// SPDX-License-Identifier: GPL-2.0-or-later
/*
   drbd.c

   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.

   Copyright (C) 2001-2008, LINBIT Information Technologies GmbH.
   Copyright (C) 1999-2008, Philipp Reisner <philipp.reisner@linbit.com>.
   Copyright (C) 2002-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.

   Thanks to Carter Burden, Bart Grantham and Gennadiy Nerubayev
   from Logicworks, Inc. for making SDP replication support possible.


 */

#define pr_fmt(fmt)     KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/jiffies.h>
#include <linux/drbd.h>
#include <linux/uaccess.h>
#include <asm/types.h>
#include <net/sock.h>
#include <linux/ctype.h>
#include <linux/mutex.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/proc_fs.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/memcontrol.h>
#include <linux/mm_inline.h>
#include <linux/slab.h>
#include <linux/random.h>
#include <linux/reboot.h>
#include <linux/notifier.h>
#include <linux/kthread.h>
#include <linux/workqueue.h>
#define __KERNEL_SYSCALLS__
#include <linux/unistd.h>
#include <linux/vmalloc.h>
#include <linux/sched/signal.h>

#include <linux/drbd_limits.h>
#include "drbd_int.h"
#include "drbd_protocol.h"
#include "drbd_req.h" /* only for _req_mod in tl_release and tl_clear */
#include "drbd_vli.h"
#include "drbd_debugfs.h"

static DEFINE_MUTEX(drbd_main_mutex);
static int drbd_open(struct block_device *bdev, fmode_t mode);
static void drbd_release(struct gendisk *gd, fmode_t mode);
static void md_sync_timer_fn(struct timer_list *t);
static int w_bitmap_io(struct drbd_work *w, int unused);

MODULE_AUTHOR("Philipp Reisner <phil@linbit.com>, "
              "Lars Ellenberg <lars@linbit.com>");
MODULE_DESCRIPTION("drbd - Distributed Replicated Block Device v" REL_VERSION);
MODULE_VERSION(REL_VERSION);
MODULE_LICENSE("GPL");
MODULE_PARM_DESC(minor_count, "Approximate number of drbd devices ("
                 __stringify(DRBD_MINOR_COUNT_MIN) "-" __stringify(DRBD_MINOR_COUNT_MAX) ")");
MODULE_ALIAS_BLOCKDEV_MAJOR(DRBD_MAJOR);

#include <linux/moduleparam.h>
/* thanks to these macros, if compiled into the kernel (not-module),
 * these become boot parameters (e.g., drbd.minor_count) */

#ifdef CONFIG_DRBD_FAULT_INJECTION
int drbd_enable_faults;
int drbd_fault_rate;
static int drbd_fault_count;
static int drbd_fault_devs;
/* bitmap of enabled faults */
module_param_named(enable_faults, drbd_enable_faults, int, 0664);
/* fault rate % value - applies to all enabled faults */
module_param_named(fault_rate, drbd_fault_rate, int, 0664);
/* count of faults inserted */
module_param_named(fault_count, drbd_fault_count, int, 0664);
/* bitmap of devices to insert faults on */
module_param_named(fault_devs, drbd_fault_devs, int, 0644);
#endif

/* module parameters we can keep static */
static bool drbd_allow_oos; /* allow_open_on_secondary */
static bool drbd_disable_sendpage;
MODULE_PARM_DESC(allow_oos, "DONT USE!");
module_param_named(allow_oos, drbd_allow_oos, bool, 0);
module_param_named(disable_sendpage, drbd_disable_sendpage, bool, 0644);

/* module parameters we share */
int drbd_proc_details; /* Detail level in proc drbd*/
module_param_named(proc_details, drbd_proc_details, int, 0644);
/* module parameters shared with defaults */
unsigned int drbd_minor_count = DRBD_MINOR_COUNT_DEF;
/* Module parameter for setting the user mode helper program
 * to run. Default is /sbin/drbdadm */
char drbd_usermode_helper[80] = "/sbin/drbdadm";
module_param_named(minor_count, drbd_minor_count, uint, 0444);
module_param_string(usermode_helper, drbd_usermode_helper, sizeof(drbd_usermode_helper), 0644);

/* in 2.6.x, our device mapping and config info contains our virtual gendisks
 * as member "struct gendisk *vdisk;"
 */
struct idr drbd_devices;
struct list_head drbd_resources;
struct mutex resources_mutex;

struct kmem_cache *drbd_request_cache;
struct kmem_cache *drbd_ee_cache;       /* peer requests */
struct kmem_cache *drbd_bm_ext_cache;   /* bitmap extents */
struct kmem_cache *drbd_al_ext_cache;   /* activity log extents */
mempool_t drbd_request_mempool;
mempool_t drbd_ee_mempool;
mempool_t drbd_md_io_page_pool;
struct bio_set drbd_md_io_bio_set;
struct bio_set drbd_io_bio_set;

/* I do not use a standard mempool, because:
   1) I want to hand out the pre-allocated objects first.
   2) I want to be able to interrupt sleeping allocation with a signal.
   Note: This is a single linked list, the next pointer is the private
         member of struct page.
 */
struct page *drbd_pp_pool;
spinlock_t   drbd_pp_lock;
int          drbd_pp_vacant;
wait_queue_head_t drbd_pp_wait;

DEFINE_RATELIMIT_STATE(drbd_ratelimit_state, 5 * HZ, 5);

static const struct block_device_operations drbd_ops = {
        .owner =   THIS_MODULE,
        .open =    drbd_open,
        .release = drbd_release,
};

struct bio *bio_alloc_drbd(gfp_t gfp_mask)
{
        struct bio *bio;

        if (!bioset_initialized(&drbd_md_io_bio_set))
                return bio_alloc(gfp_mask, 1);

        bio = bio_alloc_bioset(gfp_mask, 1, &drbd_md_io_bio_set);
        if (!bio)
                return NULL;
        return bio;
}

#ifdef __CHECKER__
/* When checking with sparse, and this is an inline function, sparse will
   give tons of false positives. When this is a real functions sparse works.
 */
int _get_ldev_if_state(struct drbd_device *device, enum drbd_disk_state mins)
{
        int io_allowed;

        atomic_inc(&device->local_cnt);
        io_allowed = (device->state.disk >= mins);
        if (!io_allowed) {
                if (atomic_dec_and_test(&device->local_cnt))
                        wake_up(&device->misc_wait);
        }
        return io_allowed;
}

#endif

/**
 * tl_release() - mark as BARRIER_ACKED all requests in the corresponding transfer log epoch
 * @connection: DRBD connection.
 * @barrier_nr: Expected identifier of the DRBD write barrier packet.
 * @set_size:   Expected number of requests before that barrier.
 *
 * In case the passed barrier_nr or set_size does not match the oldest
 * epoch of not yet barrier-acked requests, this function will cause a
 * termination of the connection.
 */
void tl_release(struct drbd_connection *connection, unsigned int barrier_nr,
                unsigned int set_size)
{
        struct drbd_request *r;
        struct drbd_request *req = NULL;
        int expect_epoch = 0;
        int expect_size = 0;

        spin_lock_irq(&connection->resource->req_lock);

        /* find oldest not yet barrier-acked write request,
         * count writes in its epoch. */
        list_for_each_entry(r, &connection->transfer_log, tl_requests) {
                const unsigned s = r->rq_state;
                if (!req) {
                        if (!(s & RQ_WRITE))
                                continue;
                        if (!(s & RQ_NET_MASK))
                                continue;
                        if (s & RQ_NET_DONE)
                                continue;
                        req = r;
                        expect_epoch = req->epoch;
                        expect_size ++;
                } else {
                        if (r->epoch != expect_epoch)
                                break;
                        if (!(s & RQ_WRITE))
                                continue;
                        /* if (s & RQ_DONE): not expected */
                        /* if (!(s & RQ_NET_MASK)): not expected */
                        expect_size++;
                }
        }

        /* first some paranoia code */
        if (req == NULL) {
                drbd_err(connection, "BAD! BarrierAck #%u received, but no epoch in tl!?\n",
                         barrier_nr);
                goto bail;
        }
        if (expect_epoch != barrier_nr) {
                drbd_err(connection, "BAD! BarrierAck #%u received, expected #%u!\n",
                         barrier_nr, expect_epoch);
                goto bail;
        }

        if (expect_size != set_size) {
                drbd_err(connection, "BAD! BarrierAck #%u received with n_writes=%u, expected n_writes=%u!\n",
                         barrier_nr, set_size, expect_size);
                goto bail;
        }

        /* Clean up list of requests processed during current epoch. */
        /* this extra list walk restart is paranoia,
         * to catch requests being barrier-acked "unexpectedly".
         * It usually should find the same req again, or some READ preceding it. */
        list_for_each_entry(req, &connection->transfer_log, tl_requests)
                if (req->epoch == expect_epoch)
                        break;
        list_for_each_entry_safe_from(req, r, &connection->transfer_log, tl_requests) {
                if (req->epoch != expect_epoch)
                        break;
                _req_mod(req, BARRIER_ACKED);
        }
        spin_unlock_irq(&connection->resource->req_lock);

        return;

bail:
        spin_unlock_irq(&connection->resource->req_lock);
        conn_request_state(connection, NS(conn, C_PROTOCOL_ERROR), CS_HARD);
}


/**
 * _tl_restart() - Walks the transfer log, and applies an action to all requests
 * @connection: DRBD connection to operate on.
 * @what:       The action/event to perform with all request objects
 *
 * @what might be one of CONNECTION_LOST_WHILE_PENDING, RESEND, FAIL_FROZEN_DISK_IO,
 * RESTART_FROZEN_DISK_IO.
 */
/* must hold resource->req_lock */
void _tl_restart(struct drbd_connection *connection, enum drbd_req_event what)
{
        struct drbd_request *req, *r;

        list_for_each_entry_safe(req, r, &connection->transfer_log, tl_requests)
                _req_mod(req, what);
}

void tl_restart(struct drbd_connection *connection, enum drbd_req_event what)
{
        spin_lock_irq(&connection->resource->req_lock);
        _tl_restart(connection, what);
        spin_unlock_irq(&connection->resource->req_lock);
}

/**
 * tl_clear() - Clears all requests and &struct drbd_tl_epoch objects out of the TL
 * @device:     DRBD device.
 *
 * This is called after the connection to the peer was lost. The storage covered
 * by the requests on the transfer gets marked as our of sync. Called from the
 * receiver thread and the worker thread.
 */
void tl_clear(struct drbd_connection *connection)
{
        tl_restart(connection, CONNECTION_LOST_WHILE_PENDING);
}

/**
 * tl_abort_disk_io() - Abort disk I/O for all requests for a certain device in the TL
 * @device:     DRBD device.
 */
void tl_abort_disk_io(struct drbd_device *device)
{
        struct drbd_connection *connection = first_peer_device(device)->connection;
        struct drbd_request *req, *r;

        spin_lock_irq(&connection->resource->req_lock);
        list_for_each_entry_safe(req, r, &connection->transfer_log, tl_requests) {
                if (!(req->rq_state & RQ_LOCAL_PENDING))
                        continue;
                if (req->device != device)
                        continue;
                _req_mod(req, ABORT_DISK_IO);
        }
        spin_unlock_irq(&connection->resource->req_lock);
}

static int drbd_thread_setup(void *arg)
{
        struct drbd_thread *thi = (struct drbd_thread *) arg;
        struct drbd_resource *resource = thi->resource;
        unsigned long flags;
        int retval;

        snprintf(current->comm, sizeof(current->comm), "drbd_%c_%s",
                 thi->name[0],
                 resource->name);

        allow_kernel_signal(DRBD_SIGKILL);
        allow_kernel_signal(SIGXCPU);
restart:
        retval = thi->function(thi);

        spin_lock_irqsave(&thi->t_lock, flags);

        /* if the receiver has been "EXITING", the last thing it did
         * was set the conn state to "StandAlone",
         * if now a re-connect request comes in, conn state goes C_UNCONNECTED,
         * and receiver thread will be "started".
         * drbd_thread_start needs to set "RESTARTING" in that case.
         * t_state check and assignment needs to be within the same spinlock,
         * so either thread_start sees EXITING, and can remap to RESTARTING,
         * or thread_start see NONE, and can proceed as normal.
         */

        if (thi->t_state == RESTARTING) {
                drbd_info(resource, "Restarting %s thread\n", thi->name);
                thi->t_state = RUNNING;
                spin_unlock_irqrestore(&thi->t_lock, flags);
                goto restart;
        }

        thi->task = NULL;
        thi->t_state = NONE;
        smp_mb();
        complete_all(&thi->stop);
        spin_unlock_irqrestore(&thi->t_lock, flags);

        drbd_info(resource, "Terminating %s\n", current->comm);

