[deliverable/linux.git] / drivers / block / drbd / drbd_main.c

/*
   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.

   drbd is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   drbd is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with drbd; see the file COPYING.  If not, write to
   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

 */

#include <linux/module.h>
#include <linux/drbd.h>
#include <asm/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>

#define __KERNEL_SYSCALLS__
#include <linux/unistd.h>
#include <linux/vmalloc.h>

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

#include "drbd_vli.h"

static DEFINE_MUTEX(drbd_main_mutex);
int drbdd_init(struct drbd_thread *);
int drbd_worker(struct drbd_thread *);
int drbd_asender(struct drbd_thread *);

int drbd_init(void);
static int drbd_open(struct block_device *bdev, fmode_t mode);
static int drbd_release(struct gendisk *gd, fmode_t mode);
static int w_md_sync(struct drbd_work *w, int unused);
static void md_sync_timer_fn(unsigned long data);
static int w_bitmap_io(struct drbd_work *w, int unused);
static int w_go_diskless(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>
/* allow_open_on_secondary */
MODULE_PARM_DESC(allow_oos, "DONT USE!");
/* thanks to these macros, if compiled into the kernel (not-module),
 * this becomes the boot parameter drbd.minor_count */
module_param(minor_count, uint, 0444);
module_param(disable_sendpage, bool, 0644);
module_param(allow_oos, bool, 0);
module_param(proc_details, int, 0644);

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

/* module parameter, defined */
unsigned int minor_count = DRBD_MINOR_COUNT_DEF;
int disable_sendpage;
int allow_oos;
int proc_details;       /* Detail level in proc drbd*/

/* Module parameter for setting the user mode helper program
 * to run. Default is /sbin/drbdadm */
char usermode_helper[80] = "/sbin/drbdadm";

module_param_string(usermode_helper, usermode_helper, sizeof(usermode_helper), 0644);

/* in 2.6.x, our device mapping and config info contains our virtual gendisks
 * as member "struct gendisk *vdisk;"
 */
struct idr minors;
struct list_head drbd_tconns;  /* list of struct drbd_tconn */
DECLARE_RWSEM(drbd_cfg_rwsem);

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;

/* 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,
};

static void bio_destructor_drbd(struct bio *bio)
{
	bio_free(bio, drbd_md_io_bio_set);
}

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

	if (!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;
	bio->bi_destructor = bio_destructor_drbd;
	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_conf *mdev, enum drbd_disk_state mins)
{
	int io_allowed;

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

#endif

/**
 * DOC: The transfer log
 *
 * The transfer log is a single linked list of &struct drbd_tl_epoch objects.
 * mdev->tconn->newest_tle points to the head, mdev->tconn->oldest_tle points to the tail
 * of the list. There is always at least one &struct drbd_tl_epoch object.
 *
 * Each &struct drbd_tl_epoch has a circular double linked list of requests
 * attached.
 */
static int tl_init(struct drbd_tconn *tconn)
{
	struct drbd_tl_epoch *b;

	/* during device minor initialization, we may well use GFP_KERNEL */
	b = kmalloc(sizeof(struct drbd_tl_epoch), GFP_KERNEL);
	if (!b)
		return 0;
	INIT_LIST_HEAD(&b->requests);
	INIT_LIST_HEAD(&b->w.list);
	b->next = NULL;
	b->br_number = 4711;
	b->n_writes = 0;
	b->w.cb = NULL; /* if this is != NULL, we need to dec_ap_pending in tl_clear */

	tconn->oldest_tle = b;
	tconn->newest_tle = b;
	INIT_LIST_HEAD(&tconn->out_of_sequence_requests);

	return 1;
}

static void tl_cleanup(struct drbd_tconn *tconn)
{
	if (tconn->oldest_tle != tconn->newest_tle)
		conn_err(tconn, "ASSERT FAILED: oldest_tle == newest_tle\n");
	if (!list_empty(&tconn->out_of_sequence_requests))
		conn_err(tconn, "ASSERT FAILED: list_empty(out_of_sequence_requests)\n");
	kfree(tconn->oldest_tle);
	tconn->oldest_tle = NULL;
	kfree(tconn->unused_spare_tle);
	tconn->unused_spare_tle = NULL;
}

/**
 * _tl_add_barrier() - Adds a barrier to the transfer log
 * @mdev:	DRBD device.
 * @new:	Barrier to be added before the current head of the TL.
 *
 * The caller must hold the req_lock.
 */
void _tl_add_barrier(struct drbd_tconn *tconn, struct drbd_tl_epoch *new)
{
	struct drbd_tl_epoch *newest_before;

	INIT_LIST_HEAD(&new->requests);
	INIT_LIST_HEAD(&new->w.list);
	new->w.cb = NULL; /* if this is != NULL, we need to dec_ap_pending in tl_clear */
	new->next = NULL;
	new->n_writes = 0;

	newest_before = tconn->newest_tle;
	/* never send a barrier number == 0, because that is special-cased
	 * when using TCQ for our write ordering code */
	new->br_number = (newest_before->br_number+1) ?: 1;
	if (tconn->newest_tle != new) {
		tconn->newest_tle->next = new;
		tconn->newest_tle = new;
	}
}

/**
 * tl_release() - Free or recycle the oldest &struct drbd_tl_epoch object of the TL
 * @mdev:	DRBD device.
 * @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
 * &struct drbd_tl_epoch objects this function will cause a termination
 * of the connection.
 */
void tl_release(struct drbd_tconn *tconn, unsigned int barrier_nr,
		unsigned int set_size)
{
	struct drbd_conf *mdev;
	struct drbd_tl_epoch *b, *nob; /* next old barrier */
	struct list_head *le, *tle;
	struct drbd_request *r;

	spin_lock_irq(&tconn->req_lock);

	b = tconn->oldest_tle;

	/* first some paranoia code */
	if (b == NULL) {
		conn_err(tconn, "BAD! BarrierAck #%u received, but no epoch in tl!?\n",
			 barrier_nr);
		goto bail;
	}
	if (b->br_number != barrier_nr) {
		conn_err(tconn, "BAD! BarrierAck #%u received, expected #%u!\n",
			 barrier_nr, b->br_number);
		goto bail;
	}
	if (b->n_writes != set_size) {
		conn_err(tconn, "BAD! BarrierAck #%u received with n_writes=%u, expected n_writes=%u!\n",
			 barrier_nr, set_size, b->n_writes);
		goto bail;
	}

	/* Clean up list of requests processed during current epoch */
	list_for_each_safe(le, tle, &b->requests) {
		r = list_entry(le, struct drbd_request, tl_requests);
		_req_mod(r, BARRIER_ACKED);
	}
	/* There could be requests on the list waiting for completion
	   of the write to the local disk. To avoid corruptions of
	   slab's data structures we have to remove the lists head.

	   Also there could have been a barrier ack out of sequence, overtaking
	   the write acks - which would be a bug and violating write ordering.
	   To not deadlock in case we lose connection while such requests are
	   still pending, we need some way to find them for the
	   _req_mode(CONNECTION_LOST_WHILE_PENDING).

	   These have been list_move'd to the out_of_sequence_requests list in
	   _req_mod(, BARRIER_ACKED) above.
	   */
	list_del_init(&b->requests);
	mdev = b->w.mdev;

	nob = b->next;
	if (test_and_clear_bit(CREATE_BARRIER, &mdev->flags)) {
		_tl_add_barrier(tconn, b);
		if (nob)
			tconn->oldest_tle = nob;
		/* if nob == NULL b was the only barrier, and becomes the new
		   barrier. Therefore tconn->oldest_tle points already to b */
	} else {
		D_ASSERT(nob != NULL);
		tconn->oldest_tle = nob;
		kfree(b);
	}

	spin_unlock_irq(&tconn->req_lock);
	dec_ap_pending(mdev);

	return;

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


/**
 * _tl_restart() - Walks the transfer log, and applies an action to all requests
 * @mdev:	DRBD device.
 * @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.
 */
void _tl_restart(struct drbd_tconn *tconn, enum drbd_req_event what)
{
	struct drbd_tl_epoch *b, *tmp, **pn;
	struct list_head *le, *tle, carry_reads;
	struct drbd_request *req;
	int rv, n_writes, n_reads;

	b = tconn->oldest_tle;
	pn = &tconn->oldest_tle;
	while (b) {
		n_writes = 0;
		n_reads = 0;
		INIT_LIST_HEAD(&carry_reads);
		list_for_each_safe(le, tle, &b->requests) {
			req = list_entry(le, struct drbd_request, tl_requests);
			rv = _req_mod(req, what);

			n_writes += (rv & MR_WRITE) >> MR_WRITE_SHIFT;
			n_reads  += (rv & MR_READ) >> MR_READ_SHIFT;
		}
		tmp = b->next;

		if (n_writes) {
			if (what == RESEND) {
				b->n_writes = n_writes;
				if (b->w.cb == NULL) {
					b->w.cb = w_send_barrier;
					inc_ap_pending(b->w.mdev);
					set_bit(CREATE_BARRIER, &b->w.mdev->flags);
				}

				drbd_queue_work(&tconn->data.work, &b->w);
			}
			pn = &b->next;
		} else {
			if (n_reads)
				list_add(&carry_reads, &b->requests);
			/* there could still be requests on that ring list,
			 * in case local io is still pending */
			list_del(&b->requests);

			/* dec_ap_pending corresponding to queue_barrier.
			 * the newest barrier may not have been queued yet,
			 * in which case w.cb is still NULL. */
			if (b->w.cb != NULL)
				dec_ap_pending(b->w.mdev);

			if (b == tconn->newest_tle) {
				/* recycle, but reinit! */
				if (tmp != NULL)
					conn_err(tconn, "ASSERT FAILED tmp == NULL");
				INIT_LIST_HEAD(&b->requests);
				list_splice(&carry_reads, &b->requests);
				INIT_LIST_HEAD(&b->w.list);
				b->w.cb = NULL;
				b->br_number = net_random();
				b->n_writes = 0;

				*pn = b;
				break;
			}
			*pn = tmp;
			kfree(b);
		}
		b = tmp;
		list_splice(&carry_reads, &b->requests);
	}
}


/**
 * tl_clear() - Clears all requests and &struct drbd_tl_epoch objects out of the TL
 * @mdev:	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_tconn *tconn)
{
	struct drbd_conf *mdev;
	struct list_head *le, *tle;
	struct drbd_request *r;
	int vnr;

	spin_lock_irq(&tconn->req_lock);

