Merge branch 'for-3.18-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj...

[cascardo/linux.git] / net / ceph / messenger.c

#include <linux/ceph/ceph_debug.h>

#include <linux/crc32c.h>
#include <linux/ctype.h>
#include <linux/highmem.h>
#include <linux/inet.h>
#include <linux/kthread.h>
#include <linux/net.h>
#include <linux/slab.h>
#include <linux/socket.h>
#include <linux/string.h>
#ifdef  CONFIG_BLOCK
#include <linux/bio.h>
#endif  /* CONFIG_BLOCK */
#include <linux/dns_resolver.h>
#include <net/tcp.h>

#include <linux/ceph/ceph_features.h>
#include <linux/ceph/libceph.h>
#include <linux/ceph/messenger.h>
#include <linux/ceph/decode.h>
#include <linux/ceph/pagelist.h>
#include <linux/export.h>

#define list_entry_next(pos, member)                                    \
        list_entry(pos->member.next, typeof(*pos), member)

/*
 * Ceph uses the messenger to exchange ceph_msg messages with other
 * hosts in the system.  The messenger provides ordered and reliable
 * delivery.  We tolerate TCP disconnects by reconnecting (with
 * exponential backoff) in the case of a fault (disconnection, bad
 * crc, protocol error).  Acks allow sent messages to be discarded by
 * the sender.
 */

/*
 * We track the state of the socket on a given connection using
 * values defined below.  The transition to a new socket state is
 * handled by a function which verifies we aren't coming from an
 * unexpected state.
 *
 *      --------
 *      | NEW* |  transient initial state
 *      --------
 *          | con_sock_state_init()
 *          v
 *      ----------
 *      | CLOSED |  initialized, but no socket (and no
 *      ----------  TCP connection)
 *       ^      \
 *       |       \ con_sock_state_connecting()
 *       |        ----------------------
 *       |                              \
 *       + con_sock_state_closed()       \
 *       |+---------------------------    \
 *       | \                          \    \
 *       |  -----------                \    \
 *       |  | CLOSING |  socket event;  \    \
 *       |  -----------  await close     \    \
 *       |       ^                        \   |
 *       |       |                         \  |
 *       |       + con_sock_state_closing() \ |
 *       |      / \                         | |
 *       |     /   ---------------          | |
 *       |    /                   \         v v
 *       |   /                    --------------
 *       |  /    -----------------| CONNECTING |  socket created, TCP
 *       |  |   /                 --------------  connect initiated
 *       |  |   | con_sock_state_connected()
 *       |  |   v
 *      -------------
 *      | CONNECTED |  TCP connection established
 *      -------------
 *
 * State values for ceph_connection->sock_state; NEW is assumed to be 0.
 */

#define CON_SOCK_STATE_NEW              0       /* -> CLOSED */
#define CON_SOCK_STATE_CLOSED           1       /* -> CONNECTING */
#define CON_SOCK_STATE_CONNECTING       2       /* -> CONNECTED or -> CLOSING */
#define CON_SOCK_STATE_CONNECTED        3       /* -> CLOSING or -> CLOSED */
#define CON_SOCK_STATE_CLOSING          4       /* -> CLOSED */

/*
 * connection states
 */
#define CON_STATE_CLOSED        1  /* -> PREOPEN */
#define CON_STATE_PREOPEN       2  /* -> CONNECTING, CLOSED */
#define CON_STATE_CONNECTING    3  /* -> NEGOTIATING, CLOSED */
#define CON_STATE_NEGOTIATING   4  /* -> OPEN, CLOSED */
#define CON_STATE_OPEN          5  /* -> STANDBY, CLOSED */
#define CON_STATE_STANDBY       6  /* -> PREOPEN, CLOSED */

/*
 * ceph_connection flag bits
 */
#define CON_FLAG_LOSSYTX           0  /* we can close channel or drop
                                       * messages on errors */
#define CON_FLAG_KEEPALIVE_PENDING 1  /* we need to send a keepalive */
#define CON_FLAG_WRITE_PENDING     2  /* we have data ready to send */
#define CON_FLAG_SOCK_CLOSED       3  /* socket state changed to closed */
#define CON_FLAG_BACKOFF           4  /* need to retry queuing delayed work */

static bool con_flag_valid(unsigned long con_flag)
{
        switch (con_flag) {
        case CON_FLAG_LOSSYTX:
        case CON_FLAG_KEEPALIVE_PENDING:
        case CON_FLAG_WRITE_PENDING:
        case CON_FLAG_SOCK_CLOSED:
        case CON_FLAG_BACKOFF:
                return true;
        default:
                return false;
        }
}

static void con_flag_clear(struct ceph_connection *con, unsigned long con_flag)
{
        BUG_ON(!con_flag_valid(con_flag));

        clear_bit(con_flag, &con->flags);
}

static void con_flag_set(struct ceph_connection *con, unsigned long con_flag)
{
        BUG_ON(!con_flag_valid(con_flag));

        set_bit(con_flag, &con->flags);
}

static bool con_flag_test(struct ceph_connection *con, unsigned long con_flag)
{
        BUG_ON(!con_flag_valid(con_flag));

        return test_bit(con_flag, &con->flags);
}

static bool con_flag_test_and_clear(struct ceph_connection *con,
                                        unsigned long con_flag)
{
        BUG_ON(!con_flag_valid(con_flag));

        return test_and_clear_bit(con_flag, &con->flags);
}

static bool con_flag_test_and_set(struct ceph_connection *con,
                                        unsigned long con_flag)
{
        BUG_ON(!con_flag_valid(con_flag));

        return test_and_set_bit(con_flag, &con->flags);
}

/* Slab caches for frequently-allocated structures */

static struct kmem_cache        *ceph_msg_cache;
static struct kmem_cache        *ceph_msg_data_cache;

/* static tag bytes (protocol control messages) */
static char tag_msg = CEPH_MSGR_TAG_MSG;
static char tag_ack = CEPH_MSGR_TAG_ACK;
static char tag_keepalive = CEPH_MSGR_TAG_KEEPALIVE;

#ifdef CONFIG_LOCKDEP
static struct lock_class_key socket_class;
#endif

/*
 * When skipping (ignoring) a block of input we read it into a "skip
 * buffer," which is this many bytes in size.
 */
#define SKIP_BUF_SIZE   1024

static void queue_con(struct ceph_connection *con);
static void cancel_con(struct ceph_connection *con);
static void con_work(struct work_struct *);
static void con_fault(struct ceph_connection *con);

/*
 * Nicely render a sockaddr as a string.  An array of formatted
 * strings is used, to approximate reentrancy.
 */
#define ADDR_STR_COUNT_LOG      5       /* log2(# address strings in array) */
#define ADDR_STR_COUNT          (1 << ADDR_STR_COUNT_LOG)
#define ADDR_STR_COUNT_MASK     (ADDR_STR_COUNT - 1)
#define MAX_ADDR_STR_LEN        64      /* 54 is enough */

static char addr_str[ADDR_STR_COUNT][MAX_ADDR_STR_LEN];
static atomic_t addr_str_seq = ATOMIC_INIT(0);

static struct page *zero_page;          /* used in certain error cases */

const char *ceph_pr_addr(const struct sockaddr_storage *ss)
{
        int i;
        char *s;
        struct sockaddr_in *in4 = (struct sockaddr_in *) ss;
        struct sockaddr_in6 *in6 = (struct sockaddr_in6 *) ss;

        i = atomic_inc_return(&addr_str_seq) & ADDR_STR_COUNT_MASK;
        s = addr_str[i];

        switch (ss->ss_family) {
        case AF_INET:
                snprintf(s, MAX_ADDR_STR_LEN, "%pI4:%hu", &in4->sin_addr,
                         ntohs(in4->sin_port));
                break;

        case AF_INET6:
                snprintf(s, MAX_ADDR_STR_LEN, "[%pI6c]:%hu", &in6->sin6_addr,
                         ntohs(in6->sin6_port));
                break;

        default:
                snprintf(s, MAX_ADDR_STR_LEN, "(unknown sockaddr family %hu)",
                         ss->ss_family);
        }

        return s;
}
EXPORT_SYMBOL(ceph_pr_addr);

static void encode_my_addr(struct ceph_messenger *msgr)
{
        memcpy(&msgr->my_enc_addr, &msgr->inst.addr, sizeof(msgr->my_enc_addr));
        ceph_encode_addr(&msgr->my_enc_addr);
}

/*
 * work queue for all reading and writing to/from the socket.
 */
static struct workqueue_struct *ceph_msgr_wq;

static int ceph_msgr_slab_init(void)
{
        BUG_ON(ceph_msg_cache);
        ceph_msg_cache = kmem_cache_create("ceph_msg",
                                        sizeof (struct ceph_msg),
                                        __alignof__(struct ceph_msg), 0, NULL);

        if (!ceph_msg_cache)
                return -ENOMEM;

        BUG_ON(ceph_msg_data_cache);
        ceph_msg_data_cache = kmem_cache_create("ceph_msg_data",
                                        sizeof (struct ceph_msg_data),
                                        __alignof__(struct ceph_msg_data),
                                        0, NULL);
        if (ceph_msg_data_cache)
                return 0;

        kmem_cache_destroy(ceph_msg_cache);
        ceph_msg_cache = NULL;

        return -ENOMEM;
}

static void ceph_msgr_slab_exit(void)
{
        BUG_ON(!ceph_msg_data_cache);
        kmem_cache_destroy(ceph_msg_data_cache);
        ceph_msg_data_cache = NULL;

        BUG_ON(!ceph_msg_cache);
        kmem_cache_destroy(ceph_msg_cache);
        ceph_msg_cache = NULL;
}

static void _ceph_msgr_exit(void)
{
        if (ceph_msgr_wq) {
                destroy_workqueue(ceph_msgr_wq);
                ceph_msgr_wq = NULL;
        }

        ceph_msgr_slab_exit();

        BUG_ON(zero_page == NULL);
        kunmap(zero_page);
        page_cache_release(zero_page);
        zero_page = NULL;
}

int ceph_msgr_init(void)
{
        BUG_ON(zero_page != NULL);
        zero_page = ZERO_PAGE(0);
        page_cache_get(zero_page);

        if (ceph_msgr_slab_init())
                return -ENOMEM;

        /*
         * The number of active work items is limited by the number of
         * connections, so leave @max_active at default.
         */
        ceph_msgr_wq = alloc_workqueue("ceph-msgr", WQ_MEM_RECLAIM, 0);
        if (ceph_msgr_wq)
                return 0;

        pr_err("msgr_init failed to create workqueue\n");
        _ceph_msgr_exit();

        return -ENOMEM;
}
EXPORT_SYMBOL(ceph_msgr_init);

void ceph_msgr_exit(void)
{
        BUG_ON(ceph_msgr_wq == NULL);

        _ceph_msgr_exit();
}
EXPORT_SYMBOL(ceph_msgr_exit);

void ceph_msgr_flush(void)
{
        flush_workqueue(ceph_msgr_wq);
}
EXPORT_SYMBOL(ceph_msgr_flush);

/* Connection socket state transition functions */

static void con_sock_state_init(struct ceph_connection *con)
{
        int old_state;

        old_state = atomic_xchg(&con->sock_state, CON_SOCK_STATE_CLOSED);
        if (WARN_ON(old_state != CON_SOCK_STATE_NEW))
                printk("%s: unexpected old state %d\n", __func__, old_state);
        dout("%s con %p sock %d -> %d\n", __func__, con, old_state,
             CON_SOCK_STATE_CLOSED);
}

static void con_sock_state_connecting(struct ceph_connection *con)
{
        int old_state;

        old_state = atomic_xchg(&con->sock_state, CON_SOCK_STATE_CONNECTING);
        if (WARN_ON(old_state != CON_SOCK_STATE_CLOSED))
                printk("%s: unexpected old state %d\n", __func__, old_state);
        dout("%s con %p sock %d -> %d\n", __func__, con, old_state,
             CON_SOCK_STATE_CONNECTING);
}

static void con_sock_state_connected(struct ceph_connection *con)
{
        int old_state;

        old_state = atomic_xchg(&con->sock_state, CON_SOCK_STATE_CONNECTED);
        if (WARN_ON(old_state != CON_SOCK_STATE_CONNECTING))
                printk("%s: unexpected old state %d\n", __func__, old_state);
        dout("%s con %p sock %d -> %d\n", __func__, con, old_state,
             CON_SOCK_STATE_CONNECTED);
}

static void con_sock_state_closing(struct ceph_connection *con)
{
        int old_state;

        old_state = atomic_xchg(&con->sock_state, CON_SOCK_STATE_CLOSING);
        if (WARN_ON(old_state != CON_SOCK_STATE_CONNECTING &&
                        old_state != CON_SOCK_STATE_CONNECTED &&
                        old_state != CON_SOCK_STATE_CLOSING))
                printk("%s: unexpected old state %d\n", __func__, old_state);
        dout("%s con %p sock %d -> %d\n", __func__, con, old_state,
             CON_SOCK_STATE_CLOSING);
}

static void con_sock_state_closed(struct ceph_connection *con)
{
        int old_state;

        old_state = atomic_xchg(&con->sock_state, CON_SOCK_STATE_CLOSED);
        if (WARN_ON(old_state != CON_SOCK_STATE_CONNECTED &&
                    old_state != CON_SOCK_STATE_CLOSING &&
                    old_state != CON_SOCK_STATE_CONNECTING &&
                    old_state != CON_SOCK_STATE_CLOSED))
                printk("%s: unexpected old state %d\n", __func__, old_state);
        dout("%s con %p sock %d -> %d\n", __func__, con, old_state,
             CON_SOCK_STATE_CLOSED);
}

