// SPDX-License-Identifier: GPL-2.0-only
/******************************************************************************
*******************************************************************************
**
**  Copyright (C) Sistina Software, Inc.  1997-2003  All rights reserved.
**  Copyright (C) 2004-2021 Red Hat, Inc.  All rights reserved.
**
**
*******************************************************************************
******************************************************************************/

/*
 * midcomms.c
 *
 * This is the appallingly named "mid-level" comms layer. It takes care about
 * deliver an on application layer "reliable" communication above the used
 * lowcomms transport layer.
 *
 * How it works:
 *
 * Each nodes keeps track of all send DLM messages in send_queue with a sequence
 * number. The receive will send an DLM_ACK message back for every DLM message
 * received at the other side. If a reconnect happens in lowcomms we will send
 * all unacknowledged dlm messages again. The receiving side might drop any already
 * received message by comparing sequence numbers.
 *
 * How version detection works:
 *
 * Due the fact that dlm has pre-configured node addresses on every side
 * it is in it's nature that every side connects at starts to transmit
 * dlm messages which ends in a race. However DLM_RCOM_NAMES, DLM_RCOM_STATUS
 * and their replies are the first messages which are exchanges. Due backwards
 * compatibility these messages are not covered by the midcomms re-transmission
 * layer. These messages have their own re-transmission handling in the dlm
 * application layer. The version field of every node will be set on these RCOM
 * messages as soon as they arrived and the node isn't yet part of the nodes
 * hash. There exists also logic to detect version mismatched if something weird
 * going on or the first messages isn't an expected one.
 *
 * Termination:
 *
 * The midcomms layer does a 4 way handshake for termination on DLM protocol
 * like TCP supports it with half-closed socket support. SCTP doesn't support
 * half-closed socket, so we do it on DLM layer. Also socket shutdown() can be
 * interrupted by .e.g. tcp reset itself. Additional there exists the othercon
 * paradigm in lowcomms which cannot be easily without breaking backwards
 * compatibility. A node cannot send anything to another node when a DLM_FIN
 * message was send. There exists additional logic to print a warning if
 * DLM wants to do it. There exists a state handling like RFC 793 but reduced
 * to termination only. The event "member removal event" describes the cluster
 * manager removed the node from internal lists, at this point DLM does not
 * send any message to the other node. There exists two cases:
 *
 * 1. The cluster member was removed and we received a FIN
 * OR
 * 2. We received a FIN but the member was not removed yet
 *
 * One of these cases will do the CLOSE_WAIT to LAST_ACK change.
 *
 *
 *                              +---------+
 *                              | CLOSED  |
 *                              +---------+
 *                                   | add member/receive RCOM version
 *                                   |            detection msg
 *                                   V
 *                              +---------+
 *                              |  ESTAB  |
 *                              +---------+
 *                       CLOSE    |     |    rcv FIN
 *                      -------   |     |    -------
 * +---------+          snd FIN  /       \   snd ACK          +---------+
 * |  FIN    |<-----------------           ------------------>|  CLOSE  |
 * | WAIT-1  |------------------                              |   WAIT  |
 * +---------+          rcv FIN  \                            +---------+
 * | rcv ACK of FIN   -------   |                            CLOSE  | member
 * | --------------   snd ACK   |                           ------- | removal
 * V        x                   V                           snd FIN V event
 * +---------+                  +---------+                   +---------+
 * |FINWAIT-2|                  | CLOSING |                   | LAST-ACK|
 * +---------+                  +---------+                   +---------+
 * |                rcv ACK of FIN |                 rcv ACK of FIN |
 * |  rcv FIN       -------------- |                 -------------- |
 * |  -------              x       V                        x       V
 *  \ snd ACK                 +---------+                   +---------+
 *   ------------------------>| CLOSED  |                   | CLOSED  |
 *                            +---------+                   +---------+
 *
 * NOTE: any state can interrupted by midcomms_close() and state will be
 * switched to CLOSED in case of fencing. There exists also some timeout
 * handling when we receive the version detection RCOM messages which is
 * made by observation.
 *
 * Future improvements:
 *
 * There exists some known issues/improvements of the dlm handling. Some
 * of them should be done in a next major dlm version bump which makes
 * it incompatible with previous versions.
 *
 * Unaligned memory access:
 *
 * There exists cases when the dlm message buffer length is not aligned
 * to 8 byte. However seems nobody detected any problem with it. This
 * can be fixed in the next major version bump of dlm.
 *
 * Version detection:
 *
 * The version detection and how it's done is related to backwards
 * compatibility. There exists better ways to make a better handling.
 * However this should be changed in the next major version bump of dlm.
 *
 * Tail Size checking:
 *
 * There exists a message tail payload in e.g. DLM_MSG however we don't
 * check it against the message length yet regarding to the receive buffer
 * length. That need to be validated.
 *
 * Fencing bad nodes:
 *
 * At timeout places or weird sequence number behaviours we should send
 * a fencing request to the cluster manager.
 */

/* Debug switch to enable a 5 seconds sleep waiting of a termination.
 * This can be useful to test fencing while termination is running.
 * This requires a setup with only gfs2 as dlm user, so that the
 * last umount will terminate the connection.
 *
 * However it became useful to test, while the 5 seconds block in umount
 * just press the reset button. In a lot of dropping the termination
 * process can could take several seconds.
 */
#define DLM_DEBUG_FENCE_TERMINATION     0

#include <trace/events/dlm.h>
#include <net/tcp.h>

#include "dlm_internal.h"
#include "lowcomms.h"
#include "config.h"
#include "memory.h"
#include "lock.h"
#include "util.h"
#include "midcomms.h"