	_tl_restart(tconn, CONNECTION_LOST_WHILE_PENDING);

	/* we expect this list to be empty. */
	if (!list_empty(&tconn->out_of_sequence_requests))
		conn_err(tconn, "ASSERT FAILED list_empty(&out_of_sequence_requests)\n");

	/* but just in case, clean it up anyways! */
	list_for_each_safe(le, tle, &tconn->out_of_sequence_requests) {
		r = list_entry(le, struct drbd_request, tl_requests);
		/* It would be nice to complete outside of spinlock.
		 * But this is easier for now. */
		_req_mod(r, CONNECTION_LOST_WHILE_PENDING);
	}

	/* ensure bit indicating barrier is required is clear */
	rcu_read_lock();
	idr_for_each_entry(&tconn->volumes, mdev, vnr)
		clear_bit(CREATE_BARRIER, &mdev->flags);
	rcu_read_unlock();

	spin_unlock_irq(&tconn->req_lock);
}

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

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

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

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) {
		conn_info(tconn, "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(&thi->stop);
	spin_unlock_irqrestore(&thi->t_lock, flags);

	conn_info(tconn, "Terminating %s\n", current->comm);

	/* Release mod reference taken when thread was started */
	module_put(THIS_MODULE);
	return retval;
}

static void drbd_thread_init(struct drbd_tconn *tconn, struct drbd_thread *thi,
			     int (*func) (struct drbd_thread *), char *name)
{
	spin_lock_init(&thi->t_lock);
	thi->task    = NULL;
	thi->t_state = NONE;
	thi->function = func;
	thi->tconn = tconn;
	strncpy(thi->name, name, ARRAY_SIZE(thi->name));
}

int drbd_thread_start(struct drbd_thread *thi)
{
	struct drbd_tconn *tconn = thi->tconn;
	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:
		conn_info(tconn, "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)) {
			conn_err(tconn, "Failed to get module reference in drbd_thread_start\n");
			spin_unlock_irqrestore(&thi->t_lock, flags);
			return false;
		}

		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->tconn->name);

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

			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;
		conn_info(tconn, "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)
			force_sig(DRBD_SIGKILL, thi->task);
	}

	spin_unlock_irqrestore(&thi->t_lock, flags);

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

static struct drbd_thread *drbd_task_to_thread(struct drbd_tconn *tconn, struct task_struct *task)
{
	struct drbd_thread *thi =
		task == tconn->receiver.task ? &tconn->receiver :
		task == tconn->asender.task  ? &tconn->asender :
		task == tconn->worker.task   ? &tconn->worker : NULL;

	return thi;
}

char *drbd_task_to_thread_name(struct drbd_tconn *tconn, struct task_struct *task)
{
	struct drbd_thread *thi = drbd_task_to_thread(tconn, task);
	return thi ? thi->name : task->comm;
}

int conn_lowest_minor(struct drbd_tconn *tconn)
{
	struct drbd_conf *mdev;
	int vnr = 0, m;

	rcu_read_lock();
	mdev = idr_get_next(&tconn->volumes, &vnr);
	m = mdev ? mdev_to_minor(mdev) : -1;
	rcu_read_unlock();

	return m;
}

#ifdef CONFIG_SMP
/**
 * drbd_calc_cpu_mask() - Generate CPU masks, spread over all CPUs
 * @mdev:	DRBD device.
 *
 * Forces all threads of a device onto the same CPU. This is beneficial for
 * DRBD's performance. May be overwritten by user's configuration.
 */
void drbd_calc_cpu_mask(struct drbd_tconn *tconn)
{
	int ord, cpu;

	/* user override. */
	if (cpumask_weight(tconn->cpu_mask))
		return;

	ord = conn_lowest_minor(tconn) % cpumask_weight(cpu_online_mask);
	for_each_online_cpu(cpu) {
		if (ord-- == 0) {
			cpumask_set_cpu(cpu, tconn->cpu_mask);
			return;
		}
	}
	/* should not be reached */
	cpumask_setall(tconn->cpu_mask);
}

/**
 * drbd_thread_current_set_cpu() - modifies the cpu mask of the _current_ thread
 * @mdev:	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 task_struct *p = current;

	if (!thi->reset_cpu_mask)
		return;
	thi->reset_cpu_mask = 0;
	set_cpus_allowed_ptr(p, thi->tconn->cpu_mask);
}
#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_tconn *tconn)
{
	if (tconn->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_tconn *tconn, int vnr,
				   void *buffer, enum drbd_packet cmd, int size)
{
	if (tconn->agreed_pro_version >= 100)
		return prepare_header100(buffer, cmd, size, vnr);
	else if (tconn->agreed_pro_version >= 95 &&
		 size > DRBD_MAX_SIZE_H80_PACKET)
		return prepare_header95(buffer, cmd, size);
	else
		return prepare_header80(buffer, cmd, size);
}

void *conn_prepare_command(struct drbd_tconn *tconn, struct drbd_socket *sock)
{
	mutex_lock(&sock->mutex);
	if (!sock->socket) {
		mutex_unlock(&sock->mutex);
		return NULL;
	}
	return sock->sbuf + drbd_header_size(tconn);
}

void *drbd_prepare_command(struct drbd_conf *mdev, struct drbd_socket *sock)
{
	return conn_prepare_command(mdev->tconn, sock);
}

static int __send_command(struct drbd_tconn *tconn, 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(tconn, vnr, sock->sbuf, cmd,
				      header_size + size);
	err = drbd_send_all(tconn, sock->socket, sock->sbuf, header_size,
			    msg_flags);
	if (data && !err)
		err = drbd_send_all(tconn, sock->socket, data, size, 0);
	return err;
}

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

	err = __send_command(tconn, 0, sock, cmd, header_size, data, size);
	mutex_unlock(&sock->mutex);
	return err;
}

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

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

int drbd_send_ping(struct drbd_tconn *tconn)
{
	struct drbd_socket *sock;

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

int drbd_send_ping_ack(struct drbd_tconn *tconn)
{
	struct drbd_socket *sock;

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

int drbd_send_sync_param(struct drbd_conf *mdev)
{
	struct drbd_socket *sock;
	struct p_rs_param_95 *p;
	int size;
	const int apv = mdev->tconn->agreed_pro_version;
	enum drbd_packet cmd;
	struct net_conf *nc;

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

	rcu_read_lock();
	nc = rcu_dereference(mdev->tconn->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(mdev)) {
		p->rate = cpu_to_be32(mdev->ldev->dc.resync_rate);
		p->c_plan_ahead = cpu_to_be32(mdev->ldev->dc.c_plan_ahead);
		p->c_delay_target = cpu_to_be32(mdev->ldev->dc.c_delay_target);
		p->c_fill_target = cpu_to_be32(mdev->ldev->dc.c_fill_target);
		p->c_max_rate = cpu_to_be32(mdev->ldev->dc.c_max_rate);
		put_ldev(mdev);
	} else {
		p->rate = cpu_to_be32(DRBD_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(mdev, sock, cmd, size, NULL, 0);
}

int drbd_send_protocol(struct drbd_tconn *tconn)
{
	struct drbd_socket *sock;
	struct p_protocol *p;
	struct net_conf *nc;
	int size, cf;

	sock = &tconn->data;
	p = conn_prepare_command(tconn, sock);
	if (!p)
		return -EIO;

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

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

	size = sizeof(*p);
	if (tconn->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->want_lose)
		cf |= CF_WANT_LOSE;
	if (nc->dry_run)
		cf |= CF_DRY_RUN;
	p->conn_flags    = cpu_to_be32(cf);

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

	return conn_send_command(tconn, sock, P_PROTOCOL, size, NULL, 0);
}

int _drbd_send_uuids(struct drbd_conf *mdev, u64 uuid_flags)
{
	struct drbd_socket *sock;
	struct p_uuids *p;
	int i;

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

	sock = &mdev->tconn->data;
	p = drbd_prepare_command(mdev, sock);
	if (!p) {
		put_ldev(mdev);
		return -EIO;
	}
	for (i = UI_CURRENT; i < UI_SIZE; i++)
		p->uuid[i] = mdev->ldev ? cpu_to_be64(mdev->ldev->md.uuid[i]) : 0;

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

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

int drbd_send_uuids(struct drbd_conf *mdev)
{
	return _drbd_send_uuids(mdev, 0);
}

int drbd_send_uuids_skip_initial_sync(struct drbd_conf *mdev)
{
	return _drbd_send_uuids(mdev, 8);
}

void drbd_print_uuids(struct drbd_conf *mdev, const char *text)
{
	if (get_ldev_if_state(mdev, D_NEGOTIATING)) {
		u64 *uuid = mdev->ldev->md.uuid;
		dev_info(DEV, "%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(mdev);
	} else {
		dev_info(DEV, "%s effective data uuid: %016llX\n",
				text,
				(unsigned long long)mdev->ed_uuid);
	}
}

void drbd_gen_and_send_sync_uuid(struct drbd_conf *mdev)
{
	struct drbd_socket *sock;
	struct p_rs_uuid *p;
	u64 uuid;

	D_ASSERT(mdev->state.disk == D_UP_TO_DATE);

	uuid = mdev->ldev->md.uuid[UI_BITMAP] + UUID_NEW_BM_OFFSET;
	drbd_uuid_set(mdev, UI_BITMAP, uuid);
	drbd_print_uuids(mdev, "updated sync UUID");
	drbd_md_sync(mdev);

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

int drbd_send_sizes(struct drbd_conf *mdev, int trigger_reply, enum dds_flags flags)
{
	struct drbd_socket *sock;
	struct p_sizes *p;
	sector_t d_size, u_size;
	int q_order_type, max_bio_size;

	if (get_ldev_if_state(mdev, D_NEGOTIATING)) {
		D_ASSERT(mdev->ldev->backing_bdev);
		d_size = drbd_get_max_capacity(mdev->ldev);
		u_size = mdev->ldev->dc.disk_size;
		q_order_type = drbd_queue_order_type(mdev);
		max_bio_size = queue_max_hw_sectors(mdev->ldev->backing_bdev->bd_disk->queue) << 9;
		max_bio_size = min_t(int, max_bio_size, DRBD_MAX_BIO_SIZE);
		put_ldev(mdev);
	} 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 */
	}

	sock = &mdev->tconn->data;
	p = drbd_prepare_command(mdev, sock);
	if (!p)
		return -EIO;
	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(mdev->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(mdev, sock, P_SIZES, sizeof(*p), NULL, 0);
}

