firewire: cdev: count references of cards during inbound transactions

[firewire-audio.git] / net / rds / send.c

/*
 * Copyright (c) 2006 Oracle.  All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */
#include <linux/kernel.h>
#include <net/sock.h>
#include <linux/in.h>
#include <linux/list.h>

#include "rds.h"
#include "rdma.h"

/* When transmitting messages in rds_send_xmit, we need to emerge from
 * time to time and briefly release the CPU. Otherwise the softlock watchdog
 * will kick our shin.
 * Also, it seems fairer to not let one busy connection stall all the
 * others.
 *
 * send_batch_count is the number of times we'll loop in send_xmit. Setting
 * it to 0 will restore the old behavior (where we looped until we had
 * drained the queue).
 */
static int send_batch_count = 64;
module_param(send_batch_count, int, 0444);
MODULE_PARM_DESC(send_batch_count, " batch factor when working the send queue");

/*
 * Reset the send state. Caller must hold c_send_lock when calling here.
 */
void rds_send_reset(struct rds_connection *conn)
{
        struct rds_message *rm, *tmp;
        unsigned long flags;

        if (conn->c_xmit_rm) {
                /* Tell the user the RDMA op is no longer mapped by the
                 * transport. This isn't entirely true (it's flushed out
                 * independently) but as the connection is down, there's
                 * no ongoing RDMA to/from that memory */
                rds_message_unmapped(conn->c_xmit_rm);
                rds_message_put(conn->c_xmit_rm);
                conn->c_xmit_rm = NULL;
        }
        conn->c_xmit_sg = 0;
        conn->c_xmit_hdr_off = 0;
        conn->c_xmit_data_off = 0;
        conn->c_xmit_rdma_sent = 0;

        conn->c_map_queued = 0;

        conn->c_unacked_packets = rds_sysctl_max_unacked_packets;
        conn->c_unacked_bytes = rds_sysctl_max_unacked_bytes;

        /* Mark messages as retransmissions, and move them to the send q */
        spin_lock_irqsave(&conn->c_lock, flags);
        list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
                set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);
                set_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags);
        }
        list_splice_init(&conn->c_retrans, &conn->c_send_queue);
        spin_unlock_irqrestore(&conn->c_lock, flags);
}

/*
 * We're making the concious trade-off here to only send one message
 * down the connection at a time.
 *   Pro:
 *      - tx queueing is a simple fifo list
 *      - reassembly is optional and easily done by transports per conn
 *      - no per flow rx lookup at all, straight to the socket
 *      - less per-frag memory and wire overhead
 *   Con:
 *      - queued acks can be delayed behind large messages
 *   Depends:
 *      - small message latency is higher behind queued large messages
 *      - large message latency isn't starved by intervening small sends
 */
int rds_send_xmit(struct rds_connection *conn)
{
        struct rds_message *rm;
        unsigned long flags;
        unsigned int tmp;
        unsigned int send_quota = send_batch_count;
        struct scatterlist *sg;
        int ret = 0;
        int was_empty = 0;
        LIST_HEAD(to_be_dropped);

        /*
         * sendmsg calls here after having queued its message on the send
         * queue.  We only have one task feeding the connection at a time.  If
         * another thread is already feeding the queue then we back off.  This
         * avoids blocking the caller and trading per-connection data between
         * caches per message.
         *
         * The sem holder will issue a retry if they notice that someone queued
         * a message after they stopped walking the send queue but before they
         * dropped the sem.
         */
        if (!mutex_trylock(&conn->c_send_lock)) {
                rds_stats_inc(s_send_sem_contention);
                ret = -ENOMEM;
                goto out;
        }

        if (conn->c_trans->xmit_prepare)
                conn->c_trans->xmit_prepare(conn);

        /*
         * spin trying to push headers and data down the connection until
         * the connection doens't make forward progress.
         */
        while (--send_quota) {
                /*
                 * See if need to send a congestion map update if we're
                 * between sending messages.  The send_sem protects our sole
                 * use of c_map_offset and _bytes.
                 * Note this is used only by transports that define a special
                 * xmit_cong_map function. For all others, we create allocate
                 * a cong_map message and treat it just like any other send.
                 */
                if (conn->c_map_bytes) {
                        ret = conn->c_trans->xmit_cong_map(conn, conn->c_lcong,
                                                conn->c_map_offset);
                        if (ret <= 0)
                                break;

