drbd_int.h

/* SPDX-License-Identifier: GPL-2.0-only */
/*
  drbd_int.h

  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 <[email protected]>.
  Copyright (C) 2002-2008, Lars Ellenberg <[email protected]>.


*/

#ifndef _DRBD_INT_H
#define _DRBD_INT_H

#include <crypto/hash.h>
#include <linux/compiler.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/sched/signal.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include <linux/tcp.h>
#include <linux/mutex.h>
#include <linux/major.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/idr.h>
#include <linux/dynamic_debug.h>
#include <net/tcp.h>
#include <linux/lru_cache.h>
#include <linux/prefetch.h>
#include <linux/drbd_genl_api.h>
#include <linux/drbd.h>
#include <linux/drbd_config.h>
#include "drbd_strings.h"
#include "drbd_state.h"
#include "drbd_protocol.h"
#include "drbd_polymorph_printk.h"

/* shared module parameters, defined in drbd_main.c */
#ifdef CONFIG_DRBD_FAULT_INJECTION
extern int drbd_enable_faults;
extern int drbd_fault_rate;
#endif

extern unsigned int drbd_minor_count;
extern char drbd_usermode_helper[];
extern int drbd_proc_details;


/* This is used to stop/restart our threads.
 * Cannot use SIGTERM nor SIGKILL, since these
 * are sent out by init on runlevel changes
 * I choose SIGHUP for now.
 */
#define DRBD_SIGKILL SIGHUP

#define ID_IN_SYNC      (4711ULL)
#define ID_OUT_OF_SYNC  (4712ULL)
#define ID_SYNCER (-1ULL)

#define UUID_NEW_BM_OFFSET ((u64)0x0001000000000000ULL)

struct drbd_device;
struct drbd_connection;
struct drbd_peer_device;

/* Defines to control fault insertion */
enum {
	DRBD_FAULT_MD_WR = 0,	/* meta data write */
	DRBD_FAULT_MD_RD = 1,	/*           read  */
	DRBD_FAULT_RS_WR = 2,	/* resync          */
	DRBD_FAULT_RS_RD = 3,
	DRBD_FAULT_DT_WR = 4,	/* data            */
	DRBD_FAULT_DT_RD = 5,
	DRBD_FAULT_DT_RA = 6,	/* data read ahead */
	DRBD_FAULT_BM_ALLOC = 7,	/* bitmap allocation */
	DRBD_FAULT_AL_EE = 8,	/* alloc ee */
	DRBD_FAULT_RECEIVE = 9, /* Changes some bytes upon receiving a [rs]data block */

	DRBD_FAULT_MAX,
};

extern unsigned int
_drbd_insert_fault(struct drbd_device *device, unsigned int type);

static inline int
drbd_insert_fault(struct drbd_device *device, unsigned int type) {
#ifdef CONFIG_DRBD_FAULT_INJECTION
	return drbd_fault_rate &&
		(drbd_enable_faults & (1<<type)) &&
		_drbd_insert_fault(device, type);
#else
	return 0;
#endif
}

/* integer division, round _UP_ to the next integer */
#define div_ceil(A, B) ((A)/(B) + ((A)%(B) ? 1 : 0))
/* usual integer division */
#define div_floor(A, B) ((A)/(B))

extern struct ratelimit_state drbd_ratelimit_state;
extern struct idr drbd_devices; /* RCU, updates: genl_lock() */
extern struct list_head drbd_resources; /* RCU, updates: genl_lock() */

extern const char *cmdname(enum drbd_packet cmd);

/* for sending/receiving the bitmap,
 * possibly in some encoding scheme */
struct bm_xfer_ctx {
	/* "const"
	 * stores total bits and long words
	 * of the bitmap, so we don't need to
	 * call the accessor functions over and again. */
	unsigned long bm_bits;
	unsigned long bm_words;
	/* during xfer, current position within the bitmap */
	unsigned long bit_offset;
	unsigned long word_offset;

	/* statistics; index: (h->command == P_BITMAP) */
	unsigned packets[2];
	unsigned bytes[2];
};

extern void INFO_bm_xfer_stats(struct drbd_peer_device *peer_device,
			       const char *direction, struct bm_xfer_ctx *c);

static inline void bm_xfer_ctx_bit_to_word_offset(struct bm_xfer_ctx *c)
{
	/* word_offset counts "native long words" (32 or 64 bit),
	 * aligned at 64 bit.
	 * Encoded packet may end at an unaligned bit offset.
	 * In case a fallback clear text packet is transmitted in
	 * between, we adjust this offset back to the last 64bit
	 * aligned "native long word", which makes coding and decoding
	 * the plain text bitmap much more convenient.  */
#if BITS_PER_LONG == 64
	c->word_offset = c->bit_offset >> 6;
#elif BITS_PER_LONG == 32
	c->word_offset = c->bit_offset >> 5;
	c->word_offset &= ~(1UL);
#else
# error "unsupported BITS_PER_LONG"
#endif
}

extern unsigned int drbd_header_size(struct drbd_connection *connection);

/**********************************************************************/
enum drbd_thread_state {
	NONE,
	RUNNING,
	EXITING,
	RESTARTING
};

struct drbd_thread {
	spinlock_t t_lock;
	struct task_struct *task;
	struct completion stop;
	enum drbd_thread_state t_state;
	int (*function) (struct drbd_thread *);
	struct drbd_resource *resource;
	struct drbd_connection *connection;
	int reset_cpu_mask;
	const char *name;
};

static inline enum drbd_thread_state get_t_state(struct drbd_thread *thi)
{
	/* THINK testing the t_state seems to be uncritical in all cases
	 * (but thread_{start,stop}), so we can read it *without* the lock.
	 *	--lge */

	smp_rmb();
	return thi->t_state;
}

struct drbd_work {
	struct list_head list;
	int (*cb)(struct drbd_work *, int cancel);
};

struct drbd_device_work {
	struct drbd_work w;
	struct drbd_device *device;
};

#include "drbd_interval.h"

extern int drbd_wait_misc(struct drbd_device *, struct drbd_interval *);

extern void lock_all_resources(void);
extern void unlock_all_resources(void);

struct drbd_request {
	struct drbd_work w;
	struct drbd_device *device;

	/* if local IO is not allowed, will be NULL.
	 * if local IO _is_ allowed, holds the locally submitted bio clone,
	 * or, after local IO completion, the ERR_PTR(error).
	 * see drbd_request_endio(). */
	struct bio *private_bio;

	struct drbd_interval i;

	/* epoch: used to check on "completion" whether this req was in
	 * the current epoch, and we therefore have to close it,
	 * causing a p_barrier packet to be send, starting a new epoch.
	 *
	 * This corresponds to "barrier" in struct p_barrier[_ack],
	 * and to "barrier_nr" in struct drbd_epoch (and various
	 * comments/function parameters/local variable names).
	 */
	unsigned int epoch;

	struct list_head tl_requests; /* ring list in the transfer log */
	struct bio *master_bio;       /* master bio pointer */

	/* see struct drbd_device */
	struct list_head req_pending_master_completion;
	struct list_head req_pending_local;

	/* for generic IO accounting */
	unsigned long start_jif;

	/* for DRBD internal statistics */

	/* Minimal set of time stamps to determine if we wait for activity log
	 * transactions, local disk or peer.  32 bit "jiffies" are good enough,
	 * we don't expect a DRBD request to be stalled for several month.
	 */

	/* before actual request processing */
	unsigned long in_actlog_jif;

	/* local disk */
	unsigned long pre_submit_jif;

	/* per connection */
	unsigned long pre_send_jif;
	unsigned long acked_jif;
	unsigned long net_done_jif;

	/* Possibly even more detail to track each phase:
	 *  master_completion_jif
	 *      how long did it take to complete the master bio
	 *      (application visible latency)
	 *  allocated_jif
	 *      how long the master bio was blocked until we finally allocated
	 *      a tracking struct
	 *  in_actlog_jif
	 *      how long did we wait for activity log transactions
	 *
	 *  net_queued_jif
	 *      when did we finally queue it for sending
	 *  pre_send_jif
	 *      when did we start sending it
	 *  post_send_jif
	 *      how long did we block in the network stack trying to send it
	 *  acked_jif
	 *      when did we receive (or fake, in protocol A) a remote ACK
	 *  net_done_jif
	 *      when did we receive final acknowledgement (P_BARRIER_ACK),
	 *      or decide, e.g. on connection loss, that we do no longer expect
	 *      anything from this peer for this request.
	 *
	 *  pre_submit_jif
	 *  post_sub_jif
	 *      when did we start submiting to the lower level device,
	 *      and how long did we block in that submit function
	 *  local_completion_jif
	 *      how long did it take the lower level device to complete this request
	 */


	/* once it hits 0, we may complete the master_bio */
	atomic_t completion_ref;
	/* once it hits 0, we may destroy this drbd_request object */
	struct kref kref;

	unsigned rq_state; /* see comments above _req_mod() */
};

struct drbd_epoch {
	struct drbd_connection *connection;
	struct list_head list;
	unsigned int barrier_nr;
	atomic_t epoch_size; /* increased on every request added. */
	atomic_t active;     /* increased on every req. added, and dec on every finished. */
	unsigned long flags;
};