/**
 * drbd_send_state() - Sends the drbd state to the peer
 * @mdev:	DRBD device.
 */
int drbd_send_state(struct drbd_conf *mdev)
{
	struct drbd_socket *sock;
	struct p_state *p;

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

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

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

}

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

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

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

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

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

	sock = &tconn->meta;
	p = conn_prepare_command(tconn, sock);
	if (p) {
		p->retcode = cpu_to_be32(retcode);
		conn_send_command(tconn, 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);
}

int fill_bitmap_rle_bits(struct drbd_conf *mdev,
			 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(mdev->tconn->net_conf)->use_rle;
	rcu_read_unlock();
	if (!use_rle || mdev->tconn->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(mdev, c->bit_offset)
				    : _drbd_bm_find_next(mdev, 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) {
			dev_err(DEV, "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) {
			dev_err(DEV, "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_conf *mdev, struct bm_xfer_ctx *c)
{
	struct drbd_socket *sock = &mdev->tconn->data;
	unsigned int header_size = drbd_header_size(mdev->tconn);
	struct p_compressed_bm *p = sock->sbuf + header_size;
	int len, err;

	len = fill_bitmap_rle_bits(mdev, 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(mdev->tconn, mdev->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(mdev, c->word_offset, num_words, p);
		err = __send_command(mdev->tconn, mdev->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(mdev, "send", c);
			return 0;
		} else
			return 1;
	}
	return -EIO;
}

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

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

	if (get_ldev(mdev)) {
		if (drbd_md_test_flag(mdev->ldev, MDF_FULL_SYNC)) {
			dev_info(DEV, "Writing the whole bitmap, MDF_FullSync was set.\n");
			drbd_bm_set_all(mdev);
			if (drbd_bm_write(mdev)) {
				/* 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! */
				dev_err(DEV, "Failed to write bitmap to disk!\n");
			} else {
				drbd_md_clear_flag(mdev, MDF_FULL_SYNC);
				drbd_md_sync(mdev);
			}
		}
		put_ldev(mdev);
	}

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

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

	return err == 0;
}

int drbd_send_bitmap(struct drbd_conf *mdev)
{
	struct drbd_socket *sock = &mdev->tconn->data;
	int err = -1;

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

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

	if (mdev->state.conn < C_CONNECTED)
		return;

	sock = &mdev->tconn->meta;
	p = drbd_prepare_command(mdev, sock);
	if (!p)
		return;
	p->barrier = barrier_nr;
	p->set_size = cpu_to_be32(set_size);
	drbd_send_command(mdev, sock, P_BARRIER_ACK, sizeof(*p), NULL, 0);
}

/**
 * _drbd_send_ack() - Sends an ack packet
 * @mdev:	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_conf *mdev, enum drbd_packet cmd,
			  u64 sector, u32 blksize, u64 block_id)
{
	struct drbd_socket *sock;
	struct p_block_ack *p;

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

	sock = &mdev->tconn->meta;
	p = drbd_prepare_command(mdev, 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(&mdev->packet_seq));
	return drbd_send_command(mdev, 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_conf *mdev, enum drbd_packet cmd,
		      struct p_data *dp, int data_size)
{
	data_size -= (mdev->tconn->agreed_pro_version >= 87 && mdev->tconn->integrity_r_tfm) ?
		crypto_hash_digestsize(mdev->tconn->integrity_r_tfm) : 0;
	_drbd_send_ack(mdev, cmd, dp->sector, cpu_to_be32(data_size),
		       dp->block_id);
}

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

/**
 * drbd_send_ack() - Sends an ack packet
 * @mdev:	DRBD device
 * @cmd:	packet command code
 * @peer_req:	peer request
 */
int drbd_send_ack(struct drbd_conf *mdev, enum drbd_packet cmd,
		  struct drbd_peer_request *peer_req)
{
	return _drbd_send_ack(mdev, 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_conf *mdev, enum drbd_packet cmd,
		     sector_t sector, int blksize, u64 block_id)
{
	return _drbd_send_ack(mdev, cmd,
			      cpu_to_be64(sector),
			      cpu_to_be32(blksize),
			      cpu_to_be64(block_id));
}

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

	sock = &mdev->tconn->data;
	p = drbd_prepare_command(mdev, 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(mdev, sock, cmd, sizeof(*p), NULL, 0);
}

int drbd_send_drequest_csum(struct drbd_conf *mdev, 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 = &mdev->tconn->data;
	p = drbd_prepare_command(mdev, 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(mdev, sock, cmd, sizeof(*p),
				 digest, digest_size);
}

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

	sock = &mdev->tconn->data;
	p = drbd_prepare_command(mdev, 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(mdev, 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_tconn *tconn, struct socket *sock)
{
	int drop_it;
	/* long elapsed = (long)(jiffies - mdev->last_received); */

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

	if (drop_it)
		return true;

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

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

static void drbd_update_congested(struct drbd_tconn *tconn)
{
	struct sock *sk = tconn->data.socket->sk;
	if (sk->sk_wmem_queued > sk->sk_sndbuf * 4 / 5)
		set_bit(NET_CONGESTED, &tconn->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_conf *mdev, struct page *page,
			      int offset, size_t size, unsigned msg_flags)
{
	struct socket *socket;
	void *addr;
	int err;

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

static int _drbd_send_page(struct drbd_conf *mdev, struct page *page,
		    int offset, size_t size, unsigned msg_flags)
{
	struct socket *socket = mdev->tconn->data.socket;
	mm_segment_t oldfs = get_fs();
	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 (disable_sendpage || (page_count(page) < 1) || PageSlab(page))
		return _drbd_no_send_page(mdev, page, offset, size, msg_flags);

	msg_flags |= MSG_NOSIGNAL;
	drbd_update_congested(mdev->tconn);
	set_fs(KERNEL_DS);
	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(mdev->tconn, socket))
					break;
				continue;
			}
			dev_warn(DEV, "%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 && mdev->cstate >= C_CONNECTED*/);
	set_fs(oldfs);
	clear_bit(NET_CONGESTED, &mdev->tconn->flags);

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

static int _drbd_send_bio(struct drbd_conf *mdev, struct bio *bio)
{
	struct bio_vec *bvec;
	int i;
	/* hint all but last page with MSG_MORE */
	__bio_for_each_segment(bvec, bio, i, 0) {
		int err;

		err = _drbd_no_send_page(mdev, bvec->bv_page,
					 bvec->bv_offset, bvec->bv_len,
					 i == bio->bi_vcnt - 1 ? 0 : MSG_MORE);
		if (err)
			return err;
	}
	return 0;
}

static int _drbd_send_zc_bio(struct drbd_conf *mdev, struct bio *bio)
{
	struct bio_vec *bvec;
	int i;
	/* hint all but last page with MSG_MORE */
	__bio_for_each_segment(bvec, bio, i, 0) {
		int err;

		err = _drbd_send_page(mdev, bvec->bv_page,
				      bvec->bv_offset, bvec->bv_len,
				      i == bio->bi_vcnt - 1 ? 0 : MSG_MORE);
		if (err)
			return err;
	}
	return 0;
}

static int _drbd_send_zc_ee(struct drbd_conf *mdev,
			    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(mdev, 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_conf *mdev, unsigned long bi_rw)
{
	if (mdev->tconn->agreed_pro_version >= 95)
		return  (bi_rw & REQ_SYNC ? DP_RW_SYNC : 0) |
			(bi_rw & REQ_FUA ? DP_FUA : 0) |
			(bi_rw & REQ_FLUSH ? DP_FLUSH : 0) |
			(bi_rw & REQ_DISCARD ? DP_DISCARD : 0);
	else
		return bi_rw & REQ_SYNC ? DP_RW_SYNC : 0;
}

/* Used to send write requests
 * R_PRIMARY -> Peer	(P_DATA)
 */
int drbd_send_dblock(struct drbd_conf *mdev, struct drbd_request *req)
{
	struct drbd_socket *sock;
	struct p_data *p;
	unsigned int dp_flags = 0;
	int dgs;
	int err;

	dgs = (mdev->tconn->agreed_pro_version >= 87 && mdev->tconn->integrity_w_tfm) ?
		crypto_hash_digestsize(mdev->tconn->integrity_w_tfm) : 0;

	sock = &mdev->tconn->data;
	p = drbd_prepare_command(mdev, sock);
	if (!p)
		return -EIO;
	p->sector = cpu_to_be64(req->i.sector);
	p->block_id = (unsigned long)req;
	p->seq_num = cpu_to_be32(req->seq_num = atomic_inc_return(&mdev->packet_seq));
	dp_flags = bio_flags_to_wire(mdev, req->master_bio->bi_rw);
	if (mdev->state.conn >= C_SYNC_SOURCE &&
	    mdev->state.conn <= C_PAUSED_SYNC_T)
		dp_flags |= DP_MAY_SET_IN_SYNC;
	if (mdev->tconn->agreed_pro_version >= 100) {
		if (req->rq_state & RQ_EXP_RECEIVE_ACK)
			dp_flags |= DP_SEND_RECEIVE_ACK;
		if (req->rq_state & RQ_EXP_WRITE_ACK)
			dp_flags |= DP_SEND_WRITE_ACK;
	}
	p->dp_flags = cpu_to_be32(dp_flags);
	if (dgs)
		drbd_csum_bio(mdev, mdev->tconn->integrity_w_tfm, req->master_bio, p + 1);
	err = __send_command(mdev->tconn, mdev->vnr, sock, P_DATA, sizeof(*p) + dgs, 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)) || dgs)
			err = _drbd_send_bio(mdev, req->master_bio);
		else
			err = _drbd_send_zc_bio(mdev, req->master_bio);