        /* Release mod reference taken when thread was started */

        if (thi->connection)
                kref_put(&thi->connection->kref, drbd_destroy_connection);
        kref_put(&resource->kref, drbd_destroy_resource);
        module_put(THIS_MODULE);
        return retval;
}

static void drbd_thread_init(struct drbd_resource *resource, struct drbd_thread *thi,
                             int (*func) (struct drbd_thread *), const char *name)
{
        spin_lock_init(&thi->t_lock);
        thi->task    = NULL;
        thi->t_state = NONE;
        thi->function = func;
        thi->resource = resource;
        thi->connection = NULL;
        thi->name = name;
}

int drbd_thread_start(struct drbd_thread *thi)
{
        struct drbd_resource *resource = thi->resource;
        struct task_struct *nt;
        unsigned long flags;

        /* is used from state engine doing drbd_thread_stop_nowait,
         * while holding the req lock irqsave */
        spin_lock_irqsave(&thi->t_lock, flags);

        switch (thi->t_state) {
        case NONE:
                drbd_info(resource, "Starting %s thread (from %s [%d])\n",
                         thi->name, current->comm, current->pid);

                /* Get ref on module for thread - this is released when thread exits */
                if (!try_module_get(THIS_MODULE)) {
                        drbd_err(resource, "Failed to get module reference in drbd_thread_start\n");
                        spin_unlock_irqrestore(&thi->t_lock, flags);
                        return false;
                }

                kref_get(&resource->kref);
                if (thi->connection)
                        kref_get(&thi->connection->kref);

                init_completion(&thi->stop);
                thi->reset_cpu_mask = 1;
                thi->t_state = RUNNING;
                spin_unlock_irqrestore(&thi->t_lock, flags);
                flush_signals(current); /* otherw. may get -ERESTARTNOINTR */

                nt = kthread_create(drbd_thread_setup, (void *) thi,
                                    "drbd_%c_%s", thi->name[0], thi->resource->name);

                if (IS_ERR(nt)) {
                        drbd_err(resource, "Couldn't start thread\n");

                        if (thi->connection)
                                kref_put(&thi->connection->kref, drbd_destroy_connection);
                        kref_put(&resource->kref, drbd_destroy_resource);
                        module_put(THIS_MODULE);
                        return false;
                }
                spin_lock_irqsave(&thi->t_lock, flags);
                thi->task = nt;
                thi->t_state = RUNNING;
                spin_unlock_irqrestore(&thi->t_lock, flags);
                wake_up_process(nt);
                break;
        case EXITING:
                thi->t_state = RESTARTING;
                drbd_info(resource, "Restarting %s thread (from %s [%d])\n",
                                thi->name, current->comm, current->pid);
                /* fall through */
        case RUNNING:
        case RESTARTING:
        default:
                spin_unlock_irqrestore(&thi->t_lock, flags);
                break;
        }

        return true;
}


void _drbd_thread_stop(struct drbd_thread *thi, int restart, int wait)
{
        unsigned long flags;

        enum drbd_thread_state ns = restart ? RESTARTING : EXITING;

        /* may be called from state engine, holding the req lock irqsave */
        spin_lock_irqsave(&thi->t_lock, flags);

        if (thi->t_state == NONE) {
                spin_unlock_irqrestore(&thi->t_lock, flags);
                if (restart)
                        drbd_thread_start(thi);
                return;
        }

        if (thi->t_state != ns) {
                if (thi->task == NULL) {
                        spin_unlock_irqrestore(&thi->t_lock, flags);
                        return;
                }

                thi->t_state = ns;
                smp_mb();
                init_completion(&thi->stop);
                if (thi->task != current)
                        send_sig(DRBD_SIGKILL, thi->task, 1);
        }

        spin_unlock_irqrestore(&thi->t_lock, flags);

        if (wait)
                wait_for_completion(&thi->stop);
}

int conn_lowest_minor(struct drbd_connection *connection)
{
        struct drbd_peer_device *peer_device;
        int vnr = 0, minor = -1;

        rcu_read_lock();
        peer_device = idr_get_next(&connection->peer_devices, &vnr);
        if (peer_device)
                minor = device_to_minor(peer_device->device);
        rcu_read_unlock();

        return minor;
}

#ifdef CONFIG_SMP
/**
 * drbd_calc_cpu_mask() - Generate CPU masks, spread over all CPUs
 *
 * Forces all threads of a resource onto the same CPU. This is beneficial for
 * DRBD's performance. May be overwritten by user's configuration.
 */
static void drbd_calc_cpu_mask(cpumask_var_t *cpu_mask)
{
        unsigned int *resources_per_cpu, min_index = ~0;

        resources_per_cpu = kcalloc(nr_cpu_ids, sizeof(*resources_per_cpu),
                                    GFP_KERNEL);
        if (resources_per_cpu) {
                struct drbd_resource *resource;
                unsigned int cpu, min = ~0;

                rcu_read_lock();
                for_each_resource_rcu(resource, &drbd_resources) {
                        for_each_cpu(cpu, resource->cpu_mask)
                                resources_per_cpu[cpu]++;
                }
                rcu_read_unlock();
                for_each_online_cpu(cpu) {
                        if (resources_per_cpu[cpu] < min) {
                                min = resources_per_cpu[cpu];
                                min_index = cpu;
                        }
                }
                kfree(resources_per_cpu);
        }
        if (min_index == ~0) {
                cpumask_setall(*cpu_mask);
                return;
        }
        cpumask_set_cpu(min_index, *cpu_mask);
}

/**
 * drbd_thread_current_set_cpu() - modifies the cpu mask of the _current_ thread
 * @device:     DRBD device.
 * @thi:        drbd_thread object
 *
 * call in the "main loop" of _all_ threads, no need for any mutex, current won't die
 * prematurely.
 */
void drbd_thread_current_set_cpu(struct drbd_thread *thi)
{
        struct drbd_resource *resource = thi->resource;
        struct task_struct *p = current;

        if (!thi->reset_cpu_mask)
                return;
        thi->reset_cpu_mask = 0;
        set_cpus_allowed_ptr(p, resource->cpu_mask);
}
#else
#define drbd_calc_cpu_mask(A) ({})
#endif

/**
 * drbd_header_size  -  size of a packet header
 *
 * The header size is a multiple of 8, so any payload following the header is
 * word aligned on 64-bit architectures.  (The bitmap send and receive code
 * relies on this.)
 */
unsigned int drbd_header_size(struct drbd_connection *connection)
{
        if (connection->agreed_pro_version >= 100) {
                BUILD_BUG_ON(!IS_ALIGNED(sizeof(struct p_header100), 8));
                return sizeof(struct p_header100);
        } else {
                BUILD_BUG_ON(sizeof(struct p_header80) !=
                             sizeof(struct p_header95));
                BUILD_BUG_ON(!IS_ALIGNED(sizeof(struct p_header80), 8));
                return sizeof(struct p_header80);
        }
}

static unsigned int prepare_header80(struct p_header80 *h, enum drbd_packet cmd, int size)
{
        h->magic   = cpu_to_be32(DRBD_MAGIC);
        h->command = cpu_to_be16(cmd);
        h->length  = cpu_to_be16(size);
        return sizeof(struct p_header80);
}

static unsigned int prepare_header95(struct p_header95 *h, enum drbd_packet cmd, int size)
{
        h->magic   = cpu_to_be16(DRBD_MAGIC_BIG);
        h->command = cpu_to_be16(cmd);
        h->length = cpu_to_be32(size);
        return sizeof(struct p_header95);
}

static unsigned int prepare_header100(struct p_header100 *h, enum drbd_packet cmd,
                                      int size, int vnr)
{
        h->magic = cpu_to_be32(DRBD_MAGIC_100);
        h->volume = cpu_to_be16(vnr);
        h->command = cpu_to_be16(cmd);
        h->length = cpu_to_be32(size);
        h->pad = 0;
        return sizeof(struct p_header100);
}

static unsigned int prepare_header(struct drbd_connection *connection, int vnr,
                                   void *buffer, enum drbd_packet cmd, int size)
{
        if (connection->agreed_pro_version >= 100)
                return prepare_header100(buffer, cmd, size, vnr);
        else if (connection->agreed_pro_version >= 95 &&
                 size > DRBD_MAX_SIZE_H80_PACKET)
                return prepare_header95(buffer, cmd, size);
        else
                return prepare_header80(buffer, cmd, size);
}

static void *__conn_prepare_command(struct drbd_connection *connection,
                                    struct drbd_socket *sock)
{
        if (!sock->socket)
                return NULL;
        return sock->sbuf + drbd_header_size(connection);
}

void *conn_prepare_command(struct drbd_connection *connection, struct drbd_socket *sock)
{
        void *p;

        mutex_lock(&sock->mutex);
        p = __conn_prepare_command(connection, sock);
        if (!p)
                mutex_unlock(&sock->mutex);

        return p;
}

void *drbd_prepare_command(struct drbd_peer_device *peer_device, struct drbd_socket *sock)
{
        return conn_prepare_command(peer_device->connection, sock);
}

static int __send_command(struct drbd_connection *connection, int vnr,
                          struct drbd_socket *sock, enum drbd_packet cmd,
                          unsigned int header_size, void *data,
                          unsigned int size)
{
        int msg_flags;
        int err;

        /*
         * Called with @data == NULL and the size of the data blocks in @size
         * for commands that send data blocks.  For those commands, omit the
         * MSG_MORE flag: this will increase the likelihood that data blocks
         * which are page aligned on the sender will end up page aligned on the
         * receiver.
         */
        msg_flags = data ? MSG_MORE : 0;

        header_size += prepare_header(connection, vnr, sock->sbuf, cmd,
                                      header_size + size);
        err = drbd_send_all(connection, sock->socket, sock->sbuf, header_size,
                            msg_flags);
        if (data && !err)
                err = drbd_send_all(connection, sock->socket, data, size, 0);
        /* DRBD protocol "pings" are latency critical.
         * This is supposed to trigger tcp_push_pending_frames() */
        if (!err && (cmd == P_PING || cmd == P_PING_ACK))
                drbd_tcp_nodelay(sock->socket);

        return err;
}

static int __conn_send_command(struct drbd_connection *connection, struct drbd_socket *sock,
                               enum drbd_packet cmd, unsigned int header_size,
                               void *data, unsigned int size)
{
        return __send_command(connection, 0, sock, cmd, header_size, data, size);
}

int conn_send_command(struct drbd_connection *connection, struct drbd_socket *sock,
                      enum drbd_packet cmd, unsigned int header_size,
                      void *data, unsigned int size)
{
        int err;

        err = __conn_send_command(connection, sock, cmd, header_size, data, size);
        mutex_unlock(&sock->mutex);
        return err;
}

int drbd_send_command(struct drbd_peer_device *peer_device, struct drbd_socket *sock,
                      enum drbd_packet cmd, unsigned int header_size,
                      void *data, unsigned int size)
{
        int err;

        err = __send_command(peer_device->connection, peer_device->device->vnr,
                             sock, cmd, header_size, data, size);
        mutex_unlock(&sock->mutex);
        return err;
}

int drbd_send_ping(struct drbd_connection *connection)
{
        struct drbd_socket *sock;

        sock = &connection->meta;
        if (!conn_prepare_command(connection, sock))
                return -EIO;
        return conn_send_command(connection, sock, P_PING, 0, NULL, 0);
}

int drbd_send_ping_ack(struct drbd_connection *connection)
{
        struct drbd_socket *sock;

        sock = &connection->meta;
        if (!conn_prepare_command(connection, sock))
                return -EIO;
        return conn_send_command(connection, sock, P_PING_ACK, 0, NULL, 0);
}

int drbd_send_sync_param(struct drbd_peer_device *peer_device)
{
        struct drbd_socket *sock;
        struct p_rs_param_95 *p;
        int size;
        const int apv = peer_device->connection->agreed_pro_version;
        enum drbd_packet cmd;
        struct net_conf *nc;
        struct disk_conf *dc;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;

        rcu_read_lock();
        nc = rcu_dereference(peer_device->connection->net_conf);

        size = apv <= 87 ? sizeof(struct p_rs_param)
                : apv == 88 ? sizeof(struct p_rs_param)
                        + strlen(nc->verify_alg) + 1
                : apv <= 94 ? sizeof(struct p_rs_param_89)
                : /* apv >= 95 */ sizeof(struct p_rs_param_95);

        cmd = apv >= 89 ? P_SYNC_PARAM89 : P_SYNC_PARAM;