                        conn->c_map_offset += ret;
                        conn->c_map_bytes -= ret;
                        if (conn->c_map_bytes)
                                continue;
                }

                /* If we're done sending the current message, clear the
                 * offset and S/G temporaries.
                 */
                rm = conn->c_xmit_rm;
                if (rm != NULL &&
                    conn->c_xmit_hdr_off == sizeof(struct rds_header) &&
                    conn->c_xmit_sg == rm->m_nents) {
                        conn->c_xmit_rm = NULL;
                        conn->c_xmit_sg = 0;
                        conn->c_xmit_hdr_off = 0;
                        conn->c_xmit_data_off = 0;
                        conn->c_xmit_rdma_sent = 0;

                        /* Release the reference to the previous message. */
                        rds_message_put(rm);
                        rm = NULL;
                }

                /* If we're asked to send a cong map update, do so.
                 */
                if (rm == NULL && test_and_clear_bit(0, &conn->c_map_queued)) {
                        if (conn->c_trans->xmit_cong_map != NULL) {
                                conn->c_map_offset = 0;
                                conn->c_map_bytes = sizeof(struct rds_header) +
                                        RDS_CONG_MAP_BYTES;
                                continue;
                        }

                        rm = rds_cong_update_alloc(conn);
                        if (IS_ERR(rm)) {
                                ret = PTR_ERR(rm);
                                break;
                        }

                        conn->c_xmit_rm = rm;
                }

                /*
                 * Grab the next message from the send queue, if there is one.
                 *
                 * c_xmit_rm holds a ref while we're sending this message down
                 * the connction.  We can use this ref while holding the
                 * send_sem.. rds_send_reset() is serialized with it.
                 */
                if (rm == NULL) {
                        unsigned int len;

                        spin_lock_irqsave(&conn->c_lock, flags);

                        if (!list_empty(&conn->c_send_queue)) {
                                rm = list_entry(conn->c_send_queue.next,
                                                struct rds_message,
                                                m_conn_item);
                                rds_message_addref(rm);

                                /*
                                 * Move the message from the send queue to the retransmit
                                 * list right away.
                                 */
                                list_move_tail(&rm->m_conn_item, &conn->c_retrans);
                        }

                        spin_unlock_irqrestore(&conn->c_lock, flags);

                        if (rm == NULL) {
                                was_empty = 1;
                                break;
                        }

                        /* Unfortunately, the way Infiniband deals with
                         * RDMA to a bad MR key is by moving the entire
                         * queue pair to error state. We cold possibly
                         * recover from that, but right now we drop the
                         * connection.
                         * Therefore, we never retransmit messages with RDMA ops.
                         */
                        if (rm->m_rdma_op &&
                            test_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags)) {
                                spin_lock_irqsave(&conn->c_lock, flags);
                                if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags))
                                        list_move(&rm->m_conn_item, &to_be_dropped);
                                spin_unlock_irqrestore(&conn->c_lock, flags);
                                rds_message_put(rm);
                                continue;
                        }

                        /* Require an ACK every once in a while */
                        len = ntohl(rm->m_inc.i_hdr.h_len);
                        if (conn->c_unacked_packets == 0 ||
                            conn->c_unacked_bytes < len) {
                                __set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);

                                conn->c_unacked_packets = rds_sysctl_max_unacked_packets;
                                conn->c_unacked_bytes = rds_sysctl_max_unacked_bytes;
                                rds_stats_inc(s_send_ack_required);
                        } else {
                                conn->c_unacked_bytes -= len;
                                conn->c_unacked_packets--;
                        }