		/* double check digest, sometimes buffers have been modified in flight. */
		if (dgs > 0 && dgs <= 64) {
			/* 64 byte, 512 bit, is the largest digest size
			 * currently supported in kernel crypto. */
			unsigned char digest[64];
			drbd_csum_bio(mdev, mdev->tconn->integrity_w_tfm, req->master_bio, digest);
			if (memcmp(p + 1, digest, dgs)) {
				dev_warn(DEV,
					"Digest mismatch, buffer modified by upper layers during write: %llus +%u\n",
					(unsigned long long)req->i.sector, req->i.size);
			}
		} /* else if (dgs > 64) {
		     ... Be noisy about digest too large ...
		} */
	}
	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_conf *mdev, enum drbd_packet cmd,
		    struct drbd_peer_request *peer_req)
{
	struct drbd_socket *sock;
	struct p_data *p;
	int err;
	int dgs;

	dgs = (mdev->tconn->agreed_pro_version >= 87 && mdev->tconn->integrity_w_tfm) ?
		crypto_hash_digestsize(mdev->tconn->integrity_w_tfm) : 0;

	sock = &mdev->tconn->data;
	p = drbd_prepare_command(mdev, sock);
	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 */
	if (dgs)
		drbd_csum_ee(mdev, mdev->tconn->integrity_w_tfm, peer_req, p + 1);
	err = __send_command(mdev->tconn, mdev->vnr, sock, cmd, sizeof(*p) + dgs, NULL, peer_req->i.size);
	if (!err)
		err = _drbd_send_zc_ee(mdev, peer_req);
	mutex_unlock(&sock->mutex);  /* locked by drbd_prepare_command() */

	return err;
}

int drbd_send_out_of_sync(struct drbd_conf *mdev, struct drbd_request *req)
{
	struct drbd_socket *sock;
	struct p_block_desc *p;

	sock = &mdev->tconn->data;
	p = drbd_prepare_command(mdev, 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(mdev, 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_tconn *tconn, struct socket *sock,
	      void *buf, size_t size, unsigned msg_flags)
{
	struct kvec iov;
	struct msghdr msg;
	int rv, sent = 0;

	if (!sock)
		return -EBADR;

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

	iov.iov_base = buf;
	iov.iov_len  = size;

	msg.msg_name       = NULL;
	msg.msg_namelen    = 0;
	msg.msg_control    = NULL;
	msg.msg_controllen = 0;
	msg.msg_flags      = msg_flags | MSG_NOSIGNAL;

	if (sock == tconn->data.socket) {
		rcu_read_lock();
		tconn->ko_count = rcu_dereference(tconn->net_conf)->ko_count;
		rcu_read_unlock();
		drbd_update_congested(tconn);
	}
	do {
		/* STRANGE
		 * tcp_sendmsg does _not_ use its size parameter at all ?
		 *
		 * -EAGAIN on timeout, -EINTR on signal.
		 */
/* THINK
 * do we need to block DRBD_SIG if sock == &meta.socket ??
 * otherwise wake_asender() might interrupt some send_*Ack !
 */
		rv = kernel_sendmsg(sock, &msg, &iov, 1, size);
		if (rv == -EAGAIN) {
			if (we_should_drop_the_connection(tconn, sock))
				break;
			else
				continue;
		}
		if (rv == -EINTR) {
			flush_signals(current);
			rv = 0;
		}
		if (rv < 0)
			break;
		sent += rv;
		iov.iov_base += rv;
		iov.iov_len  -= rv;
	} while (sent < size);

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

	if (rv <= 0) {
		if (rv != -EAGAIN) {
			conn_err(tconn, "%s_sendmsg returned %d\n",
				 sock == tconn->meta.socket ? "msock" : "sock",
				 rv);
			conn_request_state(tconn, NS(conn, C_BROKEN_PIPE), CS_HARD);
		} else
			conn_request_state(tconn, 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_tconn *tconn, struct socket *sock, void *buffer,
		  size_t size, unsigned msg_flags)
{
	int err;

	err = drbd_send(tconn, 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_conf *mdev = bdev->bd_disk->private_data;
	unsigned long flags;
	int rv = 0;

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

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

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

	return rv;
}

static int drbd_release(struct gendisk *gd, fmode_t mode)
{
	struct drbd_conf *mdev = gd->private_data;
	mutex_lock(&drbd_main_mutex);
	mdev->open_cnt--;
	mutex_unlock(&drbd_main_mutex);
	return 0;
}

static void drbd_set_defaults(struct drbd_conf *mdev)
{
	/* Beware! The actual layout differs
	 * between big endian and little endian */
	mdev->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_conf *mdev)
{
	/* the memset(,0,) did most of this.
	 * note: only assignments, no allocation in here */

	drbd_set_defaults(mdev);

	atomic_set(&mdev->ap_bio_cnt, 0);
	atomic_set(&mdev->ap_pending_cnt, 0);
	atomic_set(&mdev->rs_pending_cnt, 0);
	atomic_set(&mdev->unacked_cnt, 0);
	atomic_set(&mdev->local_cnt, 0);
	atomic_set(&mdev->pp_in_use_by_net, 0);
	atomic_set(&mdev->rs_sect_in, 0);
	atomic_set(&mdev->rs_sect_ev, 0);
	atomic_set(&mdev->ap_in_flight, 0);

	mutex_init(&mdev->md_io_mutex);
	mutex_init(&mdev->own_state_mutex);
	mdev->state_mutex = &mdev->own_state_mutex;

	spin_lock_init(&mdev->al_lock);
	spin_lock_init(&mdev->peer_seq_lock);
	spin_lock_init(&mdev->epoch_lock);

	INIT_LIST_HEAD(&mdev->active_ee);
	INIT_LIST_HEAD(&mdev->sync_ee);
	INIT_LIST_HEAD(&mdev->done_ee);
	INIT_LIST_HEAD(&mdev->read_ee);
	INIT_LIST_HEAD(&mdev->net_ee);
	INIT_LIST_HEAD(&mdev->resync_reads);
	INIT_LIST_HEAD(&mdev->resync_work.list);
	INIT_LIST_HEAD(&mdev->unplug_work.list);
	INIT_LIST_HEAD(&mdev->go_diskless.list);
	INIT_LIST_HEAD(&mdev->md_sync_work.list);
	INIT_LIST_HEAD(&mdev->start_resync_work.list);
	INIT_LIST_HEAD(&mdev->bm_io_work.w.list);

	mdev->resync_work.cb  = w_resync_timer;
	mdev->unplug_work.cb  = w_send_write_hint;
	mdev->go_diskless.cb  = w_go_diskless;
	mdev->md_sync_work.cb = w_md_sync;
	mdev->bm_io_work.w.cb = w_bitmap_io;
	mdev->start_resync_work.cb = w_start_resync;

	mdev->resync_work.mdev  = mdev;
	mdev->unplug_work.mdev  = mdev;
	mdev->go_diskless.mdev  = mdev;
	mdev->md_sync_work.mdev = mdev;
	mdev->bm_io_work.w.mdev = mdev;
	mdev->start_resync_work.mdev = mdev;

	init_timer(&mdev->resync_timer);
	init_timer(&mdev->md_sync_timer);
	init_timer(&mdev->start_resync_timer);
	init_timer(&mdev->request_timer);
	mdev->resync_timer.function = resync_timer_fn;
	mdev->resync_timer.data = (unsigned long) mdev;
	mdev->md_sync_timer.function = md_sync_timer_fn;
	mdev->md_sync_timer.data = (unsigned long) mdev;
	mdev->start_resync_timer.function = start_resync_timer_fn;
	mdev->start_resync_timer.data = (unsigned long) mdev;
	mdev->request_timer.function = request_timer_fn;
	mdev->request_timer.data = (unsigned long) mdev;

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

	/* mdev->tconn->agreed_pro_version gets initialized in drbd_connect() */
	mdev->write_ordering = WO_bdev_flush;
	mdev->resync_wenr = LC_FREE;
	mdev->peer_max_bio_size = DRBD_MAX_BIO_SIZE_SAFE;
	mdev->local_max_bio_size = DRBD_MAX_BIO_SIZE_SAFE;
}

void drbd_mdev_cleanup(struct drbd_conf *mdev)
{
	int i;
	if (mdev->tconn->receiver.t_state != NONE)
		dev_err(DEV, "ASSERT FAILED: receiver t_state == %d expected 0.\n",
				mdev->tconn->receiver.t_state);

	/* no need to lock it, I'm the only thread alive */
	if (atomic_read(&mdev->current_epoch->epoch_size) !=  0)
		dev_err(DEV, "epoch_size:%d\n", atomic_read(&mdev->current_epoch->epoch_size));
	mdev->al_writ_cnt  =
	mdev->bm_writ_cnt  =
	mdev->read_cnt     =
	mdev->recv_cnt     =
	mdev->send_cnt     =
	mdev->writ_cnt     =
	mdev->p_size       =
	mdev->rs_start     =
	mdev->rs_total     =
	mdev->rs_failed    = 0;
	mdev->rs_last_events = 0;
	mdev->rs_last_sect_ev = 0;
	for (i = 0; i < DRBD_SYNC_MARKS; i++) {
		mdev->rs_mark_left[i] = 0;
		mdev->rs_mark_time[i] = 0;
	}
	D_ASSERT(mdev->tconn->net_conf == NULL);

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

	drbd_free_resources(mdev);
	clear_bit(AL_SUSPENDED, &mdev->flags);

	D_ASSERT(list_empty(&mdev->active_ee));
	D_ASSERT(list_empty(&mdev->sync_ee));
	D_ASSERT(list_empty(&mdev->done_ee));
	D_ASSERT(list_empty(&mdev->read_ee));
	D_ASSERT(list_empty(&mdev->net_ee));
	D_ASSERT(list_empty(&mdev->resync_reads));
	D_ASSERT(list_empty(&mdev->tconn->data.work.q));
	D_ASSERT(list_empty(&mdev->tconn->meta.work.q));
	D_ASSERT(list_empty(&mdev->resync_work.list));
	D_ASSERT(list_empty(&mdev->unplug_work.list));
	D_ASSERT(list_empty(&mdev->go_diskless.list));

	drbd_set_defaults(mdev);
}


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(atomic_read(&drbd_pp_vacant)==0); */

	if (drbd_md_io_bio_set)
		bioset_free(drbd_md_io_bio_set);
	if (drbd_md_io_page_pool)
		mempool_destroy(drbd_md_io_page_pool);
	if (drbd_ee_mempool)
		mempool_destroy(drbd_ee_mempool);
	if (drbd_request_mempool)
		mempool_destroy(drbd_request_mempool);
	if (drbd_ee_cache)
		kmem_cache_destroy(drbd_ee_cache);
	if (drbd_request_cache)
		kmem_cache_destroy(drbd_request_cache);
	if (drbd_bm_ext_cache)
		kmem_cache_destroy(drbd_bm_ext_cache);
	if (drbd_al_ext_cache)
		kmem_cache_destroy(drbd_al_ext_cache);

	drbd_md_io_bio_set   = NULL;
	drbd_md_io_page_pool = NULL;
	drbd_ee_mempool      = NULL;
	drbd_request_mempool = NULL;
	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) * minor_count;
	int i;