        /* initialize verify_alg and csums_alg */
        memset(p->verify_alg, 0, 2 * SHARED_SECRET_MAX);

        if (get_ldev(peer_device->device)) {
                dc = rcu_dereference(peer_device->device->ldev->disk_conf);
                p->resync_rate = cpu_to_be32(dc->resync_rate);
                p->c_plan_ahead = cpu_to_be32(dc->c_plan_ahead);
                p->c_delay_target = cpu_to_be32(dc->c_delay_target);
                p->c_fill_target = cpu_to_be32(dc->c_fill_target);
                p->c_max_rate = cpu_to_be32(dc->c_max_rate);
                put_ldev(peer_device->device);
        } else {
                p->resync_rate = cpu_to_be32(DRBD_RESYNC_RATE_DEF);
                p->c_plan_ahead = cpu_to_be32(DRBD_C_PLAN_AHEAD_DEF);
                p->c_delay_target = cpu_to_be32(DRBD_C_DELAY_TARGET_DEF);
                p->c_fill_target = cpu_to_be32(DRBD_C_FILL_TARGET_DEF);
                p->c_max_rate = cpu_to_be32(DRBD_C_MAX_RATE_DEF);
        }

        if (apv >= 88)
                strcpy(p->verify_alg, nc->verify_alg);
        if (apv >= 89)
                strcpy(p->csums_alg, nc->csums_alg);
        rcu_read_unlock();

        return drbd_send_command(peer_device, sock, cmd, size, NULL, 0);
}

int __drbd_send_protocol(struct drbd_connection *connection, enum drbd_packet cmd)
{
        struct drbd_socket *sock;
        struct p_protocol *p;
        struct net_conf *nc;
        int size, cf;

        sock = &connection->data;
        p = __conn_prepare_command(connection, sock);
        if (!p)
                return -EIO;

        rcu_read_lock();
        nc = rcu_dereference(connection->net_conf);

        if (nc->tentative && connection->agreed_pro_version < 92) {
                rcu_read_unlock();
                mutex_unlock(&sock->mutex);
                drbd_err(connection, "--dry-run is not supported by peer");
                return -EOPNOTSUPP;
        }

        size = sizeof(*p);
        if (connection->agreed_pro_version >= 87)
                size += strlen(nc->integrity_alg) + 1;

        p->protocol      = cpu_to_be32(nc->wire_protocol);
        p->after_sb_0p   = cpu_to_be32(nc->after_sb_0p);
        p->after_sb_1p   = cpu_to_be32(nc->after_sb_1p);
        p->after_sb_2p   = cpu_to_be32(nc->after_sb_2p);
        p->two_primaries = cpu_to_be32(nc->two_primaries);
        cf = 0;
        if (nc->discard_my_data)
                cf |= CF_DISCARD_MY_DATA;
        if (nc->tentative)
                cf |= CF_DRY_RUN;
        p->conn_flags    = cpu_to_be32(cf);

        if (connection->agreed_pro_version >= 87)
                strcpy(p->integrity_alg, nc->integrity_alg);
        rcu_read_unlock();

        return __conn_send_command(connection, sock, cmd, size, NULL, 0);
}

int drbd_send_protocol(struct drbd_connection *connection)
{
        int err;

        mutex_lock(&connection->data.mutex);
        err = __drbd_send_protocol(connection, P_PROTOCOL);
        mutex_unlock(&connection->data.mutex);

        return err;
}

static int _drbd_send_uuids(struct drbd_peer_device *peer_device, u64 uuid_flags)
{
        struct drbd_device *device = peer_device->device;
        struct drbd_socket *sock;
        struct p_uuids *p;
        int i;

        if (!get_ldev_if_state(device, D_NEGOTIATING))
                return 0;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p) {
                put_ldev(device);
                return -EIO;
        }
        spin_lock_irq(&device->ldev->md.uuid_lock);
        for (i = UI_CURRENT; i < UI_SIZE; i++)
                p->uuid[i] = cpu_to_be64(device->ldev->md.uuid[i]);
        spin_unlock_irq(&device->ldev->md.uuid_lock);

        device->comm_bm_set = drbd_bm_total_weight(device);
        p->uuid[UI_SIZE] = cpu_to_be64(device->comm_bm_set);
        rcu_read_lock();
        uuid_flags |= rcu_dereference(peer_device->connection->net_conf)->discard_my_data ? 1 : 0;
        rcu_read_unlock();
        uuid_flags |= test_bit(CRASHED_PRIMARY, &device->flags) ? 2 : 0;
        uuid_flags |= device->new_state_tmp.disk == D_INCONSISTENT ? 4 : 0;
        p->uuid[UI_FLAGS] = cpu_to_be64(uuid_flags);

        put_ldev(device);
        return drbd_send_command(peer_device, sock, P_UUIDS, sizeof(*p), NULL, 0);
}

int drbd_send_uuids(struct drbd_peer_device *peer_device)
{
        return _drbd_send_uuids(peer_device, 0);
}

int drbd_send_uuids_skip_initial_sync(struct drbd_peer_device *peer_device)
{
        return _drbd_send_uuids(peer_device, 8);
}

void drbd_print_uuids(struct drbd_device *device, const char *text)
{
        if (get_ldev_if_state(device, D_NEGOTIATING)) {
                u64 *uuid = device->ldev->md.uuid;
                drbd_info(device, "%s %016llX:%016llX:%016llX:%016llX\n",
                     text,
                     (unsigned long long)uuid[UI_CURRENT],
                     (unsigned long long)uuid[UI_BITMAP],
                     (unsigned long long)uuid[UI_HISTORY_START],
                     (unsigned long long)uuid[UI_HISTORY_END]);
                put_ldev(device);
        } else {
                drbd_info(device, "%s effective data uuid: %016llX\n",
                                text,
                                (unsigned long long)device->ed_uuid);
        }
}

void drbd_gen_and_send_sync_uuid(struct drbd_peer_device *peer_device)
{
        struct drbd_device *device = peer_device->device;
        struct drbd_socket *sock;
        struct p_rs_uuid *p;
        u64 uuid;

        D_ASSERT(device, device->state.disk == D_UP_TO_DATE);

        uuid = device->ldev->md.uuid[UI_BITMAP];
        if (uuid && uuid != UUID_JUST_CREATED)
                uuid = uuid + UUID_NEW_BM_OFFSET;
        else
                get_random_bytes(&uuid, sizeof(u64));
        drbd_uuid_set(device, UI_BITMAP, uuid);
        drbd_print_uuids(device, "updated sync UUID");
        drbd_md_sync(device);

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (p) {
                p->uuid = cpu_to_be64(uuid);
                drbd_send_command(peer_device, sock, P_SYNC_UUID, sizeof(*p), NULL, 0);
        }
}

/* communicated if (agreed_features & DRBD_FF_WSAME) */
static void
assign_p_sizes_qlim(struct drbd_device *device, struct p_sizes *p,
                                        struct request_queue *q)
{
        if (q) {
                p->qlim->physical_block_size = cpu_to_be32(queue_physical_block_size(q));
                p->qlim->logical_block_size = cpu_to_be32(queue_logical_block_size(q));
                p->qlim->alignment_offset = cpu_to_be32(queue_alignment_offset(q));
                p->qlim->io_min = cpu_to_be32(queue_io_min(q));
                p->qlim->io_opt = cpu_to_be32(queue_io_opt(q));
                p->qlim->discard_enabled = blk_queue_discard(q);
                p->qlim->write_same_capable = !!q->limits.max_write_same_sectors;
        } else {
                q = device->rq_queue;
                p->qlim->physical_block_size = cpu_to_be32(queue_physical_block_size(q));
                p->qlim->logical_block_size = cpu_to_be32(queue_logical_block_size(q));
                p->qlim->alignment_offset = 0;
                p->qlim->io_min = cpu_to_be32(queue_io_min(q));
                p->qlim->io_opt = cpu_to_be32(queue_io_opt(q));
                p->qlim->discard_enabled = 0;
                p->qlim->write_same_capable = 0;
        }
}

int drbd_send_sizes(struct drbd_peer_device *peer_device, int trigger_reply, enum dds_flags flags)
{
        struct drbd_device *device = peer_device->device;
        struct drbd_socket *sock;
        struct p_sizes *p;
        sector_t d_size, u_size;
        int q_order_type;
        unsigned int max_bio_size;
        unsigned int packet_size;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;

        packet_size = sizeof(*p);
        if (peer_device->connection->agreed_features & DRBD_FF_WSAME)
                packet_size += sizeof(p->qlim[0]);

        memset(p, 0, packet_size);
        if (get_ldev_if_state(device, D_NEGOTIATING)) {
                struct request_queue *q = bdev_get_queue(device->ldev->backing_bdev);
                d_size = drbd_get_max_capacity(device->ldev);
                rcu_read_lock();
                u_size = rcu_dereference(device->ldev->disk_conf)->disk_size;
                rcu_read_unlock();
                q_order_type = drbd_queue_order_type(device);
                max_bio_size = queue_max_hw_sectors(q) << 9;
                max_bio_size = min(max_bio_size, DRBD_MAX_BIO_SIZE);
                assign_p_sizes_qlim(device, p, q);
                put_ldev(device);
        } else {
                d_size = 0;
                u_size = 0;
                q_order_type = QUEUE_ORDERED_NONE;
                max_bio_size = DRBD_MAX_BIO_SIZE; /* ... multiple BIOs per peer_request */
                assign_p_sizes_qlim(device, p, NULL);
        }

        if (peer_device->connection->agreed_pro_version <= 94)
                max_bio_size = min(max_bio_size, DRBD_MAX_SIZE_H80_PACKET);
        else if (peer_device->connection->agreed_pro_version < 100)
                max_bio_size = min(max_bio_size, DRBD_MAX_BIO_SIZE_P95);

        p->d_size = cpu_to_be64(d_size);
        p->u_size = cpu_to_be64(u_size);
        p->c_size = cpu_to_be64(trigger_reply ? 0 : drbd_get_capacity(device->this_bdev));
        p->max_bio_size = cpu_to_be32(max_bio_size);
        p->queue_order_type = cpu_to_be16(q_order_type);
        p->dds_flags = cpu_to_be16(flags);

        return drbd_send_command(peer_device, sock, P_SIZES, packet_size, NULL, 0);
}

/**
 * drbd_send_current_state() - Sends the drbd state to the peer
 * @peer_device:        DRBD peer device.
 */
int drbd_send_current_state(struct drbd_peer_device *peer_device)
{

        struct drbd_socket *sock;
        struct p_state *p;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->state = cpu_to_be32(peer_device->device->state.i); /* Within the send mutex */
        return drbd_send_command(peer_device, sock, P_STATE, sizeof(*p), NULL, 0);
}

/**
 * drbd_send_state() - After a state change, sends the new state to the peer
 * @peer_device:      DRBD peer device.
 * @state:     the state to send, not necessarily the current state.
 *
 * Each state change queues an "after_state_ch" work, which will eventually
 * send the resulting new state to the peer. If more state changes happen
 * between queuing and processing of the after_state_ch work, we still
 * want to send each intermediary state in the order it occurred.
 */
int drbd_send_state(struct drbd_peer_device *peer_device, union drbd_state state)
{
        struct drbd_socket *sock;
        struct p_state *p;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->state = cpu_to_be32(state.i); /* Within the send mutex */
        return drbd_send_command(peer_device, sock, P_STATE, sizeof(*p), NULL, 0);
}

int drbd_send_state_req(struct drbd_peer_device *peer_device, union drbd_state mask, union drbd_state val)
{
        struct drbd_socket *sock;
        struct p_req_state *p;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->mask = cpu_to_be32(mask.i);
        p->val = cpu_to_be32(val.i);
        return drbd_send_command(peer_device, sock, P_STATE_CHG_REQ, sizeof(*p), NULL, 0);
}

int conn_send_state_req(struct drbd_connection *connection, union drbd_state mask, union drbd_state val)
{
        enum drbd_packet cmd;
        struct drbd_socket *sock;
        struct p_req_state *p;

        cmd = connection->agreed_pro_version < 100 ? P_STATE_CHG_REQ : P_CONN_ST_CHG_REQ;
        sock = &connection->data;
        p = conn_prepare_command(connection, sock);
        if (!p)
                return -EIO;
        p->mask = cpu_to_be32(mask.i);
        p->val = cpu_to_be32(val.i);
        return conn_send_command(connection, sock, cmd, sizeof(*p), NULL, 0);
}

void drbd_send_sr_reply(struct drbd_peer_device *peer_device, enum drbd_state_rv retcode)
{
        struct drbd_socket *sock;
        struct p_req_state_reply *p;

        sock = &peer_device->connection->meta;
        p = drbd_prepare_command(peer_device, sock);
        if (p) {
                p->retcode = cpu_to_be32(retcode);
                drbd_send_command(peer_device, sock, P_STATE_CHG_REPLY, sizeof(*p), NULL, 0);
        }
}

void conn_send_sr_reply(struct drbd_connection *connection, enum drbd_state_rv retcode)
{
        struct drbd_socket *sock;
        struct p_req_state_reply *p;
        enum drbd_packet cmd = connection->agreed_pro_version < 100 ? P_STATE_CHG_REPLY : P_CONN_ST_CHG_REPLY;

        sock = &connection->meta;
        p = conn_prepare_command(connection, sock);
        if (p) {
                p->retcode = cpu_to_be32(retcode);
                conn_send_command(connection, sock, cmd, sizeof(*p), NULL, 0);
        }
}

static void dcbp_set_code(struct p_compressed_bm *p, enum drbd_bitmap_code code)
{
        BUG_ON(code & ~0xf);
        p->encoding = (p->encoding & ~0xf) | code;
}

static void dcbp_set_start(struct p_compressed_bm *p, int set)
{
        p->encoding = (p->encoding & ~0x80) | (set ? 0x80 : 0);
}

static void dcbp_set_pad_bits(struct p_compressed_bm *p, int n)
{
        BUG_ON(n & ~0x7);
        p->encoding = (p->encoding & (~0x7 << 4)) | (n << 4);
}

static int fill_bitmap_rle_bits(struct drbd_device *device,
                         struct p_compressed_bm *p,
                         unsigned int size,
                         struct bm_xfer_ctx *c)
{
        struct bitstream bs;
        unsigned long plain_bits;
        unsigned long tmp;
        unsigned long rl;
        unsigned len;
        unsigned toggle;
        int bits, use_rle;