/*
 * socket callback functions
 */

/* data available on socket, or listen socket received a connect */
static void ceph_sock_data_ready(struct sock *sk)
{
        struct ceph_connection *con = sk->sk_user_data;
        if (atomic_read(&con->msgr->stopping)) {
                return;
        }

        if (sk->sk_state != TCP_CLOSE_WAIT) {
                dout("%s on %p state = %lu, queueing work\n", __func__,
                     con, con->state);
                queue_con(con);
        }
}

/* socket has buffer space for writing */
static void ceph_sock_write_space(struct sock *sk)
{
        struct ceph_connection *con = sk->sk_user_data;

        /* only queue to workqueue if there is data we want to write,
         * and there is sufficient space in the socket buffer to accept
         * more data.  clear SOCK_NOSPACE so that ceph_sock_write_space()
         * doesn't get called again until try_write() fills the socket
         * buffer. See net/ipv4/tcp_input.c:tcp_check_space()
         * and net/core/stream.c:sk_stream_write_space().
         */
        if (con_flag_test(con, CON_FLAG_WRITE_PENDING)) {
                if (sk_stream_is_writeable(sk)) {
                        dout("%s %p queueing write work\n", __func__, con);
                        clear_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
                        queue_con(con);
                }
        } else {
                dout("%s %p nothing to write\n", __func__, con);
        }
}

/* socket's state has changed */
static void ceph_sock_state_change(struct sock *sk)
{
        struct ceph_connection *con = sk->sk_user_data;

        dout("%s %p state = %lu sk_state = %u\n", __func__,
             con, con->state, sk->sk_state);

        switch (sk->sk_state) {
        case TCP_CLOSE:
                dout("%s TCP_CLOSE\n", __func__);
        case TCP_CLOSE_WAIT:
                dout("%s TCP_CLOSE_WAIT\n", __func__);
                con_sock_state_closing(con);
                con_flag_set(con, CON_FLAG_SOCK_CLOSED);
                queue_con(con);
                break;
        case TCP_ESTABLISHED:
                dout("%s TCP_ESTABLISHED\n", __func__);
                con_sock_state_connected(con);
                queue_con(con);
                break;
        default:        /* Everything else is uninteresting */
                break;
        }
}

/*
 * set up socket callbacks
 */
static void set_sock_callbacks(struct socket *sock,
                               struct ceph_connection *con)
{
        struct sock *sk = sock->sk;
        sk->sk_user_data = con;
        sk->sk_data_ready = ceph_sock_data_ready;
        sk->sk_write_space = ceph_sock_write_space;
        sk->sk_state_change = ceph_sock_state_change;
}


/*
 * socket helpers
 */

/*
 * initiate connection to a remote socket.
 */
static int ceph_tcp_connect(struct ceph_connection *con)
{
        struct sockaddr_storage *paddr = &con->peer_addr.in_addr;
        struct socket *sock;
        int ret;

        BUG_ON(con->sock);
        ret = sock_create_kern(con->peer_addr.in_addr.ss_family, SOCK_STREAM,
                               IPPROTO_TCP, &sock);
        if (ret)
                return ret;
        sock->sk->sk_allocation = GFP_NOFS | __GFP_MEMALLOC;

#ifdef CONFIG_LOCKDEP
        lockdep_set_class(&sock->sk->sk_lock, &socket_class);
#endif

        set_sock_callbacks(sock, con);

        dout("connect %s\n", ceph_pr_addr(&con->peer_addr.in_addr));

        con_sock_state_connecting(con);
        ret = sock->ops->connect(sock, (struct sockaddr *)paddr, sizeof(*paddr),
                                 O_NONBLOCK);
        if (ret == -EINPROGRESS) {
                dout("connect %s EINPROGRESS sk_state = %u\n",
                     ceph_pr_addr(&con->peer_addr.in_addr),
                     sock->sk->sk_state);
        } else if (ret < 0) {
                pr_err("connect %s error %d\n",
                       ceph_pr_addr(&con->peer_addr.in_addr), ret);
                sock_release(sock);
                con->error_msg = "connect error";

                return ret;
        }

        sk_set_memalloc(sock->sk);

        con->sock = sock;
        return 0;
}

static int ceph_tcp_recvmsg(struct socket *sock, void *buf, size_t len)
{
        struct kvec iov = {buf, len};
        struct msghdr msg = { .msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL };
        int r;

        r = kernel_recvmsg(sock, &msg, &iov, 1, len, msg.msg_flags);
        if (r == -EAGAIN)
                r = 0;
        return r;
}

static int ceph_tcp_recvpage(struct socket *sock, struct page *page,
                     int page_offset, size_t length)
{
        void *kaddr;
        int ret;

        BUG_ON(page_offset + length > PAGE_SIZE);

        kaddr = kmap(page);
        BUG_ON(!kaddr);
        ret = ceph_tcp_recvmsg(sock, kaddr + page_offset, length);
        kunmap(page);

        return ret;
}

/*
 * write something.  @more is true if caller will be sending more data
 * shortly.
 */
static int ceph_tcp_sendmsg(struct socket *sock, struct kvec *iov,
                     size_t kvlen, size_t len, int more)
{
        struct msghdr msg = { .msg_flags = MSG_DONTWAIT | MSG_NOSIGNAL };
        int r;

        if (more)
                msg.msg_flags |= MSG_MORE;
        else
                msg.msg_flags |= MSG_EOR;  /* superfluous, but what the hell */

        r = kernel_sendmsg(sock, &msg, iov, kvlen, len);
        if (r == -EAGAIN)
                r = 0;
        return r;
}

static int __ceph_tcp_sendpage(struct socket *sock, struct page *page,
                     int offset, size_t size, bool more)
{
        int flags = MSG_DONTWAIT | MSG_NOSIGNAL | (more ? MSG_MORE : MSG_EOR);
        int ret;

        ret = kernel_sendpage(sock, page, offset, size, flags);
        if (ret == -EAGAIN)
                ret = 0;

        return ret;
}

static int ceph_tcp_sendpage(struct socket *sock, struct page *page,
                     int offset, size_t size, bool more)
{
        int ret;
        struct kvec iov;

        /* sendpage cannot properly handle pages with page_count == 0,
         * we need to fallback to sendmsg if that's the case */
        if (page_count(page) >= 1)
                return __ceph_tcp_sendpage(sock, page, offset, size, more);

        iov.iov_base = kmap(page) + offset;
        iov.iov_len = size;
        ret = ceph_tcp_sendmsg(sock, &iov, 1, size, more);
        kunmap(page);

        return ret;
}

/*
 * Shutdown/close the socket for the given connection.
 */
static int con_close_socket(struct ceph_connection *con)
{
        int rc = 0;

        dout("con_close_socket on %p sock %p\n", con, con->sock);
        if (con->sock) {
                rc = con->sock->ops->shutdown(con->sock, SHUT_RDWR);
                sock_release(con->sock);
                con->sock = NULL;
        }

        /*
         * Forcibly clear the SOCK_CLOSED flag.  It gets set
         * independent of the connection mutex, and we could have
         * received a socket close event before we had the chance to
         * shut the socket down.
         */
        con_flag_clear(con, CON_FLAG_SOCK_CLOSED);

        con_sock_state_closed(con);
        return rc;
}

/*
 * Reset a connection.  Discard all incoming and outgoing messages
 * and clear *_seq state.
 */
static void ceph_msg_remove(struct ceph_msg *msg)
{
        list_del_init(&msg->list_head);
        BUG_ON(msg->con == NULL);
        msg->con->ops->put(msg->con);
        msg->con = NULL;

        ceph_msg_put(msg);
}
static void ceph_msg_remove_list(struct list_head *head)
{
        while (!list_empty(head)) {
                struct ceph_msg *msg = list_first_entry(head, struct ceph_msg,
                                                        list_head);
                ceph_msg_remove(msg);
        }
}

static void reset_connection(struct ceph_connection *con)
{
        /* reset connection, out_queue, msg_ and connect_seq */
        /* discard existing out_queue and msg_seq */
        dout("reset_connection %p\n", con);
        ceph_msg_remove_list(&con->out_queue);
        ceph_msg_remove_list(&con->out_sent);

        if (con->in_msg) {
                BUG_ON(con->in_msg->con != con);
                con->in_msg->con = NULL;
                ceph_msg_put(con->in_msg);
                con->in_msg = NULL;
                con->ops->put(con);
        }

        con->connect_seq = 0;
        con->out_seq = 0;
        if (con->out_msg) {
                ceph_msg_put(con->out_msg);
                con->out_msg = NULL;
        }
        con->in_seq = 0;
        con->in_seq_acked = 0;
}

/*
 * mark a peer down.  drop any open connections.
 */
void ceph_con_close(struct ceph_connection *con)
{
        mutex_lock(&con->mutex);
        dout("con_close %p peer %s\n", con,
             ceph_pr_addr(&con->peer_addr.in_addr));
        con->state = CON_STATE_CLOSED;

        con_flag_clear(con, CON_FLAG_LOSSYTX);  /* so we retry next connect */
        con_flag_clear(con, CON_FLAG_KEEPALIVE_PENDING);
        con_flag_clear(con, CON_FLAG_WRITE_PENDING);
        con_flag_clear(con, CON_FLAG_BACKOFF);

        reset_connection(con);
        con->peer_global_seq = 0;
        cancel_con(con);
        con_close_socket(con);
        mutex_unlock(&con->mutex);
}
EXPORT_SYMBOL(ceph_con_close);

/*
 * Reopen a closed connection, with a new peer address.
 */
void ceph_con_open(struct ceph_connection *con,
                   __u8 entity_type, __u64 entity_num,
                   struct ceph_entity_addr *addr)
{
        mutex_lock(&con->mutex);
        dout("con_open %p %s\n", con, ceph_pr_addr(&addr->in_addr));

        WARN_ON(con->state != CON_STATE_CLOSED);
        con->state = CON_STATE_PREOPEN;

        con->peer_name.type = (__u8) entity_type;
        con->peer_name.num = cpu_to_le64(entity_num);

        memcpy(&con->peer_addr, addr, sizeof(*addr));
        con->delay = 0;      /* reset backoff memory */
        mutex_unlock(&con->mutex);
        queue_con(con);
}
EXPORT_SYMBOL(ceph_con_open);

/*
 * return true if this connection ever successfully opened
 */
bool ceph_con_opened(struct ceph_connection *con)
{
        return con->connect_seq > 0;
}

/*
 * initialize a new connection.
 */
void ceph_con_init(struct ceph_connection *con, void *private,
        const struct ceph_connection_operations *ops,
        struct ceph_messenger *msgr)
{
        dout("con_init %p\n", con);
        memset(con, 0, sizeof(*con));
        con->private = private;
        con->ops = ops;
        con->msgr = msgr;

        con_sock_state_init(con);

        mutex_init(&con->mutex);
        INIT_LIST_HEAD(&con->out_queue);
        INIT_LIST_HEAD(&con->out_sent);
        INIT_DELAYED_WORK(&con->work, con_work);

        con->state = CON_STATE_CLOSED;
}
EXPORT_SYMBOL(ceph_con_init);


/*
 * We maintain a global counter to order connection attempts.  Get
 * a unique seq greater than @gt.
 */
static u32 get_global_seq(struct ceph_messenger *msgr, u32 gt)
{
        u32 ret;

        spin_lock(&msgr->global_seq_lock);
        if (msgr->global_seq < gt)
                msgr->global_seq = gt;
        ret = ++msgr->global_seq;
        spin_unlock(&msgr->global_seq_lock);
        return ret;
}

static void con_out_kvec_reset(struct ceph_connection *con)
{
        con->out_kvec_left = 0;
        con->out_kvec_bytes = 0;
        con->out_kvec_cur = &con->out_kvec[0];
}

static void con_out_kvec_add(struct ceph_connection *con,
                                size_t size, void *data)
{
        int index;

        index = con->out_kvec_left;
        BUG_ON(index >= ARRAY_SIZE(con->out_kvec));

        con->out_kvec[index].iov_len = size;
        con->out_kvec[index].iov_base = data;
        con->out_kvec_left++;
        con->out_kvec_bytes += size;
}

#ifdef CONFIG_BLOCK

/*
 * For a bio data item, a piece is whatever remains of the next
 * entry in the current bio iovec, or the first entry in the next
 * bio in the list.
 */
static void ceph_msg_data_bio_cursor_init(struct ceph_msg_data_cursor *cursor,
                                        size_t length)
{
        struct ceph_msg_data *data = cursor->data;
        struct bio *bio;

        BUG_ON(data->type != CEPH_MSG_DATA_BIO);

        bio = data->bio;
        BUG_ON(!bio);

        cursor->resid = min(length, data->bio_length);
        cursor->bio = bio;
        cursor->bvec_iter = bio->bi_iter;
        cursor->last_piece =
                cursor->resid <= bio_iter_len(bio, cursor->bvec_iter);
}

static struct page *ceph_msg_data_bio_next(struct ceph_msg_data_cursor *cursor,
                                                size_t *page_offset,
                                                size_t *length)
{
        struct ceph_msg_data *data = cursor->data;
        struct bio *bio;
        struct bio_vec bio_vec;