/* drbd_epoch flag bits */
enum {
	DE_HAVE_BARRIER_NUMBER,
};

enum epoch_event {
	EV_PUT,
	EV_GOT_BARRIER_NR,
	EV_BECAME_LAST,
	EV_CLEANUP = 32, /* used as flag */
};

struct digest_info {
	int digest_size;
	void *digest;
};

struct drbd_peer_request {
	struct drbd_work w;
	struct drbd_peer_device *peer_device;
	struct drbd_epoch *epoch; /* for writes */
	struct page *pages;
	blk_opf_t opf;
	atomic_t pending_bios;
	struct drbd_interval i;
	/* see comments on ee flag bits below */
	unsigned long flags;
	unsigned long submit_jif;
	union {
		u64 block_id;
		struct digest_info *digest;
	};
};

/* Equivalent to bio_op and req_op. */
#define peer_req_op(peer_req) \
	((peer_req)->opf & REQ_OP_MASK)

/* ee flag bits.
 * While corresponding bios are in flight, the only modification will be
 * set_bit WAS_ERROR, which has to be atomic.
 * If no bios are in flight yet, or all have been completed,
 * non-atomic modification to ee->flags is ok.
 */
enum {
	__EE_CALL_AL_COMPLETE_IO,
	__EE_MAY_SET_IN_SYNC,

	/* is this a TRIM aka REQ_OP_DISCARD? */
	__EE_TRIM,
	/* explicit zero-out requested, or
	 * our lower level cannot handle trim,
	 * and we want to fall back to zeroout instead */
	__EE_ZEROOUT,

	/* In case a barrier failed,
	 * we need to resubmit without the barrier flag. */
	__EE_RESUBMITTED,

	/* we may have several bios per peer request.
	 * if any of those fail, we set this flag atomically
	 * from the endio callback */
	__EE_WAS_ERROR,

	/* This ee has a pointer to a digest instead of a block id */
	__EE_HAS_DIGEST,

	/* Conflicting local requests need to be restarted after this request */
	__EE_RESTART_REQUESTS,

	/* The peer wants a write ACK for this (wire proto C) */
	__EE_SEND_WRITE_ACK,

	/* Is set when net_conf had two_primaries set while creating this peer_req */
	__EE_IN_INTERVAL_TREE,

	/* for debugfs: */
	/* has this been submitted, or does it still wait for something else? */
	__EE_SUBMITTED,

	/* this is/was a write request */
	__EE_WRITE,

	/* hand back using mempool_free(e, drbd_buffer_page_pool) */
	__EE_RELEASE_TO_MEMPOOL,

	/* this is/was a write same request */
	__EE_WRITE_SAME,

	/* this originates from application on peer
	 * (not some resync or verify or other DRBD internal request) */
	__EE_APPLICATION,

	/* If it contains only 0 bytes, send back P_RS_DEALLOCATED */
	__EE_RS_THIN_REQ,
};
#define EE_CALL_AL_COMPLETE_IO (1<<__EE_CALL_AL_COMPLETE_IO)
#define EE_MAY_SET_IN_SYNC     (1<<__EE_MAY_SET_IN_SYNC)
#define EE_TRIM                (1<<__EE_TRIM)
#define EE_ZEROOUT             (1<<__EE_ZEROOUT)
#define EE_RESUBMITTED         (1<<__EE_RESUBMITTED)
#define EE_WAS_ERROR           (1<<__EE_WAS_ERROR)
#define EE_HAS_DIGEST          (1<<__EE_HAS_DIGEST)
#define EE_RESTART_REQUESTS	(1<<__EE_RESTART_REQUESTS)
#define EE_SEND_WRITE_ACK	(1<<__EE_SEND_WRITE_ACK)
#define EE_IN_INTERVAL_TREE	(1<<__EE_IN_INTERVAL_TREE)
#define EE_SUBMITTED		(1<<__EE_SUBMITTED)
#define EE_WRITE		(1<<__EE_WRITE)
#define EE_RELEASE_TO_MEMPOOL	(1<<__EE_RELEASE_TO_MEMPOOL)
#define EE_WRITE_SAME		(1<<__EE_WRITE_SAME)
#define EE_APPLICATION		(1<<__EE_APPLICATION)
#define EE_RS_THIN_REQ		(1<<__EE_RS_THIN_REQ)

/* flag bits per device */
enum {
	UNPLUG_REMOTE,		/* sending a "UnplugRemote" could help */
	MD_DIRTY,		/* current uuids and flags not yet on disk */
	USE_DEGR_WFC_T,		/* degr-wfc-timeout instead of wfc-timeout. */
	CL_ST_CHG_SUCCESS,
	CL_ST_CHG_FAIL,
	CRASHED_PRIMARY,	/* This node was a crashed primary.
				 * Gets cleared when the state.conn
				 * goes into C_CONNECTED state. */
	CONSIDER_RESYNC,

	MD_NO_FUA,		/* Users wants us to not use FUA/FLUSH on meta data dev */

	BITMAP_IO,		/* suspend application io;
				   once no more io in flight, start bitmap io */
	BITMAP_IO_QUEUED,       /* Started bitmap IO */
	WAS_IO_ERROR,		/* Local disk failed, returned IO error */
	WAS_READ_ERROR,		/* Local disk READ failed (set additionally to the above) */
	FORCE_DETACH,		/* Force-detach from local disk, aborting any pending local IO */
	RESYNC_AFTER_NEG,       /* Resync after online grow after the attach&negotiate finished. */
	RESIZE_PENDING,		/* Size change detected locally, waiting for the response from
				 * the peer, if it changed there as well. */
	NEW_CUR_UUID,		/* Create new current UUID when thawing IO */
	AL_SUSPENDED,		/* Activity logging is currently suspended. */
	AHEAD_TO_SYNC_SOURCE,   /* Ahead -> SyncSource queued */
	B_RS_H_DONE,		/* Before resync handler done (already executed) */
	DISCARD_MY_DATA,	/* discard_my_data flag per volume */
	READ_BALANCE_RR,

	FLUSH_PENDING,		/* if set, device->flush_jif is when we submitted that flush
				 * from drbd_flush_after_epoch() */

	/* cleared only after backing device related structures have been destroyed. */
	GOING_DISKLESS,		/* Disk is being detached, because of io-error, or admin request. */

	/* to be used in drbd_device_post_work() */
	GO_DISKLESS,		/* tell worker to schedule cleanup before detach */
	DESTROY_DISK,		/* tell worker to close backing devices and destroy related structures. */
	MD_SYNC,		/* tell worker to call drbd_md_sync() */
	RS_START,		/* tell worker to start resync/OV */
	RS_PROGRESS,		/* tell worker that resync made significant progress */
	RS_DONE,		/* tell worker that resync is done */
};

struct drbd_bitmap; /* opaque for drbd_device */

/* definition of bits in bm_flags to be used in drbd_bm_lock
 * and drbd_bitmap_io and friends. */
enum bm_flag {
	/* currently locked for bulk operation */
	BM_LOCKED_MASK = 0xf,

	/* in detail, that is: */
	BM_DONT_CLEAR = 0x1,
	BM_DONT_SET   = 0x2,
	BM_DONT_TEST  = 0x4,

	/* so we can mark it locked for bulk operation,
	 * and still allow all non-bulk operations */
	BM_IS_LOCKED  = 0x8,

	/* (test bit, count bit) allowed (common case) */
	BM_LOCKED_TEST_ALLOWED = BM_DONT_CLEAR | BM_DONT_SET | BM_IS_LOCKED,

	/* testing bits, as well as setting new bits allowed, but clearing bits
	 * would be unexpected.  Used during bitmap receive.  Setting new bits
	 * requires sending of "out-of-sync" information, though. */
	BM_LOCKED_SET_ALLOWED = BM_DONT_CLEAR | BM_IS_LOCKED,

	/* for drbd_bm_write_copy_pages, everything is allowed,
	 * only concurrent bulk operations are locked out. */
	BM_LOCKED_CHANGE_ALLOWED = BM_IS_LOCKED,
};

struct drbd_work_queue {
	struct list_head q;
	spinlock_t q_lock;  /* to protect the list. */
	wait_queue_head_t q_wait;
};

struct drbd_socket {
	struct mutex mutex;
	struct socket    *socket;
	/* this way we get our
	 * send/receive buffers off the stack */
	void *sbuf;
	void *rbuf;
};

struct drbd_md {
	u64 md_offset;		/* sector offset to 'super' block */

	u64 la_size_sect;	/* last agreed size, unit sectors */
	spinlock_t uuid_lock;
	u64 uuid[UI_SIZE];
	u64 device_uuid;
	u32 flags;
	u32 md_size_sect;

	s32 al_offset;	/* signed relative sector offset to activity log */
	s32 bm_offset;	/* signed relative sector offset to bitmap */

	/* cached value of bdev->disk_conf->meta_dev_idx (see below) */
	s32 meta_dev_idx;

	/* see al_tr_number_to_on_disk_sector() */
	u32 al_stripes;
	u32 al_stripe_size_4k;
	u32 al_size_4k; /* cached product of the above */
};

struct drbd_backing_dev {
	struct block_device *backing_bdev;
	struct file *backing_bdev_file;
	struct block_device *md_bdev;
	struct file *f_md_bdev;
	struct drbd_md md;
	struct disk_conf *disk_conf; /* RCU, for updates: resource->conf_update */
	sector_t known_size; /* last known size of that backing device */
};

struct drbd_md_io {
	struct page *page;
	unsigned long start_jif;	/* last call to drbd_md_get_buffer */
	unsigned long submit_jif;	/* last _drbd_md_sync_page_io() submit */
	const char *current_use;
	atomic_t in_use;
	unsigned int done;
	int error;
};

struct bm_io_work {
	struct drbd_work w;
	struct drbd_peer_device *peer_device;
	char *why;
	enum bm_flag flags;
	int (*io_fn)(struct drbd_device *device, struct drbd_peer_device *peer_device);
	void (*done)(struct drbd_device *device, int rv);
};

struct fifo_buffer {
	unsigned int head_index;
	unsigned int size;
	int total; /* sum of all values */
	int values[] __counted_by(size);
};
extern struct fifo_buffer *fifo_alloc(unsigned int fifo_size);