        /* may we use this feature? */
        rcu_read_lock();
        use_rle = rcu_dereference(first_peer_device(device)->connection->net_conf)->use_rle;
        rcu_read_unlock();
        if (!use_rle || first_peer_device(device)->connection->agreed_pro_version < 90)
                return 0;

        if (c->bit_offset >= c->bm_bits)
                return 0; /* nothing to do. */

        /* use at most thus many bytes */
        bitstream_init(&bs, p->code, size, 0);
        memset(p->code, 0, size);
        /* plain bits covered in this code string */
        plain_bits = 0;

        /* p->encoding & 0x80 stores whether the first run length is set.
         * bit offset is implicit.
         * start with toggle == 2 to be able to tell the first iteration */
        toggle = 2;

        /* see how much plain bits we can stuff into one packet
         * using RLE and VLI. */
        do {
                tmp = (toggle == 0) ? _drbd_bm_find_next_zero(device, c->bit_offset)
                                    : _drbd_bm_find_next(device, c->bit_offset);
                if (tmp == -1UL)
                        tmp = c->bm_bits;
                rl = tmp - c->bit_offset;

                if (toggle == 2) { /* first iteration */
                        if (rl == 0) {
                                /* the first checked bit was set,
                                 * store start value, */
                                dcbp_set_start(p, 1);
                                /* but skip encoding of zero run length */
                                toggle = !toggle;
                                continue;
                        }
                        dcbp_set_start(p, 0);
                }

                /* paranoia: catch zero runlength.
                 * can only happen if bitmap is modified while we scan it. */
                if (rl == 0) {
                        drbd_err(device, "unexpected zero runlength while encoding bitmap "
                            "t:%u bo:%lu\n", toggle, c->bit_offset);
                        return -1;
                }

                bits = vli_encode_bits(&bs, rl);
                if (bits == -ENOBUFS) /* buffer full */
                        break;
                if (bits <= 0) {
                        drbd_err(device, "error while encoding bitmap: %d\n", bits);
                        return 0;
                }

                toggle = !toggle;
                plain_bits += rl;
                c->bit_offset = tmp;
        } while (c->bit_offset < c->bm_bits);

        len = bs.cur.b - p->code + !!bs.cur.bit;

        if (plain_bits < (len << 3)) {
                /* incompressible with this method.
                 * we need to rewind both word and bit position. */
                c->bit_offset -= plain_bits;
                bm_xfer_ctx_bit_to_word_offset(c);
                c->bit_offset = c->word_offset * BITS_PER_LONG;
                return 0;
        }

        /* RLE + VLI was able to compress it just fine.
         * update c->word_offset. */
        bm_xfer_ctx_bit_to_word_offset(c);

        /* store pad_bits */
        dcbp_set_pad_bits(p, (8 - bs.cur.bit) & 0x7);

        return len;
}

/**
 * send_bitmap_rle_or_plain
 *
 * Return 0 when done, 1 when another iteration is needed, and a negative error
 * code upon failure.
 */
static int
send_bitmap_rle_or_plain(struct drbd_device *device, struct bm_xfer_ctx *c)
{
        struct drbd_socket *sock = &first_peer_device(device)->connection->data;
        unsigned int header_size = drbd_header_size(first_peer_device(device)->connection);
        struct p_compressed_bm *p = sock->sbuf + header_size;
        int len, err;

        len = fill_bitmap_rle_bits(device, p,
                        DRBD_SOCKET_BUFFER_SIZE - header_size - sizeof(*p), c);
        if (len < 0)
                return -EIO;

        if (len) {
                dcbp_set_code(p, RLE_VLI_Bits);
                err = __send_command(first_peer_device(device)->connection, device->vnr, sock,
                                     P_COMPRESSED_BITMAP, sizeof(*p) + len,
                                     NULL, 0);
                c->packets[0]++;
                c->bytes[0] += header_size + sizeof(*p) + len;

                if (c->bit_offset >= c->bm_bits)
                        len = 0; /* DONE */
        } else {
                /* was not compressible.
                 * send a buffer full of plain text bits instead. */
                unsigned int data_size;
                unsigned long num_words;
                unsigned long *p = sock->sbuf + header_size;

                data_size = DRBD_SOCKET_BUFFER_SIZE - header_size;
                num_words = min_t(size_t, data_size / sizeof(*p),
                                  c->bm_words - c->word_offset);
                len = num_words * sizeof(*p);
                if (len)
                        drbd_bm_get_lel(device, c->word_offset, num_words, p);
                err = __send_command(first_peer_device(device)->connection, device->vnr, sock, P_BITMAP, len, NULL, 0);
                c->word_offset += num_words;
                c->bit_offset = c->word_offset * BITS_PER_LONG;

                c->packets[1]++;
                c->bytes[1] += header_size + len;

                if (c->bit_offset > c->bm_bits)
                        c->bit_offset = c->bm_bits;
        }
        if (!err) {
                if (len == 0) {
                        INFO_bm_xfer_stats(device, "send", c);
                        return 0;
                } else
                        return 1;
        }
        return -EIO;
}

/* See the comment at receive_bitmap() */
static int _drbd_send_bitmap(struct drbd_device *device)
{
        struct bm_xfer_ctx c;
        int err;

        if (!expect(device->bitmap))
                return false;

        if (get_ldev(device)) {
                if (drbd_md_test_flag(device->ldev, MDF_FULL_SYNC)) {
                        drbd_info(device, "Writing the whole bitmap, MDF_FullSync was set.\n");
                        drbd_bm_set_all(device);
                        if (drbd_bm_write(device)) {
                                /* write_bm did fail! Leave full sync flag set in Meta P_DATA
                                 * but otherwise process as per normal - need to tell other
                                 * side that a full resync is required! */
                                drbd_err(device, "Failed to write bitmap to disk!\n");
                        } else {
                                drbd_md_clear_flag(device, MDF_FULL_SYNC);
                                drbd_md_sync(device);
                        }
                }
                put_ldev(device);
        }

        c = (struct bm_xfer_ctx) {
                .bm_bits = drbd_bm_bits(device),
                .bm_words = drbd_bm_words(device),
        };

        do {
                err = send_bitmap_rle_or_plain(device, &c);
        } while (err > 0);

        return err == 0;
}

int drbd_send_bitmap(struct drbd_device *device)
{
        struct drbd_socket *sock = &first_peer_device(device)->connection->data;
        int err = -1;

        mutex_lock(&sock->mutex);
        if (sock->socket)
                err = !_drbd_send_bitmap(device);
        mutex_unlock(&sock->mutex);
        return err;
}

void drbd_send_b_ack(struct drbd_connection *connection, u32 barrier_nr, u32 set_size)
{
        struct drbd_socket *sock;
        struct p_barrier_ack *p;

        if (connection->cstate < C_WF_REPORT_PARAMS)
                return;

        sock = &connection->meta;
        p = conn_prepare_command(connection, sock);
        if (!p)
                return;
        p->barrier = barrier_nr;
        p->set_size = cpu_to_be32(set_size);
        conn_send_command(connection, sock, P_BARRIER_ACK, sizeof(*p), NULL, 0);
}

/**
 * _drbd_send_ack() - Sends an ack packet
 * @device:     DRBD device.
 * @cmd:        Packet command code.
 * @sector:     sector, needs to be in big endian byte order
 * @blksize:    size in byte, needs to be in big endian byte order
 * @block_id:   Id, big endian byte order
 */
static int _drbd_send_ack(struct drbd_peer_device *peer_device, enum drbd_packet cmd,
                          u64 sector, u32 blksize, u64 block_id)
{
        struct drbd_socket *sock;
        struct p_block_ack *p;

        if (peer_device->device->state.conn < C_CONNECTED)
                return -EIO;

        sock = &peer_device->connection->meta;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->sector = sector;
        p->block_id = block_id;
        p->blksize = blksize;
        p->seq_num = cpu_to_be32(atomic_inc_return(&peer_device->device->packet_seq));
        return drbd_send_command(peer_device, sock, cmd, sizeof(*p), NULL, 0);
}

/* dp->sector and dp->block_id already/still in network byte order,
 * data_size is payload size according to dp->head,
 * and may need to be corrected for digest size. */
void drbd_send_ack_dp(struct drbd_peer_device *peer_device, enum drbd_packet cmd,
                      struct p_data *dp, int data_size)
{
        if (peer_device->connection->peer_integrity_tfm)
                data_size -= crypto_shash_digestsize(peer_device->connection->peer_integrity_tfm);
        _drbd_send_ack(peer_device, cmd, dp->sector, cpu_to_be32(data_size),
                       dp->block_id);
}

void drbd_send_ack_rp(struct drbd_peer_device *peer_device, enum drbd_packet cmd,
                      struct p_block_req *rp)
{
        _drbd_send_ack(peer_device, cmd, rp->sector, rp->blksize, rp->block_id);
}

/**
 * drbd_send_ack() - Sends an ack packet
 * @device:     DRBD device
 * @cmd:        packet command code
 * @peer_req:   peer request
 */
int drbd_send_ack(struct drbd_peer_device *peer_device, enum drbd_packet cmd,
                  struct drbd_peer_request *peer_req)
{
        return _drbd_send_ack(peer_device, cmd,
                              cpu_to_be64(peer_req->i.sector),
                              cpu_to_be32(peer_req->i.size),
                              peer_req->block_id);
}

/* This function misuses the block_id field to signal if the blocks
 * are is sync or not. */
int drbd_send_ack_ex(struct drbd_peer_device *peer_device, enum drbd_packet cmd,
                     sector_t sector, int blksize, u64 block_id)
{
        return _drbd_send_ack(peer_device, cmd,
                              cpu_to_be64(sector),
                              cpu_to_be32(blksize),
                              cpu_to_be64(block_id));
}

int drbd_send_rs_deallocated(struct drbd_peer_device *peer_device,
                             struct drbd_peer_request *peer_req)
{
        struct drbd_socket *sock;
        struct p_block_desc *p;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->sector = cpu_to_be64(peer_req->i.sector);
        p->blksize = cpu_to_be32(peer_req->i.size);
        p->pad = 0;
        return drbd_send_command(peer_device, sock, P_RS_DEALLOCATED, sizeof(*p), NULL, 0);
}

int drbd_send_drequest(struct drbd_peer_device *peer_device, int cmd,
                       sector_t sector, int size, u64 block_id)
{
        struct drbd_socket *sock;
        struct p_block_req *p;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->sector = cpu_to_be64(sector);
        p->block_id = block_id;
        p->blksize = cpu_to_be32(size);
        return drbd_send_command(peer_device, sock, cmd, sizeof(*p), NULL, 0);
}

int drbd_send_drequest_csum(struct drbd_peer_device *peer_device, sector_t sector, int size,
                            void *digest, int digest_size, enum drbd_packet cmd)
{
        struct drbd_socket *sock;
        struct p_block_req *p;

        /* FIXME: Put the digest into the preallocated socket buffer.  */

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->sector = cpu_to_be64(sector);
        p->block_id = ID_SYNCER /* unused */;
        p->blksize = cpu_to_be32(size);
        return drbd_send_command(peer_device, sock, cmd, sizeof(*p), digest, digest_size);
}

int drbd_send_ov_request(struct drbd_peer_device *peer_device, sector_t sector, int size)
{
        struct drbd_socket *sock;
        struct p_block_req *p;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->sector = cpu_to_be64(sector);
        p->block_id = ID_SYNCER /* unused */;
        p->blksize = cpu_to_be32(size);
        return drbd_send_command(peer_device, sock, P_OV_REQUEST, sizeof(*p), NULL, 0);
}

/* called on sndtimeo
 * returns false if we should retry,
 * true if we think connection is dead
 */
static int we_should_drop_the_connection(struct drbd_connection *connection, struct socket *sock)
{
        int drop_it;
        /* long elapsed = (long)(jiffies - device->last_received); */

        drop_it =   connection->meta.socket == sock
                || !connection->ack_receiver.task
                || get_t_state(&connection->ack_receiver) != RUNNING
                || connection->cstate < C_WF_REPORT_PARAMS;

        if (drop_it)
                return true;

        drop_it = !--connection->ko_count;
        if (!drop_it) {
                drbd_err(connection, "[%s/%d] sock_sendmsg time expired, ko = %u\n",
                         current->comm, current->pid, connection->ko_count);
                request_ping(connection);
        }

        return drop_it; /* && (device->state == R_PRIMARY) */;
}

static void drbd_update_congested(struct drbd_connection *connection)
{
        struct sock *sk = connection->data.socket->sk;
        if (sk->sk_wmem_queued > sk->sk_sndbuf * 4 / 5)
                set_bit(NET_CONGESTED, &connection->flags);
}