/* init value for sequence numbers for testing purpose only e.g. overflows */
#define DLM_SEQ_INIT            0
/* 5 seconds wait to sync ending of dlm */
#define DLM_SHUTDOWN_TIMEOUT    msecs_to_jiffies(5000)
#define DLM_VERSION_NOT_SET     0
#define DLM_SEND_ACK_BACK_MSG_THRESHOLD 32
#define DLM_RECV_ACK_BACK_MSG_THRESHOLD (DLM_SEND_ACK_BACK_MSG_THRESHOLD * 8)

struct midcomms_node {
        int nodeid;
        uint32_t version;
        atomic_t seq_send;
        atomic_t seq_next;
        /* These queues are unbound because we cannot drop any message in dlm.
         * We could send a fence signal for a specific node to the cluster
         * manager if queues hits some maximum value, however this handling
         * not supported yet.
         */
        struct list_head send_queue;
        spinlock_t send_queue_lock;
        atomic_t send_queue_cnt;
#define DLM_NODE_FLAG_CLOSE     1
#define DLM_NODE_FLAG_STOP_TX   2
#define DLM_NODE_FLAG_STOP_RX   3
        atomic_t ulp_delivered;
        unsigned long flags;
        wait_queue_head_t shutdown_wait;

        /* dlm tcp termination state */
#define DLM_CLOSED      1
#define DLM_ESTABLISHED 2
#define DLM_FIN_WAIT1   3
#define DLM_FIN_WAIT2   4
#define DLM_CLOSE_WAIT  5
#define DLM_LAST_ACK    6
#define DLM_CLOSING     7
        int state;
        spinlock_t state_lock;

        /* counts how many lockspaces are using this node
         * this refcount is necessary to determine if the
         * node wants to disconnect.
         */
        int users;

        /* not protected by srcu, node_hash lifetime */
        void *debugfs;

        struct hlist_node hlist;
        struct rcu_head rcu;
};

struct dlm_mhandle {
        const union dlm_packet *inner_p;
        struct midcomms_node *node;
        struct dlm_opts *opts;
        struct dlm_msg *msg;
        bool committed;
        uint32_t seq;

        void (*ack_rcv)(struct midcomms_node *node);

        /* get_mhandle/commit srcu idx exchange */
        int idx;

        struct list_head list;
        struct rcu_head rcu;
};

static struct hlist_head node_hash[CONN_HASH_SIZE];
static DEFINE_SPINLOCK(nodes_lock);
DEFINE_STATIC_SRCU(nodes_srcu);

/* This mutex prevents that midcomms_close() is running while
 * stop() or remove(). As I experienced invalid memory access
 * behaviours when DLM_DEBUG_FENCE_TERMINATION is enabled and
 * resetting machines. I will end in some double deletion in nodes
 * datastructure.
 */
static DEFINE_MUTEX(close_lock);

struct kmem_cache *dlm_midcomms_cache_create(void)
{
        return KMEM_CACHE(dlm_mhandle, 0);
}

static inline const char *dlm_state_str(int state)
{
        switch (state) {
        case DLM_CLOSED:
                return "CLOSED";
        case DLM_ESTABLISHED:
                return "ESTABLISHED";
        case DLM_FIN_WAIT1:
                return "FIN_WAIT1";
        case DLM_FIN_WAIT2:
                return "FIN_WAIT2";
        case DLM_CLOSE_WAIT:
                return "CLOSE_WAIT";
        case DLM_LAST_ACK:
                return "LAST_ACK";
        case DLM_CLOSING:
                return "CLOSING";
        default:
                return "UNKNOWN";
        }
}

const char *dlm_midcomms_state(struct midcomms_node *node)
{
        return dlm_state_str(node->state);
}

unsigned long dlm_midcomms_flags(struct midcomms_node *node)
{
        return node->flags;
}

int dlm_midcomms_send_queue_cnt(struct midcomms_node *node)
{
        return atomic_read(&node->send_queue_cnt);
}

uint32_t dlm_midcomms_version(struct midcomms_node *node)
{
        return node->version;
}

static struct midcomms_node *__find_node(int nodeid, int r)
{
        struct midcomms_node *node;

        hlist_for_each_entry_rcu(node, &node_hash[r], hlist) {
                if (node->nodeid == nodeid)
                        return node;
        }

        return NULL;
}

static void dlm_mhandle_release(struct rcu_head *rcu)
{
        struct dlm_mhandle *mh = container_of(rcu, struct dlm_mhandle, rcu);

        dlm_lowcomms_put_msg(mh->msg);
        dlm_free_mhandle(mh);
}

static void dlm_mhandle_delete(struct midcomms_node *node,
                               struct dlm_mhandle *mh)
{
        list_del_rcu(&mh->list);
        atomic_dec(&node->send_queue_cnt);
        call_rcu(&mh->rcu, dlm_mhandle_release);
}

static void dlm_send_queue_flush(struct midcomms_node *node)
{
        struct dlm_mhandle *mh;

        pr_debug("flush midcomms send queue of node %d\n", node->nodeid);

        rcu_read_lock();
        spin_lock_bh(&node->send_queue_lock);
        list_for_each_entry_rcu(mh, &node->send_queue, list) {
                dlm_mhandle_delete(node, mh);
        }
        spin_unlock_bh(&node->send_queue_lock);
        rcu_read_unlock();
}

static void midcomms_node_reset(struct midcomms_node *node)
{
        pr_debug("reset node %d\n", node->nodeid);

        atomic_set(&node->seq_next, DLM_SEQ_INIT);
        atomic_set(&node->seq_send, DLM_SEQ_INIT);
        atomic_set(&node->ulp_delivered, 0);
        node->version = DLM_VERSION_NOT_SET;
        node->flags = 0;

        dlm_send_queue_flush(node);
        node->state = DLM_CLOSED;
        wake_up(&node->shutdown_wait);
}

static struct midcomms_node *nodeid2node(int nodeid)
{
        return __find_node(nodeid, nodeid_hash(nodeid));
}

int dlm_midcomms_addr(int nodeid, struct sockaddr_storage *addr)
{
        int ret, idx, r = nodeid_hash(nodeid);
        struct midcomms_node *node;

        ret = dlm_lowcomms_addr(nodeid, addr);
        if (ret)
                return ret;

        idx = srcu_read_lock(&nodes_srcu);
        node = __find_node(nodeid, r);
        if (node) {
                srcu_read_unlock(&nodes_srcu, idx);
                return 0;
        }
        srcu_read_unlock(&nodes_srcu, idx);

        node = kmalloc_obj(*node, GFP_NOFS);
        if (!node)
                return -ENOMEM;