/* flag bits per connection */
enum {
	NET_CONGESTED,		/* The data socket is congested */
	RESOLVE_CONFLICTS,	/* Set on one node, cleared on the peer! */
	SEND_PING,
	GOT_PING_ACK,		/* set when we receive a ping_ack packet, ping_wait gets woken */
	CONN_WD_ST_CHG_REQ,	/* A cluster wide state change on the connection is active */
	CONN_WD_ST_CHG_OKAY,
	CONN_WD_ST_CHG_FAIL,
	CONN_DRY_RUN,		/* Expect disconnect after resync handshake. */
	CREATE_BARRIER,		/* next P_DATA is preceded by a P_BARRIER */
	STATE_SENT,		/* Do not change state/UUIDs while this is set */
	CALLBACK_PENDING,	/* Whether we have a call_usermodehelper(, UMH_WAIT_PROC)
				 * pending, from drbd worker context.
				 */
	DISCONNECT_SENT,

	DEVICE_WORK_PENDING,	/* tell worker that some device has pending work */
};

enum which_state { NOW, OLD = NOW, NEW };

struct drbd_resource {
	char *name;
#ifdef CONFIG_DEBUG_FS
	struct dentry *debugfs_res;
	struct dentry *debugfs_res_volumes;
	struct dentry *debugfs_res_connections;
	struct dentry *debugfs_res_in_flight_summary;
#endif
	struct kref kref;
	struct idr devices;		/* volume number to device mapping */
	struct list_head connections;
	struct list_head resources;
	struct res_opts res_opts;
	struct mutex conf_update;	/* mutex for ready-copy-update of net_conf and disk_conf */
	struct mutex adm_mutex;		/* mutex to serialize administrative requests */
	spinlock_t req_lock;

	unsigned susp:1;		/* IO suspended by user */
	unsigned susp_nod:1;		/* IO suspended because no data */
	unsigned susp_fen:1;		/* IO suspended because fence peer handler runs */

	enum write_ordering_e write_ordering;

	cpumask_var_t cpu_mask;
};

struct drbd_thread_timing_details
{
	unsigned long start_jif;
	void *cb_addr;
	const char *caller_fn;
	unsigned int line;
	unsigned int cb_nr;
};

struct drbd_connection {
	struct list_head connections;
	struct drbd_resource *resource;
#ifdef CONFIG_DEBUG_FS
	struct dentry *debugfs_conn;
	struct dentry *debugfs_conn_callback_history;
	struct dentry *debugfs_conn_oldest_requests;
#endif
	struct kref kref;
	struct idr peer_devices;	/* volume number to peer device mapping */
	enum drbd_conns cstate;		/* Only C_STANDALONE to C_WF_REPORT_PARAMS */
	struct mutex cstate_mutex;	/* Protects graceful disconnects */
	unsigned int connect_cnt;	/* Inc each time a connection is established */

	unsigned long flags;
	struct net_conf *net_conf;	/* content protected by rcu */
	wait_queue_head_t ping_wait;	/* Woken upon reception of a ping, and a state change */

	struct sockaddr_storage my_addr;
	int my_addr_len;
	struct sockaddr_storage peer_addr;
	int peer_addr_len;

	struct drbd_socket data;	/* data/barrier/cstate/parameter packets */
	struct drbd_socket meta;	/* ping/ack (metadata) packets */
	int agreed_pro_version;		/* actually used protocol version */
	u32 agreed_features;
	unsigned long last_received;	/* in jiffies, either socket */
	unsigned int ko_count;

	struct list_head transfer_log;	/* all requests not yet fully processed */

	struct crypto_shash *cram_hmac_tfm;
	struct crypto_shash *integrity_tfm;  /* checksums we compute, updates protected by connection->data->mutex */
	struct crypto_shash *peer_integrity_tfm;  /* checksums we verify, only accessed from receiver thread  */
	struct crypto_shash *csums_tfm;
	struct crypto_shash *verify_tfm;
	void *int_dig_in;
	void *int_dig_vv;

	/* receiver side */
	struct drbd_epoch *current_epoch;
	spinlock_t epoch_lock;
	unsigned int epochs;
	atomic_t current_tle_nr;	/* transfer log epoch number */
	unsigned current_tle_writes;	/* writes seen within this tl epoch */

	unsigned long last_reconnect_jif;
	/* empty member on older kernels without blk_start_plug() */
	struct blk_plug receiver_plug;
	struct drbd_thread receiver;
	struct drbd_thread worker;
	struct drbd_thread ack_receiver;
	struct workqueue_struct *ack_sender;

	/* cached pointers,
	 * so we can look up the oldest pending requests more quickly.
	 * protected by resource->req_lock */
	struct drbd_request *req_next; /* DRBD 9: todo.req_next */
	struct drbd_request *req_ack_pending;
	struct drbd_request *req_not_net_done;

	/* sender side */
	struct drbd_work_queue sender_work;

#define DRBD_THREAD_DETAILS_HIST	16
	unsigned int w_cb_nr; /* keeps counting up */
	unsigned int r_cb_nr; /* keeps counting up */
	struct drbd_thread_timing_details w_timing_details[DRBD_THREAD_DETAILS_HIST];
	struct drbd_thread_timing_details r_timing_details[DRBD_THREAD_DETAILS_HIST];

	struct {
		unsigned long last_sent_barrier_jif;

		/* whether this sender thread
		 * has processed a single write yet. */
		bool seen_any_write_yet;

		/* Which barrier number to send with the next P_BARRIER */
		int current_epoch_nr;

		/* how many write requests have been sent
		 * with req->epoch == current_epoch_nr.
		 * If none, no P_BARRIER will be sent. */
		unsigned current_epoch_writes;
	} send;
};

static inline bool has_net_conf(struct drbd_connection *connection)
{
	bool has_net_conf;

	rcu_read_lock();
	has_net_conf = rcu_dereference(connection->net_conf);
	rcu_read_unlock();

	return has_net_conf;
}

void __update_timing_details(
		struct drbd_thread_timing_details *tdp,
		unsigned int *cb_nr,
		void *cb,
		const char *fn, const unsigned int line);

#define update_worker_timing_details(c, cb) \
	__update_timing_details(c->w_timing_details, &c->w_cb_nr, cb, __func__ , __LINE__ )
#define update_receiver_timing_details(c, cb) \
	__update_timing_details(c->r_timing_details, &c->r_cb_nr, cb, __func__ , __LINE__ )

struct submit_worker {
	struct workqueue_struct *wq;
	struct work_struct worker;

	/* protected by ..->resource->req_lock */
	struct list_head writes;
};

struct drbd_peer_device {
	struct list_head peer_devices;
	struct drbd_device *device;
	struct drbd_connection *connection;
	struct work_struct send_acks_work;
#ifdef CONFIG_DEBUG_FS
	struct dentry *debugfs_peer_dev;
#endif
};

struct drbd_device {
	struct drbd_resource *resource;
	struct list_head peer_devices;
	struct list_head pending_bitmap_io;

	unsigned long flush_jif;
#ifdef CONFIG_DEBUG_FS
	struct dentry *debugfs_minor;
	struct dentry *debugfs_vol;
	struct dentry *debugfs_vol_oldest_requests;
	struct dentry *debugfs_vol_act_log_extents;
	struct dentry *debugfs_vol_resync_extents;
	struct dentry *debugfs_vol_data_gen_id;
	struct dentry *debugfs_vol_ed_gen_id;
#endif

	unsigned int vnr;	/* volume number within the connection */
	unsigned int minor;	/* device minor number */

	struct kref kref;

	/* things that are stored as / read from meta data on disk */
	unsigned long flags;

	/* configured by drbdsetup */
	struct drbd_backing_dev *ldev;

	sector_t p_size;     /* partner's disk size */
	struct request_queue *rq_queue;
	struct gendisk	    *vdisk;

	unsigned long last_reattach_jif;
	struct drbd_work resync_work;
	struct drbd_work unplug_work;
	struct timer_list resync_timer;
	struct timer_list md_sync_timer;
	struct timer_list start_resync_timer;
	struct timer_list request_timer;

	/* Used after attach while negotiating new disk state. */
	union drbd_state new_state_tmp;

	union drbd_dev_state state;
	wait_queue_head_t misc_wait;
	wait_queue_head_t state_wait;  /* upon each state change. */
	unsigned int send_cnt;
	unsigned int recv_cnt;
	unsigned int read_cnt;
	unsigned int writ_cnt;
	unsigned int al_writ_cnt;
	unsigned int bm_writ_cnt;
	atomic_t ap_bio_cnt;	 /* Requests we need to complete */
	atomic_t ap_actlog_cnt;  /* Requests waiting for activity log */
	atomic_t ap_pending_cnt; /* AP data packets on the wire, ack expected */
	atomic_t rs_pending_cnt; /* RS request/data packets on the wire */
	atomic_t unacked_cnt;	 /* Need to send replies for */
	atomic_t local_cnt;	 /* Waiting for local completion */
	atomic_t suspend_cnt;