        BUG_ON(data->type != CEPH_MSG_DATA_BIO);

        bio = cursor->bio;
        BUG_ON(!bio);

        bio_vec = bio_iter_iovec(bio, cursor->bvec_iter);

        *page_offset = (size_t) bio_vec.bv_offset;
        BUG_ON(*page_offset >= PAGE_SIZE);
        if (cursor->last_piece) /* pagelist offset is always 0 */
                *length = cursor->resid;
        else
                *length = (size_t) bio_vec.bv_len;
        BUG_ON(*length > cursor->resid);
        BUG_ON(*page_offset + *length > PAGE_SIZE);

        return bio_vec.bv_page;
}

static bool ceph_msg_data_bio_advance(struct ceph_msg_data_cursor *cursor,
                                        size_t bytes)
{
        struct bio *bio;
        struct bio_vec bio_vec;

        BUG_ON(cursor->data->type != CEPH_MSG_DATA_BIO);

        bio = cursor->bio;
        BUG_ON(!bio);

        bio_vec = bio_iter_iovec(bio, cursor->bvec_iter);

        /* Advance the cursor offset */

        BUG_ON(cursor->resid < bytes);
        cursor->resid -= bytes;

        bio_advance_iter(bio, &cursor->bvec_iter, bytes);

        if (bytes < bio_vec.bv_len)
                return false;   /* more bytes to process in this segment */

        /* Move on to the next segment, and possibly the next bio */

        if (!cursor->bvec_iter.bi_size) {
                bio = bio->bi_next;
                cursor->bio = bio;
                if (bio)
                        cursor->bvec_iter = bio->bi_iter;
                else
                        memset(&cursor->bvec_iter, 0,
                               sizeof(cursor->bvec_iter));
        }

        if (!cursor->last_piece) {
                BUG_ON(!cursor->resid);
                BUG_ON(!bio);
                /* A short read is OK, so use <= rather than == */
                if (cursor->resid <= bio_iter_len(bio, cursor->bvec_iter))
                        cursor->last_piece = true;
        }

        return true;
}
#endif /* CONFIG_BLOCK */

/*
 * For a page array, a piece comes from the first page in the array
 * that has not already been fully consumed.
 */
static void ceph_msg_data_pages_cursor_init(struct ceph_msg_data_cursor *cursor,
                                        size_t length)
{
        struct ceph_msg_data *data = cursor->data;
        int page_count;

        BUG_ON(data->type != CEPH_MSG_DATA_PAGES);

        BUG_ON(!data->pages);
        BUG_ON(!data->length);

        cursor->resid = min(length, data->length);
        page_count = calc_pages_for(data->alignment, (u64)data->length);
        cursor->page_offset = data->alignment & ~PAGE_MASK;
        cursor->page_index = 0;
        BUG_ON(page_count > (int)USHRT_MAX);
        cursor->page_count = (unsigned short)page_count;
        BUG_ON(length > SIZE_MAX - cursor->page_offset);
        cursor->last_piece = cursor->page_offset + cursor->resid <= PAGE_SIZE;
}

static struct page *
ceph_msg_data_pages_next(struct ceph_msg_data_cursor *cursor,
                                        size_t *page_offset, size_t *length)
{
        struct ceph_msg_data *data = cursor->data;

        BUG_ON(data->type != CEPH_MSG_DATA_PAGES);

        BUG_ON(cursor->page_index >= cursor->page_count);
        BUG_ON(cursor->page_offset >= PAGE_SIZE);

        *page_offset = cursor->page_offset;
        if (cursor->last_piece)
                *length = cursor->resid;
        else
                *length = PAGE_SIZE - *page_offset;

        return data->pages[cursor->page_index];
}

static bool ceph_msg_data_pages_advance(struct ceph_msg_data_cursor *cursor,
                                                size_t bytes)
{
        BUG_ON(cursor->data->type != CEPH_MSG_DATA_PAGES);

        BUG_ON(cursor->page_offset + bytes > PAGE_SIZE);

        /* Advance the cursor page offset */

        cursor->resid -= bytes;
        cursor->page_offset = (cursor->page_offset + bytes) & ~PAGE_MASK;
        if (!bytes || cursor->page_offset)
                return false;   /* more bytes to process in the current page */

        if (!cursor->resid)
                return false;   /* no more data */

        /* Move on to the next page; offset is already at 0 */

        BUG_ON(cursor->page_index >= cursor->page_count);
        cursor->page_index++;
        cursor->last_piece = cursor->resid <= PAGE_SIZE;

        return true;
}

/*
 * For a pagelist, a piece is whatever remains to be consumed in the
 * first page in the list, or the front of the next page.
 */
static void
ceph_msg_data_pagelist_cursor_init(struct ceph_msg_data_cursor *cursor,
                                        size_t length)
{
        struct ceph_msg_data *data = cursor->data;
        struct ceph_pagelist *pagelist;
        struct page *page;

        BUG_ON(data->type != CEPH_MSG_DATA_PAGELIST);

        pagelist = data->pagelist;
        BUG_ON(!pagelist);

        if (!length)
                return;         /* pagelist can be assigned but empty */

        BUG_ON(list_empty(&pagelist->head));
        page = list_first_entry(&pagelist->head, struct page, lru);

        cursor->resid = min(length, pagelist->length);
        cursor->page = page;
        cursor->offset = 0;
        cursor->last_piece = cursor->resid <= PAGE_SIZE;
}

static struct page *
ceph_msg_data_pagelist_next(struct ceph_msg_data_cursor *cursor,
                                size_t *page_offset, size_t *length)
{
        struct ceph_msg_data *data = cursor->data;
        struct ceph_pagelist *pagelist;

        BUG_ON(data->type != CEPH_MSG_DATA_PAGELIST);

        pagelist = data->pagelist;
        BUG_ON(!pagelist);

        BUG_ON(!cursor->page);
        BUG_ON(cursor->offset + cursor->resid != pagelist->length);

        /* offset of first page in pagelist is always 0 */
        *page_offset = cursor->offset & ~PAGE_MASK;
        if (cursor->last_piece)
                *length = cursor->resid;
        else
                *length = PAGE_SIZE - *page_offset;

        return cursor->page;
}

static bool ceph_msg_data_pagelist_advance(struct ceph_msg_data_cursor *cursor,
                                                size_t bytes)
{
        struct ceph_msg_data *data = cursor->data;
        struct ceph_pagelist *pagelist;

        BUG_ON(data->type != CEPH_MSG_DATA_PAGELIST);

        pagelist = data->pagelist;
        BUG_ON(!pagelist);

        BUG_ON(cursor->offset + cursor->resid != pagelist->length);
        BUG_ON((cursor->offset & ~PAGE_MASK) + bytes > PAGE_SIZE);

        /* Advance the cursor offset */

        cursor->resid -= bytes;
        cursor->offset += bytes;
        /* offset of first page in pagelist is always 0 */
        if (!bytes || cursor->offset & ~PAGE_MASK)
                return false;   /* more bytes to process in the current page */

        if (!cursor->resid)
                return false;   /* no more data */

        /* Move on to the next page */

        BUG_ON(list_is_last(&cursor->page->lru, &pagelist->head));
        cursor->page = list_entry_next(cursor->page, lru);
        cursor->last_piece = cursor->resid <= PAGE_SIZE;

        return true;
}

/*
 * Message data is handled (sent or received) in pieces, where each
 * piece resides on a single page.  The network layer might not
 * consume an entire piece at once.  A data item's cursor keeps
 * track of which piece is next to process and how much remains to
 * be processed in that piece.  It also tracks whether the current
 * piece is the last one in the data item.
 */
static void __ceph_msg_data_cursor_init(struct ceph_msg_data_cursor *cursor)
{
        size_t length = cursor->total_resid;

        switch (cursor->data->type) {
        case CEPH_MSG_DATA_PAGELIST:
                ceph_msg_data_pagelist_cursor_init(cursor, length);
                break;
        case CEPH_MSG_DATA_PAGES:
                ceph_msg_data_pages_cursor_init(cursor, length);
                break;
#ifdef CONFIG_BLOCK
        case CEPH_MSG_DATA_BIO:
                ceph_msg_data_bio_cursor_init(cursor, length);
                break;
#endif /* CONFIG_BLOCK */
        case CEPH_MSG_DATA_NONE:
        default:
                /* BUG(); */
                break;
        }
        cursor->need_crc = true;
}

static void ceph_msg_data_cursor_init(struct ceph_msg *msg, size_t length)
{
        struct ceph_msg_data_cursor *cursor = &msg->cursor;
        struct ceph_msg_data *data;

        BUG_ON(!length);
        BUG_ON(length > msg->data_length);
        BUG_ON(list_empty(&msg->data));

        cursor->data_head = &msg->data;
        cursor->total_resid = length;
        data = list_first_entry(&msg->data, struct ceph_msg_data, links);
        cursor->data = data;

        __ceph_msg_data_cursor_init(cursor);
}

/*
 * Return the page containing the next piece to process for a given
 * data item, and supply the page offset and length of that piece.
 * Indicate whether this is the last piece in this data item.
 */
static struct page *ceph_msg_data_next(struct ceph_msg_data_cursor *cursor,
                                        size_t *page_offset, size_t *length,
                                        bool *last_piece)
{
        struct page *page;

        switch (cursor->data->type) {
        case CEPH_MSG_DATA_PAGELIST:
                page = ceph_msg_data_pagelist_next(cursor, page_offset, length);
                break;
        case CEPH_MSG_DATA_PAGES:
                page = ceph_msg_data_pages_next(cursor, page_offset, length);
                break;
#ifdef CONFIG_BLOCK
        case CEPH_MSG_DATA_BIO:
                page = ceph_msg_data_bio_next(cursor, page_offset, length);
                break;
#endif /* CONFIG_BLOCK */
        case CEPH_MSG_DATA_NONE:
        default:
                page = NULL;
                break;
        }
        BUG_ON(!page);
        BUG_ON(*page_offset + *length > PAGE_SIZE);
        BUG_ON(!*length);
        if (last_piece)
                *last_piece = cursor->last_piece;

        return page;
}

/*
 * Returns true if the result moves the cursor on to the next piece
 * of the data item.
 */
static bool ceph_msg_data_advance(struct ceph_msg_data_cursor *cursor,
                                size_t bytes)
{
        bool new_piece;

        BUG_ON(bytes > cursor->resid);
        switch (cursor->data->type) {
        case CEPH_MSG_DATA_PAGELIST:
                new_piece = ceph_msg_data_pagelist_advance(cursor, bytes);
                break;
        case CEPH_MSG_DATA_PAGES:
                new_piece = ceph_msg_data_pages_advance(cursor, bytes);
                break;
#ifdef CONFIG_BLOCK
        case CEPH_MSG_DATA_BIO:
                new_piece = ceph_msg_data_bio_advance(cursor, bytes);
                break;
#endif /* CONFIG_BLOCK */
        case CEPH_MSG_DATA_NONE:
        default:
                BUG();
                break;
        }
        cursor->total_resid -= bytes;

        if (!cursor->resid && cursor->total_resid) {
                WARN_ON(!cursor->last_piece);
                BUG_ON(list_is_last(&cursor->data->links, cursor->data_head));
                cursor->data = list_entry_next(cursor->data, links);
                __ceph_msg_data_cursor_init(cursor);
                new_piece = true;
        }
        cursor->need_crc = new_piece;

        return new_piece;
}

static void prepare_message_data(struct ceph_msg *msg, u32 data_len)
{
        BUG_ON(!msg);
        BUG_ON(!data_len);

        /* Initialize data cursor */

        ceph_msg_data_cursor_init(msg, (size_t)data_len);
}

/*
 * Prepare footer for currently outgoing message, and finish things
 * off.  Assumes out_kvec* are already valid.. we just add on to the end.
 */
static void prepare_write_message_footer(struct ceph_connection *con)
{
        struct ceph_msg *m = con->out_msg;
        int v = con->out_kvec_left;

        m->footer.flags |= CEPH_MSG_FOOTER_COMPLETE;

        dout("prepare_write_message_footer %p\n", con);
        con->out_kvec_is_msg = true;
        con->out_kvec[v].iov_base = &m->footer;
        con->out_kvec[v].iov_len = sizeof(m->footer);
        con->out_kvec_bytes += sizeof(m->footer);
        con->out_kvec_left++;
        con->out_more = m->more_to_follow;
        con->out_msg_done = true;
}

/*
 * Prepare headers for the next outgoing message.
 */
static void prepare_write_message(struct ceph_connection *con)
{
        struct ceph_msg *m;
        u32 crc;

        con_out_kvec_reset(con);
        con->out_kvec_is_msg = true;
        con->out_msg_done = false;

        /* Sneak an ack in there first?  If we can get it into the same
         * TCP packet that's a good thing. */
        if (con->in_seq > con->in_seq_acked) {
                con->in_seq_acked = con->in_seq;
                con_out_kvec_add(con, sizeof (tag_ack), &tag_ack);
                con->out_temp_ack = cpu_to_le64(con->in_seq_acked);
                con_out_kvec_add(con, sizeof (con->out_temp_ack),
                        &con->out_temp_ack);
        }

        BUG_ON(list_empty(&con->out_queue));
        m = list_first_entry(&con->out_queue, struct ceph_msg, list_head);
        con->out_msg = m;
        BUG_ON(m->con != con);

        /* put message on sent list */
        ceph_msg_get(m);
        list_move_tail(&m->list_head, &con->out_sent);