        node->nodeid = nodeid;
        spin_lock_init(&node->state_lock);
        spin_lock_init(&node->send_queue_lock);
        atomic_set(&node->send_queue_cnt, 0);
        INIT_LIST_HEAD(&node->send_queue);
        init_waitqueue_head(&node->shutdown_wait);
        node->users = 0;
        midcomms_node_reset(node);

        spin_lock_bh(&nodes_lock);
        hlist_add_head_rcu(&node->hlist, &node_hash[r]);
        spin_unlock_bh(&nodes_lock);

        node->debugfs = dlm_create_debug_comms_file(nodeid, node);
        return 0;
}

static int dlm_send_ack(int nodeid, uint32_t seq)
{
        int mb_len = sizeof(struct dlm_header);
        struct dlm_header *m_header;
        struct dlm_msg *msg;
        char *ppc;

        msg = dlm_lowcomms_new_msg(nodeid, mb_len, &ppc, NULL, NULL);
        if (!msg)
                return -ENOMEM;

        m_header = (struct dlm_header *)ppc;

        m_header->h_version = cpu_to_le32(DLM_HEADER_MAJOR | DLM_HEADER_MINOR);
        m_header->h_nodeid = cpu_to_le32(dlm_our_nodeid());
        m_header->h_length = cpu_to_le16(mb_len);
        m_header->h_cmd = DLM_ACK;
        m_header->u.h_seq = cpu_to_le32(seq);

        dlm_lowcomms_commit_msg(msg);
        dlm_lowcomms_put_msg(msg);

        return 0;
}

static void dlm_send_ack_threshold(struct midcomms_node *node,
                                   uint32_t threshold)
{
        uint32_t oval, nval;
        bool send_ack;

        /* let only send one user trigger threshold to send ack back */
        do {
                oval = atomic_read(&node->ulp_delivered);
                send_ack = (oval > threshold);
                /* abort if threshold is not reached */
                if (!send_ack)
                        break;

                nval = 0;
                /* try to reset ulp_delivered counter */
        } while (atomic_cmpxchg(&node->ulp_delivered, oval, nval) != oval);

        if (send_ack)
                dlm_send_ack(node->nodeid, atomic_read(&node->seq_next));
}

static int dlm_send_fin(struct midcomms_node *node,
                        void (*ack_rcv)(struct midcomms_node *node))
{
        int mb_len = sizeof(struct dlm_header);
        struct dlm_header *m_header;
        struct dlm_mhandle *mh;
        char *ppc;

        mh = dlm_midcomms_get_mhandle(node->nodeid, mb_len, &ppc);
        if (!mh)
                return -ENOMEM;

        set_bit(DLM_NODE_FLAG_STOP_TX, &node->flags);
        mh->ack_rcv = ack_rcv;

        m_header = (struct dlm_header *)ppc;

        m_header->h_version = cpu_to_le32(DLM_HEADER_MAJOR | DLM_HEADER_MINOR);
        m_header->h_nodeid = cpu_to_le32(dlm_our_nodeid());
        m_header->h_length = cpu_to_le16(mb_len);
        m_header->h_cmd = DLM_FIN;

        pr_debug("sending fin msg to node %d\n", node->nodeid);
        dlm_midcomms_commit_mhandle(mh, NULL, 0);

        return 0;
}

static void dlm_receive_ack(struct midcomms_node *node, uint32_t seq)
{
        struct dlm_mhandle *mh;

        rcu_read_lock();
        list_for_each_entry_rcu(mh, &node->send_queue, list) {
                if (before(mh->seq, seq)) {
                        if (mh->ack_rcv)
                                mh->ack_rcv(node);
                } else {
                        /* send queue should be ordered */
                        break;
                }
        }

        spin_lock_bh(&node->send_queue_lock);
        list_for_each_entry_rcu(mh, &node->send_queue, list) {
                if (before(mh->seq, seq)) {
                        dlm_mhandle_delete(node, mh);
                } else {
                        /* send queue should be ordered */
                        break;
                }
        }
        spin_unlock_bh(&node->send_queue_lock);
        rcu_read_unlock();
}

static void dlm_pas_fin_ack_rcv(struct midcomms_node *node)
{
        spin_lock_bh(&node->state_lock);
        pr_debug("receive passive fin ack from node %d with state %s\n",
                 node->nodeid, dlm_state_str(node->state));

        switch (node->state) {
        case DLM_LAST_ACK:
                /* DLM_CLOSED */
                midcomms_node_reset(node);
                break;
        case DLM_CLOSED:
                /* not valid but somehow we got what we want */
                wake_up(&node->shutdown_wait);
                break;
        default:
                spin_unlock_bh(&node->state_lock);
                log_print("%s: unexpected state: %d",
                          __func__, node->state);
                WARN_ON_ONCE(1);
                return;
        }
        spin_unlock_bh(&node->state_lock);
}

static void dlm_receive_buffer_3_2_trace(uint32_t seq,
                                         const union dlm_packet *p)
{
        switch (p->header.h_cmd) {
        case DLM_MSG:
                trace_dlm_recv_message(dlm_our_nodeid(), seq, &p->message);
                break;
        case DLM_RCOM:
                trace_dlm_recv_rcom(dlm_our_nodeid(), seq, &p->rcom);
                break;
        default:
                break;
        }
}

static void dlm_midcomms_receive_buffer(const union dlm_packet *p,
                                        struct midcomms_node *node,
                                        uint32_t seq)
{
        bool is_expected_seq;
        uint32_t oval, nval;

        do {
                oval = atomic_read(&node->seq_next);
                is_expected_seq = (oval == seq);
                if (!is_expected_seq)
                        break;

                nval = oval + 1;
        } while (atomic_cmpxchg(&node->seq_next, oval, nval) != oval);

        if (is_expected_seq) {
                switch (p->header.h_cmd) {
                case DLM_FIN:
                        spin_lock_bh(&node->state_lock);
                        pr_debug("receive fin msg from node %d with state %s\n",
                                 node->nodeid, dlm_state_str(node->state));

                        switch (node->state) {
                        case DLM_ESTABLISHED:
                                dlm_send_ack(node->nodeid, nval);

