload,
             u16 payload_size, xpc_notify_func func, void *key)
{
    struct xpc_partition *part = &xpc_partitions[partid];
    enum xp_retval ret = xpUnknownReason;

    dev_dbg(xpc_chan, "payload=0x%p, partid=%d, channel=%d\n", payload,
        partid, ch_number);

    DBUG_ON(partid < 0 || partid >= xp_max_npartitions);
    DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);
    DBUG_ON(payload == NULL);
    DBUG_ON(func == NULL);

    if (xpc_part_ref(part)) {
        ret = xpc_arch_ops.send_payload(&part->channels[ch_number],
              flags, payload, payload_size, XPC_N_CALL, func, key);
        xpc_part_deref(part);
    }
    return ret;
}

/*
 * Deliver a message's payload to its intended recipient.
 */
void
xpc_deliver_payload(struct xpc_channel *ch)
{
    void *payload;

    payload = xpc_arch_ops.get_deliverable_payload(ch);
    if (payload != NULL) {

        /*
         * This ref is taken to protect the payload itself from being
         * freed before the user is finished with it, which the user
         * indicates by calling xpc_initiate_received().
         */
        xpc_msgqueue_ref(ch);

        atomic_inc(&ch->kthreads_active);

        if (ch->func != NULL) {
            dev_dbg(xpc_chan, "ch->func() called, payload=0x%p "
                "partid=%d channel=%d\n", payload, ch->partid,
                ch->number);

            /* deliver the message to its intended recipient */
            ch->func(xpMsgReceived, ch->partid, ch->number, payload,
                 ch->key);

            dev_dbg(xpc_chan, "ch->func() returned, payload=0x%p "
                "partid=%d channel=%d\n", payload, ch->partid,
                ch->number);
        }

        atomic_dec(&ch->kthreads_active);
    }
}

/*
 * Acknowledge receipt of a delivered message's payload.
 *
 * This function, although called by users, does not call xpc_part_ref() to
 * ensure that the partition infrastructure is in place. It relies on the
 * fact that we called xpc_msgqueue_ref() in xpc_deliver_payload().
 *
 * Arguments:
 *
 *  partid - ID of partition to which the channel is connected.
 *  ch_number - channel # message received on.
 *  payload - pointer to the payload area allocated via
 *          xpc_initiate_send() or xpc_initiate_send_notify().
 */
void
xpc_initiate_received(short partid, int ch_number, void *payload)
{
    struct xpc_partition *part = &xpc_partitions[partid];
    struct xpc_channel *ch;

    DBUG_ON(partid < 0 || partid >= xp_max_npartitions);
    DBUG_ON(ch_number < 0 || ch_number >= part->nchannels);

    ch = &part->channels[ch_number];
    xpc_arch_ops.received_payload(ch, payload);

    /* the call to xpc_msgqueue_ref() was done by xpc_deliver_payload()  */
    xpc_msgqueue_deref(ch);
}