	/* Interval tree of pending local requests */
	struct rb_root read_requests;
	struct rb_root write_requests;

	/* for statistics and timeouts */
	/* [0] read, [1] write */
	struct list_head pending_master_completion[2];
	struct list_head pending_completion[2];

	/* use checksums for *this* resync */
	bool use_csums;
	/* blocks to resync in this run [unit BM_BLOCK_SIZE] */
	unsigned long rs_total;
	/* number of resync blocks that failed in this run */
	unsigned long rs_failed;
	/* Syncer's start time [unit jiffies] */
	unsigned long rs_start;
	/* cumulated time in PausedSyncX state [unit jiffies] */
	unsigned long rs_paused;
	/* skipped because csum was equal [unit BM_BLOCK_SIZE] */
	unsigned long rs_same_csum;
#define DRBD_SYNC_MARKS 8
#define DRBD_SYNC_MARK_STEP (3*HZ)
	/* block not up-to-date at mark [unit BM_BLOCK_SIZE] */
	unsigned long rs_mark_left[DRBD_SYNC_MARKS];
	/* marks's time [unit jiffies] */
	unsigned long rs_mark_time[DRBD_SYNC_MARKS];
	/* current index into rs_mark_{left,time} */
	int rs_last_mark;
	unsigned long rs_last_bcast; /* [unit jiffies] */

	/* where does the admin want us to start? (sector) */
	sector_t ov_start_sector;
	sector_t ov_stop_sector;
	/* where are we now? (sector) */
	sector_t ov_position;
	/* Start sector of out of sync range (to merge printk reporting). */
	sector_t ov_last_oos_start;
	/* size of out-of-sync range in sectors. */
	sector_t ov_last_oos_size;
	unsigned long ov_left; /* in bits */

	struct drbd_bitmap *bitmap;
	unsigned long bm_resync_fo; /* bit offset for drbd_bm_find_next */

	/* Used to track operations of resync... */
	struct lru_cache *resync;
	/* Number of locked elements in resync LRU */
	unsigned int resync_locked;
	/* resync extent number waiting for application requests */
	unsigned int resync_wenr;

	int open_cnt;
	u64 *p_uuid;

	struct list_head active_ee; /* IO in progress (P_DATA gets written to disk) */
	struct list_head sync_ee;   /* IO in progress (P_RS_DATA_REPLY gets written to disk) */
	struct list_head done_ee;   /* need to send P_WRITE_ACK */
	struct list_head read_ee;   /* [RS]P_DATA_REQUEST being read */

	struct list_head resync_reads;
	atomic_t pp_in_use;		/* allocated from page pool */
	atomic_t pp_in_use_by_net;	/* sendpage()d, still referenced by tcp */
	wait_queue_head_t ee_wait;
	struct drbd_md_io md_io;
	spinlock_t al_lock;
	wait_queue_head_t al_wait;
	struct lru_cache *act_log;	/* activity log */
	unsigned int al_tr_number;
	int al_tr_cycle;
	wait_queue_head_t seq_wait;
	atomic_t packet_seq;
	unsigned int peer_seq;
	spinlock_t peer_seq_lock;
	unsigned long comm_bm_set; /* communicated number of set bits. */
	struct bm_io_work bm_io_work;
	u64 ed_uuid; /* UUID of the exposed data */
	struct mutex own_state_mutex;
	struct mutex *state_mutex; /* either own_state_mutex or first_peer_device(device)->connection->cstate_mutex */
	char congestion_reason;  /* Why we where congested... */
	atomic_t rs_sect_in; /* for incoming resync data rate, SyncTarget */
	atomic_t rs_sect_ev; /* for submitted resync data rate, both */
	int rs_last_sect_ev; /* counter to compare with */
	int rs_last_events;  /* counter of read or write "events" (unit sectors)
			      * on the lower level device when we last looked. */
	int c_sync_rate; /* current resync rate after syncer throttle magic */
	struct fifo_buffer *rs_plan_s; /* correction values of resync planer (RCU, connection->conn_update) */
	int rs_in_flight; /* resync sectors in flight (to proxy, in proxy and from proxy) */
	atomic_t ap_in_flight; /* App sectors in flight (waiting for ack) */
	unsigned int peer_max_bio_size;
	unsigned int local_max_bio_size;

	/* any requests that would block in drbd_make_request()
	 * are deferred to this single-threaded work queue */
	struct submit_worker submit;
};

struct drbd_bm_aio_ctx {
	struct drbd_device *device;
	struct list_head list; /* on device->pending_bitmap_io */;
	unsigned long start_jif;
	atomic_t in_flight;
	unsigned int done;
	unsigned flags;
#define BM_AIO_COPY_PAGES	1
#define BM_AIO_WRITE_HINTED	2
#define BM_AIO_WRITE_ALL_PAGES	4
#define BM_AIO_READ		8
	int error;
	struct kref kref;
};

struct drbd_config_context {
	/* assigned from drbd_genlmsghdr */
	unsigned int minor;
	/* assigned from request attributes, if present */
	unsigned int volume;
#define VOLUME_UNSPECIFIED		(-1U)
	/* pointer into the request skb,
	 * limited lifetime! */
	char *resource_name;
	struct nlattr *my_addr;
	struct nlattr *peer_addr;

	/* reply buffer */
	struct sk_buff *reply_skb;
	/* pointer into reply buffer */
	struct drbd_genlmsghdr *reply_dh;
	/* resolved from attributes, if possible */
	struct drbd_device *device;
	struct drbd_resource *resource;
	struct drbd_connection *connection;
};

static inline struct drbd_device *minor_to_device(unsigned int minor)
{
	return (struct drbd_device *)idr_find(&drbd_devices, minor);
}

static inline struct drbd_peer_device *first_peer_device(struct drbd_device *device)
{
	return list_first_entry_or_null(&device->peer_devices, struct drbd_peer_device, peer_devices);
}

static inline struct drbd_peer_device *
conn_peer_device(struct drbd_connection *connection, int volume_number)
{
	return idr_find(&connection->peer_devices, volume_number);
}

#define for_each_resource(resource, _resources) \
	list_for_each_entry(resource, _resources, resources)

#define for_each_resource_rcu(resource, _resources) \
	list_for_each_entry_rcu(resource, _resources, resources)

#define for_each_resource_safe(resource, tmp, _resources) \
	list_for_each_entry_safe(resource, tmp, _resources, resources)

#define for_each_connection(connection, resource) \
	list_for_each_entry(connection, &resource->connections, connections)

#define for_each_connection_rcu(connection, resource) \
	list_for_each_entry_rcu(connection, &resource->connections, connections)

#define for_each_connection_safe(connection, tmp, resource) \
	list_for_each_entry_safe(connection, tmp, &resource->connections, connections)

#define for_each_peer_device(peer_device, device) \
	list_for_each_entry(peer_device, &device->peer_devices, peer_devices)

#define for_each_peer_device_rcu(peer_device, device) \
	list_for_each_entry_rcu(peer_device, &device->peer_devices, peer_devices)

#define for_each_peer_device_safe(peer_device, tmp, device) \
	list_for_each_entry_safe(peer_device, tmp, &device->peer_devices, peer_devices)

static inline unsigned int device_to_minor(struct drbd_device *device)
{
	return device->minor;
}

/*
 * function declarations
 *************************/

/* drbd_main.c */

enum dds_flags {
	DDSF_FORCED    = 1,
	DDSF_NO_RESYNC = 2, /* Do not run a resync for the new space */
};

extern void drbd_init_set_defaults(struct drbd_device *device);
extern int  drbd_thread_start(struct drbd_thread *thi);
extern void _drbd_thread_stop(struct drbd_thread *thi, int restart, int wait);
#ifdef CONFIG_SMP
extern void drbd_thread_current_set_cpu(struct drbd_thread *thi);
#else
#define drbd_thread_current_set_cpu(A) ({})
#endif
extern void tl_release(struct drbd_connection *, unsigned int barrier_nr,
		       unsigned int set_size);
extern void tl_clear(struct drbd_connection *);
extern void drbd_free_sock(struct drbd_connection *connection);
extern int drbd_send(struct drbd_connection *connection, struct socket *sock,
		     void *buf, size_t size, unsigned msg_flags);
extern int drbd_send_all(struct drbd_connection *, struct socket *, void *, size_t,
			 unsigned);

extern int __drbd_send_protocol(struct drbd_connection *connection, enum drbd_packet cmd);
extern int drbd_send_protocol(struct drbd_connection *connection);
extern int drbd_send_uuids(struct drbd_peer_device *);
extern int drbd_send_uuids_skip_initial_sync(struct drbd_peer_device *);
extern void drbd_gen_and_send_sync_uuid(struct drbd_peer_device *);
extern int drbd_send_sizes(struct drbd_peer_device *, int trigger_reply, enum dds_flags flags);
extern int drbd_send_state(struct drbd_peer_device *, union drbd_state s);
extern int drbd_send_current_state(struct drbd_peer_device *);
extern int drbd_send_sync_param(struct drbd_peer_device *);
extern void drbd_send_b_ack(struct drbd_connection *connection, u32 barrier_nr,
			    u32 set_size);
extern int drbd_send_ack(struct drbd_peer_device *, enum drbd_packet,
			 struct drbd_peer_request *);
extern void drbd_send_ack_rp(struct drbd_peer_device *, enum drbd_packet,
			     struct p_block_req *rp);
extern void drbd_send_ack_dp(struct drbd_peer_device *, enum drbd_packet,
			     struct p_data *dp, int data_size);
extern int drbd_send_ack_ex(struct drbd_peer_device *, enum drbd_packet,
			    sector_t sector, int blksize, u64 block_id);
extern int drbd_send_out_of_sync(struct drbd_peer_device *, struct drbd_request *);
extern int drbd_send_block(struct drbd_peer_device *, enum drbd_packet,
			   struct drbd_peer_request *);
extern int drbd_send_dblock(struct drbd_peer_device *, struct drbd_request *req);
extern int drbd_send_drequest(struct drbd_peer_device *, int cmd,
			      sector_t sector, int size, u64 block_id);
extern int drbd_send_drequest_csum(struct drbd_peer_device *, sector_t sector,
				   int size, void *digest, int digest_size,
				   enum drbd_packet cmd);
extern int drbd_send_ov_request(struct drbd_peer_device *, sector_t sector, int size);