                                /* passive shutdown DLM_LAST_ACK case 1
                                 * additional we check if the node is used by
                                 * cluster manager events at all.
                                 */
                                if (node->users == 0) {
                                        node->state = DLM_LAST_ACK;
                                        pr_debug("switch node %d to state %s case 1\n",
                                                 node->nodeid, dlm_state_str(node->state));
                                        set_bit(DLM_NODE_FLAG_STOP_RX, &node->flags);
                                        dlm_send_fin(node, dlm_pas_fin_ack_rcv);
                                } else {
                                        node->state = DLM_CLOSE_WAIT;
                                        pr_debug("switch node %d to state %s\n",
                                                 node->nodeid, dlm_state_str(node->state));
                                }
                                break;
                        case DLM_FIN_WAIT1:
                                dlm_send_ack(node->nodeid, nval);
                                node->state = DLM_CLOSING;
                                set_bit(DLM_NODE_FLAG_STOP_RX, &node->flags);
                                pr_debug("switch node %d to state %s\n",
                                         node->nodeid, dlm_state_str(node->state));
                                break;
                        case DLM_FIN_WAIT2:
                                dlm_send_ack(node->nodeid, nval);
                                midcomms_node_reset(node);
                                pr_debug("switch node %d to state %s\n",
                                         node->nodeid, dlm_state_str(node->state));
                                break;
                        case DLM_LAST_ACK:
                                /* probably remove_member caught it, do nothing */
                                break;
                        default:
                                spin_unlock_bh(&node->state_lock);
                                log_print("%s: unexpected state: %d",
                                          __func__, node->state);
                                WARN_ON_ONCE(1);
                                return;
                        }
                        spin_unlock_bh(&node->state_lock);
                        break;
                default:
                        WARN_ON_ONCE(test_bit(DLM_NODE_FLAG_STOP_RX, &node->flags));
                        dlm_receive_buffer_3_2_trace(seq, p);
                        dlm_receive_buffer(p, node->nodeid);
                        atomic_inc(&node->ulp_delivered);
                        /* unlikely case to send ack back when we don't transmit */
                        dlm_send_ack_threshold(node, DLM_RECV_ACK_BACK_MSG_THRESHOLD);
                        break;
                }
        } else {
                /* retry to ack message which we already have by sending back
                 * current node->seq_next number as ack.
                 */
                if (seq < oval)
                        dlm_send_ack(node->nodeid, oval);

                log_print_ratelimited("ignore dlm msg because seq mismatch, seq: %u, expected: %u, nodeid: %d",
                                      seq, oval, node->nodeid);
        }
}

static int dlm_opts_check_msglen(const union dlm_packet *p, uint16_t msglen,
                                 int nodeid)
{
        int len = msglen;

        /* we only trust outer header msglen because
         * it's checked against receive buffer length.
         */
        if (len < sizeof(struct dlm_opts))
                return -1;
        len -= sizeof(struct dlm_opts);

        if (len < le16_to_cpu(p->opts.o_optlen))
                return -1;
        len -= le16_to_cpu(p->opts.o_optlen);

        switch (p->opts.o_nextcmd) {
        case DLM_FIN:
                if (len < sizeof(struct dlm_header)) {
                        log_print("fin too small: %d, will skip this message from node %d",
                                  len, nodeid);
                        return -1;
                }

                break;
        case DLM_MSG:
                if (len < sizeof(struct dlm_message)) {
                        log_print("msg too small: %d, will skip this message from node %d",
                                  msglen, nodeid);
                        return -1;
                }

                break;
        case DLM_RCOM:
                if (len < sizeof(struct dlm_rcom)) {
                        log_print("rcom msg too small: %d, will skip this message from node %d",
                                  len, nodeid);
                        return -1;
                }

                break;
        default:
                log_print("unsupported o_nextcmd received: %u, will skip this message from node %d",
                          p->opts.o_nextcmd, nodeid);
                return -1;
        }

        return 0;
}

static void dlm_midcomms_receive_buffer_3_2(const union dlm_packet *p, int nodeid)
{
        uint16_t msglen = le16_to_cpu(p->header.h_length);
        struct midcomms_node *node;
        uint32_t seq;
        int ret, idx;

        idx = srcu_read_lock(&nodes_srcu);
        node = nodeid2node(nodeid);
        if (WARN_ON_ONCE(!node))
                goto out;

        switch (node->version) {
        case DLM_VERSION_NOT_SET:
                node->version = DLM_VERSION_3_2;
                wake_up(&node->shutdown_wait);
                log_print("version 0x%08x for node %d detected", DLM_VERSION_3_2,
                          node->nodeid);

                spin_lock(&node->state_lock);
                switch (node->state) {
                case DLM_CLOSED:
                        node->state = DLM_ESTABLISHED;
                        pr_debug("switch node %d to state %s\n",
                                 node->nodeid, dlm_state_str(node->state));
                        break;
                default:
                        break;
                }
                spin_unlock(&node->state_lock);

                break;
        case DLM_VERSION_3_2:
                break;
        default:
                log_print_ratelimited("version mismatch detected, assumed 0x%08x but node %d has 0x%08x",
                                      DLM_VERSION_3_2, node->nodeid, node->version);
                goto out;
        }

        switch (p->header.h_cmd) {
        case DLM_RCOM:
                /* these rcom message we use to determine version.
                 * they have their own retransmission handling and
                 * are the first messages of dlm.
                 *
                 * length already checked.
                 */
                switch (p->rcom.rc_type) {
                case cpu_to_le32(DLM_RCOM_NAMES):
                        fallthrough;
                case cpu_to_le32(DLM_RCOM_NAMES_REPLY):
                        fallthrough;
                case cpu_to_le32(DLM_RCOM_STATUS):
                        fallthrough;
                case cpu_to_le32(DLM_RCOM_STATUS_REPLY):
                        break;
                default:
                        log_print("unsupported rcom type received: %u, will skip this message from node %d",
                                  le32_to_cpu(p->rcom.rc_type), nodeid);
                        goto out;
                }

                WARN_ON_ONCE(test_bit(DLM_NODE_FLAG_STOP_RX, &node->flags));
                dlm_receive_buffer(p, nodeid);
                break;
        case DLM_OPTS:
                seq = le32_to_cpu(p->header.u.h_seq);

                ret = dlm_opts_check_msglen(p, msglen, nodeid);
                if (ret < 0) {
                        log_print("opts msg too small: %u, will skip this message from node %d",
                                  msglen, nodeid);
                        goto out;
                }

                p = (union dlm_packet *)((unsigned char *)p->opts.o_opts +
                                         le16_to_cpu(p->opts.o_optlen));