                        conn->c_xmit_rm = rm;
                }

                /*
                 * Try and send an rdma message.  Let's see if we can
                 * keep this simple and require that the transport either
                 * send the whole rdma or none of it.
                 */
                if (rm->m_rdma_op && !conn->c_xmit_rdma_sent) {
                        ret = conn->c_trans->xmit_rdma(conn, rm->m_rdma_op);
                        if (ret)
                                break;
                        conn->c_xmit_rdma_sent = 1;
                        /* The transport owns the mapped memory for now.
                         * You can't unmap it while it's on the send queue */
                        set_bit(RDS_MSG_MAPPED, &rm->m_flags);
                }

                if (conn->c_xmit_hdr_off < sizeof(struct rds_header) ||
                    conn->c_xmit_sg < rm->m_nents) {
                        ret = conn->c_trans->xmit(conn, rm,
                                                  conn->c_xmit_hdr_off,
                                                  conn->c_xmit_sg,
                                                  conn->c_xmit_data_off);
                        if (ret <= 0)
                                break;

                        if (conn->c_xmit_hdr_off < sizeof(struct rds_header)) {
                                tmp = min_t(int, ret,
                                            sizeof(struct rds_header) -
                                            conn->c_xmit_hdr_off);
                                conn->c_xmit_hdr_off += tmp;
                                ret -= tmp;
                        }

                        sg = &rm->m_sg[conn->c_xmit_sg];
                        while (ret) {
                                tmp = min_t(int, ret, sg->length -
                                                      conn->c_xmit_data_off);
                                conn->c_xmit_data_off += tmp;
                                ret -= tmp;
                                if (conn->c_xmit_data_off == sg->length) {
                                        conn->c_xmit_data_off = 0;
                                        sg++;
                                        conn->c_xmit_sg++;
                                        BUG_ON(ret != 0 &&
                                               conn->c_xmit_sg == rm->m_nents);
                                }
                        }
                }
        }

        /* Nuke any messages we decided not to retransmit. */
        if (!list_empty(&to_be_dropped))
                rds_send_remove_from_sock(&to_be_dropped, RDS_RDMA_DROPPED);

        if (conn->c_trans->xmit_complete)
                conn->c_trans->xmit_complete(conn);

        /*
         * We might be racing with another sender who queued a message but
         * backed off on noticing that we held the c_send_lock.  If we check
         * for queued messages after dropping the sem then either we'll
         * see the queued message or the queuer will get the sem.  If we
         * notice the queued message then we trigger an immediate retry.
         *
         * We need to be careful only to do this when we stopped processing
         * the send queue because it was empty.  It's the only way we
         * stop processing the loop when the transport hasn't taken
         * responsibility for forward progress.
         */
        mutex_unlock(&conn->c_send_lock);

        if (conn->c_map_bytes || (send_quota == 0 && !was_empty)) {
                /* We exhausted the send quota, but there's work left to
                 * do. Return and (re-)schedule the send worker.
                 */
                ret = -EAGAIN;
        }

        if (ret == 0 && was_empty) {
                /* A simple bit test would be way faster than taking the
                 * spin lock */
                spin_lock_irqsave(&conn->c_lock, flags);
                if (!list_empty(&conn->c_send_queue)) {
                        rds_stats_inc(s_send_sem_queue_raced);
                        ret = -EAGAIN;
                }
                spin_unlock_irqrestore(&conn->c_lock, flags);
        }
out:
        return ret;
}

static void rds_send_sndbuf_remove(struct rds_sock *rs, struct rds_message *rm)
{
        u32 len = be32_to_cpu(rm->m_inc.i_hdr.h_len);

        assert_spin_locked(&rs->rs_lock);

        BUG_ON(rs->rs_snd_bytes < len);
        rs->rs_snd_bytes -= len;

        if (rs->rs_snd_bytes == 0)
                rds_stats_inc(s_send_queue_empty);
}

static inline int rds_send_is_acked(struct rds_message *rm, u64 ack,
                                    is_acked_func is_acked)
{
        if (is_acked)
                return is_acked(rm, ack);
        return be64_to_cpu(rm->m_inc.i_hdr.h_sequence) <= ack;
}