extern int drbd_send_bitmap(struct drbd_device *device, struct drbd_peer_device *peer_device);
extern void drbd_send_sr_reply(struct drbd_peer_device *, enum drbd_state_rv retcode);
extern void conn_send_sr_reply(struct drbd_connection *connection, enum drbd_state_rv retcode);
extern int drbd_send_rs_deallocated(struct drbd_peer_device *, struct drbd_peer_request *);
extern void drbd_backing_dev_free(struct drbd_device *device, struct drbd_backing_dev *ldev);
extern void drbd_device_cleanup(struct drbd_device *device);
extern void drbd_print_uuids(struct drbd_device *device, const char *text);
extern void drbd_queue_unplug(struct drbd_device *device);

extern void conn_md_sync(struct drbd_connection *connection);
extern void drbd_md_write(struct drbd_device *device, void *buffer);
extern void drbd_md_sync(struct drbd_device *device);
extern int  drbd_md_read(struct drbd_device *device, struct drbd_backing_dev *bdev);
extern void drbd_uuid_set(struct drbd_device *device, int idx, u64 val) __must_hold(local);
extern void _drbd_uuid_set(struct drbd_device *device, int idx, u64 val) __must_hold(local);
extern void drbd_uuid_new_current(struct drbd_device *device) __must_hold(local);
extern void drbd_uuid_set_bm(struct drbd_device *device, u64 val) __must_hold(local);
extern void drbd_uuid_move_history(struct drbd_device *device) __must_hold(local);
extern void __drbd_uuid_set(struct drbd_device *device, int idx, u64 val) __must_hold(local);
extern void drbd_md_set_flag(struct drbd_device *device, int flags) __must_hold(local);
extern void drbd_md_clear_flag(struct drbd_device *device, int flags)__must_hold(local);
extern int drbd_md_test_flag(struct drbd_backing_dev *, int);
extern void drbd_md_mark_dirty(struct drbd_device *device);
extern void drbd_queue_bitmap_io(struct drbd_device *device,
				 int (*io_fn)(struct drbd_device *, struct drbd_peer_device *),
				 void (*done)(struct drbd_device *, int),
				 char *why, enum bm_flag flags,
				 struct drbd_peer_device *peer_device);
extern int drbd_bitmap_io(struct drbd_device *device,
		int (*io_fn)(struct drbd_device *, struct drbd_peer_device *),
		char *why, enum bm_flag flags,
		struct drbd_peer_device *peer_device);
extern int drbd_bitmap_io_from_worker(struct drbd_device *device,
		int (*io_fn)(struct drbd_device *, struct drbd_peer_device *),
		char *why, enum bm_flag flags,
		struct drbd_peer_device *peer_device);
extern int drbd_bmio_set_n_write(struct drbd_device *device,
		struct drbd_peer_device *peer_device) __must_hold(local);
extern int drbd_bmio_clear_n_write(struct drbd_device *device,
		struct drbd_peer_device *peer_device) __must_hold(local);

/* Meta data layout
 *
 * We currently have two possible layouts.
 * Offsets in (512 byte) sectors.
 * external:
 *   |----------- md_size_sect ------------------|
 *   [ 4k superblock ][ activity log ][  Bitmap  ]
 *   | al_offset == 8 |
 *   | bm_offset = al_offset + X      |
 *  ==> bitmap sectors = md_size_sect - bm_offset
 *
 *  Variants:
 *     old, indexed fixed size meta data:
 *
 * internal:
 *            |----------- md_size_sect ------------------|
 * [data.....][  Bitmap  ][ activity log ][ 4k superblock ][padding*]
 *                        | al_offset < 0 |
 *            | bm_offset = al_offset - Y |
 *  ==> bitmap sectors = Y = al_offset - bm_offset
 *
 *  [padding*] are zero or up to 7 unused 512 Byte sectors to the
 *  end of the device, so that the [4k superblock] will be 4k aligned.
 *
 *  The activity log consists of 4k transaction blocks,
 *  which are written in a ring-buffer, or striped ring-buffer like fashion,
 *  which are writtensize used to be fixed 32kB,
 *  but is about to become configurable.
 */

/* Our old fixed size meta data layout
 * allows up to about 3.8TB, so if you want more,
 * you need to use the "flexible" meta data format. */
#define MD_128MB_SECT (128LLU << 11)  /* 128 MB, unit sectors */
#define MD_4kB_SECT	 8
#define MD_32kB_SECT	64

/* One activity log extent represents 4M of storage */
#define AL_EXTENT_SHIFT 22
#define AL_EXTENT_SIZE (1<<AL_EXTENT_SHIFT)

/* We could make these currently hardcoded constants configurable
 * variables at create-md time (or even re-configurable at runtime?).
 * Which will require some more changes to the DRBD "super block"
 * and attach code.
 *
 * updates per transaction:
 *   This many changes to the active set can be logged with one transaction.
 *   This number is arbitrary.
 * context per transaction:
 *   This many context extent numbers are logged with each transaction.
 *   This number is resulting from the transaction block size (4k), the layout
 *   of the transaction header, and the number of updates per transaction.
 *   See drbd_actlog.c:struct al_transaction_on_disk
 * */
#define AL_UPDATES_PER_TRANSACTION	 64	// arbitrary
#define AL_CONTEXT_PER_TRANSACTION	919	// (4096 - 36 - 6*64)/4

#if BITS_PER_LONG == 32
#define LN2_BPL 5
#define cpu_to_lel(A) cpu_to_le32(A)
#define lel_to_cpu(A) le32_to_cpu(A)
#elif BITS_PER_LONG == 64
#define LN2_BPL 6
#define cpu_to_lel(A) cpu_to_le64(A)
#define lel_to_cpu(A) le64_to_cpu(A)
#else
#error "LN2 of BITS_PER_LONG unknown!"
#endif

/* resync bitmap */
/* 16MB sized 'bitmap extent' to track syncer usage */
struct bm_extent {
	int rs_left; /* number of bits set (out of sync) in this extent. */
	int rs_failed; /* number of failed resync requests in this extent. */
	unsigned long flags;
	struct lc_element lce;
};

#define BME_NO_WRITES  0  /* bm_extent.flags: no more requests on this one! */
#define BME_LOCKED     1  /* bm_extent.flags: syncer active on this one. */
#define BME_PRIORITY   2  /* finish resync IO on this extent ASAP! App IO waiting! */

/* drbd_bitmap.c */
/*
 * We need to store one bit for a block.
 * Example: 1GB disk @ 4096 byte blocks ==> we need 32 KB bitmap.
 * Bit 0 ==> local node thinks this block is binary identical on both nodes
 * Bit 1 ==> local node thinks this block needs to be synced.
 */

#define SLEEP_TIME (HZ/10)

/* We do bitmap IO in units of 4k blocks.
 * We also still have a hardcoded 4k per bit relation. */
#define BM_BLOCK_SHIFT	12			 /* 4k per bit */
#define BM_BLOCK_SIZE	 (1<<BM_BLOCK_SHIFT)
/* mostly arbitrarily set the represented size of one bitmap extent,
 * aka resync extent, to 16 MiB (which is also 512 Byte worth of bitmap
 * at 4k per bit resolution) */
#define BM_EXT_SHIFT	 24	/* 16 MiB per resync extent */
#define BM_EXT_SIZE	 (1<<BM_EXT_SHIFT)

#if (BM_EXT_SHIFT != 24) || (BM_BLOCK_SHIFT != 12)
#error "HAVE YOU FIXED drbdmeta AS WELL??"
#endif

/* thus many _storage_ sectors are described by one bit */
#define BM_SECT_TO_BIT(x)   ((x)>>(BM_BLOCK_SHIFT-9))
#define BM_BIT_TO_SECT(x)   ((sector_t)(x)<<(BM_BLOCK_SHIFT-9))
#define BM_SECT_PER_BIT     BM_BIT_TO_SECT(1)

/* bit to represented kilo byte conversion */
#define Bit2KB(bits) ((bits)<<(BM_BLOCK_SHIFT-10))

/* in which _bitmap_ extent (resp. sector) the bit for a certain
 * _storage_ sector is located in */
#define BM_SECT_TO_EXT(x)   ((x)>>(BM_EXT_SHIFT-9))
#define BM_BIT_TO_EXT(x)    ((x) >> (BM_EXT_SHIFT - BM_BLOCK_SHIFT))

/* first storage sector a bitmap extent corresponds to */
#define BM_EXT_TO_SECT(x)   ((sector_t)(x) << (BM_EXT_SHIFT-9))
/* how much _storage_ sectors we have per bitmap extent */
#define BM_SECT_PER_EXT     BM_EXT_TO_SECT(1)
/* how many bits are covered by one bitmap extent (resync extent) */
#define BM_BITS_PER_EXT     (1UL << (BM_EXT_SHIFT - BM_BLOCK_SHIFT))