                /* recheck inner msglen just if it's not garbage */
                msglen = le16_to_cpu(p->header.h_length);
                switch (p->header.h_cmd) {
                case DLM_RCOM:
                        if (msglen < sizeof(struct dlm_rcom)) {
                                log_print("inner rcom msg too small: %u, will skip this message from node %d",
                                          msglen, nodeid);
                                goto out;
                        }

                        break;
                case DLM_MSG:
                        if (msglen < sizeof(struct dlm_message)) {
                                log_print("inner msg too small: %u, will skip this message from node %d",
                                          msglen, nodeid);
                                goto out;
                        }

                        break;
                case DLM_FIN:
                        if (msglen < sizeof(struct dlm_header)) {
                                log_print("inner fin too small: %u, will skip this message from node %d",
                                          msglen, nodeid);
                                goto out;
                        }

                        break;
                default:
                        log_print("unsupported inner h_cmd received: %u, will skip this message from node %d",
                                  msglen, nodeid);
                        goto out;
                }

                dlm_midcomms_receive_buffer(p, node, seq);
                break;
        case DLM_ACK:
                seq = le32_to_cpu(p->header.u.h_seq);
                dlm_receive_ack(node, seq);
                break;
        default:
                log_print("unsupported h_cmd received: %u, will skip this message from node %d",
                          p->header.h_cmd, nodeid);
                break;
        }

out:
        srcu_read_unlock(&nodes_srcu, idx);
}

static void dlm_midcomms_receive_buffer_3_1(const union dlm_packet *p, int nodeid)
{
        uint16_t msglen = le16_to_cpu(p->header.h_length);
        struct midcomms_node *node;
        int idx;

        idx = srcu_read_lock(&nodes_srcu);
        node = nodeid2node(nodeid);
        if (WARN_ON_ONCE(!node)) {
                srcu_read_unlock(&nodes_srcu, idx);
                return;
        }

        switch (node->version) {
        case DLM_VERSION_NOT_SET:
                node->version = DLM_VERSION_3_1;
                wake_up(&node->shutdown_wait);
                log_print("version 0x%08x for node %d detected", DLM_VERSION_3_1,
                          node->nodeid);
                break;
        case DLM_VERSION_3_1:
                break;
        default:
                log_print_ratelimited("version mismatch detected, assumed 0x%08x but node %d has 0x%08x",
                                      DLM_VERSION_3_1, node->nodeid, node->version);
                srcu_read_unlock(&nodes_srcu, idx);
                return;
        }
        srcu_read_unlock(&nodes_srcu, idx);

        switch (p->header.h_cmd) {
        case DLM_RCOM:
                /* length already checked */
                break;
        case DLM_MSG:
                if (msglen < sizeof(struct dlm_message)) {
                        log_print("msg too small: %u, will skip this message from node %d",
                                  msglen, nodeid);
                        return;
                }

                break;
        default:
                log_print("unsupported h_cmd received: %u, will skip this message from node %d",
                          p->header.h_cmd, nodeid);
                return;
        }

        dlm_receive_buffer(p, nodeid);
}

int dlm_validate_incoming_buffer(int nodeid, unsigned char *buf, int len)
{
        const unsigned char *ptr = buf;
        const struct dlm_header *hd;
        uint16_t msglen;
        int ret = 0;

        while (len >= sizeof(struct dlm_header)) {
                hd = (struct dlm_header *)ptr;

                /* no message should be more than DLM_MAX_SOCKET_BUFSIZE or
                 * less than dlm_header size.
                 *
                 * Some messages does not have a 8 byte length boundary yet
                 * which can occur in a unaligned memory access of some dlm
                 * messages. However this problem need to be fixed at the
                 * sending side, for now it seems nobody run into architecture
                 * related issues yet but it slows down some processing.
                 * Fixing this issue should be scheduled in future by doing
                 * the next major version bump.
                 */
                msglen = le16_to_cpu(hd->h_length);
                if (msglen > DLM_MAX_SOCKET_BUFSIZE ||
                    msglen < sizeof(struct dlm_header)) {
                        log_print("received invalid length header: %u from node %d, will abort message parsing",
                                  msglen, nodeid);
                        return -EBADMSG;
                }

                /* caller will take care that leftover
                 * will be parsed next call with more data
                 */
                if (msglen > len)
                        break;

                ret += msglen;
                len -= msglen;
                ptr += msglen;
        }

        return ret;
}

/*
 * Called from the low-level comms layer to process a buffer of
 * commands.
 */
int dlm_process_incoming_buffer(int nodeid, unsigned char *buf, int len)
{
        const unsigned char *ptr = buf;
        const struct dlm_header *hd;
        uint16_t msglen;
        int ret = 0;

        while (len >= sizeof(struct dlm_header)) {
                hd = (struct dlm_header *)ptr;

                msglen = le16_to_cpu(hd->h_length);
                if (msglen > len)
                        break;

                switch (hd->h_version) {
                case cpu_to_le32(DLM_VERSION_3_1):
                        dlm_midcomms_receive_buffer_3_1((const union dlm_packet *)ptr, nodeid);
                        break;
                case cpu_to_le32(DLM_VERSION_3_2):
                        dlm_midcomms_receive_buffer_3_2((const union dlm_packet *)ptr, nodeid);
                        break;
                default:
                        log_print("received invalid version header: %u from node %d, will skip this message",
                                  le32_to_cpu(hd->h_version), nodeid);
                        break;
                }

                ret += msglen;
                len -= msglen;
                ptr += msglen;
        }

        return ret;
}

void dlm_midcomms_unack_msg_resend(int nodeid)
{
        struct midcomms_node *node;
        struct dlm_mhandle *mh;
        int idx, ret;

        idx = srcu_read_lock(&nodes_srcu);
        node = nodeid2node(nodeid);
        if (WARN_ON_ONCE(!node)) {
                srcu_read_unlock(&nodes_srcu, idx);
                return;
        }