/*
 * Returns true if there are no messages on the send and retransmit queues
 * which have a sequence number greater than or equal to the given sequence
 * number.
 */
int rds_send_acked_before(struct rds_connection *conn, u64 seq)
{
        struct rds_message *rm, *tmp;
        int ret = 1;

        spin_lock(&conn->c_lock);

        list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
                if (be64_to_cpu(rm->m_inc.i_hdr.h_sequence) < seq)
                        ret = 0;
                break;
        }

        list_for_each_entry_safe(rm, tmp, &conn->c_send_queue, m_conn_item) {
                if (be64_to_cpu(rm->m_inc.i_hdr.h_sequence) < seq)
                        ret = 0;
                break;
        }

        spin_unlock(&conn->c_lock);

        return ret;
}

/*
 * This is pretty similar to what happens below in the ACK
 * handling code - except that we call here as soon as we get
 * the IB send completion on the RDMA op and the accompanying
 * message.
 */
void rds_rdma_send_complete(struct rds_message *rm, int status)
{
        struct rds_sock *rs = NULL;
        struct rds_rdma_op *ro;
        struct rds_notifier *notifier;

        spin_lock(&rm->m_rs_lock);

        ro = rm->m_rdma_op;
        if (test_bit(RDS_MSG_ON_SOCK, &rm->m_flags) &&
            ro && ro->r_notify && ro->r_notifier) {
                notifier = ro->r_notifier;
                rs = rm->m_rs;
                sock_hold(rds_rs_to_sk(rs));

                notifier->n_status = status;
                spin_lock(&rs->rs_lock);
                list_add_tail(&notifier->n_list, &rs->rs_notify_queue);
                spin_unlock(&rs->rs_lock);

                ro->r_notifier = NULL;
        }

        spin_unlock(&rm->m_rs_lock);

        if (rs) {
                rds_wake_sk_sleep(rs);
                sock_put(rds_rs_to_sk(rs));
        }
}
EXPORT_SYMBOL_GPL(rds_rdma_send_complete);

/*
 * This is the same as rds_rdma_send_complete except we
 * don't do any locking - we have all the ingredients (message,
 * socket, socket lock) and can just move the notifier.
 */
static inline void
__rds_rdma_send_complete(struct rds_sock *rs, struct rds_message *rm, int status)
{
        struct rds_rdma_op *ro;

        ro = rm->m_rdma_op;
        if (ro && ro->r_notify && ro->r_notifier) {
                ro->r_notifier->n_status = status;
                list_add_tail(&ro->r_notifier->n_list, &rs->rs_notify_queue);
                ro->r_notifier = NULL;
        }

        /* No need to wake the app - caller does this */
}

/*
 * This is called from the IB send completion when we detect
 * a RDMA operation that failed with remote access error.
 * So speed is not an issue here.
 */
struct rds_message *rds_send_get_message(struct rds_connection *conn,
                                         struct rds_rdma_op *op)
{
        struct rds_message *rm, *tmp, *found = NULL;
        unsigned long flags;

        spin_lock_irqsave(&conn->c_lock, flags);

        list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
                if (rm->m_rdma_op == op) {
                        atomic_inc(&rm->m_refcount);
                        found = rm;
                        goto out;
                }
        }

        list_for_each_entry_safe(rm, tmp, &conn->c_send_queue, m_conn_item) {
                if (rm->m_rdma_op == op) {
                        atomic_inc(&rm->m_refcount);
                        found = rm;
                        break;
                }
        }

out:
        spin_unlock_irqrestore(&conn->c_lock, flags);

        return found;
}
EXPORT_SYMBOL_GPL(rds_send_get_message);

/*
 * This removes messages from the socket's list if they're on it.  The list
 * argument must be private to the caller, we must be able to modify it
 * without locks.  The messages must have a reference held for their
 * position on the list.  This function will drop that reference after
 * removing the messages from the 'messages' list regardless of if it found
 * the messages on the socket list or not.
 */
void rds_send_remove_from_sock(struct list_head *messages, int status)
{
        unsigned long flags = 0; /* silence gcc :P */
        struct rds_sock *rs = NULL;
        struct rds_message *rm;

        local_irq_save(flags);
        while (!list_empty(messages)) {
                rm = list_entry(messages->next, struct rds_message,
                                m_conn_item);
                list_del_init(&rm->m_conn_item);