#define BM_BLOCKS_PER_BM_EXT_MASK  (BM_BITS_PER_EXT - 1)


/* in one sector of the bitmap, we have this many activity_log extents. */
#define AL_EXT_PER_BM_SECT  (1 << (BM_EXT_SHIFT - AL_EXTENT_SHIFT))

/* the extent in "PER_EXTENT" below is an activity log extent
 * we need that many (long words/bytes) to store the bitmap
 *		     of one AL_EXTENT_SIZE chunk of storage.
 * we can store the bitmap for that many AL_EXTENTS within
 * one sector of the _on_disk_ bitmap:
 * bit	 0	  bit 37   bit 38	     bit (512*8)-1
 *	     ...|........|........|.. // ..|........|
 * sect. 0	 `296	  `304			   ^(512*8*8)-1
 *
#define BM_WORDS_PER_EXT    ( (AL_EXT_SIZE/BM_BLOCK_SIZE) / BITS_PER_LONG )
#define BM_BYTES_PER_EXT    ( (AL_EXT_SIZE/BM_BLOCK_SIZE) / 8 )  // 128
#define BM_EXT_PER_SECT	    ( 512 / BM_BYTES_PER_EXTENT )	 //   4
 */

#define DRBD_MAX_SECTORS_32 (0xffffffffLU)
/* we have a certain meta data variant that has a fixed on-disk size of 128
 * MiB, of which 4k are our "superblock", and 32k are the fixed size activity
 * log, leaving this many sectors for the bitmap.
 */

#define DRBD_MAX_SECTORS_FIXED_BM \
	  ((MD_128MB_SECT - MD_32kB_SECT - MD_4kB_SECT) * (1LL<<(BM_EXT_SHIFT-9)))
#define DRBD_MAX_SECTORS      DRBD_MAX_SECTORS_FIXED_BM
/* 16 TB in units of sectors */
#if BITS_PER_LONG == 32
/* adjust by one page worth of bitmap,
 * so we won't wrap around in drbd_bm_find_next_bit.
 * you should use 64bit OS for that much storage, anyways. */
#define DRBD_MAX_SECTORS_FLEX BM_BIT_TO_SECT(0xffff7fff)
#else
/* we allow up to 1 PiB now on 64bit architecture with "flexible" meta data */
#define DRBD_MAX_SECTORS_FLEX (1UL << 51)
/* corresponds to (1UL << 38) bits right now. */
#endif

/* Estimate max bio size as 256 * PAGE_SIZE,
 * so for typical PAGE_SIZE of 4k, that is (1<<20) Byte.
 * Since we may live in a mixed-platform cluster,
 * we limit us to a platform agnostic constant here for now.
 * A followup commit may allow even bigger BIO sizes,
 * once we thought that through. */
#define DRBD_MAX_BIO_SIZE (1U << 20)
#if DRBD_MAX_BIO_SIZE > (BIO_MAX_VECS << PAGE_SHIFT)
#error Architecture not supported: DRBD_MAX_BIO_SIZE > BIO_MAX_SIZE
#endif
#define DRBD_MAX_BIO_SIZE_SAFE (1U << 12)       /* Works always = 4k */

#define DRBD_MAX_SIZE_H80_PACKET (1U << 15) /* Header 80 only allows packets up to 32KiB data */
#define DRBD_MAX_BIO_SIZE_P95    (1U << 17) /* Protocol 95 to 99 allows bios up to 128KiB */

/* For now, don't allow more than half of what we can "activate" in one
 * activity log transaction to be discarded in one go. We may need to rework
 * drbd_al_begin_io() to allow for even larger discard ranges */
#define DRBD_MAX_BATCH_BIO_SIZE	 (AL_UPDATES_PER_TRANSACTION/2*AL_EXTENT_SIZE)
#define DRBD_MAX_BBIO_SECTORS    (DRBD_MAX_BATCH_BIO_SIZE >> 9)

extern int  drbd_bm_init(struct drbd_device *device);
extern int  drbd_bm_resize(struct drbd_device *device, sector_t sectors, int set_new_bits);
extern void drbd_bm_cleanup(struct drbd_device *device);
extern void drbd_bm_set_all(struct drbd_device *device);
extern void drbd_bm_clear_all(struct drbd_device *device);
/* set/clear/test only a few bits at a time */
extern int  drbd_bm_set_bits(
		struct drbd_device *device, unsigned long s, unsigned long e);
extern int  drbd_bm_clear_bits(
		struct drbd_device *device, unsigned long s, unsigned long e);
extern int drbd_bm_count_bits(
	struct drbd_device *device, const unsigned long s, const unsigned long e);
/* bm_set_bits variant for use while holding drbd_bm_lock,
 * may process the whole bitmap in one go */
extern void _drbd_bm_set_bits(struct drbd_device *device,
		const unsigned long s, const unsigned long e);
extern int  drbd_bm_test_bit(struct drbd_device *device, unsigned long bitnr);
extern int  drbd_bm_e_weight(struct drbd_device *device, unsigned long enr);
extern int  drbd_bm_read(struct drbd_device *device,
		struct drbd_peer_device *peer_device) __must_hold(local);
extern void drbd_bm_mark_for_writeout(struct drbd_device *device, int page_nr);
extern int  drbd_bm_write(struct drbd_device *device,
		struct drbd_peer_device *peer_device) __must_hold(local);
extern void drbd_bm_reset_al_hints(struct drbd_device *device) __must_hold(local);
extern int  drbd_bm_write_hinted(struct drbd_device *device) __must_hold(local);
extern int  drbd_bm_write_lazy(struct drbd_device *device, unsigned upper_idx) __must_hold(local);
extern int drbd_bm_write_all(struct drbd_device *device,
		struct drbd_peer_device *peer_device) __must_hold(local);
extern int  drbd_bm_write_copy_pages(struct drbd_device *device,
		struct drbd_peer_device *peer_device) __must_hold(local);
extern size_t	     drbd_bm_words(struct drbd_device *device);
extern unsigned long drbd_bm_bits(struct drbd_device *device);
extern sector_t      drbd_bm_capacity(struct drbd_device *device);

#define DRBD_END_OF_BITMAP	(~(unsigned long)0)
extern unsigned long drbd_bm_find_next(struct drbd_device *device, unsigned long bm_fo);
/* bm_find_next variants for use while you hold drbd_bm_lock() */
extern unsigned long _drbd_bm_find_next(struct drbd_device *device, unsigned long bm_fo);
extern unsigned long _drbd_bm_find_next_zero(struct drbd_device *device, unsigned long bm_fo);
extern unsigned long _drbd_bm_total_weight(struct drbd_device *device);
extern unsigned long drbd_bm_total_weight(struct drbd_device *device);
/* for receive_bitmap */
extern void drbd_bm_merge_lel(struct drbd_device *device, size_t offset,
		size_t number, unsigned long *buffer);
/* for _drbd_send_bitmap */
extern void drbd_bm_get_lel(struct drbd_device *device, size_t offset,
		size_t number, unsigned long *buffer);

extern void drbd_bm_lock(struct drbd_device *device, char *why, enum bm_flag flags);
extern void drbd_bm_unlock(struct drbd_device *device);
/* drbd_main.c */

extern struct kmem_cache *drbd_request_cache;
extern struct kmem_cache *drbd_ee_cache;	/* peer requests */
extern struct kmem_cache *drbd_bm_ext_cache;	/* bitmap extents */
extern struct kmem_cache *drbd_al_ext_cache;	/* activity log extents */
extern mempool_t drbd_request_mempool;
extern mempool_t drbd_ee_mempool;

/* We also need a standard (emergency-reserve backed) page pool
 * for meta data IO (activity log, bitmap).
 * We can keep it global, as long as it is used as "N pages at a time".
 * 128 should be plenty, currently we probably can get away with as few as 1.
 */
#define DRBD_MIN_POOL_PAGES	128
extern mempool_t drbd_md_io_page_pool;
extern mempool_t drbd_buffer_page_pool;

/* We also need to make sure we get a bio
 * when we need it for housekeeping purposes */
extern struct bio_set drbd_md_io_bio_set;

/* And a bio_set for cloning */
extern struct bio_set drbd_io_bio_set;

extern struct mutex resources_mutex;

extern enum drbd_ret_code drbd_create_device(struct drbd_config_context *adm_ctx, unsigned int minor);
extern void drbd_destroy_device(struct kref *kref);
extern void drbd_delete_device(struct drbd_device *device);

extern struct drbd_resource *drbd_create_resource(const char *name);
extern void drbd_free_resource(struct drbd_resource *resource);

extern int set_resource_options(struct drbd_resource *resource, struct res_opts *res_opts);
extern struct drbd_connection *conn_create(const char *name, struct res_opts *res_opts);
extern void drbd_destroy_connection(struct kref *kref);
extern struct drbd_connection *conn_get_by_addrs(void *my_addr, int my_addr_len,
					    void *peer_addr, int peer_addr_len);
extern struct drbd_resource *drbd_find_resource(const char *name);
extern void drbd_destroy_resource(struct kref *kref);
extern void conn_free_crypto(struct drbd_connection *connection);

/* drbd_req */
extern void do_submit(struct work_struct *ws);
extern void __drbd_make_request(struct drbd_device *, struct bio *);
void drbd_submit_bio(struct bio *bio);