        /* old protocol, we don't support to retransmit on failure */
        switch (node->version) {
        case DLM_VERSION_3_2:
                break;
        default:
                srcu_read_unlock(&nodes_srcu, idx);
                return;
        }

        rcu_read_lock();
        list_for_each_entry_rcu(mh, &node->send_queue, list) {
                if (!mh->committed)
                        continue;

                ret = dlm_lowcomms_resend_msg(mh->msg);
                if (!ret)
                        log_print_ratelimited("retransmit dlm msg, seq %u, nodeid %d",
                                              mh->seq, node->nodeid);
        }
        rcu_read_unlock();
        srcu_read_unlock(&nodes_srcu, idx);
}

static void dlm_fill_opts_header(struct dlm_opts *opts, uint16_t inner_len,
                                 uint32_t seq)
{
        opts->o_header.h_cmd = DLM_OPTS;
        opts->o_header.h_version = cpu_to_le32(DLM_HEADER_MAJOR | DLM_HEADER_MINOR);
        opts->o_header.h_nodeid = cpu_to_le32(dlm_our_nodeid());
        opts->o_header.h_length = cpu_to_le16(DLM_MIDCOMMS_OPT_LEN + inner_len);
        opts->o_header.u.h_seq = cpu_to_le32(seq);
}

static void midcomms_new_msg_cb(void *data)
{
        struct dlm_mhandle *mh = data;

        atomic_inc(&mh->node->send_queue_cnt);

        spin_lock_bh(&mh->node->send_queue_lock);
        list_add_tail_rcu(&mh->list, &mh->node->send_queue);
        spin_unlock_bh(&mh->node->send_queue_lock);

        mh->seq = atomic_fetch_inc(&mh->node->seq_send);
}

static struct dlm_msg *dlm_midcomms_get_msg_3_2(struct dlm_mhandle *mh, int nodeid,
                                                int len, char **ppc)
{
        struct dlm_opts *opts;
        struct dlm_msg *msg;

        msg = dlm_lowcomms_new_msg(nodeid, len + DLM_MIDCOMMS_OPT_LEN,
                                   ppc, midcomms_new_msg_cb, mh);
        if (!msg)
                return NULL;

        opts = (struct dlm_opts *)*ppc;
        mh->opts = opts;

        /* add possible options here */
        dlm_fill_opts_header(opts, len, mh->seq);

        *ppc += sizeof(*opts);
        mh->inner_p = (const union dlm_packet *)*ppc;
        return msg;
}

/* avoid false positive for nodes_srcu, unlock happens in
 * dlm_midcomms_commit_mhandle which is a must call if success
 */
#ifndef __CHECKER__
struct dlm_mhandle *dlm_midcomms_get_mhandle(int nodeid, int len, char **ppc)
{
        struct midcomms_node *node;
        struct dlm_mhandle *mh;
        struct dlm_msg *msg;
        int idx;

        idx = srcu_read_lock(&nodes_srcu);
        node = nodeid2node(nodeid);
        if (WARN_ON_ONCE(!node))
                goto err;

        /* this is a bug, however we going on and hope it will be resolved */
        WARN_ON_ONCE(test_bit(DLM_NODE_FLAG_STOP_TX, &node->flags));

        mh = dlm_allocate_mhandle();
        if (!mh)
                goto err;

        mh->committed = false;
        mh->ack_rcv = NULL;
        mh->idx = idx;
        mh->node = node;

        switch (node->version) {
        case DLM_VERSION_3_1:
                msg = dlm_lowcomms_new_msg(nodeid, len, ppc, NULL, NULL);
                if (!msg) {
                        dlm_free_mhandle(mh);
                        goto err;
                }

                break;
        case DLM_VERSION_3_2:
                /* send ack back if necessary */
                dlm_send_ack_threshold(node, DLM_SEND_ACK_BACK_MSG_THRESHOLD);

                msg = dlm_midcomms_get_msg_3_2(mh, nodeid, len, ppc);
                if (!msg) {
                        dlm_free_mhandle(mh);
                        goto err;
                }
                break;
        default:
                dlm_free_mhandle(mh);
                WARN_ON_ONCE(1);
                goto err;
        }

        mh->msg = msg;

        /* keep in mind that is a must to call
         * dlm_midcomms_commit_msg() which releases
         * nodes_srcu using mh->idx which is assumed
         * here that the application will call it.
         */
        return mh;

err:
        srcu_read_unlock(&nodes_srcu, idx);
        return NULL;
}
#endif

static void dlm_midcomms_commit_msg_3_2_trace(const struct dlm_mhandle *mh,
                                              const void *name, int namelen)
{
        switch (mh->inner_p->header.h_cmd) {
        case DLM_MSG:
                trace_dlm_send_message(mh->node->nodeid, mh->seq,
                                       &mh->inner_p->message,
                                       name, namelen);
                break;
        case DLM_RCOM:
                trace_dlm_send_rcom(mh->node->nodeid, mh->seq,
                                    &mh->inner_p->rcom);
                break;
        default:
                /* nothing to trace */
                break;
        }
}

static void dlm_midcomms_commit_msg_3_2(struct dlm_mhandle *mh,
                                        const void *name, int namelen)
{
        /* nexthdr chain for fast lookup */
        mh->opts->o_nextcmd = mh->inner_p->header.h_cmd;
        mh->committed = true;
        dlm_midcomms_commit_msg_3_2_trace(mh, name, namelen);
        dlm_lowcomms_commit_msg(mh->msg);
}