	/* prepare our caches and mempools */
	drbd_request_mempool = NULL;
	drbd_ee_cache        = NULL;
	drbd_request_cache   = NULL;
	drbd_bm_ext_cache    = NULL;
	drbd_al_ext_cache    = NULL;
	drbd_pp_pool         = NULL;
	drbd_md_io_page_pool = NULL;
	drbd_md_io_bio_set   = NULL;

	/* 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 */
	drbd_md_io_bio_set = bioset_create(DRBD_MIN_POOL_PAGES, 0);
	if (drbd_md_io_bio_set == NULL)
		goto Enomem;

	drbd_md_io_page_pool = mempool_create_page_pool(DRBD_MIN_POOL_PAGES, 0);
	if (drbd_md_io_page_pool == NULL)
		goto Enomem;

	drbd_request_mempool = mempool_create(number,
		mempool_alloc_slab, mempool_free_slab, drbd_request_cache);
	if (drbd_request_mempool == NULL)
		goto Enomem;

	drbd_ee_mempool = mempool_create(number,
		mempool_alloc_slab, mempool_free_slab, drbd_ee_cache);
	if (drbd_ee_mempool == NULL)
		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 int drbd_notify_sys(struct notifier_block *this, unsigned long code,
	void *unused)
{
	/* just so we have it.  you never know what interesting things we
	 * might want to do here some day...
	 */

	return NOTIFY_DONE;
}

static struct notifier_block drbd_notifier = {
	.notifier_call = drbd_notify_sys,
};

static void drbd_release_all_peer_reqs(struct drbd_conf *mdev)
{
	int rr;

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

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

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

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

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

/* caution. no locking. */
void drbd_delete_device(struct drbd_conf *mdev)
{
	idr_remove(&mdev->tconn->volumes, mdev->vnr);
	idr_remove(&minors, mdev_to_minor(mdev));
	synchronize_rcu();

	/* paranoia asserts */
	D_ASSERT(mdev->open_cnt == 0);
	D_ASSERT(list_empty(&mdev->tconn->data.work.q));
	/* end paranoia asserts */

	del_gendisk(mdev->vdisk);

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

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

	drbd_free_resources(mdev);

	drbd_release_all_peer_reqs(mdev);

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

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

	kfree(mdev->current_epoch);
	if (mdev->bitmap) /* should no longer be there. */
		drbd_bm_cleanup(mdev);
	__free_page(mdev->md_io_page);
	put_disk(mdev->vdisk);
	blk_cleanup_queue(mdev->rq_queue);
	kfree(mdev);
}

static void drbd_cleanup(void)
{
	unsigned int i;
	struct drbd_conf *mdev;

	unregister_reboot_notifier(&drbd_notifier);

	/* 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);

	drbd_genl_unregister();

	down_write(&drbd_cfg_rwsem);
	idr_for_each_entry(&minors, mdev, i)
		drbd_delete_device(mdev);
	up_write(&drbd_cfg_rwsem);

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

	idr_destroy(&minors);

	printk(KERN_INFO "drbd: module cleanup done.\n");
}

/**
 * drbd_congested() - Callback for pdflush
 * @congested_data:	User data
 * @bdi_bits:		Bits pdflush is currently interested in
 *
 * Returns 1<<BDI_async_congested and/or 1<<BDI_sync_congested if we are congested.
 */
static int drbd_congested(void *congested_data, int bdi_bits)
{
	struct drbd_conf *mdev = congested_data;
	struct request_queue *q;
	char reason = '-';
	int r = 0;

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

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

	if (bdi_bits & (1 << BDI_async_congested) && test_bit(NET_CONGESTED, &mdev->tconn->flags)) {
		r |= (1 << BDI_async_congested);
		reason = reason == 'b' ? 'a' : 'n';
	}

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

static void drbd_init_workqueue(struct drbd_work_queue* wq)
{
	sema_init(&wq->s, 0);
	spin_lock_init(&wq->q_lock);
	INIT_LIST_HEAD(&wq->q);
}

struct drbd_tconn *conn_by_name(const char *name)
{
	struct drbd_tconn *tconn;

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

	down_read(&drbd_cfg_rwsem);
	list_for_each_entry(tconn, &drbd_tconns, all_tconn) {
		if (!strcmp(tconn->name, name))
			goto found;
	}
	tconn = NULL;
found:
	up_read(&drbd_cfg_rwsem);
	return tconn;
}

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_tconn *tconn)
{
	crypto_free_hash(tconn->cram_hmac_tfm);
	crypto_free_hash(tconn->integrity_w_tfm);
	crypto_free_hash(tconn->integrity_r_tfm);
	kfree(tconn->int_dig_in);
	kfree(tconn->int_dig_vv);
	tconn->cram_hmac_tfm = NULL;
	tconn->integrity_w_tfm = NULL;
	tconn->integrity_r_tfm = NULL;
	tconn->int_dig_in = NULL;
	tconn->int_dig_vv = NULL;
}

struct drbd_tconn *drbd_new_tconn(const char *name)
{
	struct drbd_tconn *tconn;

	tconn = kzalloc(sizeof(struct drbd_tconn), GFP_KERNEL);
	if (!tconn)
		return NULL;

	tconn->name = kstrdup(name, GFP_KERNEL);
	if (!tconn->name)
		goto fail;

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

	if (!zalloc_cpumask_var(&tconn->cpu_mask, GFP_KERNEL))
		goto fail;

	if (!tl_init(tconn))
		goto fail;

	tconn->cstate = C_STANDALONE;
	mutex_init(&tconn->cstate_mutex);
	spin_lock_init(&tconn->req_lock);
	mutex_init(&tconn->net_conf_update);
	init_waitqueue_head(&tconn->ping_wait);
	idr_init(&tconn->volumes);

	drbd_init_workqueue(&tconn->data.work);
	mutex_init(&tconn->data.mutex);

	drbd_init_workqueue(&tconn->meta.work);
	mutex_init(&tconn->meta.mutex);

	drbd_thread_init(tconn, &tconn->receiver, drbdd_init, "receiver");
	drbd_thread_init(tconn, &tconn->worker, drbd_worker, "worker");
	drbd_thread_init(tconn, &tconn->asender, drbd_asender, "asender");

	tconn->res_opts = (struct res_opts) {
		{}, 0, /* cpu_mask */
		DRBD_ON_NO_DATA_DEF, /* on_no_data */
	};

	down_write(&drbd_cfg_rwsem);
	list_add_tail(&tconn->all_tconn, &drbd_tconns);
	up_write(&drbd_cfg_rwsem);

	return tconn;

fail:
	tl_cleanup(tconn);
	free_cpumask_var(tconn->cpu_mask);
	drbd_free_socket(&tconn->meta);
	drbd_free_socket(&tconn->data);
	kfree(tconn->name);
	kfree(tconn);

	return NULL;
}

void drbd_free_tconn(struct drbd_tconn *tconn)
{
	list_del(&tconn->all_tconn);
	idr_destroy(&tconn->volumes);

	free_cpumask_var(tconn->cpu_mask);
	drbd_free_socket(&tconn->meta);
	drbd_free_socket(&tconn->data);
	kfree(tconn->name);
	kfree(tconn->int_dig_in);
	kfree(tconn->int_dig_vv);
	kfree(tconn);
}

enum drbd_ret_code conn_new_minor(struct drbd_tconn *tconn, unsigned int minor, int vnr)
{
	struct drbd_conf *mdev;
	struct gendisk *disk;
	struct request_queue *q;
	int vnr_got = vnr;
	int minor_got = minor;
	enum drbd_ret_code err = ERR_NOMEM;

	mdev = minor_to_mdev(minor);
	if (mdev)
		return ERR_MINOR_EXISTS;

	/* GFP_KERNEL, we are outside of all write-out paths */
	mdev = kzalloc(sizeof(struct drbd_conf), GFP_KERNEL);
	if (!mdev)
		return ERR_NOMEM;

	mdev->tconn = tconn;
	mdev->minor = minor;
	mdev->vnr = vnr;

	drbd_init_set_defaults(mdev);

	q = blk_alloc_queue(GFP_KERNEL);
	if (!q)
		goto out_no_q;
	mdev->rq_queue = q;
	q->queuedata   = mdev;

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

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

	q->backing_dev_info.congested_fn = drbd_congested;
	q->backing_dev_info.congested_data = mdev;

	blk_queue_make_request(q, drbd_make_request);
	/* 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);
	blk_queue_bounce_limit(q, BLK_BOUNCE_ANY);
	blk_queue_merge_bvec(q, drbd_merge_bvec);
	q->queue_lock = &mdev->tconn->req_lock; /* needed since we use */

	mdev->md_io_page = alloc_page(GFP_KERNEL);
	if (!mdev->md_io_page)
		goto out_no_io_page;

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

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

	INIT_LIST_HEAD(&mdev->current_epoch->list);
	mdev->epochs = 1;

	if (!idr_pre_get(&minors, GFP_KERNEL))
		goto out_no_minor_idr;
	if (idr_get_new_above(&minors, mdev, minor, &minor_got))
		goto out_no_minor_idr;
	if (minor_got != minor) {
		err = ERR_MINOR_EXISTS;
		drbd_msg_put_info("requested minor exists already");
		goto out_idr_remove_minor;
	}

	if (!idr_pre_get(&tconn->volumes, GFP_KERNEL))
		goto out_idr_remove_minor;
	if (idr_get_new_above(&tconn->volumes, mdev, vnr, &vnr_got))
		goto out_idr_remove_minor;
	if (vnr_got != vnr) {
		err = ERR_INVALID_REQUEST;
		drbd_msg_put_info("requested volume exists already");
		goto out_idr_remove_vol;
	}
	add_disk(disk);