        /*
         * only assign outgoing seq # if we haven't sent this message
         * yet.  if it is requeued, resend with it's original seq.
         */
        if (m->needs_out_seq) {
                m->hdr.seq = cpu_to_le64(++con->out_seq);
                m->needs_out_seq = false;
        }
        WARN_ON(m->data_length != le32_to_cpu(m->hdr.data_len));

        dout("prepare_write_message %p seq %lld type %d len %d+%d+%zd\n",
             m, con->out_seq, le16_to_cpu(m->hdr.type),
             le32_to_cpu(m->hdr.front_len), le32_to_cpu(m->hdr.middle_len),
             m->data_length);
        BUG_ON(le32_to_cpu(m->hdr.front_len) != m->front.iov_len);

        /* tag + hdr + front + middle */
        con_out_kvec_add(con, sizeof (tag_msg), &tag_msg);
        con_out_kvec_add(con, sizeof (m->hdr), &m->hdr);
        con_out_kvec_add(con, m->front.iov_len, m->front.iov_base);

        if (m->middle)
                con_out_kvec_add(con, m->middle->vec.iov_len,
                        m->middle->vec.iov_base);

        /* fill in crc (except data pages), footer */
        crc = crc32c(0, &m->hdr, offsetof(struct ceph_msg_header, crc));
        con->out_msg->hdr.crc = cpu_to_le32(crc);
        con->out_msg->footer.flags = 0;

        crc = crc32c(0, m->front.iov_base, m->front.iov_len);
        con->out_msg->footer.front_crc = cpu_to_le32(crc);
        if (m->middle) {
                crc = crc32c(0, m->middle->vec.iov_base,
                                m->middle->vec.iov_len);
                con->out_msg->footer.middle_crc = cpu_to_le32(crc);
        } else
                con->out_msg->footer.middle_crc = 0;
        dout("%s front_crc %u middle_crc %u\n", __func__,
             le32_to_cpu(con->out_msg->footer.front_crc),
             le32_to_cpu(con->out_msg->footer.middle_crc));

        /* is there a data payload? */
        con->out_msg->footer.data_crc = 0;
        if (m->data_length) {
                prepare_message_data(con->out_msg, m->data_length);
                con->out_more = 1;  /* data + footer will follow */
        } else {
                /* no, queue up footer too and be done */
                prepare_write_message_footer(con);
        }

        con_flag_set(con, CON_FLAG_WRITE_PENDING);
}

/*
 * Prepare an ack.
 */
static void prepare_write_ack(struct ceph_connection *con)
{
        dout("prepare_write_ack %p %llu -> %llu\n", con,
             con->in_seq_acked, con->in_seq);
        con->in_seq_acked = con->in_seq;

        con_out_kvec_reset(con);

        con_out_kvec_add(con, sizeof (tag_ack), &tag_ack);

        con->out_temp_ack = cpu_to_le64(con->in_seq_acked);
        con_out_kvec_add(con, sizeof (con->out_temp_ack),
                                &con->out_temp_ack);

        con->out_more = 1;  /* more will follow.. eventually.. */
        con_flag_set(con, CON_FLAG_WRITE_PENDING);
}

/*
 * Prepare to share the seq during handshake
 */
static void prepare_write_seq(struct ceph_connection *con)
{
        dout("prepare_write_seq %p %llu -> %llu\n", con,
             con->in_seq_acked, con->in_seq);
        con->in_seq_acked = con->in_seq;

        con_out_kvec_reset(con);

        con->out_temp_ack = cpu_to_le64(con->in_seq_acked);
        con_out_kvec_add(con, sizeof (con->out_temp_ack),
                         &con->out_temp_ack);

        con_flag_set(con, CON_FLAG_WRITE_PENDING);
}

/*
 * Prepare to write keepalive byte.
 */
static void prepare_write_keepalive(struct ceph_connection *con)
{
        dout("prepare_write_keepalive %p\n", con);
        con_out_kvec_reset(con);
        con_out_kvec_add(con, sizeof (tag_keepalive), &tag_keepalive);
        con_flag_set(con, CON_FLAG_WRITE_PENDING);
}

/*
 * Connection negotiation.
 */

static struct ceph_auth_handshake *get_connect_authorizer(struct ceph_connection *con,
                                                int *auth_proto)
{
        struct ceph_auth_handshake *auth;

        if (!con->ops->get_authorizer) {
                con->out_connect.authorizer_protocol = CEPH_AUTH_UNKNOWN;
                con->out_connect.authorizer_len = 0;
                return NULL;
        }

        /* Can't hold the mutex while getting authorizer */
        mutex_unlock(&con->mutex);
        auth = con->ops->get_authorizer(con, auth_proto, con->auth_retry);
        mutex_lock(&con->mutex);

        if (IS_ERR(auth))
                return auth;
        if (con->state != CON_STATE_NEGOTIATING)
                return ERR_PTR(-EAGAIN);

        con->auth_reply_buf = auth->authorizer_reply_buf;
        con->auth_reply_buf_len = auth->authorizer_reply_buf_len;
        return auth;
}

/*
 * We connected to a peer and are saying hello.
 */
static void prepare_write_banner(struct ceph_connection *con)
{
        con_out_kvec_add(con, strlen(CEPH_BANNER), CEPH_BANNER);
        con_out_kvec_add(con, sizeof (con->msgr->my_enc_addr),
                                        &con->msgr->my_enc_addr);

        con->out_more = 0;
        con_flag_set(con, CON_FLAG_WRITE_PENDING);
}

static int prepare_write_connect(struct ceph_connection *con)
{
        unsigned int global_seq = get_global_seq(con->msgr, 0);
        int proto;
        int auth_proto;
        struct ceph_auth_handshake *auth;

        switch (con->peer_name.type) {
        case CEPH_ENTITY_TYPE_MON:
                proto = CEPH_MONC_PROTOCOL;
                break;
        case CEPH_ENTITY_TYPE_OSD:
                proto = CEPH_OSDC_PROTOCOL;
                break;
        case CEPH_ENTITY_TYPE_MDS:
                proto = CEPH_MDSC_PROTOCOL;
                break;
        default:
                BUG();
        }

        dout("prepare_write_connect %p cseq=%d gseq=%d proto=%d\n", con,
             con->connect_seq, global_seq, proto);

        con->out_connect.features = cpu_to_le64(con->msgr->supported_features);
        con->out_connect.host_type = cpu_to_le32(CEPH_ENTITY_TYPE_CLIENT);
        con->out_connect.connect_seq = cpu_to_le32(con->connect_seq);
        con->out_connect.global_seq = cpu_to_le32(global_seq);
        con->out_connect.protocol_version = cpu_to_le32(proto);
        con->out_connect.flags = 0;

        auth_proto = CEPH_AUTH_UNKNOWN;
        auth = get_connect_authorizer(con, &auth_proto);
        if (IS_ERR(auth))
                return PTR_ERR(auth);

        con->out_connect.authorizer_protocol = cpu_to_le32(auth_proto);
        con->out_connect.authorizer_len = auth ?
                cpu_to_le32(auth->authorizer_buf_len) : 0;

        con_out_kvec_add(con, sizeof (con->out_connect),
                                        &con->out_connect);
        if (auth && auth->authorizer_buf_len)
                con_out_kvec_add(con, auth->authorizer_buf_len,
                                        auth->authorizer_buf);

        con->out_more = 0;
        con_flag_set(con, CON_FLAG_WRITE_PENDING);

        return 0;
}

/*
 * write as much of pending kvecs to the socket as we can.
 *  1 -> done
 *  0 -> socket full, but more to do
 * <0 -> error
 */
static int write_partial_kvec(struct ceph_connection *con)
{
        int ret;

        dout("write_partial_kvec %p %d left\n", con, con->out_kvec_bytes);
        while (con->out_kvec_bytes > 0) {
                ret = ceph_tcp_sendmsg(con->sock, con->out_kvec_cur,
                                       con->out_kvec_left, con->out_kvec_bytes,
                                       con->out_more);
                if (ret <= 0)
                        goto out;
                con->out_kvec_bytes -= ret;
                if (con->out_kvec_bytes == 0)
                        break;            /* done */

                /* account for full iov entries consumed */
                while (ret >= con->out_kvec_cur->iov_len) {
                        BUG_ON(!con->out_kvec_left);
                        ret -= con->out_kvec_cur->iov_len;
                        con->out_kvec_cur++;
                        con->out_kvec_left--;
                }
                /* and for a partially-consumed entry */
                if (ret) {
                        con->out_kvec_cur->iov_len -= ret;
                        con->out_kvec_cur->iov_base += ret;
                }
        }
        con->out_kvec_left = 0;
        con->out_kvec_is_msg = false;
        ret = 1;
out:
        dout("write_partial_kvec %p %d left in %d kvecs ret = %d\n", con,
             con->out_kvec_bytes, con->out_kvec_left, ret);
        return ret;  /* done! */
}

static u32 ceph_crc32c_page(u32 crc, struct page *page,
                                unsigned int page_offset,
                                unsigned int length)
{
        char *kaddr;

        kaddr = kmap(page);
        BUG_ON(kaddr == NULL);
        crc = crc32c(crc, kaddr + page_offset, length);
        kunmap(page);

        return crc;
}
/*
 * Write as much message data payload as we can.  If we finish, queue
 * up the footer.
 *  1 -> done, footer is now queued in out_kvec[].
 *  0 -> socket full, but more to do
 * <0 -> error
 */
static int write_partial_message_data(struct ceph_connection *con)
{
        struct ceph_msg *msg = con->out_msg;
        struct ceph_msg_data_cursor *cursor = &msg->cursor;
        bool do_datacrc = !con->msgr->nocrc;
        u32 crc;

        dout("%s %p msg %p\n", __func__, con, msg);

        if (list_empty(&msg->data))
                return -EINVAL;

        /*
         * Iterate through each page that contains data to be
         * written, and send as much as possible for each.
         *
         * If we are calculating the data crc (the default), we will
         * need to map the page.  If we have no pages, they have
         * been revoked, so use the zero page.
         */
        crc = do_datacrc ? le32_to_cpu(msg->footer.data_crc) : 0;
        while (cursor->resid) {
                struct page *page;
                size_t page_offset;
                size_t length;
                bool last_piece;
                bool need_crc;
                int ret;

                page = ceph_msg_data_next(&msg->cursor, &page_offset, &length,
                                                        &last_piece);
                ret = ceph_tcp_sendpage(con->sock, page, page_offset,
                                      length, last_piece);
                if (ret <= 0) {
                        if (do_datacrc)
                                msg->footer.data_crc = cpu_to_le32(crc);

                        return ret;
                }
                if (do_datacrc && cursor->need_crc)
                        crc = ceph_crc32c_page(crc, page, page_offset, length);
                need_crc = ceph_msg_data_advance(&msg->cursor, (size_t)ret);
        }

        dout("%s %p msg %p done\n", __func__, con, msg);

        /* prepare and queue up footer, too */
        if (do_datacrc)
                msg->footer.data_crc = cpu_to_le32(crc);
        else
                msg->footer.flags |= CEPH_MSG_FOOTER_NOCRC;
        con_out_kvec_reset(con);
        prepare_write_message_footer(con);

        return 1;       /* must return > 0 to indicate success */
}

/*
 * write some zeros
 */
static int write_partial_skip(struct ceph_connection *con)
{
        int ret;

        while (con->out_skip > 0) {
                size_t size = min(con->out_skip, (int) PAGE_CACHE_SIZE);

                ret = ceph_tcp_sendpage(con->sock, zero_page, 0, size, true);
                if (ret <= 0)
                        goto out;
                con->out_skip -= ret;
        }
        ret = 1;
out:
        return ret;
}

/*
 * Prepare to read connection handshake, or an ack.
 */
static void prepare_read_banner(struct ceph_connection *con)
{
        dout("prepare_read_banner %p\n", con);
        con->in_base_pos = 0;
}

static void prepare_read_connect(struct ceph_connection *con)
{
        dout("prepare_read_connect %p\n", con);
        con->in_base_pos = 0;
}

static void prepare_read_ack(struct ceph_connection *con)
{
        dout("prepare_read_ack %p\n", con);
        con->in_base_pos = 0;
}

static void prepare_read_seq(struct ceph_connection *con)
{
        dout("prepare_read_seq %p\n", con);
        con->in_base_pos = 0;
        con->in_tag = CEPH_MSGR_TAG_SEQ;
}

static void prepare_read_tag(struct ceph_connection *con)
{
        dout("prepare_read_tag %p\n", con);
        con->in_base_pos = 0;
        con->in_tag = CEPH_MSGR_TAG_READY;
}

/*
 * Prepare to read a message.
 */
static int prepare_read_message(struct ceph_connection *con)
{
        dout("prepare_read_message %p\n", con);
        BUG_ON(con->in_msg != NULL);
        con->in_base_pos = 0;
        con->in_front_crc = con->in_middle_crc = con->in_data_crc = 0;
        return 0;
}


static int read_partial(struct ceph_connection *con,
                        int end, int size, void *object)
{
        while (con->in_base_pos < end) {
                int left = end - con->in_base_pos;
                int have = size - left;
                int ret = ceph_tcp_recvmsg(con->sock, object + have, left);
                if (ret <= 0)
                        return ret;
                con->in_base_pos += ret;
        }
        return 1;
}