/* avoid false positive for nodes_srcu, lock was happen in
 * dlm_midcomms_get_mhandle
 */
#ifndef __CHECKER__
void dlm_midcomms_commit_mhandle(struct dlm_mhandle *mh,
                                 const void *name, int namelen)
{

        switch (mh->node->version) {
        case DLM_VERSION_3_1:
                srcu_read_unlock(&nodes_srcu, mh->idx);

                dlm_lowcomms_commit_msg(mh->msg);
                dlm_lowcomms_put_msg(mh->msg);
                /* mh is not part of rcu list in this case */
                dlm_free_mhandle(mh);
                break;
        case DLM_VERSION_3_2:
                /* held rcu read lock here, because we sending the
                 * dlm message out, when we do that we could receive
                 * an ack back which releases the mhandle and we
                 * get a use after free.
                 */
                rcu_read_lock();
                dlm_midcomms_commit_msg_3_2(mh, name, namelen);
                srcu_read_unlock(&nodes_srcu, mh->idx);
                rcu_read_unlock();
                break;
        default:
                srcu_read_unlock(&nodes_srcu, mh->idx);
                WARN_ON_ONCE(1);
                break;
        }
}
#endif

int dlm_midcomms_start(void)
{
        return dlm_lowcomms_start();
}

void dlm_midcomms_stop(void)
{
        dlm_lowcomms_stop();
}

void dlm_midcomms_init(void)
{
        int i;

        for (i = 0; i < CONN_HASH_SIZE; i++)
                INIT_HLIST_HEAD(&node_hash[i]);

        dlm_lowcomms_init();
}

static void midcomms_node_release(struct rcu_head *rcu)
{
        struct midcomms_node *node = container_of(rcu, struct midcomms_node, rcu);

        WARN_ON_ONCE(atomic_read(&node->send_queue_cnt));
        dlm_send_queue_flush(node);
        kfree(node);
}

void dlm_midcomms_exit(void)
{
        struct midcomms_node *node;
        int i, idx;

        idx = srcu_read_lock(&nodes_srcu);
        for (i = 0; i < CONN_HASH_SIZE; i++) {
                hlist_for_each_entry_rcu(node, &node_hash[i], hlist) {
                        dlm_delete_debug_comms_file(node->debugfs);

                        spin_lock(&nodes_lock);
                        hlist_del_rcu(&node->hlist);
                        spin_unlock(&nodes_lock);

                        call_srcu(&nodes_srcu, &node->rcu, midcomms_node_release);
                }
        }
        srcu_read_unlock(&nodes_srcu, idx);

        dlm_lowcomms_exit();
}

static void dlm_act_fin_ack_rcv(struct midcomms_node *node)
{
        spin_lock_bh(&node->state_lock);
        pr_debug("receive active fin ack from node %d with state %s\n",
                 node->nodeid, dlm_state_str(node->state));

        switch (node->state) {
        case DLM_FIN_WAIT1:
                node->state = DLM_FIN_WAIT2;
                pr_debug("switch node %d to state %s\n",
                         node->nodeid, dlm_state_str(node->state));
                break;
        case DLM_CLOSING:
                midcomms_node_reset(node);
                pr_debug("switch node %d to state %s\n",
                         node->nodeid, dlm_state_str(node->state));
                break;
        case DLM_CLOSED:
                /* not valid but somehow we got what we want */
                wake_up(&node->shutdown_wait);
                break;
        default:
                spin_unlock_bh(&node->state_lock);
                log_print("%s: unexpected state: %d",
                          __func__, node->state);
                WARN_ON_ONCE(1);
                return;
        }
        spin_unlock_bh(&node->state_lock);
}

void dlm_midcomms_add_member(int nodeid)
{
        struct midcomms_node *node;
        int idx;

        idx = srcu_read_lock(&nodes_srcu);
        node = nodeid2node(nodeid);
        if (WARN_ON_ONCE(!node)) {
                srcu_read_unlock(&nodes_srcu, idx);
                return;
        }

        spin_lock_bh(&node->state_lock);
        if (!node->users) {
                pr_debug("receive add member from node %d with state %s\n",
                         node->nodeid, dlm_state_str(node->state));
                switch (node->state) {
                case DLM_ESTABLISHED:
                        break;
                case DLM_CLOSED:
                        node->state = DLM_ESTABLISHED;
                        pr_debug("switch node %d to state %s\n",
                                 node->nodeid, dlm_state_str(node->state));
                        break;
                default:
                        /* some invalid state passive shutdown
                         * was failed, we try to reset and
                         * hope it will go on.
                         */
                        log_print("reset node %d because shutdown stuck",
                                  node->nodeid);

                        midcomms_node_reset(node);
                        node->state = DLM_ESTABLISHED;
                        break;
                }
        }

        node->users++;
        pr_debug("node %d users inc count %d\n", nodeid, node->users);
        spin_unlock_bh(&node->state_lock);

        srcu_read_unlock(&nodes_srcu, idx);
}

void dlm_midcomms_remove_member(int nodeid)
{
        struct midcomms_node *node;
        int idx;

        idx = srcu_read_lock(&nodes_srcu);
        node = nodeid2node(nodeid);
        /* in case of dlm_midcomms_close() removes node */
        if (!node) {
                srcu_read_unlock(&nodes_srcu, idx);
                return;
        }

        spin_lock_bh(&node->state_lock);
        /* case of dlm_midcomms_addr() created node but
         * was not added before because dlm_midcomms_close()
         * removed the node
         */
        if (!node->users) {
                spin_unlock_bh(&node->state_lock);
                srcu_read_unlock(&nodes_srcu, idx);
                return;
        }

        node->users--;
        pr_debug("node %d users dec count %d\n", nodeid, node->users);

        /* hitting users count to zero means the
         * other side is running dlm_midcomms_stop()
         * we meet us to have a clean disconnect.
         */
        if (node->users == 0) {
                pr_debug("receive remove member from node %d with state %s\n",
                         node->nodeid, dlm_state_str(node->state));
                switch (node->state) {
                case DLM_ESTABLISHED:
                        break;
                case DLM_CLOSE_WAIT:
                        /* passive shutdown DLM_LAST_ACK case 2 */
                        node->state = DLM_LAST_ACK;
                        pr_debug("switch node %d to state %s case 2\n",
                                 node->nodeid, dlm_state_str(node->state));
                        set_bit(DLM_NODE_FLAG_STOP_RX, &node->flags);
                        dlm_send_fin(node, dlm_pas_fin_ack_rcv);
                        break;
                case DLM_LAST_ACK:
                        /* probably receive fin caught it, do nothing */
                        break;
                case DLM_CLOSED:
                        /* already gone, do nothing */
                        break;
                default:
                        log_print("%s: unexpected state: %d",
                                  __func__, node->state);
                        break;
                }
        }
        spin_unlock_bh(&node->state_lock);