	/* inherit the connection state */
	mdev->state.conn = tconn->cstate;
	if (mdev->state.conn == C_WF_REPORT_PARAMS)
		drbd_connected(vnr, mdev, tconn);

	return NO_ERROR;

out_idr_remove_vol:
	idr_remove(&tconn->volumes, vnr_got);
out_idr_remove_minor:
	idr_remove(&minors, minor_got);
	synchronize_rcu();
out_no_minor_idr:
	kfree(mdev->current_epoch);
out_no_epoch:
	drbd_bm_cleanup(mdev);
out_no_bitmap:
	__free_page(mdev->md_io_page);
out_no_io_page:
	put_disk(disk);
out_no_disk:
	blk_cleanup_queue(q);
out_no_q:
	kfree(mdev);
	return err;
}

int __init drbd_init(void)
{
	int err;

	if (minor_count < DRBD_MINOR_COUNT_MIN || minor_count > DRBD_MINOR_COUNT_MAX) {
		printk(KERN_ERR
		       "drbd: invalid minor_count (%d)\n", minor_count);
#ifdef MODULE
		return -EINVAL;
#else
		minor_count = 8;
#endif
	}

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

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


	register_reboot_notifier(&drbd_notifier);

	/*
	 * allocate all necessary structs
	 */
	err = -ENOMEM;

	init_waitqueue_head(&drbd_pp_wait);

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

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

	drbd_proc = proc_create_data("drbd", S_IFREG | S_IRUGO , NULL, &drbd_proc_fops, NULL);
	if (!drbd_proc)	{
		printk(KERN_ERR "drbd: unable to register proc file\n");
		goto fail;
	}

	rwlock_init(&global_state_lock);
	INIT_LIST_HEAD(&drbd_tconns);

	printk(KERN_INFO "drbd: initialized. "
	       "Version: " REL_VERSION " (api:%d/proto:%d-%d)\n",
	       API_VERSION, PRO_VERSION_MIN, PRO_VERSION_MAX);
	printk(KERN_INFO "drbd: %s\n", drbd_buildtag());
	printk(KERN_INFO "drbd: registered as block device major %d\n",
		DRBD_MAJOR);

	return 0; /* Success! */

fail:
	drbd_cleanup();
	if (err == -ENOMEM)
		/* currently always the case */
		printk(KERN_ERR "drbd: ran out of memory\n");
	else
		printk(KERN_ERR "drbd: initialization failure\n");
	return err;
}

void drbd_free_bc(struct drbd_backing_dev *ldev)
{
	if (ldev == NULL)
		return;

	blkdev_put(ldev->backing_bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
	blkdev_put(ldev->md_bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);

	kfree(ldev);
}

void drbd_free_sock(struct drbd_tconn *tconn)
{
	if (tconn->data.socket) {
		mutex_lock(&tconn->data.mutex);
		kernel_sock_shutdown(tconn->data.socket, SHUT_RDWR);
		sock_release(tconn->data.socket);
		tconn->data.socket = NULL;
		mutex_unlock(&tconn->data.mutex);
	}
	if (tconn->meta.socket) {
		mutex_lock(&tconn->meta.mutex);
		kernel_sock_shutdown(tconn->meta.socket, SHUT_RDWR);
		sock_release(tconn->meta.socket);
		tconn->meta.socket = NULL;
		mutex_unlock(&tconn->meta.mutex);
	}
}


void drbd_free_resources(struct drbd_conf *mdev)
{
	crypto_free_hash(mdev->tconn->csums_tfm);
	mdev->tconn->csums_tfm = NULL;
	crypto_free_hash(mdev->tconn->verify_tfm);
	mdev->tconn->verify_tfm = NULL;
	crypto_free_hash(mdev->tconn->cram_hmac_tfm);
	mdev->tconn->cram_hmac_tfm = NULL;
	crypto_free_hash(mdev->tconn->integrity_w_tfm);
	mdev->tconn->integrity_w_tfm = NULL;
	crypto_free_hash(mdev->tconn->integrity_r_tfm);
	mdev->tconn->integrity_r_tfm = NULL;

	drbd_free_sock(mdev->tconn);

	__no_warn(local,
		  drbd_free_bc(mdev->ldev);
		  mdev->ldev = NULL;);
}

/* meta data management */

struct meta_data_on_disk {
	u64 la_size;           /* last agreed size. */
	u64 uuid[UI_SIZE];   /* UUIDs. */
	u64 device_uuid;
	u64 reserved_u64_1;
	u32 flags;             /* MDF */
	u32 magic;
	u32 md_size_sect;
	u32 al_offset;         /* offset to this block */
	u32 al_nr_extents;     /* important for restoring the AL */
	      /* `-- act_log->nr_elements <-- ldev->dc.al_extents */
	u32 bm_offset;         /* offset to the bitmap, from here */
	u32 bm_bytes_per_bit;  /* BM_BLOCK_SIZE */
	u32 la_peer_max_bio_size;   /* last peer max_bio_size */
	u32 reserved_u32[3];

} __packed;

/**
 * drbd_md_sync() - Writes the meta data super block if the MD_DIRTY flag bit is set
 * @mdev:	DRBD device.
 */
void drbd_md_sync(struct drbd_conf *mdev)
{
	struct meta_data_on_disk *buffer;
	sector_t sector;
	int i;

	del_timer(&mdev->md_sync_timer);
	/* timer may be rearmed by drbd_md_mark_dirty() now. */
	if (!test_and_clear_bit(MD_DIRTY, &mdev->flags))
		return;

	/* We use here D_FAILED and not D_ATTACHING because we try to write
	 * metadata even if we detach due to a disk failure! */
	if (!get_ldev_if_state(mdev, D_FAILED))
		return;

	mutex_lock(&mdev->md_io_mutex);
	buffer = (struct meta_data_on_disk *)page_address(mdev->md_io_page);
	memset(buffer, 0, 512);

	buffer->la_size = cpu_to_be64(drbd_get_capacity(mdev->this_bdev));
	for (i = UI_CURRENT; i < UI_SIZE; i++)
		buffer->uuid[i] = cpu_to_be64(mdev->ldev->md.uuid[i]);
	buffer->flags = cpu_to_be32(mdev->ldev->md.flags);
	buffer->magic = cpu_to_be32(DRBD_MD_MAGIC);

	buffer->md_size_sect  = cpu_to_be32(mdev->ldev->md.md_size_sect);
	buffer->al_offset     = cpu_to_be32(mdev->ldev->md.al_offset);
	buffer->al_nr_extents = cpu_to_be32(mdev->act_log->nr_elements);
	buffer->bm_bytes_per_bit = cpu_to_be32(BM_BLOCK_SIZE);
	buffer->device_uuid = cpu_to_be64(mdev->ldev->md.device_uuid);

	buffer->bm_offset = cpu_to_be32(mdev->ldev->md.bm_offset);
	buffer->la_peer_max_bio_size = cpu_to_be32(mdev->peer_max_bio_size);

	D_ASSERT(drbd_md_ss__(mdev, mdev->ldev) == mdev->ldev->md.md_offset);
	sector = mdev->ldev->md.md_offset;

	if (drbd_md_sync_page_io(mdev, mdev->ldev, sector, WRITE)) {
		/* this was a try anyways ... */
		dev_err(DEV, "meta data update failed!\n");
		drbd_chk_io_error(mdev, 1, true);
	}

	/* Update mdev->ldev->md.la_size_sect,
	 * since we updated it on metadata. */
	mdev->ldev->md.la_size_sect = drbd_get_capacity(mdev->this_bdev);

	mutex_unlock(&mdev->md_io_mutex);
	put_ldev(mdev);
}

/**
 * drbd_md_read() - Reads in the meta data super block
 * @mdev:	DRBD device.
 * @bdev:	Device from which the meta data should be read in.
 *
 * Return 0 (NO_ERROR) on success, and an enum drbd_ret_code in case
 * something goes wrong.  Currently only: ERR_IO_MD_DISK, ERR_MD_INVALID.
 */
int drbd_md_read(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
{
	struct meta_data_on_disk *buffer;
	int i, rv = NO_ERROR;

	if (!get_ldev_if_state(mdev, D_ATTACHING))
		return ERR_IO_MD_DISK;

	mutex_lock(&mdev->md_io_mutex);
	buffer = (struct meta_data_on_disk *)page_address(mdev->md_io_page);

	if (drbd_md_sync_page_io(mdev, bdev, bdev->md.md_offset, READ)) {
		/* NOTE: can't do normal error processing here as this is
		   called BEFORE disk is attached */
		dev_err(DEV, "Error while reading metadata.\n");
		rv = ERR_IO_MD_DISK;
		goto err;
	}

	if (buffer->magic != cpu_to_be32(DRBD_MD_MAGIC)) {
		dev_err(DEV, "Error while reading metadata, magic not found.\n");
		rv = ERR_MD_INVALID;
		goto err;
	}
	if (be32_to_cpu(buffer->al_offset) != bdev->md.al_offset) {
		dev_err(DEV, "unexpected al_offset: %d (expected %d)\n",
		    be32_to_cpu(buffer->al_offset), bdev->md.al_offset);
		rv = ERR_MD_INVALID;
		goto err;
	}
	if (be32_to_cpu(buffer->bm_offset) != bdev->md.bm_offset) {
		dev_err(DEV, "unexpected bm_offset: %d (expected %d)\n",
		    be32_to_cpu(buffer->bm_offset), bdev->md.bm_offset);
		rv = ERR_MD_INVALID;
		goto err;
	}
	if (be32_to_cpu(buffer->md_size_sect) != bdev->md.md_size_sect) {
		dev_err(DEV, "unexpected md_size: %u (expected %u)\n",
		    be32_to_cpu(buffer->md_size_sect), bdev->md.md_size_sect);
		rv = ERR_MD_INVALID;
		goto err;
	}

	if (be32_to_cpu(buffer->bm_bytes_per_bit) != BM_BLOCK_SIZE) {
		dev_err(DEV, "unexpected bm_bytes_per_bit: %u (expected %u)\n",
		    be32_to_cpu(buffer->bm_bytes_per_bit), BM_BLOCK_SIZE);
		rv = ERR_MD_INVALID;
		goto err;
	}