/*
 * Read all or part of the connect-side handshake on a new connection
 */
static int read_partial_banner(struct ceph_connection *con)
{
        int size;
        int end;
        int ret;

        dout("read_partial_banner %p at %d\n", con, con->in_base_pos);

        /* peer's banner */
        size = strlen(CEPH_BANNER);
        end = size;
        ret = read_partial(con, end, size, con->in_banner);
        if (ret <= 0)
                goto out;

        size = sizeof (con->actual_peer_addr);
        end += size;
        ret = read_partial(con, end, size, &con->actual_peer_addr);
        if (ret <= 0)
                goto out;

        size = sizeof (con->peer_addr_for_me);
        end += size;
        ret = read_partial(con, end, size, &con->peer_addr_for_me);
        if (ret <= 0)
                goto out;

out:
        return ret;
}

static int read_partial_connect(struct ceph_connection *con)
{
        int size;
        int end;
        int ret;

        dout("read_partial_connect %p at %d\n", con, con->in_base_pos);

        size = sizeof (con->in_reply);
        end = size;
        ret = read_partial(con, end, size, &con->in_reply);
        if (ret <= 0)
                goto out;

        size = le32_to_cpu(con->in_reply.authorizer_len);
        end += size;
        ret = read_partial(con, end, size, con->auth_reply_buf);
        if (ret <= 0)
                goto out;

        dout("read_partial_connect %p tag %d, con_seq = %u, g_seq = %u\n",
             con, (int)con->in_reply.tag,
             le32_to_cpu(con->in_reply.connect_seq),
             le32_to_cpu(con->in_reply.global_seq));
out:
        return ret;

}

/*
 * Verify the hello banner looks okay.
 */
static int verify_hello(struct ceph_connection *con)
{
        if (memcmp(con->in_banner, CEPH_BANNER, strlen(CEPH_BANNER))) {
                pr_err("connect to %s got bad banner\n",
                       ceph_pr_addr(&con->peer_addr.in_addr));
                con->error_msg = "protocol error, bad banner";
                return -1;
        }
        return 0;
}

static bool addr_is_blank(struct sockaddr_storage *ss)
{
        switch (ss->ss_family) {
        case AF_INET:
                return ((struct sockaddr_in *)ss)->sin_addr.s_addr == 0;
        case AF_INET6:
                return
                     ((struct sockaddr_in6 *)ss)->sin6_addr.s6_addr32[0] == 0 &&
                     ((struct sockaddr_in6 *)ss)->sin6_addr.s6_addr32[1] == 0 &&
                     ((struct sockaddr_in6 *)ss)->sin6_addr.s6_addr32[2] == 0 &&
                     ((struct sockaddr_in6 *)ss)->sin6_addr.s6_addr32[3] == 0;
        }
        return false;
}

static int addr_port(struct sockaddr_storage *ss)
{
        switch (ss->ss_family) {
        case AF_INET:
                return ntohs(((struct sockaddr_in *)ss)->sin_port);
        case AF_INET6:
                return ntohs(((struct sockaddr_in6 *)ss)->sin6_port);
        }
        return 0;
}

static void addr_set_port(struct sockaddr_storage *ss, int p)
{
        switch (ss->ss_family) {
        case AF_INET:
                ((struct sockaddr_in *)ss)->sin_port = htons(p);
                break;
        case AF_INET6:
                ((struct sockaddr_in6 *)ss)->sin6_port = htons(p);
                break;
        }
}

/*
 * Unlike other *_pton function semantics, zero indicates success.
 */
static int ceph_pton(const char *str, size_t len, struct sockaddr_storage *ss,
                char delim, const char **ipend)
{
        struct sockaddr_in *in4 = (struct sockaddr_in *) ss;
        struct sockaddr_in6 *in6 = (struct sockaddr_in6 *) ss;

        memset(ss, 0, sizeof(*ss));

        if (in4_pton(str, len, (u8 *)&in4->sin_addr.s_addr, delim, ipend)) {
                ss->ss_family = AF_INET;
                return 0;
        }

        if (in6_pton(str, len, (u8 *)&in6->sin6_addr.s6_addr, delim, ipend)) {
                ss->ss_family = AF_INET6;
                return 0;
        }

        return -EINVAL;
}

/*
 * Extract hostname string and resolve using kernel DNS facility.
 */
#ifdef CONFIG_CEPH_LIB_USE_DNS_RESOLVER
static int ceph_dns_resolve_name(const char *name, size_t namelen,
                struct sockaddr_storage *ss, char delim, const char **ipend)
{
        const char *end, *delim_p;
        char *colon_p, *ip_addr = NULL;
        int ip_len, ret;

        /*
         * The end of the hostname occurs immediately preceding the delimiter or
         * the port marker (':') where the delimiter takes precedence.
         */
        delim_p = memchr(name, delim, namelen);
        colon_p = memchr(name, ':', namelen);

        if (delim_p && colon_p)
                end = delim_p < colon_p ? delim_p : colon_p;
        else if (!delim_p && colon_p)
                end = colon_p;
        else {
                end = delim_p;
                if (!end) /* case: hostname:/ */
                        end = name + namelen;
        }

        if (end <= name)
                return -EINVAL;

        /* do dns_resolve upcall */
        ip_len = dns_query(NULL, name, end - name, NULL, &ip_addr, NULL);
        if (ip_len > 0)
                ret = ceph_pton(ip_addr, ip_len, ss, -1, NULL);
        else
                ret = -ESRCH;

        kfree(ip_addr);

        *ipend = end;

        pr_info("resolve '%.*s' (ret=%d): %s\n", (int)(end - name), name,
                        ret, ret ? "failed" : ceph_pr_addr(ss));

        return ret;
}
#else
static inline int ceph_dns_resolve_name(const char *name, size_t namelen,
                struct sockaddr_storage *ss, char delim, const char **ipend)
{
        return -EINVAL;
}
#endif

/*
 * Parse a server name (IP or hostname). If a valid IP address is not found
 * then try to extract a hostname to resolve using userspace DNS upcall.
 */
static int ceph_parse_server_name(const char *name, size_t namelen,
                        struct sockaddr_storage *ss, char delim, const char **ipend)
{
        int ret;

        ret = ceph_pton(name, namelen, ss, delim, ipend);
        if (ret)
                ret = ceph_dns_resolve_name(name, namelen, ss, delim, ipend);

        return ret;
}

/*
 * Parse an ip[:port] list into an addr array.  Use the default
 * monitor port if a port isn't specified.
 */
int ceph_parse_ips(const char *c, const char *end,
                   struct ceph_entity_addr *addr,
                   int max_count, int *count)
{
        int i, ret = -EINVAL;
        const char *p = c;

        dout("parse_ips on '%.*s'\n", (int)(end-c), c);
        for (i = 0; i < max_count; i++) {
                const char *ipend;
                struct sockaddr_storage *ss = &addr[i].in_addr;
                int port;
                char delim = ',';

                if (*p == '[') {
                        delim = ']';
                        p++;
                }

                ret = ceph_parse_server_name(p, end - p, ss, delim, &ipend);
                if (ret)
                        goto bad;
                ret = -EINVAL;

                p = ipend;

                if (delim == ']') {
                        if (*p != ']') {
                                dout("missing matching ']'\n");
                                goto bad;
                        }
                        p++;
                }

                /* port? */
                if (p < end && *p == ':') {
                        port = 0;
                        p++;
                        while (p < end && *p >= '0' && *p <= '9') {
                                port = (port * 10) + (*p - '0');
                                p++;
                        }
                        if (port == 0)
                                port = CEPH_MON_PORT;
                        else if (port > 65535)
                                goto bad;
                } else {
                        port = CEPH_MON_PORT;
                }

                addr_set_port(ss, port);

                dout("parse_ips got %s\n", ceph_pr_addr(ss));

                if (p == end)
                        break;
                if (*p != ',')
                        goto bad;
                p++;
        }

        if (p != end)
                goto bad;

        if (count)
                *count = i + 1;
        return 0;

bad:
        pr_err("parse_ips bad ip '%.*s'\n", (int)(end - c), c);
        return ret;
}
EXPORT_SYMBOL(ceph_parse_ips);

static int process_banner(struct ceph_connection *con)
{
        dout("process_banner on %p\n", con);

        if (verify_hello(con) < 0)
                return -1;

        ceph_decode_addr(&con->actual_peer_addr);
        ceph_decode_addr(&con->peer_addr_for_me);

        /*
         * Make sure the other end is who we wanted.  note that the other
         * end may not yet know their ip address, so if it's 0.0.0.0, give
         * them the benefit of the doubt.
         */
        if (memcmp(&con->peer_addr, &con->actual_peer_addr,
                   sizeof(con->peer_addr)) != 0 &&
            !(addr_is_blank(&con->actual_peer_addr.in_addr) &&
              con->actual_peer_addr.nonce == con->peer_addr.nonce)) {
                pr_warn("wrong peer, want %s/%d, got %s/%d\n",
                        ceph_pr_addr(&con->peer_addr.in_addr),
                        (int)le32_to_cpu(con->peer_addr.nonce),
                        ceph_pr_addr(&con->actual_peer_addr.in_addr),
                        (int)le32_to_cpu(con->actual_peer_addr.nonce));
                con->error_msg = "wrong peer at address";
                return -1;
        }

        /*
         * did we learn our address?
         */
        if (addr_is_blank(&con->msgr->inst.addr.in_addr)) {
                int port = addr_port(&con->msgr->inst.addr.in_addr);

                memcpy(&con->msgr->inst.addr.in_addr,
                       &con->peer_addr_for_me.in_addr,
                       sizeof(con->peer_addr_for_me.in_addr));
                addr_set_port(&con->msgr->inst.addr.in_addr, port);
                encode_my_addr(con->msgr);
                dout("process_banner learned my addr is %s\n",
                     ceph_pr_addr(&con->msgr->inst.addr.in_addr));
        }

        return 0;
}

static int process_connect(struct ceph_connection *con)
{
        u64 sup_feat = con->msgr->supported_features;
        u64 req_feat = con->msgr->required_features;
        u64 server_feat = ceph_sanitize_features(
                                le64_to_cpu(con->in_reply.features));
        int ret;

        dout("process_connect on %p tag %d\n", con, (int)con->in_tag);

        switch (con->in_reply.tag) {
        case CEPH_MSGR_TAG_FEATURES:
                pr_err("%s%lld %s feature set mismatch,"
                       " my %llx < server's %llx, missing %llx\n",
                       ENTITY_NAME(con->peer_name),
                       ceph_pr_addr(&con->peer_addr.in_addr),
                       sup_feat, server_feat, server_feat & ~sup_feat);
                con->error_msg = "missing required protocol features";
                reset_connection(con);
                return -1;

        case CEPH_MSGR_TAG_BADPROTOVER:
                pr_err("%s%lld %s protocol version mismatch,"
                       " my %d != server's %d\n",
                       ENTITY_NAME(con->peer_name),
                       ceph_pr_addr(&con->peer_addr.in_addr),
                       le32_to_cpu(con->out_connect.protocol_version),
                       le32_to_cpu(con->in_reply.protocol_version));
                con->error_msg = "protocol version mismatch";
                reset_connection(con);
                return -1;

        case CEPH_MSGR_TAG_BADAUTHORIZER:
                con->auth_retry++;
                dout("process_connect %p got BADAUTHORIZER attempt %d\n", con,
                     con->auth_retry);
                if (con->auth_retry == 2) {
                        con->error_msg = "connect authorization failure";
                        return -1;
                }
                con_out_kvec_reset(con);
                ret = prepare_write_connect(con);
                if (ret < 0)
                        return ret;
                prepare_read_connect(con);
                break;

        case CEPH_MSGR_TAG_RESETSESSION:
                /*
                 * If we connected with a large connect_seq but the peer
                 * has no record of a session with us (no connection, or
                 * connect_seq == 0), they will send RESETSESION to indicate
                 * that they must have reset their session, and may have
                 * dropped messages.
                 */
                dout("process_connect got RESET peer seq %u\n",
                     le32_to_cpu(con->in_reply.connect_seq));
                pr_err("%s%lld %s connection reset\n",
                       ENTITY_NAME(con->peer_name),
                       ceph_pr_addr(&con->peer_addr.in_addr));
                reset_connection(con);
                con_out_kvec_reset(con);
                ret = prepare_write_connect(con);
                if (ret < 0)
                        return ret;
                prepare_read_connect(con);