/* drbd_nl.c */

extern struct mutex notification_mutex;

extern void drbd_suspend_io(struct drbd_device *device);
extern void drbd_resume_io(struct drbd_device *device);
extern char *ppsize(char *buf, unsigned long long size);
extern sector_t drbd_new_dev_size(struct drbd_device *, struct drbd_backing_dev *, sector_t, int);
enum determine_dev_size {
	DS_ERROR_SHRINK = -3,
	DS_ERROR_SPACE_MD = -2,
	DS_ERROR = -1,
	DS_UNCHANGED = 0,
	DS_SHRUNK = 1,
	DS_GREW = 2,
	DS_GREW_FROM_ZERO = 3,
};
extern enum determine_dev_size
drbd_determine_dev_size(struct drbd_device *, enum dds_flags, struct resize_parms *) __must_hold(local);
extern void resync_after_online_grow(struct drbd_device *);
extern void drbd_reconsider_queue_parameters(struct drbd_device *device,
			struct drbd_backing_dev *bdev, struct o_qlim *o);
extern enum drbd_state_rv drbd_set_role(struct drbd_device *device,
					enum drbd_role new_role,
					int force);
extern bool conn_try_outdate_peer(struct drbd_connection *connection);
extern void conn_try_outdate_peer_async(struct drbd_connection *connection);
extern enum drbd_peer_state conn_khelper(struct drbd_connection *connection, char *cmd);
extern int drbd_khelper(struct drbd_device *device, char *cmd);

/* drbd_worker.c */
/* bi_end_io handlers */
extern void drbd_md_endio(struct bio *bio);
extern void drbd_peer_request_endio(struct bio *bio);
extern void drbd_request_endio(struct bio *bio);
extern int drbd_worker(struct drbd_thread *thi);
enum drbd_ret_code drbd_resync_after_valid(struct drbd_device *device, int o_minor);
void drbd_resync_after_changed(struct drbd_device *device);
extern void drbd_start_resync(struct drbd_device *device, enum drbd_conns side);
extern void resume_next_sg(struct drbd_device *device);
extern void suspend_other_sg(struct drbd_device *device);
extern int drbd_resync_finished(struct drbd_peer_device *peer_device);
/* maybe rather drbd_main.c ? */
extern void *drbd_md_get_buffer(struct drbd_device *device, const char *intent);
extern void drbd_md_put_buffer(struct drbd_device *device);
extern int drbd_md_sync_page_io(struct drbd_device *device,
		struct drbd_backing_dev *bdev, sector_t sector, enum req_op op);
extern void drbd_ov_out_of_sync_found(struct drbd_peer_device *peer_device,
		sector_t sector, int size);
extern void wait_until_done_or_force_detached(struct drbd_device *device,
		struct drbd_backing_dev *bdev, unsigned int *done);
extern void drbd_rs_controller_reset(struct drbd_peer_device *peer_device);

static inline void ov_out_of_sync_print(struct drbd_peer_device *peer_device)
{
	struct drbd_device *device = peer_device->device;

	if (device->ov_last_oos_size) {
		drbd_err(peer_device, "Out of sync: start=%llu, size=%lu (sectors)\n",
		     (unsigned long long)device->ov_last_oos_start,
		     (unsigned long)device->ov_last_oos_size);
	}
	device->ov_last_oos_size = 0;
}


extern void drbd_csum_bio(struct crypto_shash *, struct bio *, void *);
extern void drbd_csum_ee(struct crypto_shash *, struct drbd_peer_request *,
			 void *);
/* worker callbacks */
extern int w_e_end_data_req(struct drbd_work *, int);
extern int w_e_end_rsdata_req(struct drbd_work *, int);
extern int w_e_end_csum_rs_req(struct drbd_work *, int);
extern int w_e_end_ov_reply(struct drbd_work *, int);
extern int w_e_end_ov_req(struct drbd_work *, int);
extern int w_ov_finished(struct drbd_work *, int);
extern int w_resync_timer(struct drbd_work *, int);
extern int w_send_write_hint(struct drbd_work *, int);
extern int w_send_dblock(struct drbd_work *, int);
extern int w_send_read_req(struct drbd_work *, int);
extern int w_restart_disk_io(struct drbd_work *, int);
extern int w_send_out_of_sync(struct drbd_work *, int);

extern void resync_timer_fn(struct timer_list *t);
extern void start_resync_timer_fn(struct timer_list *t);

extern void drbd_endio_write_sec_final(struct drbd_peer_request *peer_req);

/* drbd_receiver.c */
extern int drbd_issue_discard_or_zero_out(struct drbd_device *device,
		sector_t start, unsigned int nr_sectors, int flags);
extern int drbd_receiver(struct drbd_thread *thi);
extern int drbd_ack_receiver(struct drbd_thread *thi);
extern void drbd_send_acks_wf(struct work_struct *ws);
extern bool drbd_rs_c_min_rate_throttle(struct drbd_device *device);
extern bool drbd_rs_should_slow_down(struct drbd_peer_device *peer_device, sector_t sector,
		bool throttle_if_app_is_waiting);
extern int drbd_submit_peer_request(struct drbd_peer_request *peer_req);
extern int drbd_free_peer_reqs(struct drbd_device *, struct list_head *);
extern struct drbd_peer_request *drbd_alloc_peer_req(struct drbd_peer_device *, u64,
						     sector_t, unsigned int,
						     unsigned int,
						     gfp_t) __must_hold(local);
extern void drbd_free_peer_req(struct drbd_device *device, struct drbd_peer_request *req);
extern struct page *drbd_alloc_pages(struct drbd_peer_device *, unsigned int, bool);
extern void _drbd_clear_done_ee(struct drbd_device *device, struct list_head *to_be_freed);
extern int drbd_connected(struct drbd_peer_device *);

/* sets the number of 512 byte sectors of our virtual device */
void drbd_set_my_capacity(struct drbd_device *device, sector_t size);

/*
 * used to submit our private bio
 */
static inline void drbd_submit_bio_noacct(struct drbd_device *device,
					     int fault_type, struct bio *bio)
{
	__release(local);
	if (!bio->bi_bdev) {
		drbd_err(device, "drbd_submit_bio_noacct: bio->bi_bdev == NULL\n");
		bio->bi_status = BLK_STS_IOERR;
		bio_endio(bio);
		return;
	}

	if (drbd_insert_fault(device, fault_type))
		bio_io_error(bio);
	else
		submit_bio_noacct(bio);
}

void drbd_bump_write_ordering(struct drbd_resource *resource, struct drbd_backing_dev *bdev,
			      enum write_ordering_e wo);

/* drbd_proc.c */
extern struct proc_dir_entry *drbd_proc;
int drbd_seq_show(struct seq_file *seq, void *v);

/* drbd_actlog.c */
extern bool drbd_al_begin_io_prepare(struct drbd_device *device, struct drbd_interval *i);
extern int drbd_al_begin_io_nonblock(struct drbd_device *device, struct drbd_interval *i);
extern void drbd_al_begin_io_commit(struct drbd_device *device);
extern bool drbd_al_begin_io_fastpath(struct drbd_device *device, struct drbd_interval *i);
extern void drbd_al_begin_io(struct drbd_device *device, struct drbd_interval *i);
extern void drbd_al_complete_io(struct drbd_device *device, struct drbd_interval *i);
extern void drbd_rs_complete_io(struct drbd_device *device, sector_t sector);
extern int drbd_rs_begin_io(struct drbd_device *device, sector_t sector);
extern int drbd_try_rs_begin_io(struct drbd_peer_device *peer_device, sector_t sector);
extern void drbd_rs_cancel_all(struct drbd_device *device);
extern int drbd_rs_del_all(struct drbd_device *device);
extern void drbd_rs_failed_io(struct drbd_peer_device *peer_device,
		sector_t sector, int size);
extern void drbd_advance_rs_marks(struct drbd_peer_device *peer_device, unsigned long still_to_go);

enum update_sync_bits_mode { RECORD_RS_FAILED, SET_OUT_OF_SYNC, SET_IN_SYNC };
extern int __drbd_change_sync(struct drbd_peer_device *peer_device, sector_t sector, int size,
		enum update_sync_bits_mode mode);
#define drbd_set_in_sync(peer_device, sector, size) \
	__drbd_change_sync(peer_device, sector, size, SET_IN_SYNC)
#define drbd_set_out_of_sync(peer_device, sector, size) \
	__drbd_change_sync(peer_device, sector, size, SET_OUT_OF_SYNC)
#define drbd_rs_failed_io(peer_device, sector, size) \
	__drbd_change_sync(peer_device, sector, size, RECORD_RS_FAILED)
extern void drbd_al_shrink(struct drbd_device *device);
extern int drbd_al_initialize(struct drbd_device *, void *);

/* drbd_nl.c */
/* state info broadcast */
struct sib_info {
	enum drbd_state_info_bcast_reason sib_reason;
	union {
		struct {
			char *helper_name;
			unsigned helper_exit_code;
		};
		struct {
			union drbd_state os;
			union drbd_state ns;
		};
	};
};
void drbd_bcast_event(struct drbd_device *device, const struct sib_info *sib);

extern int notify_resource_state(struct sk_buff *,
				  unsigned int,
				  struct drbd_resource *,
				  struct resource_info *,
				  enum drbd_notification_type);
extern int notify_device_state(struct sk_buff *,
				unsigned int,
				struct drbd_device *,
				struct device_info *,
				enum drbd_notification_type);
extern int notify_connection_state(struct sk_buff *,
				    unsigned int,
				    struct drbd_connection *,
				    struct connection_info *,
				    enum drbd_notification_type);
extern int notify_peer_device_state(struct sk_buff *,
				     unsigned int,
				     struct drbd_peer_device *,
				     struct peer_device_info *,
				     enum drbd_notification_type);
extern void notify_helper(enum drbd_notification_type, struct drbd_device *,
			  struct drbd_connection *, const char *, int);