                /*
                 * If we see this flag cleared then we're *sure* that someone
                 * else beat us to removing it from the sock.  If we race
                 * with their flag update we'll get the lock and then really
                 * see that the flag has been cleared.
                 *
                 * The message spinlock makes sure nobody clears rm->m_rs
                 * while we're messing with it. It does not prevent the
                 * message from being removed from the socket, though.
                 */
                spin_lock(&rm->m_rs_lock);
                if (!test_bit(RDS_MSG_ON_SOCK, &rm->m_flags))
                        goto unlock_and_drop;

                if (rs != rm->m_rs) {
                        if (rs) {
                                spin_unlock(&rs->rs_lock);
                                rds_wake_sk_sleep(rs);
                                sock_put(rds_rs_to_sk(rs));
                        }
                        rs = rm->m_rs;
                        spin_lock(&rs->rs_lock);
                        sock_hold(rds_rs_to_sk(rs));
                }

                if (test_and_clear_bit(RDS_MSG_ON_SOCK, &rm->m_flags)) {
                        struct rds_rdma_op *ro = rm->m_rdma_op;
                        struct rds_notifier *notifier;

                        list_del_init(&rm->m_sock_item);
                        rds_send_sndbuf_remove(rs, rm);

                        if (ro && ro->r_notifier && (status || ro->r_notify)) {
                                notifier = ro->r_notifier;
                                list_add_tail(&notifier->n_list,
                                                &rs->rs_notify_queue);
                                if (!notifier->n_status)
                                        notifier->n_status = status;
                                rm->m_rdma_op->r_notifier = NULL;
                        }
                        rds_message_put(rm);
                        rm->m_rs = NULL;
                }

unlock_and_drop:
                spin_unlock(&rm->m_rs_lock);
                rds_message_put(rm);
        }

        if (rs) {
                spin_unlock(&rs->rs_lock);
                rds_wake_sk_sleep(rs);
                sock_put(rds_rs_to_sk(rs));
        }
        local_irq_restore(flags);
}

/*
 * Transports call here when they've determined that the receiver queued
 * messages up to, and including, the given sequence number.  Messages are
 * moved to the retrans queue when rds_send_xmit picks them off the send
 * queue. This means that in the TCP case, the message may not have been
 * assigned the m_ack_seq yet - but that's fine as long as tcp_is_acked
 * checks the RDS_MSG_HAS_ACK_SEQ bit.
 *
 * XXX It's not clear to me how this is safely serialized with socket
 * destruction.  Maybe it should bail if it sees SOCK_DEAD.
 */
void rds_send_drop_acked(struct rds_connection *conn, u64 ack,
                         is_acked_func is_acked)
{
        struct rds_message *rm, *tmp;
        unsigned long flags;
        LIST_HEAD(list);

        spin_lock_irqsave(&conn->c_lock, flags);

        list_for_each_entry_safe(rm, tmp, &conn->c_retrans, m_conn_item) {
                if (!rds_send_is_acked(rm, ack, is_acked))
                        break;

                list_move(&rm->m_conn_item, &list);
                clear_bit(RDS_MSG_ON_CONN, &rm->m_flags);
        }

        /* order flag updates with spin locks */
        if (!list_empty(&list))
                smp_mb__after_clear_bit();

        spin_unlock_irqrestore(&conn->c_lock, flags);

        /* now remove the messages from the sock list as needed */
        rds_send_remove_from_sock(&list, RDS_RDMA_SUCCESS);
}
EXPORT_SYMBOL_GPL(rds_send_drop_acked);

void rds_send_drop_to(struct rds_sock *rs, struct sockaddr_in *dest)
{
        struct rds_message *rm, *tmp;
        struct rds_connection *conn;
        unsigned long flags, flags2;
        LIST_HEAD(list);
        int wake = 0;

        /* get all the messages we're dropping under the rs lock */
        spin_lock_irqsave(&rs->rs_lock, flags);

        list_for_each_entry_safe(rm, tmp, &rs->rs_send_queue, m_sock_item) {
                if (dest && (dest->sin_addr.s_addr != rm->m_daddr ||
                             dest->sin_port != rm->m_inc.i_hdr.h_dport))
                        continue;

                wake = 1;
                list_move(&rm->m_sock_item, &list);
                rds_send_sndbuf_remove(rs, rm);
                clear_bit(RDS_MSG_ON_SOCK, &rm->m_flags);

                /* If this is a RDMA operation, notify the app. */
                __rds_rdma_send_complete(rs, rm, RDS_RDMA_CANCELED);
        }