                /* Tell ceph about it. */
                mutex_unlock(&con->mutex);
                pr_info("reset on %s%lld\n", ENTITY_NAME(con->peer_name));
                if (con->ops->peer_reset)
                        con->ops->peer_reset(con);
                mutex_lock(&con->mutex);
                if (con->state != CON_STATE_NEGOTIATING)
                        return -EAGAIN;
                break;

        case CEPH_MSGR_TAG_RETRY_SESSION:
                /*
                 * If we sent a smaller connect_seq than the peer has, try
                 * again with a larger value.
                 */
                dout("process_connect got RETRY_SESSION my seq %u, peer %u\n",
                     le32_to_cpu(con->out_connect.connect_seq),
                     le32_to_cpu(con->in_reply.connect_seq));
                con->connect_seq = le32_to_cpu(con->in_reply.connect_seq);
                con_out_kvec_reset(con);
                ret = prepare_write_connect(con);
                if (ret < 0)
                        return ret;
                prepare_read_connect(con);
                break;

        case CEPH_MSGR_TAG_RETRY_GLOBAL:
                /*
                 * If we sent a smaller global_seq than the peer has, try
                 * again with a larger value.
                 */
                dout("process_connect got RETRY_GLOBAL my %u peer_gseq %u\n",
                     con->peer_global_seq,
                     le32_to_cpu(con->in_reply.global_seq));
                get_global_seq(con->msgr,
                               le32_to_cpu(con->in_reply.global_seq));
                con_out_kvec_reset(con);
                ret = prepare_write_connect(con);
                if (ret < 0)
                        return ret;
                prepare_read_connect(con);
                break;

        case CEPH_MSGR_TAG_SEQ:
        case CEPH_MSGR_TAG_READY:
                if (req_feat & ~server_feat) {
                        pr_err("%s%lld %s protocol feature mismatch,"
                               " my required %llx > server's %llx, need %llx\n",
                               ENTITY_NAME(con->peer_name),
                               ceph_pr_addr(&con->peer_addr.in_addr),
                               req_feat, server_feat, req_feat & ~server_feat);
                        con->error_msg = "missing required protocol features";
                        reset_connection(con);
                        return -1;
                }

                WARN_ON(con->state != CON_STATE_NEGOTIATING);
                con->state = CON_STATE_OPEN;
                con->auth_retry = 0;    /* we authenticated; clear flag */
                con->peer_global_seq = le32_to_cpu(con->in_reply.global_seq);
                con->connect_seq++;
                con->peer_features = server_feat;
                dout("process_connect got READY gseq %d cseq %d (%d)\n",
                     con->peer_global_seq,
                     le32_to_cpu(con->in_reply.connect_seq),
                     con->connect_seq);
                WARN_ON(con->connect_seq !=
                        le32_to_cpu(con->in_reply.connect_seq));

                if (con->in_reply.flags & CEPH_MSG_CONNECT_LOSSY)
                        con_flag_set(con, CON_FLAG_LOSSYTX);

                con->delay = 0;      /* reset backoff memory */

                if (con->in_reply.tag == CEPH_MSGR_TAG_SEQ) {
                        prepare_write_seq(con);
                        prepare_read_seq(con);
                } else {
                        prepare_read_tag(con);
                }
                break;

        case CEPH_MSGR_TAG_WAIT:
                /*
                 * If there is a connection race (we are opening
                 * connections to each other), one of us may just have
                 * to WAIT.  This shouldn't happen if we are the
                 * client.
                 */
                pr_err("process_connect got WAIT as client\n");
                con->error_msg = "protocol error, got WAIT as client";
                return -1;

        default:
                pr_err("connect protocol error, will retry\n");
                con->error_msg = "protocol error, garbage tag during connect";
                return -1;
        }
        return 0;
}


/*
 * read (part of) an ack
 */
static int read_partial_ack(struct ceph_connection *con)
{
        int size = sizeof (con->in_temp_ack);
        int end = size;

        return read_partial(con, end, size, &con->in_temp_ack);
}

/*
 * We can finally discard anything that's been acked.
 */
static void process_ack(struct ceph_connection *con)
{
        struct ceph_msg *m;
        u64 ack = le64_to_cpu(con->in_temp_ack);
        u64 seq;

        while (!list_empty(&con->out_sent)) {
                m = list_first_entry(&con->out_sent, struct ceph_msg,
                                     list_head);
                seq = le64_to_cpu(m->hdr.seq);
                if (seq > ack)
                        break;
                dout("got ack for seq %llu type %d at %p\n", seq,
                     le16_to_cpu(m->hdr.type), m);
                m->ack_stamp = jiffies;
                ceph_msg_remove(m);
        }
        prepare_read_tag(con);
}


static int read_partial_message_section(struct ceph_connection *con,
                                        struct kvec *section,
                                        unsigned int sec_len, u32 *crc)
{
        int ret, left;

        BUG_ON(!section);

        while (section->iov_len < sec_len) {
                BUG_ON(section->iov_base == NULL);
                left = sec_len - section->iov_len;
                ret = ceph_tcp_recvmsg(con->sock, (char *)section->iov_base +
                                       section->iov_len, left);
                if (ret <= 0)
                        return ret;
                section->iov_len += ret;
        }
        if (section->iov_len == sec_len)
                *crc = crc32c(0, section->iov_base, section->iov_len);

        return 1;
}

static int read_partial_msg_data(struct ceph_connection *con)
{
        struct ceph_msg *msg = con->in_msg;
        struct ceph_msg_data_cursor *cursor = &msg->cursor;
        const bool do_datacrc = !con->msgr->nocrc;
        struct page *page;
        size_t page_offset;
        size_t length;
        u32 crc = 0;
        int ret;

        BUG_ON(!msg);
        if (list_empty(&msg->data))
                return -EIO;

        if (do_datacrc)
                crc = con->in_data_crc;
        while (cursor->resid) {
                page = ceph_msg_data_next(&msg->cursor, &page_offset, &length,
                                                        NULL);
                ret = ceph_tcp_recvpage(con->sock, page, page_offset, length);
                if (ret <= 0) {
                        if (do_datacrc)
                                con->in_data_crc = crc;

                        return ret;
                }

                if (do_datacrc)
                        crc = ceph_crc32c_page(crc, page, page_offset, ret);
                (void) ceph_msg_data_advance(&msg->cursor, (size_t)ret);
        }
        if (do_datacrc)
                con->in_data_crc = crc;

        return 1;       /* must return > 0 to indicate success */
}

/*
 * read (part of) a message.
 */
static int ceph_con_in_msg_alloc(struct ceph_connection *con, int *skip);

static int read_partial_message(struct ceph_connection *con)
{
        struct ceph_msg *m = con->in_msg;
        int size;
        int end;
        int ret;
        unsigned int front_len, middle_len, data_len;
        bool do_datacrc = !con->msgr->nocrc;
        u64 seq;
        u32 crc;

        dout("read_partial_message con %p msg %p\n", con, m);

        /* header */
        size = sizeof (con->in_hdr);
        end = size;
        ret = read_partial(con, end, size, &con->in_hdr);
        if (ret <= 0)
                return ret;

        crc = crc32c(0, &con->in_hdr, offsetof(struct ceph_msg_header, crc));
        if (cpu_to_le32(crc) != con->in_hdr.crc) {
                pr_err("read_partial_message bad hdr "
                       " crc %u != expected %u\n",
                       crc, con->in_hdr.crc);
                return -EBADMSG;
        }

        front_len = le32_to_cpu(con->in_hdr.front_len);
        if (front_len > CEPH_MSG_MAX_FRONT_LEN)
                return -EIO;
        middle_len = le32_to_cpu(con->in_hdr.middle_len);
        if (middle_len > CEPH_MSG_MAX_MIDDLE_LEN)
                return -EIO;
        data_len = le32_to_cpu(con->in_hdr.data_len);
        if (data_len > CEPH_MSG_MAX_DATA_LEN)
                return -EIO;

        /* verify seq# */
        seq = le64_to_cpu(con->in_hdr.seq);
        if ((s64)seq - (s64)con->in_seq < 1) {
                pr_info("skipping %s%lld %s seq %lld expected %lld\n",
                        ENTITY_NAME(con->peer_name),
                        ceph_pr_addr(&con->peer_addr.in_addr),
                        seq, con->in_seq + 1);
                con->in_base_pos = -front_len - middle_len - data_len -
                        sizeof(m->footer);
                con->in_tag = CEPH_MSGR_TAG_READY;
                return 0;
        } else if ((s64)seq - (s64)con->in_seq > 1) {
                pr_err("read_partial_message bad seq %lld expected %lld\n",
                       seq, con->in_seq + 1);
                con->error_msg = "bad message sequence # for incoming message";
                return -EBADMSG;
        }

        /* allocate message? */
        if (!con->in_msg) {
                int skip = 0;

                dout("got hdr type %d front %d data %d\n", con->in_hdr.type,
                     front_len, data_len);
                ret = ceph_con_in_msg_alloc(con, &skip);
                if (ret < 0)
                        return ret;

                BUG_ON(!con->in_msg ^ skip);
                if (con->in_msg && data_len > con->in_msg->data_length) {
                        pr_warn("%s skipping long message (%u > %zd)\n",
                                __func__, data_len, con->in_msg->data_length);
                        ceph_msg_put(con->in_msg);
                        con->in_msg = NULL;
                        skip = 1;
                }
                if (skip) {
                        /* skip this message */
                        dout("alloc_msg said skip message\n");
                        con->in_base_pos = -front_len - middle_len - data_len -
                                sizeof(m->footer);
                        con->in_tag = CEPH_MSGR_TAG_READY;
                        con->in_seq++;
                        return 0;
                }

                BUG_ON(!con->in_msg);
                BUG_ON(con->in_msg->con != con);
                m = con->in_msg;
                m->front.iov_len = 0;    /* haven't read it yet */
                if (m->middle)
                        m->middle->vec.iov_len = 0;

                /* prepare for data payload, if any */

                if (data_len)
                        prepare_message_data(con->in_msg, data_len);
        }

        /* front */
        ret = read_partial_message_section(con, &m->front, front_len,
                                           &con->in_front_crc);
        if (ret <= 0)
                return ret;

        /* middle */
        if (m->middle) {
                ret = read_partial_message_section(con, &m->middle->vec,
                                                   middle_len,
                                                   &con->in_middle_crc);
                if (ret <= 0)
                        return ret;
        }

        /* (page) data */
        if (data_len) {
                ret = read_partial_msg_data(con);
                if (ret <= 0)
                        return ret;
        }

        /* footer */
        size = sizeof (m->footer);
        end += size;
        ret = read_partial(con, end, size, &m->footer);
        if (ret <= 0)
                return ret;

        dout("read_partial_message got msg %p %d (%u) + %d (%u) + %d (%u)\n",
             m, front_len, m->footer.front_crc, middle_len,
             m->footer.middle_crc, data_len, m->footer.data_crc);

        /* crc ok? */
        if (con->in_front_crc != le32_to_cpu(m->footer.front_crc)) {
                pr_err("read_partial_message %p front crc %u != exp. %u\n",
                       m, con->in_front_crc, m->footer.front_crc);
                return -EBADMSG;
        }
        if (con->in_middle_crc != le32_to_cpu(m->footer.middle_crc)) {
                pr_err("read_partial_message %p middle crc %u != exp %u\n",
                       m, con->in_middle_crc, m->footer.middle_crc);
                return -EBADMSG;
        }
        if (do_datacrc &&
            (m->footer.flags & CEPH_MSG_FOOTER_NOCRC) == 0 &&
            con->in_data_crc != le32_to_cpu(m->footer.data_crc)) {
                pr_err("read_partial_message %p data crc %u != exp. %u\n", m,
                       con->in_data_crc, le32_to_cpu(m->footer.data_crc));
                return -EBADMSG;
        }

        return 1; /* done! */
}

/*
 * Process message.  This happens in the worker thread.  The callback should
 * be careful not to do anything that waits on other incoming messages or it
 * may deadlock.
 */
static void process_message(struct ceph_connection *con)
{
        struct ceph_msg *msg;

        BUG_ON(con->in_msg->con != con);
        con->in_msg->con = NULL;
        msg = con->in_msg;
        con->in_msg = NULL;
        con->ops->put(con);

        /* if first message, set peer_name */
        if (con->peer_name.type == 0)
                con->peer_name = msg->hdr.src;

        con->in_seq++;
        mutex_unlock(&con->mutex);

        dout("===== %p %llu from %s%lld %d=%s len %d+%d (%u %u %u) =====\n",
             msg, le64_to_cpu(msg->hdr.seq),
             ENTITY_NAME(msg->hdr.src),
             le16_to_cpu(msg->hdr.type),
             ceph_msg_type_name(le16_to_cpu(msg->hdr.type)),
             le32_to_cpu(msg->hdr.front_len),
             le32_to_cpu(msg->hdr.data_len),
             con->in_front_crc, con->in_middle_crc, con->in_data_crc);
        con->ops->dispatch(con, msg);

        mutex_lock(&con->mutex);
}


/*
 * Write something to the socket.  Called in a worker thread when the
 * socket appears to be writeable and we have something ready to send.
 */
static int try_write(struct ceph_connection *con)
{
        int ret = 1;

        dout("try_write start %p state %lu\n", con, con->state);

more:
        dout("try_write out_kvec_bytes %d\n", con->out_kvec_bytes);

        /* open the socket first? */
        if (con->state == CON_STATE_PREOPEN) {
                BUG_ON(con->sock);
                con->state = CON_STATE_CONNECTING;

                con_out_kvec_reset(con);
                prepare_write_banner(con);
                prepare_read_banner(con);

                BUG_ON(con->in_msg);
                con->in_tag = CEPH_MSGR_TAG_READY;
                dout("try_write initiating connect on %p new state %lu\n",
                     con, con->state);
                ret = ceph_tcp_connect(con);
                if (ret < 0) {
                        con->error_msg = "connect error";
                        goto out;
                }
        }

more_kvec:
        /* kvec data queued? */
        if (con->out_skip) {
                ret = write_partial_skip(con);
                if (ret <= 0)
                        goto out;
        }
        if (con->out_kvec_left) {
                ret = write_partial_kvec(con);
                if (ret <= 0)
                        goto out;
        }