/* The idea of sendpage seems to be to put some kind of reference
 * to the page into the skb, and to hand it over to the NIC. In
 * this process get_page() gets called.
 *
 * As soon as the page was really sent over the network put_page()
 * gets called by some part of the network layer. [ NIC driver? ]
 *
 * [ get_page() / put_page() increment/decrement the count. If count
 *   reaches 0 the page will be freed. ]
 *
 * This works nicely with pages from FSs.
 * But this means that in protocol A we might signal IO completion too early!
 *
 * In order not to corrupt data during a resync we must make sure
 * that we do not reuse our own buffer pages (EEs) to early, therefore
 * we have the net_ee list.
 *
 * XFS seems to have problems, still, it submits pages with page_count == 0!
 * As a workaround, we disable sendpage on pages
 * with page_count == 0 or PageSlab.
 */
static int _drbd_no_send_page(struct drbd_peer_device *peer_device, struct page *page,
                              int offset, size_t size, unsigned msg_flags)
{
        struct socket *socket;
        void *addr;
        int err;

        socket = peer_device->connection->data.socket;
        addr = kmap(page) + offset;
        err = drbd_send_all(peer_device->connection, socket, addr, size, msg_flags);
        kunmap(page);
        if (!err)
                peer_device->device->send_cnt += size >> 9;
        return err;
}

static int _drbd_send_page(struct drbd_peer_device *peer_device, struct page *page,
                    int offset, size_t size, unsigned msg_flags)
{
        struct socket *socket = peer_device->connection->data.socket;
        int len = size;
        int err = -EIO;

        /* e.g. XFS meta- & log-data is in slab pages, which have a
         * page_count of 0 and/or have PageSlab() set.
         * we cannot use send_page for those, as that does get_page();
         * put_page(); and would cause either a VM_BUG directly, or
         * __page_cache_release a page that would actually still be referenced
         * by someone, leading to some obscure delayed Oops somewhere else. */
        if (drbd_disable_sendpage || (page_count(page) < 1) || PageSlab(page))
                return _drbd_no_send_page(peer_device, page, offset, size, msg_flags);

        msg_flags |= MSG_NOSIGNAL;
        drbd_update_congested(peer_device->connection);
        do {
                int sent;

                sent = socket->ops->sendpage(socket, page, offset, len, msg_flags);
                if (sent <= 0) {
                        if (sent == -EAGAIN) {
                                if (we_should_drop_the_connection(peer_device->connection, socket))
                                        break;
                                continue;
                        }
                        drbd_warn(peer_device->device, "%s: size=%d len=%d sent=%d\n",
                             __func__, (int)size, len, sent);
                        if (sent < 0)
                                err = sent;
                        break;
                }
                len    -= sent;
                offset += sent;
        } while (len > 0 /* THINK && device->cstate >= C_CONNECTED*/);
        clear_bit(NET_CONGESTED, &peer_device->connection->flags);

        if (len == 0) {
                err = 0;
                peer_device->device->send_cnt += size >> 9;
        }
        return err;
}

static int _drbd_send_bio(struct drbd_peer_device *peer_device, struct bio *bio)
{
        struct bio_vec bvec;
        struct bvec_iter iter;

        /* hint all but last page with MSG_MORE */
        bio_for_each_segment(bvec, bio, iter) {
                int err;

                err = _drbd_no_send_page(peer_device, bvec.bv_page,
                                         bvec.bv_offset, bvec.bv_len,
                                         bio_iter_last(bvec, iter)
                                         ? 0 : MSG_MORE);
                if (err)
                        return err;
                /* REQ_OP_WRITE_SAME has only one segment */
                if (bio_op(bio) == REQ_OP_WRITE_SAME)
                        break;
        }
        return 0;
}

static int _drbd_send_zc_bio(struct drbd_peer_device *peer_device, struct bio *bio)
{
        struct bio_vec bvec;
        struct bvec_iter iter;

        /* hint all but last page with MSG_MORE */
        bio_for_each_segment(bvec, bio, iter) {
                int err;

                err = _drbd_send_page(peer_device, bvec.bv_page,
                                      bvec.bv_offset, bvec.bv_len,
                                      bio_iter_last(bvec, iter) ? 0 : MSG_MORE);
                if (err)
                        return err;
                /* REQ_OP_WRITE_SAME has only one segment */
                if (bio_op(bio) == REQ_OP_WRITE_SAME)
                        break;
        }
        return 0;
}

static int _drbd_send_zc_ee(struct drbd_peer_device *peer_device,
                            struct drbd_peer_request *peer_req)
{
        struct page *page = peer_req->pages;
        unsigned len = peer_req->i.size;
        int err;

        /* hint all but last page with MSG_MORE */
        page_chain_for_each(page) {
                unsigned l = min_t(unsigned, len, PAGE_SIZE);

                err = _drbd_send_page(peer_device, page, 0, l,
                                      page_chain_next(page) ? MSG_MORE : 0);
                if (err)
                        return err;
                len -= l;
        }
        return 0;
}

static u32 bio_flags_to_wire(struct drbd_connection *connection,
                             struct bio *bio)
{
        if (connection->agreed_pro_version >= 95)
                return  (bio->bi_opf & REQ_SYNC ? DP_RW_SYNC : 0) |
                        (bio->bi_opf & REQ_FUA ? DP_FUA : 0) |
                        (bio->bi_opf & REQ_PREFLUSH ? DP_FLUSH : 0) |
                        (bio_op(bio) == REQ_OP_WRITE_SAME ? DP_WSAME : 0) |
                        (bio_op(bio) == REQ_OP_DISCARD ? DP_DISCARD : 0) |
                        (bio_op(bio) == REQ_OP_WRITE_ZEROES ?
                          ((connection->agreed_features & DRBD_FF_WZEROES) ?
                           (DP_ZEROES |(!(bio->bi_opf & REQ_NOUNMAP) ? DP_DISCARD : 0))
                           : DP_DISCARD)
                        : 0);
        else
                return bio->bi_opf & REQ_SYNC ? DP_RW_SYNC : 0;
}

/* Used to send write or TRIM aka REQ_OP_DISCARD requests
 * R_PRIMARY -> Peer    (P_DATA, P_TRIM)
 */
int drbd_send_dblock(struct drbd_peer_device *peer_device, struct drbd_request *req)
{
        struct drbd_device *device = peer_device->device;
        struct drbd_socket *sock;
        struct p_data *p;
        struct p_wsame *wsame = NULL;
        void *digest_out;
        unsigned int dp_flags = 0;
        int digest_size;
        int err;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        digest_size = peer_device->connection->integrity_tfm ?
                      crypto_shash_digestsize(peer_device->connection->integrity_tfm) : 0;

        if (!p)
                return -EIO;
        p->sector = cpu_to_be64(req->i.sector);
        p->block_id = (unsigned long)req;
        p->seq_num = cpu_to_be32(atomic_inc_return(&device->packet_seq));
        dp_flags = bio_flags_to_wire(peer_device->connection, req->master_bio);
        if (device->state.conn >= C_SYNC_SOURCE &&
            device->state.conn <= C_PAUSED_SYNC_T)
                dp_flags |= DP_MAY_SET_IN_SYNC;
        if (peer_device->connection->agreed_pro_version >= 100) {
                if (req->rq_state & RQ_EXP_RECEIVE_ACK)
                        dp_flags |= DP_SEND_RECEIVE_ACK;
                /* During resync, request an explicit write ack,
                 * even in protocol != C */
                if (req->rq_state & RQ_EXP_WRITE_ACK
                || (dp_flags & DP_MAY_SET_IN_SYNC))
                        dp_flags |= DP_SEND_WRITE_ACK;
        }
        p->dp_flags = cpu_to_be32(dp_flags);

        if (dp_flags & (DP_DISCARD|DP_ZEROES)) {
                enum drbd_packet cmd = (dp_flags & DP_ZEROES) ? P_ZEROES : P_TRIM;
                struct p_trim *t = (struct p_trim*)p;
                t->size = cpu_to_be32(req->i.size);
                err = __send_command(peer_device->connection, device->vnr, sock, cmd, sizeof(*t), NULL, 0);
                goto out;
        }
        if (dp_flags & DP_WSAME) {
                /* this will only work if DRBD_FF_WSAME is set AND the
                 * handshake agreed that all nodes and backend devices are
                 * WRITE_SAME capable and agree on logical_block_size */
                wsame = (struct p_wsame*)p;
                digest_out = wsame + 1;
                wsame->size = cpu_to_be32(req->i.size);
        } else
                digest_out = p + 1;

        /* our digest is still only over the payload.
         * TRIM does not carry any payload. */
        if (digest_size)
                drbd_csum_bio(peer_device->connection->integrity_tfm, req->master_bio, digest_out);
        if (wsame) {
                err =
                    __send_command(peer_device->connection, device->vnr, sock, P_WSAME,
                                   sizeof(*wsame) + digest_size, NULL,
                                   bio_iovec(req->master_bio).bv_len);
        } else
                err =
                    __send_command(peer_device->connection, device->vnr, sock, P_DATA,
                                   sizeof(*p) + digest_size, NULL, req->i.size);
        if (!err) {
                /* For protocol A, we have to memcpy the payload into
                 * socket buffers, as we may complete right away
                 * as soon as we handed it over to tcp, at which point the data
                 * pages may become invalid.
                 *
                 * For data-integrity enabled, we copy it as well, so we can be
                 * sure that even if the bio pages may still be modified, it
                 * won't change the data on the wire, thus if the digest checks
                 * out ok after sending on this side, but does not fit on the
                 * receiving side, we sure have detected corruption elsewhere.
                 */
                if (!(req->rq_state & (RQ_EXP_RECEIVE_ACK | RQ_EXP_WRITE_ACK)) || digest_size)
                        err = _drbd_send_bio(peer_device, req->master_bio);
                else
                        err = _drbd_send_zc_bio(peer_device, req->master_bio);

                /* double check digest, sometimes buffers have been modified in flight. */
                if (digest_size > 0 && digest_size <= 64) {
                        /* 64 byte, 512 bit, is the largest digest size
                         * currently supported in kernel crypto. */
                        unsigned char digest[64];
                        drbd_csum_bio(peer_device->connection->integrity_tfm, req->master_bio, digest);
                        if (memcmp(p + 1, digest, digest_size)) {
                                drbd_warn(device,
                                        "Digest mismatch, buffer modified by upper layers during write: %llus +%u\n",
                                        (unsigned long long)req->i.sector, req->i.size);
                        }
                } /* else if (digest_size > 64) {
                     ... Be noisy about digest too large ...
                } */
        }
out:
        mutex_unlock(&sock->mutex);  /* locked by drbd_prepare_command() */

        return err;
}

/* answer packet, used to send data back for read requests:
 *  Peer       -> (diskless) R_PRIMARY   (P_DATA_REPLY)
 *  C_SYNC_SOURCE -> C_SYNC_TARGET         (P_RS_DATA_REPLY)
 */
int drbd_send_block(struct drbd_peer_device *peer_device, enum drbd_packet cmd,
                    struct drbd_peer_request *peer_req)
{
        struct drbd_device *device = peer_device->device;
        struct drbd_socket *sock;
        struct p_data *p;
        int err;
        int digest_size;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);

        digest_size = peer_device->connection->integrity_tfm ?
                      crypto_shash_digestsize(peer_device->connection->integrity_tfm) : 0;

        if (!p)
                return -EIO;
        p->sector = cpu_to_be64(peer_req->i.sector);
        p->block_id = peer_req->block_id;
        p->seq_num = 0;  /* unused */
        p->dp_flags = 0;
        if (digest_size)
                drbd_csum_ee(peer_device->connection->integrity_tfm, peer_req, p + 1);
        err = __send_command(peer_device->connection, device->vnr, sock, cmd, sizeof(*p) + digest_size, NULL, peer_req->i.size);
        if (!err)
                err = _drbd_send_zc_ee(peer_device, peer_req);
        mutex_unlock(&sock->mutex);  /* locked by drbd_prepare_command() */

        return err;
}

int drbd_send_out_of_sync(struct drbd_peer_device *peer_device, struct drbd_request *req)
{
        struct drbd_socket *sock;
        struct p_block_desc *p;

        sock = &peer_device->connection->data;
        p = drbd_prepare_command(peer_device, sock);
        if (!p)
                return -EIO;
        p->sector = cpu_to_be64(req->i.sector);
        p->blksize = cpu_to_be32(req->i.size);
        return drbd_send_command(peer_device, sock, P_OUT_OF_SYNC, sizeof(*p), NULL, 0);
}

/*
  drbd_send distinguishes two cases:

  Packets sent via the data socket "sock"
  and packets sent via the meta data socket "msock"

                    sock                      msock
  -----------------+-------------------------+------------------------------
  timeout           conf.timeout / 2          conf.timeout / 2
  timeout action    send a ping via msock     Abort communication
                                              and close all sockets
*/