        /* order flag updates with the rs lock */
        if (wake)
                smp_mb__after_clear_bit();

        spin_unlock_irqrestore(&rs->rs_lock, flags);

        if (wake)
                rds_wake_sk_sleep(rs);

        conn = NULL;

        /* now remove the messages from the conn list as needed */
        list_for_each_entry(rm, &list, m_sock_item) {
                /* We do this here rather than in the loop above, so that
                 * we don't have to nest m_rs_lock under rs->rs_lock */
                spin_lock_irqsave(&rm->m_rs_lock, flags2);
                rm->m_rs = NULL;
                spin_unlock_irqrestore(&rm->m_rs_lock, flags2);

                /*
                 * If we see this flag cleared then we're *sure* that someone
                 * else beat us to removing it from the conn.  If we race
                 * with their flag update we'll get the lock and then really
                 * see that the flag has been cleared.
                 */
                if (!test_bit(RDS_MSG_ON_CONN, &rm->m_flags))
                        continue;

                if (conn != rm->m_inc.i_conn) {
                        if (conn)
                                spin_unlock_irqrestore(&conn->c_lock, flags);
                        conn = rm->m_inc.i_conn;
                        spin_lock_irqsave(&conn->c_lock, flags);
                }

                if (test_and_clear_bit(RDS_MSG_ON_CONN, &rm->m_flags)) {
                        list_del_init(&rm->m_conn_item);
                        rds_message_put(rm);
                }
        }

        if (conn)
                spin_unlock_irqrestore(&conn->c_lock, flags);

        while (!list_empty(&list)) {
                rm = list_entry(list.next, struct rds_message, m_sock_item);
                list_del_init(&rm->m_sock_item);

                rds_message_wait(rm);
                rds_message_put(rm);
        }
}

/*
 * we only want this to fire once so we use the callers 'queued'.  It's
 * possible that another thread can race with us and remove the
 * message from the flow with RDS_CANCEL_SENT_TO.
 */
static int rds_send_queue_rm(struct rds_sock *rs, struct rds_connection *conn,
                             struct rds_message *rm, __be16 sport,
                             __be16 dport, int *queued)
{
        unsigned long flags;
        u32 len;

        if (*queued)
                goto out;

        len = be32_to_cpu(rm->m_inc.i_hdr.h_len);

        /* this is the only place which holds both the socket's rs_lock
         * and the connection's c_lock */
        spin_lock_irqsave(&rs->rs_lock, flags);

        /*
         * If there is a little space in sndbuf, we don't queue anything,
         * and userspace gets -EAGAIN. But poll() indicates there's send
         * room. This can lead to bad behavior (spinning) if snd_bytes isn't
         * freed up by incoming acks. So we check the *old* value of
         * rs_snd_bytes here to allow the last msg to exceed the buffer,
         * and poll() now knows no more data can be sent.
         */
        if (rs->rs_snd_bytes < rds_sk_sndbuf(rs)) {
                rs->rs_snd_bytes += len;

                /* let recv side know we are close to send space exhaustion.
                 * This is probably not the optimal way to do it, as this
                 * means we set the flag on *all* messages as soon as our
                 * throughput hits a certain threshold.
                 */
                if (rs->rs_snd_bytes >= rds_sk_sndbuf(rs) / 2)
                        __set_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags);

                list_add_tail(&rm->m_sock_item, &rs->rs_send_queue);
                set_bit(RDS_MSG_ON_SOCK, &rm->m_flags);
                rds_message_addref(rm);
                rm->m_rs = rs;

                /* The code ordering is a little weird, but we're
                   trying to minimize the time we hold c_lock */
                rds_message_populate_header(&rm->m_inc.i_hdr, sport, dport, 0);
                rm->m_inc.i_conn = conn;
                rds_message_addref(rm);

                spin_lock(&conn->c_lock);
                rm->m_inc.i_hdr.h_sequence = cpu_to_be64(conn->c_next_tx_seq++);
                list_add_tail(&rm->m_conn_item, &conn->c_send_queue);
                set_bit(RDS_MSG_ON_CONN, &rm->m_flags);
                spin_unlock(&conn->c_lock);

                rdsdebug("queued msg %p len %d, rs %p bytes %d seq %llu\n",
                         rm, len, rs, rs->rs_snd_bytes,
                         (unsigned long long)be64_to_cpu(rm->m_inc.i_hdr.h_sequence));