        srcu_read_unlock(&nodes_srcu, idx);
}

void dlm_midcomms_version_wait(void)
{
        struct midcomms_node *node;
        int i, idx, ret;

        idx = srcu_read_lock(&nodes_srcu);
        for (i = 0; i < CONN_HASH_SIZE; i++) {
                hlist_for_each_entry_rcu(node, &node_hash[i], hlist) {
                        ret = wait_event_timeout(node->shutdown_wait,
                                                 node->version != DLM_VERSION_NOT_SET ||
                                                 node->state == DLM_CLOSED ||
                                                 test_bit(DLM_NODE_FLAG_CLOSE, &node->flags),
                                                 DLM_SHUTDOWN_TIMEOUT);
                        if (!ret || test_bit(DLM_NODE_FLAG_CLOSE, &node->flags))
                                pr_debug("version wait timed out for node %d with state %s\n",
                                         node->nodeid, dlm_state_str(node->state));
                }
        }
        srcu_read_unlock(&nodes_srcu, idx);
}

static void midcomms_shutdown(struct midcomms_node *node)
{
        int ret;

        /* old protocol, we don't wait for pending operations */
        switch (node->version) {
        case DLM_VERSION_3_2:
                break;
        default:
                return;
        }

        spin_lock_bh(&node->state_lock);
        pr_debug("receive active shutdown for node %d with state %s\n",
                 node->nodeid, dlm_state_str(node->state));
        switch (node->state) {
        case DLM_ESTABLISHED:
                node->state = DLM_FIN_WAIT1;
                pr_debug("switch node %d to state %s case 2\n",
                         node->nodeid, dlm_state_str(node->state));
                dlm_send_fin(node, dlm_act_fin_ack_rcv);
                break;
        case DLM_CLOSED:
                /* we have what we want */
                break;
        default:
                /* busy to enter DLM_FIN_WAIT1, wait until passive
                 * done in shutdown_wait to enter DLM_CLOSED.
                 */
                break;
        }
        spin_unlock_bh(&node->state_lock);

        if (DLM_DEBUG_FENCE_TERMINATION)
                msleep(5000);

        /* wait for other side dlm + fin */
        ret = wait_event_timeout(node->shutdown_wait,
                                 node->state == DLM_CLOSED ||
                                 test_bit(DLM_NODE_FLAG_CLOSE, &node->flags),
                                 DLM_SHUTDOWN_TIMEOUT);
        if (!ret)
                pr_debug("active shutdown timed out for node %d with state %s\n",
                         node->nodeid, dlm_state_str(node->state));
        else
                pr_debug("active shutdown done for node %d with state %s\n",
                         node->nodeid, dlm_state_str(node->state));
}

void dlm_midcomms_shutdown(void)
{
        struct midcomms_node *node;
        int i, idx;

        mutex_lock(&close_lock);
        idx = srcu_read_lock(&nodes_srcu);
        for (i = 0; i < CONN_HASH_SIZE; i++) {
                hlist_for_each_entry_rcu(node, &node_hash[i], hlist) {
                        midcomms_shutdown(node);
                }
        }

        dlm_lowcomms_shutdown();

        for (i = 0; i < CONN_HASH_SIZE; i++) {
                hlist_for_each_entry_rcu(node, &node_hash[i], hlist) {
                        midcomms_node_reset(node);
                }
        }
        srcu_read_unlock(&nodes_srcu, idx);
        mutex_unlock(&close_lock);
}

int dlm_midcomms_close(int nodeid)
{
        struct midcomms_node *node;
        int idx, ret;

        idx = srcu_read_lock(&nodes_srcu);
        /* Abort pending close/remove operation */
        node = nodeid2node(nodeid);
        if (node) {
                /* let shutdown waiters leave */
                set_bit(DLM_NODE_FLAG_CLOSE, &node->flags);
                wake_up(&node->shutdown_wait);
        }
        srcu_read_unlock(&nodes_srcu, idx);

        synchronize_srcu(&nodes_srcu);

        mutex_lock(&close_lock);
        idx = srcu_read_lock(&nodes_srcu);
        node = nodeid2node(nodeid);
        if (!node) {
                srcu_read_unlock(&nodes_srcu, idx);
                mutex_unlock(&close_lock);
                return dlm_lowcomms_close(nodeid);
        }

        ret = dlm_lowcomms_close(nodeid);
        dlm_delete_debug_comms_file(node->debugfs);

        spin_lock_bh(&nodes_lock);
        hlist_del_rcu(&node->hlist);
        spin_unlock_bh(&nodes_lock);
        srcu_read_unlock(&nodes_srcu, idx);

        /* wait that all readers left until flush send queue */
        synchronize_srcu(&nodes_srcu);

        /* drop all pending dlm messages, this is fine as
         * this function get called when the node is fenced
         */
        dlm_send_queue_flush(node);

        call_srcu(&nodes_srcu, &node->rcu, midcomms_node_release);
        mutex_unlock(&close_lock);

        return ret;
}

/* debug functionality to send raw dlm msg from user space */
struct dlm_rawmsg_data {
        struct midcomms_node *node;
        void *buf;
};

static void midcomms_new_rawmsg_cb(void *data)
{
        struct dlm_rawmsg_data *rd = data;
        struct dlm_header *h = rd->buf;

        switch (h->h_version) {
        case cpu_to_le32(DLM_VERSION_3_1):
                break;
        default:
                switch (h->h_cmd) {
                case DLM_OPTS:
                        if (!h->u.h_seq)
                                h->u.h_seq = cpu_to_le32(atomic_fetch_inc(&rd->node->seq_send));
                        break;
                default:
                        break;
                }
                break;
        }
}

int dlm_midcomms_rawmsg_send(struct midcomms_node *node, void *buf,
                             int buflen)
{
        struct dlm_rawmsg_data rd;
        struct dlm_msg *msg;
        char *msgbuf;

        rd.node = node;
        rd.buf = buf;

        msg = dlm_lowcomms_new_msg(node->nodeid, buflen, &msgbuf,
                                   midcomms_new_rawmsg_cb, &rd);
        if (!msg)
                return -ENOMEM;

        memcpy(msgbuf, buf, buflen);
        dlm_lowcomms_commit_msg(msg);
        return 0;
}