	bdev->md.la_size_sect = be64_to_cpu(buffer->la_size);
	for (i = UI_CURRENT; i < UI_SIZE; i++)
		bdev->md.uuid[i] = be64_to_cpu(buffer->uuid[i]);
	bdev->md.flags = be32_to_cpu(buffer->flags);
	bdev->dc.al_extents = be32_to_cpu(buffer->al_nr_extents);
	bdev->md.device_uuid = be64_to_cpu(buffer->device_uuid);

	spin_lock_irq(&mdev->tconn->req_lock);
	if (mdev->state.conn < C_CONNECTED) {
		int peer;
		peer = be32_to_cpu(buffer->la_peer_max_bio_size);
		peer = max_t(int, peer, DRBD_MAX_BIO_SIZE_SAFE);
		mdev->peer_max_bio_size = peer;
	}
	spin_unlock_irq(&mdev->tconn->req_lock);

	if (bdev->dc.al_extents < 7)
		bdev->dc.al_extents = 127;

 err:
	mutex_unlock(&mdev->md_io_mutex);
	put_ldev(mdev);

	return rv;
}

/**
 * drbd_md_mark_dirty() - Mark meta data super block as dirty
 * @mdev:	DRBD device.
 *
 * Call this function if you change anything that should be written to
 * the meta-data super block. This function sets MD_DIRTY, and starts a
 * timer that ensures that within five seconds you have to call drbd_md_sync().
 */
#ifdef DEBUG
void drbd_md_mark_dirty_(struct drbd_conf *mdev, unsigned int line, const char *func)
{
	if (!test_and_set_bit(MD_DIRTY, &mdev->flags)) {
		mod_timer(&mdev->md_sync_timer, jiffies + HZ);
		mdev->last_md_mark_dirty.line = line;
		mdev->last_md_mark_dirty.func = func;
	}
}
#else
void drbd_md_mark_dirty(struct drbd_conf *mdev)
{
	if (!test_and_set_bit(MD_DIRTY, &mdev->flags))
		mod_timer(&mdev->md_sync_timer, jiffies + 5*HZ);
}
#endif

static void drbd_uuid_move_history(struct drbd_conf *mdev) __must_hold(local)
{
	int i;

	for (i = UI_HISTORY_START; i < UI_HISTORY_END; i++)
		mdev->ldev->md.uuid[i+1] = mdev->ldev->md.uuid[i];
}

void _drbd_uuid_set(struct drbd_conf *mdev, int idx, u64 val) __must_hold(local)
{
	if (idx == UI_CURRENT) {
		if (mdev->state.role == R_PRIMARY)
			val |= 1;
		else
			val &= ~((u64)1);

		drbd_set_ed_uuid(mdev, val);
	}

	mdev->ldev->md.uuid[idx] = val;
	drbd_md_mark_dirty(mdev);
}


void drbd_uuid_set(struct drbd_conf *mdev, int idx, u64 val) __must_hold(local)
{
	if (mdev->ldev->md.uuid[idx]) {
		drbd_uuid_move_history(mdev);
		mdev->ldev->md.uuid[UI_HISTORY_START] = mdev->ldev->md.uuid[idx];
	}
	_drbd_uuid_set(mdev, idx, val);
}

/**
 * drbd_uuid_new_current() - Creates a new current UUID
 * @mdev:	DRBD device.
 *
 * Creates a new current UUID, and rotates the old current UUID into
 * the bitmap slot. Causes an incremental resync upon next connect.
 */
void drbd_uuid_new_current(struct drbd_conf *mdev) __must_hold(local)
{
	u64 val;
	unsigned long long bm_uuid = mdev->ldev->md.uuid[UI_BITMAP];

	if (bm_uuid)
		dev_warn(DEV, "bm UUID was already set: %llX\n", bm_uuid);

	mdev->ldev->md.uuid[UI_BITMAP] = mdev->ldev->md.uuid[UI_CURRENT];

	get_random_bytes(&val, sizeof(u64));
	_drbd_uuid_set(mdev, UI_CURRENT, val);
	drbd_print_uuids(mdev, "new current UUID");
	/* get it to stable storage _now_ */
	drbd_md_sync(mdev);
}

void drbd_uuid_set_bm(struct drbd_conf *mdev, u64 val) __must_hold(local)
{
	if (mdev->ldev->md.uuid[UI_BITMAP] == 0 && val == 0)
		return;

	if (val == 0) {
		drbd_uuid_move_history(mdev);
		mdev->ldev->md.uuid[UI_HISTORY_START] = mdev->ldev->md.uuid[UI_BITMAP];
		mdev->ldev->md.uuid[UI_BITMAP] = 0;
	} else {
		unsigned long long bm_uuid = mdev->ldev->md.uuid[UI_BITMAP];
		if (bm_uuid)
			dev_warn(DEV, "bm UUID was already set: %llX\n", bm_uuid);

		mdev->ldev->md.uuid[UI_BITMAP] = val & ~((u64)1);
	}
	drbd_md_mark_dirty(mdev);
}

/**
 * drbd_bmio_set_n_write() - io_fn for drbd_queue_bitmap_io() or drbd_bitmap_io()
 * @mdev:	DRBD device.
 *
 * Sets all bits in the bitmap and writes the whole bitmap to stable storage.
 */
int drbd_bmio_set_n_write(struct drbd_conf *mdev)
{
	int rv = -EIO;

	if (get_ldev_if_state(mdev, D_ATTACHING)) {
		drbd_md_set_flag(mdev, MDF_FULL_SYNC);
		drbd_md_sync(mdev);
		drbd_bm_set_all(mdev);

		rv = drbd_bm_write(mdev);

		if (!rv) {
			drbd_md_clear_flag(mdev, MDF_FULL_SYNC);
			drbd_md_sync(mdev);
		}

		put_ldev(mdev);
	}

	return rv;
}

/**
 * drbd_bmio_clear_n_write() - io_fn for drbd_queue_bitmap_io() or drbd_bitmap_io()
 * @mdev:	DRBD device.
 *
 * Clears all bits in the bitmap and writes the whole bitmap to stable storage.
 */
int drbd_bmio_clear_n_write(struct drbd_conf *mdev)
{
	int rv = -EIO;

	drbd_resume_al(mdev);
	if (get_ldev_if_state(mdev, D_ATTACHING)) {
		drbd_bm_clear_all(mdev);
		rv = drbd_bm_write(mdev);
		put_ldev(mdev);
	}

	return rv;
}

static int w_bitmap_io(struct drbd_work *w, int unused)
{
	struct bm_io_work *work = container_of(w, struct bm_io_work, w);
	struct drbd_conf *mdev = w->mdev;
	int rv = -EIO;

	D_ASSERT(atomic_read(&mdev->ap_bio_cnt) == 0);

	if (get_ldev(mdev)) {
		drbd_bm_lock(mdev, work->why, work->flags);
		rv = work->io_fn(mdev);
		drbd_bm_unlock(mdev);
		put_ldev(mdev);
	}

	clear_bit_unlock(BITMAP_IO, &mdev->flags);
	wake_up(&mdev->misc_wait);

	if (work->done)
		work->done(mdev, rv);

	clear_bit(BITMAP_IO_QUEUED, &mdev->flags);
	work->why = NULL;
	work->flags = 0;

	return 0;
}

void drbd_ldev_destroy(struct drbd_conf *mdev)
{
	lc_destroy(mdev->resync);
	mdev->resync = NULL;
	lc_destroy(mdev->act_log);
	mdev->act_log = NULL;
	__no_warn(local,
		drbd_free_bc(mdev->ldev);
		mdev->ldev = NULL;);

	clear_bit(GO_DISKLESS, &mdev->flags);
}

static int w_go_diskless(struct drbd_work *w, int unused)
{
	struct drbd_conf *mdev = w->mdev;

	D_ASSERT(mdev->state.disk == D_FAILED);
	/* we cannot assert local_cnt == 0 here, as get_ldev_if_state will
	 * inc/dec it frequently. Once we are D_DISKLESS, no one will touch
	 * the protected members anymore, though, so once put_ldev reaches zero
	 * again, it will be safe to free them. */
	drbd_force_state(mdev, NS(disk, D_DISKLESS));
	return 0;
}

void drbd_go_diskless(struct drbd_conf *mdev)
{
	D_ASSERT(mdev->state.disk == D_FAILED);
	if (!test_and_set_bit(GO_DISKLESS, &mdev->flags))
		drbd_queue_work(&mdev->tconn->data.work, &mdev->go_diskless);
}

/**
 * drbd_queue_bitmap_io() - Queues an IO operation on the whole bitmap
 * @mdev:	DRBD device.
 * @io_fn:	IO callback to be called when bitmap IO is possible
 * @done:	callback to be called after the bitmap IO was performed
 * @why:	Descriptive text of the reason for doing the IO
 *
 * While IO on the bitmap happens we freeze application IO thus we ensure
 * that drbd_set_out_of_sync() can not be called. This function MAY ONLY be
 * called from worker context. It MUST NOT be used while a previous such
 * work is still pending!
 */
void drbd_queue_bitmap_io(struct drbd_conf *mdev,
			  int (*io_fn)(struct drbd_conf *),
			  void (*done)(struct drbd_conf *, int),
			  char *why, enum bm_flag flags)
{
	D_ASSERT(current == mdev->tconn->worker.task);

	D_ASSERT(!test_bit(BITMAP_IO_QUEUED, &mdev->flags));
	D_ASSERT(!test_bit(BITMAP_IO, &mdev->flags));
	D_ASSERT(list_empty(&mdev->bm_io_work.w.list));
	if (mdev->bm_io_work.why)
		dev_err(DEV, "FIXME going to queue '%s' but '%s' still pending?\n",
			why, mdev->bm_io_work.why);

	mdev->bm_io_work.io_fn = io_fn;
	mdev->bm_io_work.done = done;
	mdev->bm_io_work.why = why;
	mdev->bm_io_work.flags = flags;

	spin_lock_irq(&mdev->tconn->req_lock);
	set_bit(BITMAP_IO, &mdev->flags);
	if (atomic_read(&mdev->ap_bio_cnt) == 0) {
		if (!test_and_set_bit(BITMAP_IO_QUEUED, &mdev->flags))
			drbd_queue_work(&mdev->tconn->data.work, &mdev->bm_io_work.w);
	}
	spin_unlock_irq(&mdev->tconn->req_lock);
}