/*
 * you must have down()ed the appropriate [m]sock_mutex elsewhere!
 */
int drbd_send(struct drbd_connection *connection, struct socket *sock,
              void *buf, size_t size, unsigned msg_flags)
{
        struct kvec iov = {.iov_base = buf, .iov_len = size};
        struct msghdr msg = {.msg_flags = msg_flags | MSG_NOSIGNAL};
        int rv, sent = 0;

        if (!sock)
                return -EBADR;

        /* THINK  if (signal_pending) return ... ? */

        iov_iter_kvec(&msg.msg_iter, WRITE, &iov, 1, size);

        if (sock == connection->data.socket) {
                rcu_read_lock();
                connection->ko_count = rcu_dereference(connection->net_conf)->ko_count;
                rcu_read_unlock();
                drbd_update_congested(connection);
        }
        do {
                rv = sock_sendmsg(sock, &msg);
                if (rv == -EAGAIN) {
                        if (we_should_drop_the_connection(connection, sock))
                                break;
                        else
                                continue;
                }
                if (rv == -EINTR) {
                        flush_signals(current);
                        rv = 0;
                }
                if (rv < 0)
                        break;
                sent += rv;
        } while (sent < size);

        if (sock == connection->data.socket)
                clear_bit(NET_CONGESTED, &connection->flags);

        if (rv <= 0) {
                if (rv != -EAGAIN) {
                        drbd_err(connection, "%s_sendmsg returned %d\n",
                                 sock == connection->meta.socket ? "msock" : "sock",
                                 rv);
                        conn_request_state(connection, NS(conn, C_BROKEN_PIPE), CS_HARD);
                } else
                        conn_request_state(connection, NS(conn, C_TIMEOUT), CS_HARD);
        }

        return sent;
}

/**
 * drbd_send_all  -  Send an entire buffer
 *
 * Returns 0 upon success and a negative error value otherwise.
 */
int drbd_send_all(struct drbd_connection *connection, struct socket *sock, void *buffer,
                  size_t size, unsigned msg_flags)
{
        int err;

        err = drbd_send(connection, sock, buffer, size, msg_flags);
        if (err < 0)
                return err;
        if (err != size)
                return -EIO;
        return 0;
}

static int drbd_open(struct block_device *bdev, fmode_t mode)
{
        struct drbd_device *device = bdev->bd_disk->private_data;
        unsigned long flags;
        int rv = 0;

        mutex_lock(&drbd_main_mutex);
        spin_lock_irqsave(&device->resource->req_lock, flags);
        /* to have a stable device->state.role
         * and no race with updating open_cnt */

        if (device->state.role != R_PRIMARY) {
                if (mode & FMODE_WRITE)
                        rv = -EROFS;
                else if (!drbd_allow_oos)
                        rv = -EMEDIUMTYPE;
        }

        if (!rv)
                device->open_cnt++;
        spin_unlock_irqrestore(&device->resource->req_lock, flags);
        mutex_unlock(&drbd_main_mutex);

        return rv;
}

static void drbd_release(struct gendisk *gd, fmode_t mode)
{
        struct drbd_device *device = gd->private_data;
        mutex_lock(&drbd_main_mutex);
        device->open_cnt--;
        mutex_unlock(&drbd_main_mutex);
}

/* need to hold resource->req_lock */
void drbd_queue_unplug(struct drbd_device *device)
{
        if (device->state.pdsk >= D_INCONSISTENT && device->state.conn >= C_CONNECTED) {
                D_ASSERT(device, device->state.role == R_PRIMARY);
                if (test_and_clear_bit(UNPLUG_REMOTE, &device->flags)) {
                        drbd_queue_work_if_unqueued(
                                &first_peer_device(device)->connection->sender_work,
                                &device->unplug_work);
                }
        }
}

static void drbd_set_defaults(struct drbd_device *device)
{
        /* Beware! The actual layout differs
         * between big endian and little endian */
        device->state = (union drbd_dev_state) {
                { .role = R_SECONDARY,
                  .peer = R_UNKNOWN,
                  .conn = C_STANDALONE,
                  .disk = D_DISKLESS,
                  .pdsk = D_UNKNOWN,
                } };
}

void drbd_init_set_defaults(struct drbd_device *device)
{
        /* the memset(,0,) did most of this.
         * note: only assignments, no allocation in here */

        drbd_set_defaults(device);

        atomic_set(&device->ap_bio_cnt, 0);
        atomic_set(&device->ap_actlog_cnt, 0);
        atomic_set(&device->ap_pending_cnt, 0);
        atomic_set(&device->rs_pending_cnt, 0);
        atomic_set(&device->unacked_cnt, 0);
        atomic_set(&device->local_cnt, 0);
        atomic_set(&device->pp_in_use_by_net, 0);
        atomic_set(&device->rs_sect_in, 0);
        atomic_set(&device->rs_sect_ev, 0);
        atomic_set(&device->ap_in_flight, 0);
        atomic_set(&device->md_io.in_use, 0);

        mutex_init(&device->own_state_mutex);
        device->state_mutex = &device->own_state_mutex;

        spin_lock_init(&device->al_lock);
        spin_lock_init(&device->peer_seq_lock);

        INIT_LIST_HEAD(&device->active_ee);
        INIT_LIST_HEAD(&device->sync_ee);
        INIT_LIST_HEAD(&device->done_ee);

        INIT_LIST_HEAD(&device->read_ee);
        INIT_LIST_HEAD(&device->net_ee);
        INIT_LIST_HEAD(&device->resync_reads);
        INIT_LIST_HEAD(&device->resync_work.list);
        INIT_LIST_HEAD(&device->unplug_work.list);
        INIT_LIST_HEAD(&device->bm_io_work.w.list);
        INIT_LIST_HEAD(&device->pending_master_completion[0]);
        INIT_LIST_HEAD(&device->pending_master_completion[1]);
        INIT_LIST_HEAD(&device->pending_completion[0]);
        INIT_LIST_HEAD(&device->pending_completion[1]);

        device->resync_work.cb  = w_resync_timer;
        device->unplug_work.cb  = w_send_write_hint;
        device->bm_io_work.w.cb = w_bitmap_io;

        timer_setup(&device->resync_timer, resync_timer_fn, 0);
        timer_setup(&device->md_sync_timer, md_sync_timer_fn, 0);
        timer_setup(&device->start_resync_timer, start_resync_timer_fn, 0);
        timer_setup(&device->request_timer, request_timer_fn, 0);

        init_waitqueue_head(&device->misc_wait);
        init_waitqueue_head(&device->state_wait);
        init_waitqueue_head(&device->ee_wait);
        init_waitqueue_head(&device->al_wait);
        init_waitqueue_head(&device->seq_wait);

        device->resync_wenr = LC_FREE;
        device->peer_max_bio_size = DRBD_MAX_BIO_SIZE_SAFE;
        device->local_max_bio_size = DRBD_MAX_BIO_SIZE_SAFE;
}

static void _drbd_set_my_capacity(struct drbd_device *device, sector_t size)
{
        /* set_capacity(device->this_bdev->bd_disk, size); */
        set_capacity(device->vdisk, size);
        device->this_bdev->bd_inode->i_size = (loff_t)size << 9;
}

void drbd_set_my_capacity(struct drbd_device *device, sector_t size)
{
        char ppb[10];
        _drbd_set_my_capacity(device, size);
        drbd_info(device, "size = %s (%llu KB)\n",
                ppsize(ppb, size>>1), (unsigned long long)size>>1);
}

void drbd_device_cleanup(struct drbd_device *device)
{
        int i;
        if (first_peer_device(device)->connection->receiver.t_state != NONE)
                drbd_err(device, "ASSERT FAILED: receiver t_state == %d expected 0.\n",
                                first_peer_device(device)->connection->receiver.t_state);

        device->al_writ_cnt  =
        device->bm_writ_cnt  =
        device->read_cnt     =
        device->recv_cnt     =
        device->send_cnt     =
        device->writ_cnt     =
        device->p_size       =
        device->rs_start     =
        device->rs_total     =
        device->rs_failed    = 0;
        device->rs_last_events = 0;
        device->rs_last_sect_ev = 0;
        for (i = 0; i < DRBD_SYNC_MARKS; i++) {
                device->rs_mark_left[i] = 0;
                device->rs_mark_time[i] = 0;
        }
        D_ASSERT(device, first_peer_device(device)->connection->net_conf == NULL);

        _drbd_set_my_capacity(device, 0);
        if (device->bitmap) {
                /* maybe never allocated. */
                drbd_bm_resize(device, 0, 1);
                drbd_bm_cleanup(device);
        }

        drbd_backing_dev_free(device, device->ldev);
        device->ldev = NULL;

        clear_bit(AL_SUSPENDED, &device->flags);

        D_ASSERT(device, list_empty(&device->active_ee));
        D_ASSERT(device, list_empty(&device->sync_ee));
        D_ASSERT(device, list_empty(&device->done_ee));
        D_ASSERT(device, list_empty(&device->read_ee));
        D_ASSERT(device, list_empty(&device->net_ee));
        D_ASSERT(device, list_empty(&device->resync_reads));
        D_ASSERT(device, list_empty(&first_peer_device(device)->connection->sender_work.q));
        D_ASSERT(device, list_empty(&device->resync_work.list));
        D_ASSERT(device, list_empty(&device->unplug_work.list));

        drbd_set_defaults(device);
}


static void drbd_destroy_mempools(void)
{
        struct page *page;

        while (drbd_pp_pool) {
                page = drbd_pp_pool;
                drbd_pp_pool = (struct page *)page_private(page);
                __free_page(page);
                drbd_pp_vacant--;
        }

        /* D_ASSERT(device, atomic_read(&drbd_pp_vacant)==0); */

        bioset_exit(&drbd_io_bio_set);
        bioset_exit(&drbd_md_io_bio_set);
        mempool_exit(&drbd_md_io_page_pool);
        mempool_exit(&drbd_ee_mempool);
        mempool_exit(&drbd_request_mempool);
        kmem_cache_destroy(drbd_ee_cache);
        kmem_cache_destroy(drbd_request_cache);
        kmem_cache_destroy(drbd_bm_ext_cache);
        kmem_cache_destroy(drbd_al_ext_cache);

        drbd_ee_cache        = NULL;
        drbd_request_cache   = NULL;
        drbd_bm_ext_cache    = NULL;
        drbd_al_ext_cache    = NULL;

        return;
}

static int drbd_create_mempools(void)
{
        struct page *page;
        const int number = (DRBD_MAX_BIO_SIZE/PAGE_SIZE) * drbd_minor_count;
        int i, ret;

        /* caches */
        drbd_request_cache = kmem_cache_create(
                "drbd_req", sizeof(struct drbd_request), 0, 0, NULL);
        if (drbd_request_cache == NULL)
                goto Enomem;

        drbd_ee_cache = kmem_cache_create(
                "drbd_ee", sizeof(struct drbd_peer_request), 0, 0, NULL);
        if (drbd_ee_cache == NULL)
                goto Enomem;

        drbd_bm_ext_cache = kmem_cache_create(
                "drbd_bm", sizeof(struct bm_extent), 0, 0, NULL);
        if (drbd_bm_ext_cache == NULL)
                goto Enomem;

        drbd_al_ext_cache = kmem_cache_create(
                "drbd_al", sizeof(struct lc_element), 0, 0, NULL);
        if (drbd_al_ext_cache == NULL)
                goto Enomem;

        /* mempools */
        ret = bioset_init(&drbd_io_bio_set, BIO_POOL_SIZE, 0, 0);
        if (ret)
                goto Enomem;

        ret = bioset_init(&drbd_md_io_bio_set, DRBD_MIN_POOL_PAGES, 0,
                          BIOSET_NEED_BVECS);
        if (ret)
                goto Enomem;

        ret = mempool_init_page_pool(&drbd_md_io_page_pool, DRBD_MIN_POOL_PAGES, 0);
        if (ret)
                goto Enomem;

        ret = mempool_init_slab_pool(&drbd_request_mempool, number,
                                     drbd_request_cache);
        if (ret)
                goto Enomem;

        ret = mempool_init_slab_pool(&drbd_ee_mempool, number, drbd_ee_cache);
        if (ret)
                goto Enomem;

        /* drbd's page pool */
        spin_lock_init(&drbd_pp_lock);

        for (i = 0; i < number; i++) {
                page = alloc_page(GFP_HIGHUSER);
                if (!page)
                        goto Enomem;
                set_page_private(page, (unsigned long)drbd_pp_pool);
                drbd_pp_pool = page;
        }
        drbd_pp_vacant = number;

        return 0;