                *queued = 1;
        }

        spin_unlock_irqrestore(&rs->rs_lock, flags);
out:
        return *queued;
}

static int rds_cmsg_send(struct rds_sock *rs, struct rds_message *rm,
                         struct msghdr *msg, int *allocated_mr)
{
        struct cmsghdr *cmsg;
        int ret = 0;

        for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg)) {
                if (!CMSG_OK(msg, cmsg))
                        return -EINVAL;

                if (cmsg->cmsg_level != SOL_RDS)
                        continue;

                /* As a side effect, RDMA_DEST and RDMA_MAP will set
                 * rm->m_rdma_cookie and rm->m_rdma_mr.
                 */
                switch (cmsg->cmsg_type) {
                case RDS_CMSG_RDMA_ARGS:
                        ret = rds_cmsg_rdma_args(rs, rm, cmsg);
                        break;

                case RDS_CMSG_RDMA_DEST:
                        ret = rds_cmsg_rdma_dest(rs, rm, cmsg);
                        break;

                case RDS_CMSG_RDMA_MAP:
                        ret = rds_cmsg_rdma_map(rs, rm, cmsg);
                        if (!ret)
                                *allocated_mr = 1;
                        break;

                default:
                        return -EINVAL;
                }

                if (ret)
                        break;
        }

        return ret;
}

int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
                size_t payload_len)
{
        struct sock *sk = sock->sk;
        struct rds_sock *rs = rds_sk_to_rs(sk);
        struct sockaddr_in *usin = (struct sockaddr_in *)msg->msg_name;
        __be32 daddr;
        __be16 dport;
        struct rds_message *rm = NULL;
        struct rds_connection *conn;
        int ret = 0;
        int queued = 0, allocated_mr = 0;
        int nonblock = msg->msg_flags & MSG_DONTWAIT;
        long timeo = sock_rcvtimeo(sk, nonblock);

        /* Mirror Linux UDP mirror of BSD error message compatibility */
        /* XXX: Perhaps MSG_MORE someday */
        if (msg->msg_flags & ~(MSG_DONTWAIT | MSG_CMSG_COMPAT)) {
                printk(KERN_INFO "msg_flags 0x%08X\n", msg->msg_flags);
                ret = -EOPNOTSUPP;
                goto out;
        }

        if (msg->msg_namelen) {
                /* XXX fail non-unicast destination IPs? */
                if (msg->msg_namelen < sizeof(*usin) || usin->sin_family != AF_INET) {
                        ret = -EINVAL;
                        goto out;
                }
                daddr = usin->sin_addr.s_addr;
                dport = usin->sin_port;
        } else {
                /* We only care about consistency with ->connect() */
                lock_sock(sk);
                daddr = rs->rs_conn_addr;
                dport = rs->rs_conn_port;
                release_sock(sk);
        }

        /* racing with another thread binding seems ok here */
        if (daddr == 0 || rs->rs_bound_addr == 0) {
                ret = -ENOTCONN; /* XXX not a great errno */
                goto out;
        }

        rm = rds_message_copy_from_user(msg->msg_iov, payload_len);
        if (IS_ERR(rm)) {
                ret = PTR_ERR(rm);
                rm = NULL;
                goto out;
        }

        rm->m_daddr = daddr;

        /* rds_conn_create has a spinlock that runs with IRQ off.
         * Caching the conn in the socket helps a lot. */
        if (rs->rs_conn && rs->rs_conn->c_faddr == daddr)
                conn = rs->rs_conn;
        else {
                conn = rds_conn_create_outgoing(rs->rs_bound_addr, daddr,
                                        rs->rs_transport,
                                        sock->sk->sk_allocation);
                if (IS_ERR(conn)) {
                        ret = PTR_ERR(conn);
                        goto out;
                }
                rs->rs_conn = conn;
        }

        /* Parse any control messages the user may have included. */
        ret = rds_cmsg_send(rs, rm, msg, &allocated_mr);
        if (ret)
                goto out;

        if ((rm->m_rdma_cookie || rm->m_rdma_op) &&
            conn->c_trans->xmit_rdma == NULL) {
                if (printk_ratelimit())
                        printk(KERN_NOTICE "rdma_op %p conn xmit_rdma %p\n",
                                rm->m_rdma_op, conn->c_trans->xmit_rdma);
                ret = -EOPNOTSUPP;
                goto out;
        }