/**
 * drbd_bitmap_io() -  Does an IO operation on the whole bitmap
 * @mdev:	DRBD device.
 * @io_fn:	IO callback to be called when bitmap IO is possible
 * @why:	Descriptive text of the reason for doing the IO
 *
 * freezes application IO while that the actual IO operations runs. This
 * functions MAY NOT be called from worker context.
 */
int drbd_bitmap_io(struct drbd_conf *mdev, int (*io_fn)(struct drbd_conf *),
		char *why, enum bm_flag flags)
{
	int rv;

	D_ASSERT(current != mdev->tconn->worker.task);

	if ((flags & BM_LOCKED_SET_ALLOWED) == 0)
		drbd_suspend_io(mdev);

	drbd_bm_lock(mdev, why, flags);
	rv = io_fn(mdev);
	drbd_bm_unlock(mdev);

	if ((flags & BM_LOCKED_SET_ALLOWED) == 0)
		drbd_resume_io(mdev);

	return rv;
}

void drbd_md_set_flag(struct drbd_conf *mdev, int flag) __must_hold(local)
{
	if ((mdev->ldev->md.flags & flag) != flag) {
		drbd_md_mark_dirty(mdev);
		mdev->ldev->md.flags |= flag;
	}
}

void drbd_md_clear_flag(struct drbd_conf *mdev, int flag) __must_hold(local)
{
	if ((mdev->ldev->md.flags & flag) != 0) {
		drbd_md_mark_dirty(mdev);
		mdev->ldev->md.flags &= ~flag;
	}
}
int drbd_md_test_flag(struct drbd_backing_dev *bdev, int flag)
{
	return (bdev->md.flags & flag) != 0;
}

static void md_sync_timer_fn(unsigned long data)
{
	struct drbd_conf *mdev = (struct drbd_conf *) data;

	drbd_queue_work_front(&mdev->tconn->data.work, &mdev->md_sync_work);
}

static int w_md_sync(struct drbd_work *w, int unused)
{
	struct drbd_conf *mdev = w->mdev;

	dev_warn(DEV, "md_sync_timer expired! Worker calls drbd_md_sync().\n");
#ifdef DEBUG
	dev_warn(DEV, "last md_mark_dirty: %s:%u\n",
		mdev->last_md_mark_dirty.func, mdev->last_md_mark_dirty.line);
#endif
	drbd_md_sync(mdev);
	return 0;
}

const char *cmdname(enum drbd_packet cmd)
{
	/* THINK may need to become several global tables
	 * when we want to support more than
	 * one PRO_VERSION */
	static const char *cmdnames[] = {
		[P_DATA]	        = "Data",
		[P_DATA_REPLY]	        = "DataReply",
		[P_RS_DATA_REPLY]	= "RSDataReply",
		[P_BARRIER]	        = "Barrier",
		[P_BITMAP]	        = "ReportBitMap",
		[P_BECOME_SYNC_TARGET]  = "BecomeSyncTarget",
		[P_BECOME_SYNC_SOURCE]  = "BecomeSyncSource",
		[P_UNPLUG_REMOTE]	= "UnplugRemote",
		[P_DATA_REQUEST]	= "DataRequest",
		[P_RS_DATA_REQUEST]     = "RSDataRequest",
		[P_SYNC_PARAM]	        = "SyncParam",
		[P_SYNC_PARAM89]	= "SyncParam89",
		[P_PROTOCOL]            = "ReportProtocol",
		[P_UUIDS]	        = "ReportUUIDs",
		[P_SIZES]	        = "ReportSizes",
		[P_STATE]	        = "ReportState",
		[P_SYNC_UUID]           = "ReportSyncUUID",
		[P_AUTH_CHALLENGE]      = "AuthChallenge",
		[P_AUTH_RESPONSE]	= "AuthResponse",
		[P_PING]		= "Ping",
		[P_PING_ACK]	        = "PingAck",
		[P_RECV_ACK]	        = "RecvAck",
		[P_WRITE_ACK]	        = "WriteAck",
		[P_RS_WRITE_ACK]	= "RSWriteAck",
		[P_DISCARD_WRITE]        = "DiscardWrite",
		[P_NEG_ACK]	        = "NegAck",
		[P_NEG_DREPLY]	        = "NegDReply",
		[P_NEG_RS_DREPLY]	= "NegRSDReply",
		[P_BARRIER_ACK]	        = "BarrierAck",
		[P_STATE_CHG_REQ]       = "StateChgRequest",
		[P_STATE_CHG_REPLY]     = "StateChgReply",
		[P_OV_REQUEST]          = "OVRequest",
		[P_OV_REPLY]            = "OVReply",
		[P_OV_RESULT]           = "OVResult",
		[P_CSUM_RS_REQUEST]     = "CsumRSRequest",
		[P_RS_IS_IN_SYNC]	= "CsumRSIsInSync",
		[P_COMPRESSED_BITMAP]   = "CBitmap",
		[P_DELAY_PROBE]         = "DelayProbe",
		[P_OUT_OF_SYNC]		= "OutOfSync",
		[P_RETRY_WRITE]		= "RetryWrite",
		[P_RS_CANCEL]		= "RSCancel",
		[P_CONN_ST_CHG_REQ]	= "conn_st_chg_req",
		[P_CONN_ST_CHG_REPLY]	= "conn_st_chg_reply",

		/* enum drbd_packet, but not commands - obsoleted flags:
		 *	P_MAY_IGNORE
		 *	P_MAX_OPT_CMD
		 */
	};

	/* too big for the array: 0xfffX */
	if (cmd == P_INITIAL_META)
		return "InitialMeta";
	if (cmd == P_INITIAL_DATA)
		return "InitialData";
	if (cmd == P_CONNECTION_FEATURES)
		return "ConnectionFeatures";
	if (cmd >= ARRAY_SIZE(cmdnames))
		return "Unknown";
	return cmdnames[cmd];
}

/**
 * drbd_wait_misc  -  wait for a request to make progress
 * @mdev:	device associated with the request
 * @i:		the struct drbd_interval embedded in struct drbd_request or
 *		struct drbd_peer_request
 */
int drbd_wait_misc(struct drbd_conf *mdev, struct drbd_interval *i)
{
	struct net_conf *nc;
	DEFINE_WAIT(wait);
	long timeout;

	rcu_read_lock();
	nc = rcu_dereference(mdev->tconn->net_conf);
	if (!nc) {
		rcu_read_unlock();
		return -ETIMEDOUT;
	}
	timeout = nc->ko_count ? nc->timeout * HZ / 10 * nc->ko_count : MAX_SCHEDULE_TIMEOUT;
	rcu_read_unlock();

	/* Indicate to wake up mdev->misc_wait on progress.  */
	i->waiting = true;
	prepare_to_wait(&mdev->misc_wait, &wait, TASK_INTERRUPTIBLE);
	spin_unlock_irq(&mdev->tconn->req_lock);
	timeout = schedule_timeout(timeout);
	finish_wait(&mdev->misc_wait, &wait);
	spin_lock_irq(&mdev->tconn->req_lock);
	if (!timeout || mdev->state.conn < C_CONNECTED)
		return -ETIMEDOUT;
	if (signal_pending(current))
		return -ERESTARTSYS;
	return 0;
}

#ifdef CONFIG_DRBD_FAULT_INJECTION
/* Fault insertion support including random number generator shamelessly
 * stolen from kernel/rcutorture.c */
struct fault_random_state {
	unsigned long state;
	unsigned long count;
};

#define FAULT_RANDOM_MULT 39916801  /* prime */
#define FAULT_RANDOM_ADD	479001701 /* prime */
#define FAULT_RANDOM_REFRESH 10000

/*
 * Crude but fast random-number generator.  Uses a linear congruential
 * generator, with occasional help from get_random_bytes().
 */
static unsigned long
_drbd_fault_random(struct fault_random_state *rsp)
{
	long refresh;

	if (!rsp->count--) {
		get_random_bytes(&refresh, sizeof(refresh));
		rsp->state += refresh;
		rsp->count = FAULT_RANDOM_REFRESH;
	}
	rsp->state = rsp->state * FAULT_RANDOM_MULT + FAULT_RANDOM_ADD;
	return swahw32(rsp->state);
}

static char *
_drbd_fault_str(unsigned int type) {
	static char *_faults[] = {
		[DRBD_FAULT_MD_WR] = "Meta-data write",
		[DRBD_FAULT_MD_RD] = "Meta-data read",
		[DRBD_FAULT_RS_WR] = "Resync write",
		[DRBD_FAULT_RS_RD] = "Resync read",
		[DRBD_FAULT_DT_WR] = "Data write",
		[DRBD_FAULT_DT_RD] = "Data read",
		[DRBD_FAULT_DT_RA] = "Data read ahead",
		[DRBD_FAULT_BM_ALLOC] = "BM allocation",
		[DRBD_FAULT_AL_EE] = "EE allocation",
		[DRBD_FAULT_RECEIVE] = "receive data corruption",
	};

	return (type < DRBD_FAULT_MAX) ? _faults[type] : "**Unknown**";
}

unsigned int
_drbd_insert_fault(struct drbd_conf *mdev, unsigned int type)
{
	static struct fault_random_state rrs = {0, 0};

	unsigned int ret = (
		(fault_devs == 0 ||
			((1 << mdev_to_minor(mdev)) & fault_devs) != 0) &&
		(((_drbd_fault_random(&rrs) % 100) + 1) <= fault_rate));

	if (ret) {
		fault_count++;

		if (__ratelimit(&drbd_ratelimit_state))
			dev_warn(DEV, "***Simulating %s failure\n",
				_drbd_fault_str(type));
	}

	return ret;
}
#endif

const char *drbd_buildtag(void)
{
	/* DRBD built from external sources has here a reference to the
	   git hash of the source code. */

	static char buildtag[38] = "\0uilt-in";

	if (buildtag[0] == 0) {
#ifdef CONFIG_MODULES
		if (THIS_MODULE != NULL)
			sprintf(buildtag, "srcversion: %-24s", THIS_MODULE->srcversion);
		else
#endif
			buildtag[0] = 'b';
	}

	return buildtag;
}

module_init(drbd_init)
module_exit(drbd_cleanup)

EXPORT_SYMBOL(drbd_conn_str);
EXPORT_SYMBOL(drbd_role_str);
EXPORT_SYMBOL(drbd_disk_str);
EXPORT_SYMBOL(drbd_set_st_err_str);