        /* msg pages? */
        if (con->out_msg) {
                if (con->out_msg_done) {
                        ceph_msg_put(con->out_msg);
                        con->out_msg = NULL;   /* we're done with this one */
                        goto do_next;
                }

                ret = write_partial_message_data(con);
                if (ret == 1)
                        goto more_kvec;  /* we need to send the footer, too! */
                if (ret == 0)
                        goto out;
                if (ret < 0) {
                        dout("try_write write_partial_message_data err %d\n",
                             ret);
                        goto out;
                }
        }

do_next:
        if (con->state == CON_STATE_OPEN) {
                /* is anything else pending? */
                if (!list_empty(&con->out_queue)) {
                        prepare_write_message(con);
                        goto more;
                }
                if (con->in_seq > con->in_seq_acked) {
                        prepare_write_ack(con);
                        goto more;
                }
                if (con_flag_test_and_clear(con, CON_FLAG_KEEPALIVE_PENDING)) {
                        prepare_write_keepalive(con);
                        goto more;
                }
        }

        /* Nothing to do! */
        con_flag_clear(con, CON_FLAG_WRITE_PENDING);
        dout("try_write nothing else to write.\n");
        ret = 0;
out:
        dout("try_write done on %p ret %d\n", con, ret);
        return ret;
}



/*
 * Read what we can from the socket.
 */
static int try_read(struct ceph_connection *con)
{
        int ret = -1;

more:
        dout("try_read start on %p state %lu\n", con, con->state);
        if (con->state != CON_STATE_CONNECTING &&
            con->state != CON_STATE_NEGOTIATING &&
            con->state != CON_STATE_OPEN)
                return 0;

        BUG_ON(!con->sock);

        dout("try_read tag %d in_base_pos %d\n", (int)con->in_tag,
             con->in_base_pos);

        if (con->state == CON_STATE_CONNECTING) {
                dout("try_read connecting\n");
                ret = read_partial_banner(con);
                if (ret <= 0)
                        goto out;
                ret = process_banner(con);
                if (ret < 0)
                        goto out;

                con->state = CON_STATE_NEGOTIATING;

                /*
                 * Received banner is good, exchange connection info.
                 * Do not reset out_kvec, as sending our banner raced
                 * with receiving peer banner after connect completed.
                 */
                ret = prepare_write_connect(con);
                if (ret < 0)
                        goto out;
                prepare_read_connect(con);

                /* Send connection info before awaiting response */
                goto out;
        }

        if (con->state == CON_STATE_NEGOTIATING) {
                dout("try_read negotiating\n");
                ret = read_partial_connect(con);
                if (ret <= 0)
                        goto out;
                ret = process_connect(con);
                if (ret < 0)
                        goto out;
                goto more;
        }

        WARN_ON(con->state != CON_STATE_OPEN);

        if (con->in_base_pos < 0) {
                /*
                 * skipping + discarding content.
                 *
                 * FIXME: there must be a better way to do this!
                 */
                static char buf[SKIP_BUF_SIZE];
                int skip = min((int) sizeof (buf), -con->in_base_pos);

                dout("skipping %d / %d bytes\n", skip, -con->in_base_pos);
                ret = ceph_tcp_recvmsg(con->sock, buf, skip);
                if (ret <= 0)
                        goto out;
                con->in_base_pos += ret;
                if (con->in_base_pos)
                        goto more;
        }
        if (con->in_tag == CEPH_MSGR_TAG_READY) {
                /*
                 * what's next?
                 */
                ret = ceph_tcp_recvmsg(con->sock, &con->in_tag, 1);
                if (ret <= 0)
                        goto out;
                dout("try_read got tag %d\n", (int)con->in_tag);
                switch (con->in_tag) {
                case CEPH_MSGR_TAG_MSG:
                        prepare_read_message(con);
                        break;
                case CEPH_MSGR_TAG_ACK:
                        prepare_read_ack(con);
                        break;
                case CEPH_MSGR_TAG_CLOSE:
                        con_close_socket(con);
                        con->state = CON_STATE_CLOSED;
                        goto out;
                default:
                        goto bad_tag;
                }
        }
        if (con->in_tag == CEPH_MSGR_TAG_MSG) {
                ret = read_partial_message(con);
                if (ret <= 0) {
                        switch (ret) {
                        case -EBADMSG:
                                con->error_msg = "bad crc";
                                ret = -EIO;
                                break;
                        case -EIO:
                                con->error_msg = "io error";
                                break;
                        }
                        goto out;
                }
                if (con->in_tag == CEPH_MSGR_TAG_READY)
                        goto more;
                process_message(con);
                if (con->state == CON_STATE_OPEN)
                        prepare_read_tag(con);
                goto more;
        }
        if (con->in_tag == CEPH_MSGR_TAG_ACK ||
            con->in_tag == CEPH_MSGR_TAG_SEQ) {
                /*
                 * the final handshake seq exchange is semantically
                 * equivalent to an ACK
                 */
                ret = read_partial_ack(con);
                if (ret <= 0)
                        goto out;
                process_ack(con);
                goto more;
        }

out:
        dout("try_read done on %p ret %d\n", con, ret);
        return ret;

bad_tag:
        pr_err("try_read bad con->in_tag = %d\n", (int)con->in_tag);
        con->error_msg = "protocol error, garbage tag";
        ret = -1;
        goto out;
}


/*
 * Atomically queue work on a connection after the specified delay.
 * Bump @con reference to avoid races with connection teardown.
 * Returns 0 if work was queued, or an error code otherwise.
 */
static int queue_con_delay(struct ceph_connection *con, unsigned long delay)
{
        if (!con->ops->get(con)) {
                dout("%s %p ref count 0\n", __func__, con);
                return -ENOENT;
        }

        if (!queue_delayed_work(ceph_msgr_wq, &con->work, delay)) {
                dout("%s %p - already queued\n", __func__, con);
                con->ops->put(con);
                return -EBUSY;
        }

        dout("%s %p %lu\n", __func__, con, delay);
        return 0;
}

static void queue_con(struct ceph_connection *con)
{
        (void) queue_con_delay(con, 0);
}

static void cancel_con(struct ceph_connection *con)
{
        if (cancel_delayed_work(&con->work)) {
                dout("%s %p\n", __func__, con);
                con->ops->put(con);
        }
}

static bool con_sock_closed(struct ceph_connection *con)
{
        if (!con_flag_test_and_clear(con, CON_FLAG_SOCK_CLOSED))
                return false;

#define CASE(x)                                                         \
        case CON_STATE_ ## x:                                           \
                con->error_msg = "socket closed (con state " #x ")";    \
                break;

        switch (con->state) {
        CASE(CLOSED);
        CASE(PREOPEN);
        CASE(CONNECTING);
        CASE(NEGOTIATING);
        CASE(OPEN);
        CASE(STANDBY);
        default:
                pr_warn("%s con %p unrecognized state %lu\n",
                        __func__, con, con->state);
                con->error_msg = "unrecognized con state";
                BUG();
                break;
        }
#undef CASE

        return true;
}

static bool con_backoff(struct ceph_connection *con)
{
        int ret;

        if (!con_flag_test_and_clear(con, CON_FLAG_BACKOFF))
                return false;

        ret = queue_con_delay(con, round_jiffies_relative(con->delay));
        if (ret) {
                dout("%s: con %p FAILED to back off %lu\n", __func__,
                        con, con->delay);
                BUG_ON(ret == -ENOENT);
                con_flag_set(con, CON_FLAG_BACKOFF);
        }

        return true;
}

/* Finish fault handling; con->mutex must *not* be held here */

static void con_fault_finish(struct ceph_connection *con)
{
        /*
         * in case we faulted due to authentication, invalidate our
         * current tickets so that we can get new ones.
         */
        if (con->auth_retry && con->ops->invalidate_authorizer) {
                dout("calling invalidate_authorizer()\n");
                con->ops->invalidate_authorizer(con);
        }

        if (con->ops->fault)
                con->ops->fault(con);
}

/*
 * Do some work on a connection.  Drop a connection ref when we're done.
 */
static void con_work(struct work_struct *work)
{
        struct ceph_connection *con = container_of(work, struct ceph_connection,
                                                   work.work);
        unsigned long pflags = current->flags;
        bool fault;

        current->flags |= PF_MEMALLOC;

        mutex_lock(&con->mutex);
        while (true) {
                int ret;

                if ((fault = con_sock_closed(con))) {
                        dout("%s: con %p SOCK_CLOSED\n", __func__, con);
                        break;
                }
                if (con_backoff(con)) {
                        dout("%s: con %p BACKOFF\n", __func__, con);
                        break;
                }
                if (con->state == CON_STATE_STANDBY) {
                        dout("%s: con %p STANDBY\n", __func__, con);
                        break;
                }
                if (con->state == CON_STATE_CLOSED) {
                        dout("%s: con %p CLOSED\n", __func__, con);
                        BUG_ON(con->sock);
                        break;
                }
                if (con->state == CON_STATE_PREOPEN) {
                        dout("%s: con %p PREOPEN\n", __func__, con);
                        BUG_ON(con->sock);
                }

                ret = try_read(con);
                if (ret < 0) {
                        if (ret == -EAGAIN)
                                continue;
                        con->error_msg = "socket error on read";
                        fault = true;
                        break;
                }

                ret = try_write(con);
                if (ret < 0) {
                        if (ret == -EAGAIN)
                                continue;
                        con->error_msg = "socket error on write";
                        fault = true;
                }

                break;  /* If we make it to here, we're done */
        }
        if (fault)
                con_fault(con);
        mutex_unlock(&con->mutex);

        if (fault)
                con_fault_finish(con);

        con->ops->put(con);

        tsk_restore_flags(current, pflags, PF_MEMALLOC);
}

/*
 * Generic error/fault handler.  A retry mechanism is used with
 * exponential backoff
 */
static void con_fault(struct ceph_connection *con)
{
        pr_warn("%s%lld %s %s\n", ENTITY_NAME(con->peer_name),
                ceph_pr_addr(&con->peer_addr.in_addr), con->error_msg);
        dout("fault %p state %lu to peer %s\n",
             con, con->state, ceph_pr_addr(&con->peer_addr.in_addr));

        WARN_ON(con->state != CON_STATE_CONNECTING &&
               con->state != CON_STATE_NEGOTIATING &&
               con->state != CON_STATE_OPEN);

        con_close_socket(con);

        if (con_flag_test(con, CON_FLAG_LOSSYTX)) {
                dout("fault on LOSSYTX channel, marking CLOSED\n");
                con->state = CON_STATE_CLOSED;
                return;
        }

        if (con->in_msg) {
                BUG_ON(con->in_msg->con != con);
                con->in_msg->con = NULL;
                ceph_msg_put(con->in_msg);
                con->in_msg = NULL;
                con->ops->put(con);
        }

        /* Requeue anything that hasn't been acked */
        list_splice_init(&con->out_sent, &con->out_queue);

        /* If there are no messages queued or keepalive pending, place
         * the connection in a STANDBY state */
        if (list_empty(&con->out_queue) &&
            !con_flag_test(con, CON_FLAG_KEEPALIVE_PENDING)) {
                dout("fault %p setting STANDBY clearing WRITE_PENDING\n", con);
                con_flag_clear(con, CON_FLAG_WRITE_PENDING);
                con->state = CON_STATE_STANDBY;
        } else {
                /* retry after a delay. */
                con->state = CON_STATE_PREOPEN;
                if (con->delay == 0)
                        con->delay = BASE_DELAY_INTERVAL;
                else if (con->delay < MAX_DELAY_INTERVAL)
                        con->delay *= 2;
                con_flag_set(con, CON_FLAG_BACKOFF);
                queue_con(con);
        }
}



/*
 * initialize a new messenger instance
 */
void ceph_messenger_init(struct ceph_messenger *msgr,
                        struct ceph_entity_addr *myaddr,
                        u64 supported_features,
                        u64 required_features,
                        bool nocrc)
{
        msgr->supported_features = supported_features;
        msgr->required_features = required_features;

        spin_lock_init(&msgr->global_seq_lock);

        if (myaddr)
                msgr->inst.addr = *myaddr;

        /* select a random nonce */
        msgr->inst.addr.type = 0;
        get_random_bytes(&msgr->inst.addr.nonce, sizeof(msgr->inst.addr.nonce));
        encode_my_addr(msgr);
        msgr->nocrc = nocrc;

        atomic_set(&msgr->stopping, 0);

        dout("%s %p\n", __func__, msgr);
}
EXPORT_SYMBOL(ceph_messenger_init);

static void clear_standby(struct ceph_connection *con)
{
        /* come back from STANDBY? */
        if (con->state == CON_STATE_STANDBY) {
                dout("clear_standby %p and ++connect_seq\n", con);
                con->state = CON_STATE_PREOPEN;
                con->connect_seq++;
                WARN_ON(con_flag_test(con, CON_FLAG_WRITE_PENDING));
                WARN_ON(con_flag_test(con, CON_FLAG_KEEPALIVE_PENDING));
        }
}

/*
 * Queue up an outgoing message on the given connection.
 */
void ceph_con_send(struct ceph_connection *con, struct ceph_msg *msg)
{
        /* set src+dst */
        msg->hdr.src = con->msgr->inst.name;
        BUG_ON(msg->front.iov_len != le32_to_cpu(msg->hdr.front_len));
        msg->needs_out_seq = true;

        mutex_lock(&con->mutex);

        if (con->state == CON_STATE_CLOSED) {
                dout("con_send %p closed, dropping %p\n", con, msg);
                ceph_msg_put(msg);
                mutex_unlock(&con->mutex);
                return;
        }