Enomem:
        drbd_destroy_mempools(); /* in case we allocated some */
        return -ENOMEM;
}

static void drbd_release_all_peer_reqs(struct drbd_device *device)
{
        int rr;

        rr = drbd_free_peer_reqs(device, &device->active_ee);
        if (rr)
                drbd_err(device, "%d EEs in active list found!\n", rr);

        rr = drbd_free_peer_reqs(device, &device->sync_ee);
        if (rr)
                drbd_err(device, "%d EEs in sync list found!\n", rr);

        rr = drbd_free_peer_reqs(device, &device->read_ee);
        if (rr)
                drbd_err(device, "%d EEs in read list found!\n", rr);

        rr = drbd_free_peer_reqs(device, &device->done_ee);
        if (rr)
                drbd_err(device, "%d EEs in done list found!\n", rr);

        rr = drbd_free_peer_reqs(device, &device->net_ee);
        if (rr)
                drbd_err(device, "%d EEs in net list found!\n", rr);
}

/* caution. no locking. */
void drbd_destroy_device(struct kref *kref)
{
        struct drbd_device *device = container_of(kref, struct drbd_device, kref);
        struct drbd_resource *resource = device->resource;
        struct drbd_peer_device *peer_device, *tmp_peer_device;

        del_timer_sync(&device->request_timer);

        /* paranoia asserts */
        D_ASSERT(device, device->open_cnt == 0);
        /* end paranoia asserts */

        /* cleanup stuff that may have been allocated during
         * device (re-)configuration or state changes */

        if (device->this_bdev)
                bdput(device->this_bdev);

        drbd_backing_dev_free(device, device->ldev);
        device->ldev = NULL;

        drbd_release_all_peer_reqs(device);

        lc_destroy(device->act_log);
        lc_destroy(device->resync);

        kfree(device->p_uuid);
        /* device->p_uuid = NULL; */

        if (device->bitmap) /* should no longer be there. */
                drbd_bm_cleanup(device);
        __free_page(device->md_io.page);
        put_disk(device->vdisk);
        blk_cleanup_queue(device->rq_queue);
        kfree(device->rs_plan_s);

        /* not for_each_connection(connection, resource):
         * those may have been cleaned up and disassociated already.
         */
        for_each_peer_device_safe(peer_device, tmp_peer_device, device) {
                kref_put(&peer_device->connection->kref, drbd_destroy_connection);
                kfree(peer_device);
        }
        memset(device, 0xfd, sizeof(*device));
        kfree(device);
        kref_put(&resource->kref, drbd_destroy_resource);
}

/* One global retry thread, if we need to push back some bio and have it
 * reinserted through our make request function.
 */
static struct retry_worker {
        struct workqueue_struct *wq;
        struct work_struct worker;

        spinlock_t lock;
        struct list_head writes;
} retry;

static void do_retry(struct work_struct *ws)
{
        struct retry_worker *retry = container_of(ws, struct retry_worker, worker);
        LIST_HEAD(writes);
        struct drbd_request *req, *tmp;

        spin_lock_irq(&retry->lock);
        list_splice_init(&retry->writes, &writes);
        spin_unlock_irq(&retry->lock);

        list_for_each_entry_safe(req, tmp, &writes, tl_requests) {
                struct drbd_device *device = req->device;
                struct bio *bio = req->master_bio;
                unsigned long start_jif = req->start_jif;
                bool expected;

                expected =
                        expect(atomic_read(&req->completion_ref) == 0) &&
                        expect(req->rq_state & RQ_POSTPONED) &&
                        expect((req->rq_state & RQ_LOCAL_PENDING) == 0 ||
                                (req->rq_state & RQ_LOCAL_ABORTED) != 0);

                if (!expected)
                        drbd_err(device, "req=%p completion_ref=%d rq_state=%x\n",
                                req, atomic_read(&req->completion_ref),
                                req->rq_state);

                /* We still need to put one kref associated with the
                 * "completion_ref" going zero in the code path that queued it
                 * here.  The request object may still be referenced by a
                 * frozen local req->private_bio, in case we force-detached.
                 */
                kref_put(&req->kref, drbd_req_destroy);

                /* A single suspended or otherwise blocking device may stall
                 * all others as well.  Fortunately, this code path is to
                 * recover from a situation that "should not happen":
                 * concurrent writes in multi-primary setup.
                 * In a "normal" lifecycle, this workqueue is supposed to be
                 * destroyed without ever doing anything.
                 * If it turns out to be an issue anyways, we can do per
                 * resource (replication group) or per device (minor) retry
                 * workqueues instead.
                 */

                /* We are not just doing generic_make_request(),
                 * as we want to keep the start_time information. */
                inc_ap_bio(device);
                __drbd_make_request(device, bio, start_jif);
        }
}

/* called via drbd_req_put_completion_ref(),
 * holds resource->req_lock */
void drbd_restart_request(struct drbd_request *req)
{
        unsigned long flags;
        spin_lock_irqsave(&retry.lock, flags);
        list_move_tail(&req->tl_requests, &retry.writes);
        spin_unlock_irqrestore(&retry.lock, flags);

        /* Drop the extra reference that would otherwise
         * have been dropped by complete_master_bio.
         * do_retry() needs to grab a new one. */
        dec_ap_bio(req->device);

        queue_work(retry.wq, &retry.worker);
}

void drbd_destroy_resource(struct kref *kref)
{
        struct drbd_resource *resource =
                container_of(kref, struct drbd_resource, kref);

        idr_destroy(&resource->devices);
        free_cpumask_var(resource->cpu_mask);
        kfree(resource->name);
        memset(resource, 0xf2, sizeof(*resource));
        kfree(resource);
}

void drbd_free_resource(struct drbd_resource *resource)
{
        struct drbd_connection *connection, *tmp;

        for_each_connection_safe(connection, tmp, resource) {
                list_del(&connection->connections);
                drbd_debugfs_connection_cleanup(connection);
                kref_put(&connection->kref, drbd_destroy_connection);
        }
        drbd_debugfs_resource_cleanup(resource);
        kref_put(&resource->kref, drbd_destroy_resource);
}

static void drbd_cleanup(void)
{
        unsigned int i;
        struct drbd_device *device;
        struct drbd_resource *resource, *tmp;

        /* first remove proc,
         * drbdsetup uses it's presence to detect
         * whether DRBD is loaded.
         * If we would get stuck in proc removal,
         * but have netlink already deregistered,
         * some drbdsetup commands may wait forever
         * for an answer.
         */
        if (drbd_proc)
                remove_proc_entry("drbd", NULL);

        if (retry.wq)
                destroy_workqueue(retry.wq);

        drbd_genl_unregister();

        idr_for_each_entry(&drbd_devices, device, i)
                drbd_delete_device(device);

        /* not _rcu since, no other updater anymore. Genl already unregistered */
        for_each_resource_safe(resource, tmp, &drbd_resources) {
                list_del(&resource->resources);
                drbd_free_resource(resource);
        }

        drbd_debugfs_cleanup();

        drbd_destroy_mempools();
        unregister_blkdev(DRBD_MAJOR, "drbd");

        idr_destroy(&drbd_devices);

        pr_info("module cleanup done.\n");
}

/**
 * drbd_congested() - Callback for the flusher thread
 * @congested_data:     User data
 * @bdi_bits:           Bits the BDI flusher thread is currently interested in
 *
 * Returns 1<<WB_async_congested and/or 1<<WB_sync_congested if we are congested.
 */
static int drbd_congested(void *congested_data, int bdi_bits)
{
        struct drbd_device *device = congested_data;
        struct request_queue *q;
        char reason = '-';
        int r = 0;

        if (!may_inc_ap_bio(device)) {
                /* DRBD has frozen IO */
                r = bdi_bits;
                reason = 'd';
                goto out;
        }

        if (test_bit(CALLBACK_PENDING, &first_peer_device(device)->connection->flags)) {
                r |= (1 << WB_async_congested);
                /* Without good local data, we would need to read from remote,
                 * and that would need the worker thread as well, which is
                 * currently blocked waiting for that usermode helper to
                 * finish.
                 */
                if (!get_ldev_if_state(device, D_UP_TO_DATE))
                        r |= (1 << WB_sync_congested);
                else
                        put_ldev(device);
                r &= bdi_bits;
                reason = 'c';
                goto out;
        }

        if (get_ldev(device)) {
                q = bdev_get_queue(device->ldev->backing_bdev);
                r = bdi_congested(q->backing_dev_info, bdi_bits);
                put_ldev(device);
                if (r)
                        reason = 'b';
        }

        if (bdi_bits & (1 << WB_async_congested) &&
            test_bit(NET_CONGESTED, &first_peer_device(device)->connection->flags)) {
                r |= (1 << WB_async_congested);
                reason = reason == 'b' ? 'a' : 'n';
        }

out:
        device->congestion_reason = reason;
        return r;
}

static void drbd_init_workqueue(struct drbd_work_queue* wq)
{
        spin_lock_init(&wq->q_lock);
        INIT_LIST_HEAD(&wq->q);
        init_waitqueue_head(&wq->q_wait);
}

struct completion_work {
        struct drbd_work w;
        struct completion done;
};

static int w_complete(struct drbd_work *w, int cancel)
{
        struct completion_work *completion_work =
                container_of(w, struct completion_work, w);

        complete(&completion_work->done);
        return 0;
}

void drbd_flush_workqueue(struct drbd_work_queue *work_queue)
{
        struct completion_work completion_work;

        completion_work.w.cb = w_complete;
        init_completion(&completion_work.done);
        drbd_queue_work(work_queue, &completion_work.w);
        wait_for_completion(&completion_work.done);
}

struct drbd_resource *drbd_find_resource(const char *name)
{
        struct drbd_resource *resource;

        if (!name || !name[0])
                return NULL;

        rcu_read_lock();
        for_each_resource_rcu(resource, &drbd_resources) {
                if (!strcmp(resource->name, name)) {
                        kref_get(&resource->kref);
                        goto found;
                }
        }
        resource = NULL;
found:
        rcu_read_unlock();
        return resource;
}

struct drbd_connection *conn_get_by_addrs(void *my_addr, int my_addr_len,
                                     void *peer_addr, int peer_addr_len)
{
        struct drbd_resource *resource;
        struct drbd_connection *connection;

        rcu_read_lock();
        for_each_resource_rcu(resource, &drbd_resources) {
                for_each_connection_rcu(connection, resource) {
                        if (connection->my_addr_len == my_addr_len &&
                            connection->peer_addr_len == peer_addr_len &&
                            !memcmp(&connection->my_addr, my_addr, my_addr_len) &&
                            !memcmp(&connection->peer_addr, peer_addr, peer_addr_len)) {
                                kref_get(&connection->kref);
                                goto found;
                        }
                }
        }
        connection = NULL;
found:
        rcu_read_unlock();
        return connection;
}

static int drbd_alloc_socket(struct drbd_socket *socket)
{
        socket->rbuf = (void *) __get_free_page(GFP_KERNEL);
        if (!socket->rbuf)
                return -ENOMEM;
        socket->sbuf = (void *) __get_free_page(GFP_KERNEL);
        if (!socket->sbuf)
                return -ENOMEM;
        return 0;
}

static void drbd_free_socket(struct drbd_socket *socket)
{
        free_page((unsigned long) socket->sbuf);
        free_page((unsigned long) socket->rbuf);
}

void conn_free_crypto(struct drbd_connection *connection)
{
        drbd_free_sock(connection);

        crypto_free_shash(connection->csums_tfm);
        crypto_free_shash(connection->verify_tfm);
        crypto_free_shash(connection->cram_hmac_tfm);
        crypto_free_shash(connection->integrity_tfm);
        crypto_free_shash(connection->peer_integrity_tfm);
        kfree(connection->int_dig_in);
        kfree(connection->int_dig_vv);

        connection->csums_tfm = NULL;
        connection->verify_tfm = NULL;
        connection->cram_hmac_tfm = NULL;
        connection->integrity_tfm = NULL;
        connection->peer_integrity_tfm = NULL;
        connection->int_dig_in = NULL;
        connection->int_dig_vv = NULL;
}

int set_resource_options(struct drbd_resource *resource, struct res_opts *res_opts)
{
        struct drbd_connection *connection;
        cpumask_var_t new_cpu_mask;
        int err;

        if (!zalloc_cpumask_var(&new_cpu_mask, GFP_KERNEL))
                return -ENOMEM;

        /* silently ignore cpu mask on UP kernel */
        if (nr_cpu_ids > 1 && res_opts->cpu_mask[0] != 0) {
                err = bitmap_parse(res_opts->cpu_mask, DRBD_CPU_MASK_SIZE,
                                   cpumask_bits(new_cpu_mask), nr_cpu_ids);
                if (err == -EOVERFLOW) {
                        /* So what. mask it out. */
                        cpumask_var_t tmp_cpu_mask;
                        if (zalloc_cpumask_var(&tmp_cpu_mask, GFP_KERNEL)) {
                                cpumask_setall(tmp_cpu_mask);
                                cpumask_and(new_cpu_mask, new_cpu_mask, tmp_cpu_mask);
                                drbd_warn(resource, "Overflow in bitmap_parse(%.12s%s), truncating to %u bits\n",
                                        res_opts->cpu_mask,
                                        strlen(res_opts->cpu_mask) > 12 ? "..." : "",
                                        nr_cpu_ids);
                                free_cpumask_var(tmp_cpu_mask);
                                err = 0;
                        }
                }
                if (err) {
                        drbd_warn(resource, "bitmap_parse() failed with %d\n", err);
                        /* retcode = ERR_CPU_MASK_PARSE; */
                        goto fail;
                }
        }
        resource->res_opts = *res_opts;
        if (cpumask_empty(new_cpu_mask))
                drbd_calc_cpu_mask(&new_cpu_mask);
        if (!cpumask_equal(resource->cpu_mask, new_cpu_mask)) {
                cpumask_copy(resource->cpu_mask, new_cpu_mask);
                for_each_connection_rcu(connection, resource) {
                        connection->receiver.reset_cpu_mask = 1;
                        connection->ack_receiver.reset_cpu_mask = 1;
                        connection->worker.reset_cpu_mask = 1;
                }
        }
        err = 0;

fail:
        free_cpumask_var(new_cpu_mask);
        return err;