        /* If the connection is down, trigger a connect. We may
         * have scheduled a delayed reconnect however - in this case
         * we should not interfere.
         */
        if (rds_conn_state(conn) == RDS_CONN_DOWN &&
            !test_and_set_bit(RDS_RECONNECT_PENDING, &conn->c_flags))
                queue_delayed_work(rds_wq, &conn->c_conn_w, 0);

        ret = rds_cong_wait(conn->c_fcong, dport, nonblock, rs);
        if (ret)
                goto out;

        while (!rds_send_queue_rm(rs, conn, rm, rs->rs_bound_port,
                                  dport, &queued)) {
                rds_stats_inc(s_send_queue_full);
                /* XXX make sure this is reasonable */
                if (payload_len > rds_sk_sndbuf(rs)) {
                        ret = -EMSGSIZE;
                        goto out;
                }
                if (nonblock) {
                        ret = -EAGAIN;
                        goto out;
                }

                timeo = wait_event_interruptible_timeout(*sk->sk_sleep,
                                        rds_send_queue_rm(rs, conn, rm,
                                                          rs->rs_bound_port,
                                                          dport,
                                                          &queued),
                                        timeo);
                rdsdebug("sendmsg woke queued %d timeo %ld\n", queued, timeo);
                if (timeo > 0 || timeo == MAX_SCHEDULE_TIMEOUT)
                        continue;

                ret = timeo;
                if (ret == 0)
                        ret = -ETIMEDOUT;
                goto out;
        }

        /*
         * By now we've committed to the send.  We reuse rds_send_worker()
         * to retry sends in the rds thread if the transport asks us to.
         */
        rds_stats_inc(s_send_queued);

        if (!test_bit(RDS_LL_SEND_FULL, &conn->c_flags))
                rds_send_worker(&conn->c_send_w.work);

        rds_message_put(rm);
        return payload_len;

out:
        /* If the user included a RDMA_MAP cmsg, we allocated a MR on the fly.
         * If the sendmsg goes through, we keep the MR. If it fails with EAGAIN
         * or in any other way, we need to destroy the MR again */
        if (allocated_mr)
                rds_rdma_unuse(rs, rds_rdma_cookie_key(rm->m_rdma_cookie), 1);

        if (rm)
                rds_message_put(rm);
        return ret;
}

/*
 * Reply to a ping packet.
 */
int
rds_send_pong(struct rds_connection *conn, __be16 dport)
{
        struct rds_message *rm;
        unsigned long flags;
        int ret = 0;

        rm = rds_message_alloc(0, GFP_ATOMIC);
        if (rm == NULL) {
                ret = -ENOMEM;
                goto out;
        }

        rm->m_daddr = conn->c_faddr;

        /* If the connection is down, trigger a connect. We may
         * have scheduled a delayed reconnect however - in this case
         * we should not interfere.
         */
        if (rds_conn_state(conn) == RDS_CONN_DOWN &&
            !test_and_set_bit(RDS_RECONNECT_PENDING, &conn->c_flags))
                queue_delayed_work(rds_wq, &conn->c_conn_w, 0);

        ret = rds_cong_wait(conn->c_fcong, dport, 1, NULL);
        if (ret)
                goto out;

        spin_lock_irqsave(&conn->c_lock, flags);
        list_add_tail(&rm->m_conn_item, &conn->c_send_queue);
        set_bit(RDS_MSG_ON_CONN, &rm->m_flags);
        rds_message_addref(rm);
        rm->m_inc.i_conn = conn;

        rds_message_populate_header(&rm->m_inc.i_hdr, 0, dport,
                                    conn->c_next_tx_seq);
        conn->c_next_tx_seq++;
        spin_unlock_irqrestore(&conn->c_lock, flags);

        rds_stats_inc(s_send_queued);
        rds_stats_inc(s_send_pong);

        queue_delayed_work(rds_wq, &conn->c_send_w, 0);
        rds_message_put(rm);
        return 0;

out:
        if (rm)
                rds_message_put(rm);
        return ret;
}