Adds a nolock function to the w1 interface to avoid locking the

[linux-2.6/next.git] / drivers / misc / sgi-xp / xpc_channel.c

/*
 * 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);
}