}

struct drbd_resource *drbd_create_resource(const char *name)
{
        struct drbd_resource *resource;

        resource = kzalloc(sizeof(struct drbd_resource), GFP_KERNEL);
        if (!resource)
                goto fail;
        resource->name = kstrdup(name, GFP_KERNEL);
        if (!resource->name)
                goto fail_free_resource;
        if (!zalloc_cpumask_var(&resource->cpu_mask, GFP_KERNEL))
                goto fail_free_name;
        kref_init(&resource->kref);
        idr_init(&resource->devices);
        INIT_LIST_HEAD(&resource->connections);
        resource->write_ordering = WO_BDEV_FLUSH;
        list_add_tail_rcu(&resource->resources, &drbd_resources);
        mutex_init(&resource->conf_update);
        mutex_init(&resource->adm_mutex);
        spin_lock_init(&resource->req_lock);
        drbd_debugfs_resource_add(resource);
        return resource;

fail_free_name:
        kfree(resource->name);
fail_free_resource:
        kfree(resource);
fail:
        return NULL;
}

/* caller must be under adm_mutex */
struct drbd_connection *conn_create(const char *name, struct res_opts *res_opts)
{
        struct drbd_resource *resource;
        struct drbd_connection *connection;

        connection = kzalloc(sizeof(struct drbd_connection), GFP_KERNEL);
        if (!connection)
                return NULL;

        if (drbd_alloc_socket(&connection->data))
                goto fail;
        if (drbd_alloc_socket(&connection->meta))
                goto fail;

        connection->current_epoch = kzalloc(sizeof(struct drbd_epoch), GFP_KERNEL);
        if (!connection->current_epoch)
                goto fail;

        INIT_LIST_HEAD(&connection->transfer_log);

        INIT_LIST_HEAD(&connection->current_epoch->list);
        connection->epochs = 1;
        spin_lock_init(&connection->epoch_lock);

        connection->send.seen_any_write_yet = false;
        connection->send.current_epoch_nr = 0;
        connection->send.current_epoch_writes = 0;

        resource = drbd_create_resource(name);
        if (!resource)
                goto fail;

        connection->cstate = C_STANDALONE;
        mutex_init(&connection->cstate_mutex);
        init_waitqueue_head(&connection->ping_wait);
        idr_init(&connection->peer_devices);

        drbd_init_workqueue(&connection->sender_work);
        mutex_init(&connection->data.mutex);
        mutex_init(&connection->meta.mutex);

        drbd_thread_init(resource, &connection->receiver, drbd_receiver, "receiver");
        connection->receiver.connection = connection;
        drbd_thread_init(resource, &connection->worker, drbd_worker, "worker");
        connection->worker.connection = connection;
        drbd_thread_init(resource, &connection->ack_receiver, drbd_ack_receiver, "ack_recv");
        connection->ack_receiver.connection = connection;

        kref_init(&connection->kref);

        connection->resource = resource;

        if (set_resource_options(resource, res_opts))
                goto fail_resource;

        kref_get(&resource->kref);
        list_add_tail_rcu(&connection->connections, &resource->connections);
        drbd_debugfs_connection_add(connection);
        return connection;

fail_resource:
        list_del(&resource->resources);
        drbd_free_resource(resource);
fail:
        kfree(connection->current_epoch);
        drbd_free_socket(&connection->meta);
        drbd_free_socket(&connection->data);
        kfree(connection);
        return NULL;
}

void drbd_destroy_connection(struct kref *kref)
{
        struct drbd_connection *connection = container_of(kref, struct drbd_connection, kref);
        struct drbd_resource *resource = connection->resource;

        if (atomic_read(&connection->current_epoch->epoch_size) !=  0)
                drbd_err(connection, "epoch_size:%d\n", atomic_read(&connection->current_epoch->epoch_size));
        kfree(connection->current_epoch);

        idr_destroy(&connection->peer_devices);

        drbd_free_socket(&connection->meta);
        drbd_free_socket(&connection->data);
        kfree(connection->int_dig_in);
        kfree(connection->int_dig_vv);
        memset(connection, 0xfc, sizeof(*connection));
        kfree(connection);
        kref_put(&resource->kref, drbd_destroy_resource);
}

static int init_submitter(struct drbd_device *device)
{
        /* opencoded create_singlethread_workqueue(),
         * to be able to say "drbd%d", ..., minor */
        device->submit.wq =
                alloc_ordered_workqueue("drbd%u_submit", WQ_MEM_RECLAIM, device->minor);
        if (!device->submit.wq)
                return -ENOMEM;

        INIT_WORK(&device->submit.worker, do_submit);
        INIT_LIST_HEAD(&device->submit.writes);
        return 0;
}

enum drbd_ret_code drbd_create_device(struct drbd_config_context *adm_ctx, unsigned int minor)
{
        struct drbd_resource *resource = adm_ctx->resource;
        struct drbd_connection *connection;
        struct drbd_device *device;
        struct drbd_peer_device *peer_device, *tmp_peer_device;
        struct gendisk *disk;
        struct request_queue *q;
        int id;
        int vnr = adm_ctx->volume;
        enum drbd_ret_code err = ERR_NOMEM;

        device = minor_to_device(minor);
        if (device)
                return ERR_MINOR_OR_VOLUME_EXISTS;

        /* GFP_KERNEL, we are outside of all write-out paths */
        device = kzalloc(sizeof(struct drbd_device), GFP_KERNEL);
        if (!device)
                return ERR_NOMEM;
        kref_init(&device->kref);

        kref_get(&resource->kref);
        device->resource = resource;
        device->minor = minor;
        device->vnr = vnr;

        drbd_init_set_defaults(device);

        q = blk_alloc_queue_node(GFP_KERNEL, NUMA_NO_NODE);
        if (!q)
                goto out_no_q;
        device->rq_queue = q;
        q->queuedata   = device;

        disk = alloc_disk(1);
        if (!disk)
                goto out_no_disk;
        device->vdisk = disk;

        set_disk_ro(disk, true);

        disk->queue = q;
        disk->major = DRBD_MAJOR;
        disk->first_minor = minor;
        disk->fops = &drbd_ops;
        sprintf(disk->disk_name, "drbd%d", minor);
        disk->private_data = device;

        device->this_bdev = bdget(MKDEV(DRBD_MAJOR, minor));
        /* we have no partitions. we contain only ourselves. */
        device->this_bdev->bd_contains = device->this_bdev;

        q->backing_dev_info->congested_fn = drbd_congested;
        q->backing_dev_info->congested_data = device;

        blk_queue_make_request(q, drbd_make_request);
        blk_queue_write_cache(q, true, true);
        /* Setting the max_hw_sectors to an odd value of 8kibyte here
           This triggers a max_bio_size message upon first attach or connect */
        blk_queue_max_hw_sectors(q, DRBD_MAX_BIO_SIZE_SAFE >> 8);

        device->md_io.page = alloc_page(GFP_KERNEL);
        if (!device->md_io.page)
                goto out_no_io_page;

        if (drbd_bm_init(device))
                goto out_no_bitmap;
        device->read_requests = RB_ROOT;
        device->write_requests = RB_ROOT;

        id = idr_alloc(&drbd_devices, device, minor, minor + 1, GFP_KERNEL);
        if (id < 0) {
                if (id == -ENOSPC)
                        err = ERR_MINOR_OR_VOLUME_EXISTS;
                goto out_no_minor_idr;
        }
        kref_get(&device->kref);

        id = idr_alloc(&resource->devices, device, vnr, vnr + 1, GFP_KERNEL);
        if (id < 0) {
                if (id == -ENOSPC)
                        err = ERR_MINOR_OR_VOLUME_EXISTS;
                goto out_idr_remove_minor;
        }
        kref_get(&device->kref);

        INIT_LIST_HEAD(&device->peer_devices);
        INIT_LIST_HEAD(&device->pending_bitmap_io);
        for_each_connection(connection, resource) {
                peer_device = kzalloc(sizeof(struct drbd_peer_device), GFP_KERNEL);
                if (!peer_device)
                        goto out_idr_remove_from_resource;
                peer_device->connection = connection;
                peer_device->device = device;

                list_add(&peer_device->peer_devices, &device->peer_devices);
                kref_get(&device->kref);

                id = idr_alloc(&connection->peer_devices, peer_device, vnr, vnr + 1, GFP_KERNEL);
                if (id < 0) {
                        if (id == -ENOSPC)
                                err = ERR_INVALID_REQUEST;
                        goto out_idr_remove_from_resource;
                }
                kref_get(&connection->kref);
                INIT_WORK(&peer_device->send_acks_work, drbd_send_acks_wf);
        }

        if (init_submitter(device)) {
                err = ERR_NOMEM;
                goto out_idr_remove_vol;
        }

        add_disk(disk);

        /* inherit the connection state */
        device->state.conn = first_connection(resource)->cstate;
        if (device->state.conn == C_WF_REPORT_PARAMS) {
                for_each_peer_device(peer_device, device)
                        drbd_connected(peer_device);
        }
        /* move to create_peer_device() */
        for_each_peer_device(peer_device, device)
                drbd_debugfs_peer_device_add(peer_device);
        drbd_debugfs_device_add(device);
        return NO_ERROR;

out_idr_remove_vol:
        idr_remove(&connection->peer_devices, vnr);
out_idr_remove_from_resource:
        for_each_connection(connection, resource) {
                peer_device = idr_remove(&connection->peer_devices, vnr);
                if (peer_device)
                        kref_put(&connection->kref, drbd_destroy_connection);
        }
        for_each_peer_device_safe(peer_device, tmp_peer_device, device) {
                list_del(&peer_device->peer_devices);
                kfree(peer_device);
        }
        idr_remove(&resource->devices, vnr);
out_idr_remove_minor:
        idr_remove(&drbd_devices, minor);
        synchronize_rcu();
out_no_minor_idr:
        drbd_bm_cleanup(device);
out_no_bitmap:
        __free_page(device->md_io.page);
out_no_io_page:
        put_disk(disk);
out_no_disk:
        blk_cleanup_queue(q);
out_no_q:
        kref_put(&resource->kref, drbd_destroy_resource);
        kfree(device);
        return err;
}

void drbd_delete_device(struct drbd_device *device)
{
        struct drbd_resource *resource = device->resource;
        struct drbd_connection *connection;
        struct drbd_peer_device *peer_device;

        /* move to free_peer_device() */
        for_each_peer_device(peer_device, device)
                drbd_debugfs_peer_device_cleanup(peer_device);
        drbd_debugfs_device_cleanup(device);
        for_each_connection(connection, resource) {
                idr_remove(&connection->peer_devices, device->vnr);
                kref_put(&device->kref, drbd_destroy_device);
        }
        idr_remove(&resource->devices, device->vnr);
        kref_put(&device->kref, drbd_destroy_device);
        idr_remove(&drbd_devices, device_to_minor(device));
        kref_put(&device->kref, drbd_destroy_device);
        del_gendisk(device->vdisk);
        synchronize_rcu();
        kref_put(&device->kref, drbd_destroy_device);
}

static int __init drbd_init(void)
{
        int err;

        if (drbd_minor_count < DRBD_MINOR_COUNT_MIN || drbd_minor_count > DRBD_MINOR_COUNT_MAX) {
                pr_err("invalid minor_count (%d)\n", drbd_minor_count);
#ifdef MODULE
                return -EINVAL;
#else
                drbd_minor_count = DRBD_MINOR_COUNT_DEF;
#endif
        }

        err = register_blkdev(DRBD_MAJOR, "drbd");
        if (err) {
                pr_err("unable to register block device major %d\n",
                       DRBD_MAJOR);
                return err;
        }

        /*
         * allocate all necessary structs
         */
        init_waitqueue_head(&drbd_pp_wait);

        drbd_proc = NULL; /* play safe for drbd_cleanup */
        idr_init(&drbd_devices);

        mutex_init(&resources_mutex);
        INIT_LIST_HEAD(&drbd_resources);

        err = drbd_genl_register();
        if (err) {
                pr_err("unable to register generic netlink family\n");
                goto fail;
        }

        err = drbd_create_mempools();
        if (err)
                goto fail;

        err = -ENOMEM;
        drbd_proc = proc_create_single("drbd", S_IFREG | 0444 , NULL, drbd_seq_show);
        if (!drbd_proc) {