        BUG_ON(msg->con != NULL);
        msg->con = con->ops->get(con);
        BUG_ON(msg->con == NULL);

        BUG_ON(!list_empty(&msg->list_head));
        list_add_tail(&msg->list_head, &con->out_queue);
        dout("----- %p to %s%lld %d=%s len %d+%d+%d -----\n", msg,
             ENTITY_NAME(con->peer_name), le16_to_cpu(msg->hdr.type),
             ceph_msg_type_name(le16_to_cpu(msg->hdr.type)),
             le32_to_cpu(msg->hdr.front_len),
             le32_to_cpu(msg->hdr.middle_len),
             le32_to_cpu(msg->hdr.data_len));

        clear_standby(con);
        mutex_unlock(&con->mutex);

        /* if there wasn't anything waiting to send before, queue
         * new work */
        if (con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
                queue_con(con);
}
EXPORT_SYMBOL(ceph_con_send);

/*
 * Revoke a message that was previously queued for send
 */
void ceph_msg_revoke(struct ceph_msg *msg)
{
        struct ceph_connection *con = msg->con;

        if (!con)
                return;         /* Message not in our possession */

        mutex_lock(&con->mutex);
        if (!list_empty(&msg->list_head)) {
                dout("%s %p msg %p - was on queue\n", __func__, con, msg);
                list_del_init(&msg->list_head);
                BUG_ON(msg->con == NULL);
                msg->con->ops->put(msg->con);
                msg->con = NULL;
                msg->hdr.seq = 0;

                ceph_msg_put(msg);
        }
        if (con->out_msg == msg) {
                dout("%s %p msg %p - was sending\n", __func__, con, msg);
                con->out_msg = NULL;
                if (con->out_kvec_is_msg) {
                        con->out_skip = con->out_kvec_bytes;
                        con->out_kvec_is_msg = false;
                }
                msg->hdr.seq = 0;

                ceph_msg_put(msg);
        }
        mutex_unlock(&con->mutex);
}

/*
 * Revoke a message that we may be reading data into
 */
void ceph_msg_revoke_incoming(struct ceph_msg *msg)
{
        struct ceph_connection *con;

        BUG_ON(msg == NULL);
        if (!msg->con) {
                dout("%s msg %p null con\n", __func__, msg);

                return;         /* Message not in our possession */
        }

        con = msg->con;
        mutex_lock(&con->mutex);
        if (con->in_msg == msg) {
                unsigned int front_len = le32_to_cpu(con->in_hdr.front_len);
                unsigned int middle_len = le32_to_cpu(con->in_hdr.middle_len);
                unsigned int data_len = le32_to_cpu(con->in_hdr.data_len);

                /* skip rest of message */
                dout("%s %p msg %p revoked\n", __func__, con, msg);
                con->in_base_pos = con->in_base_pos -
                                sizeof(struct ceph_msg_header) -
                                front_len -
                                middle_len -
                                data_len -
                                sizeof(struct ceph_msg_footer);
                ceph_msg_put(con->in_msg);
                con->in_msg = NULL;
                con->in_tag = CEPH_MSGR_TAG_READY;
                con->in_seq++;
        } else {
                dout("%s %p in_msg %p msg %p no-op\n",
                     __func__, con, con->in_msg, msg);
        }
        mutex_unlock(&con->mutex);
}

/*
 * Queue a keepalive byte to ensure the tcp connection is alive.
 */
void ceph_con_keepalive(struct ceph_connection *con)
{
        dout("con_keepalive %p\n", con);
        mutex_lock(&con->mutex);
        clear_standby(con);
        mutex_unlock(&con->mutex);
        if (con_flag_test_and_set(con, CON_FLAG_KEEPALIVE_PENDING) == 0 &&
            con_flag_test_and_set(con, CON_FLAG_WRITE_PENDING) == 0)
                queue_con(con);
}
EXPORT_SYMBOL(ceph_con_keepalive);

static struct ceph_msg_data *ceph_msg_data_create(enum ceph_msg_data_type type)
{
        struct ceph_msg_data *data;

        if (WARN_ON(!ceph_msg_data_type_valid(type)))
                return NULL;

        data = kmem_cache_zalloc(ceph_msg_data_cache, GFP_NOFS);
        if (data)
                data->type = type;
        INIT_LIST_HEAD(&data->links);

        return data;
}

static void ceph_msg_data_destroy(struct ceph_msg_data *data)
{
        if (!data)
                return;

        WARN_ON(!list_empty(&data->links));
        if (data->type == CEPH_MSG_DATA_PAGELIST)
                ceph_pagelist_release(data->pagelist);
        kmem_cache_free(ceph_msg_data_cache, data);
}

void ceph_msg_data_add_pages(struct ceph_msg *msg, struct page **pages,
                size_t length, size_t alignment)
{
        struct ceph_msg_data *data;

        BUG_ON(!pages);
        BUG_ON(!length);

        data = ceph_msg_data_create(CEPH_MSG_DATA_PAGES);
        BUG_ON(!data);
        data->pages = pages;
        data->length = length;
        data->alignment = alignment & ~PAGE_MASK;

        list_add_tail(&data->links, &msg->data);
        msg->data_length += length;
}
EXPORT_SYMBOL(ceph_msg_data_add_pages);

void ceph_msg_data_add_pagelist(struct ceph_msg *msg,
                                struct ceph_pagelist *pagelist)
{
        struct ceph_msg_data *data;

        BUG_ON(!pagelist);
        BUG_ON(!pagelist->length);

        data = ceph_msg_data_create(CEPH_MSG_DATA_PAGELIST);
        BUG_ON(!data);
        data->pagelist = pagelist;

        list_add_tail(&data->links, &msg->data);
        msg->data_length += pagelist->length;
}
EXPORT_SYMBOL(ceph_msg_data_add_pagelist);

#ifdef  CONFIG_BLOCK
void ceph_msg_data_add_bio(struct ceph_msg *msg, struct bio *bio,
                size_t length)
{
        struct ceph_msg_data *data;

        BUG_ON(!bio);

        data = ceph_msg_data_create(CEPH_MSG_DATA_BIO);
        BUG_ON(!data);
        data->bio = bio;
        data->bio_length = length;

        list_add_tail(&data->links, &msg->data);
        msg->data_length += length;
}
EXPORT_SYMBOL(ceph_msg_data_add_bio);
#endif  /* CONFIG_BLOCK */

/*
 * construct a new message with given type, size
 * the new msg has a ref count of 1.
 */
struct ceph_msg *ceph_msg_new(int type, int front_len, gfp_t flags,
                              bool can_fail)
{
        struct ceph_msg *m;

        m = kmem_cache_zalloc(ceph_msg_cache, flags);
        if (m == NULL)
                goto out;

        m->hdr.type = cpu_to_le16(type);
        m->hdr.priority = cpu_to_le16(CEPH_MSG_PRIO_DEFAULT);
        m->hdr.front_len = cpu_to_le32(front_len);

        INIT_LIST_HEAD(&m->list_head);
        kref_init(&m->kref);
        INIT_LIST_HEAD(&m->data);

        /* front */
        if (front_len) {
                m->front.iov_base = ceph_kvmalloc(front_len, flags);
                if (m->front.iov_base == NULL) {
                        dout("ceph_msg_new can't allocate %d bytes\n",
                             front_len);
                        goto out2;
                }
        } else {
                m->front.iov_base = NULL;
        }
        m->front_alloc_len = m->front.iov_len = front_len;

        dout("ceph_msg_new %p front %d\n", m, front_len);
        return m;

out2:
        ceph_msg_put(m);
out:
        if (!can_fail) {
                pr_err("msg_new can't create type %d front %d\n", type,
                       front_len);
                WARN_ON(1);
        } else {
                dout("msg_new can't create type %d front %d\n", type,
                     front_len);
        }
        return NULL;
}
EXPORT_SYMBOL(ceph_msg_new);

/*
 * Allocate "middle" portion of a message, if it is needed and wasn't
 * allocated by alloc_msg.  This allows us to read a small fixed-size
 * per-type header in the front and then gracefully fail (i.e.,
 * propagate the error to the caller based on info in the front) when
 * the middle is too large.
 */
static int ceph_alloc_middle(struct ceph_connection *con, struct ceph_msg *msg)
{
        int type = le16_to_cpu(msg->hdr.type);
        int middle_len = le32_to_cpu(msg->hdr.middle_len);

        dout("alloc_middle %p type %d %s middle_len %d\n", msg, type,
             ceph_msg_type_name(type), middle_len);
        BUG_ON(!middle_len);
        BUG_ON(msg->middle);

        msg->middle = ceph_buffer_new(middle_len, GFP_NOFS);
        if (!msg->middle)
                return -ENOMEM;
        return 0;
}

/*
 * Allocate a message for receiving an incoming message on a
 * connection, and save the result in con->in_msg.  Uses the
 * connection's private alloc_msg op if available.
 *
 * Returns 0 on success, or a negative error code.
 *
 * On success, if we set *skip = 1:
 *  - the next message should be skipped and ignored.
 *  - con->in_msg == NULL
 * or if we set *skip = 0:
 *  - con->in_msg is non-null.
 * On error (ENOMEM, EAGAIN, ...),
 *  - con->in_msg == NULL
 */
static int ceph_con_in_msg_alloc(struct ceph_connection *con, int *skip)
{
        struct ceph_msg_header *hdr = &con->in_hdr;
        int middle_len = le32_to_cpu(hdr->middle_len);
        struct ceph_msg *msg;
        int ret = 0;

        BUG_ON(con->in_msg != NULL);
        BUG_ON(!con->ops->alloc_msg);

        mutex_unlock(&con->mutex);
        msg = con->ops->alloc_msg(con, hdr, skip);
        mutex_lock(&con->mutex);
        if (con->state != CON_STATE_OPEN) {
                if (msg)
                        ceph_msg_put(msg);
                return -EAGAIN;
        }
        if (msg) {
                BUG_ON(*skip);
                con->in_msg = msg;
                con->in_msg->con = con->ops->get(con);
                BUG_ON(con->in_msg->con == NULL);
        } else {
                /*
                 * Null message pointer means either we should skip
                 * this message or we couldn't allocate memory.  The
                 * former is not an error.
                 */
                if (*skip)
                        return 0;
                con->error_msg = "error allocating memory for incoming message";

                return -ENOMEM;
        }
        memcpy(&con->in_msg->hdr, &con->in_hdr, sizeof(con->in_hdr));

        if (middle_len && !con->in_msg->middle) {
                ret = ceph_alloc_middle(con, con->in_msg);
                if (ret < 0) {
                        ceph_msg_put(con->in_msg);
                        con->in_msg = NULL;
                }
        }

        return ret;
}


/*
 * Free a generically kmalloc'd message.
 */
static void ceph_msg_free(struct ceph_msg *m)
{
        dout("%s %p\n", __func__, m);
        ceph_kvfree(m->front.iov_base);
        kmem_cache_free(ceph_msg_cache, m);
}

static void ceph_msg_release(struct kref *kref)
{
        struct ceph_msg *m = container_of(kref, struct ceph_msg, kref);
        LIST_HEAD(data);
        struct list_head *links;
        struct list_head *next;

        dout("%s %p\n", __func__, m);
        WARN_ON(!list_empty(&m->list_head));

        /* drop middle, data, if any */
        if (m->middle) {
                ceph_buffer_put(m->middle);
                m->middle = NULL;
        }

        list_splice_init(&m->data, &data);
        list_for_each_safe(links, next, &data) {
                struct ceph_msg_data *data;

                data = list_entry(links, struct ceph_msg_data, links);
                list_del_init(links);
                ceph_msg_data_destroy(data);
        }
        m->data_length = 0;

        if (m->pool)
                ceph_msgpool_put(m->pool, m);
        else
                ceph_msg_free(m);
}

struct ceph_msg *ceph_msg_get(struct ceph_msg *msg)
{
        dout("%s %p (was %d)\n", __func__, msg,
             atomic_read(&msg->kref.refcount));
        kref_get(&msg->kref);
        return msg;
}
EXPORT_SYMBOL(ceph_msg_get);

void ceph_msg_put(struct ceph_msg *msg)
{
        dout("%s %p (was %d)\n", __func__, msg,
             atomic_read(&msg->kref.refcount));
        kref_put(&msg->kref, ceph_msg_release);
}
EXPORT_SYMBOL(ceph_msg_put);

void ceph_msg_dump(struct ceph_msg *msg)
{
        pr_debug("msg_dump %p (front_alloc_len %d length %zd)\n", msg,
                 msg->front_alloc_len, msg->data_length);
        print_hex_dump(KERN_DEBUG, "header: ",
                       DUMP_PREFIX_OFFSET, 16, 1,
                       &msg->hdr, sizeof(msg->hdr), true);
        print_hex_dump(KERN_DEBUG, " front: ",
                       DUMP_PREFIX_OFFSET, 16, 1,
                       msg->front.iov_base, msg->front.iov_len, true);
        if (msg->middle)
                print_hex_dump(KERN_DEBUG, "middle: ",
                               DUMP_PREFIX_OFFSET, 16, 1,
                               msg->middle->vec.iov_base,
                               msg->middle->vec.iov_len, true);
        print_hex_dump(KERN_DEBUG, "footer: ",
                       DUMP_PREFIX_OFFSET, 16, 1,
                       &msg->footer, sizeof(msg->footer), true);
}
EXPORT_SYMBOL(ceph_msg_dump);