/*
 * inline helper functions
 *************************/

/* see also page_chain_add and friends in drbd_receiver.c */
static inline struct page *page_chain_next(struct page *page)
{
	return (struct page *)page_private(page);
}
#define page_chain_for_each(page) \
	for (; page && ({ prefetch(page_chain_next(page)); 1; }); \
			page = page_chain_next(page))
#define page_chain_for_each_safe(page, n) \
	for (; page && ({ n = page_chain_next(page); 1; }); page = n)


static inline union drbd_state drbd_read_state(struct drbd_device *device)
{
	struct drbd_resource *resource = device->resource;
	union drbd_state rv;

	rv.i = device->state.i;
	rv.susp = resource->susp;
	rv.susp_nod = resource->susp_nod;
	rv.susp_fen = resource->susp_fen;

	return rv;
}

enum drbd_force_detach_flags {
	DRBD_READ_ERROR,
	DRBD_WRITE_ERROR,
	DRBD_META_IO_ERROR,
	DRBD_FORCE_DETACH,
};

#define __drbd_chk_io_error(m,f) __drbd_chk_io_error_(m,f, __func__)
static inline void __drbd_chk_io_error_(struct drbd_device *device,
		enum drbd_force_detach_flags df,
		const char *where)
{
	enum drbd_io_error_p ep;

	rcu_read_lock();
	ep = rcu_dereference(device->ldev->disk_conf)->on_io_error;
	rcu_read_unlock();
	switch (ep) {
	case EP_PASS_ON: /* FIXME would this be better named "Ignore"? */
		if (df == DRBD_READ_ERROR || df == DRBD_WRITE_ERROR) {
			if (drbd_ratelimit())
				drbd_err(device, "Local IO failed in %s.\n", where);
			if (device->state.disk > D_INCONSISTENT)
				_drbd_set_state(_NS(device, disk, D_INCONSISTENT), CS_HARD, NULL);
			break;
		}
		fallthrough;	/* for DRBD_META_IO_ERROR or DRBD_FORCE_DETACH */
	case EP_DETACH:
	case EP_CALL_HELPER:
		/* Remember whether we saw a READ or WRITE error.
		 *
		 * Recovery of the affected area for WRITE failure is covered
		 * by the activity log.
		 * READ errors may fall outside that area though. Certain READ
		 * errors can be "healed" by writing good data to the affected
		 * blocks, which triggers block re-allocation in lower layers.
		 *
		 * If we can not write the bitmap after a READ error,
		 * we may need to trigger a full sync (see w_go_diskless()).
		 *
		 * Force-detach is not really an IO error, but rather a
		 * desperate measure to try to deal with a completely
		 * unresponsive lower level IO stack.
		 * Still it should be treated as a WRITE error.
		 *
		 * Meta IO error is always WRITE error:
		 * we read meta data only once during attach,
		 * which will fail in case of errors.
		 */
		set_bit(WAS_IO_ERROR, &device->flags);
		if (df == DRBD_READ_ERROR)
			set_bit(WAS_READ_ERROR, &device->flags);
		if (df == DRBD_FORCE_DETACH)
			set_bit(FORCE_DETACH, &device->flags);
		if (device->state.disk > D_FAILED) {
			_drbd_set_state(_NS(device, disk, D_FAILED), CS_HARD, NULL);
			drbd_err(device,
				"Local IO failed in %s. Detaching...\n", where);
		}
		break;
	}
}

/**
 * drbd_chk_io_error: Handle the on_io_error setting, should be called from all io completion handlers
 * @device:	 DRBD device.
 * @error:	 Error code passed to the IO completion callback
 * @forcedetach: Force detach. I.e. the error happened while accessing the meta data
 *
 * See also drbd_main.c:after_state_ch() if (os.disk > D_FAILED && ns.disk == D_FAILED)
 */
#define drbd_chk_io_error(m,e,f) drbd_chk_io_error_(m,e,f, __func__)
static inline void drbd_chk_io_error_(struct drbd_device *device,
	int error, enum drbd_force_detach_flags forcedetach, const char *where)
{
	if (error) {
		unsigned long flags;
		spin_lock_irqsave(&device->resource->req_lock, flags);
		__drbd_chk_io_error_(device, forcedetach, where);
		spin_unlock_irqrestore(&device->resource->req_lock, flags);
	}
}


/**
 * drbd_md_first_sector() - Returns the first sector number of the meta data area
 * @bdev:	Meta data block device.
 *
 * BTW, for internal meta data, this happens to be the maximum capacity
 * we could agree upon with our peer node.
 */
static inline sector_t drbd_md_first_sector(struct drbd_backing_dev *bdev)
{
	switch (bdev->md.meta_dev_idx) {
	case DRBD_MD_INDEX_INTERNAL:
	case DRBD_MD_INDEX_FLEX_INT:
		return bdev->md.md_offset + bdev->md.bm_offset;
	case DRBD_MD_INDEX_FLEX_EXT:
	default:
		return bdev->md.md_offset;
	}
}

/**
 * drbd_md_last_sector() - Return the last sector number of the meta data area
 * @bdev:	Meta data block device.
 */
static inline sector_t drbd_md_last_sector(struct drbd_backing_dev *bdev)
{
	switch (bdev->md.meta_dev_idx) {
	case DRBD_MD_INDEX_INTERNAL:
	case DRBD_MD_INDEX_FLEX_INT:
		return bdev->md.md_offset + MD_4kB_SECT -1;
	case DRBD_MD_INDEX_FLEX_EXT:
	default:
		return bdev->md.md_offset + bdev->md.md_size_sect -1;
	}
}

/* Returns the number of 512 byte sectors of the device */
static inline sector_t drbd_get_capacity(struct block_device *bdev)
{
	return bdev ? bdev_nr_sectors(bdev) : 0;
}

/**
 * drbd_get_max_capacity() - Returns the capacity we announce to out peer
 * @bdev:	Meta data block device.
 *
 * returns the capacity we announce to out peer.  we clip ourselves at the
 * various MAX_SECTORS, because if we don't, current implementation will
 * oops sooner or later
 */
static inline sector_t drbd_get_max_capacity(struct drbd_backing_dev *bdev)
{
	sector_t s;

	switch (bdev->md.meta_dev_idx) {
	case DRBD_MD_INDEX_INTERNAL:
	case DRBD_MD_INDEX_FLEX_INT:
		s = drbd_get_capacity(bdev->backing_bdev)
			? min_t(sector_t, DRBD_MAX_SECTORS_FLEX,
				drbd_md_first_sector(bdev))
			: 0;
		break;
	case DRBD_MD_INDEX_FLEX_EXT:
		s = min_t(sector_t, DRBD_MAX_SECTORS_FLEX,
				drbd_get_capacity(bdev->backing_bdev));
		/* clip at maximum size the meta device can support */
		s = min_t(sector_t, s,
			BM_EXT_TO_SECT(bdev->md.md_size_sect
				     - bdev->md.bm_offset));
		break;
	default:
		s = min_t(sector_t, DRBD_MAX_SECTORS,
				drbd_get_capacity(bdev->backing_bdev));
	}
	return s;
}

/**
 * drbd_md_ss() - Return the sector number of our meta data super block
 * @bdev:	Meta data block device.
 */
static inline sector_t drbd_md_ss(struct drbd_backing_dev *bdev)
{
	const int meta_dev_idx = bdev->md.meta_dev_idx;

	if (meta_dev_idx == DRBD_MD_INDEX_FLEX_EXT)
		return 0;

	/* Since drbd08, internal meta data is always "flexible".
	 * position: last 4k aligned block of 4k size */
	if (meta_dev_idx == DRBD_MD_INDEX_INTERNAL ||
	    meta_dev_idx == DRBD_MD_INDEX_FLEX_INT)
		return (drbd_get_capacity(bdev->backing_bdev) & ~7ULL) - 8;

	/* external, some index; this is the old fixed size layout */
	return MD_128MB_SECT * bdev->md.meta_dev_idx;
}

static inline void
drbd_queue_work(struct drbd_work_queue *q, struct drbd_work *w)
{
	unsigned long flags;
	spin_lock_irqsave(&q->q_lock, flags);
	list_add_tail(&w->list, &q->q);
	spin_unlock_irqrestore(&q->q_lock, flags);
	wake_up(&q->q_wait);
}

static inline void
drbd_queue_work_if_unqueued(struct drbd_work_queue *q, struct drbd_work *w)
{
	unsigned long flags;
	spin_lock_irqsave(&q->q_lock, flags);
	if (list_empty_careful(&w->list))
		list_add_tail(&w->list, &q->q);
	spin_unlock_irqrestore(&q->q_lock, flags);
	wake_up(&q->q_wait);
}

static inline void
drbd_device_post_work(struct drbd_device *device, int work_bit)
{
	if (!test_and_set_bit(work_bit, &device->flags)) {
		struct drbd_connection *connection =
			first_peer_device(device)->connection;
		struct drbd_work_queue *q = &connection->sender_work;
		if (!test_and_set_bit(DEVICE_WORK_PENDING, &connection->flags))
			wake_up(&q->q_wait);
	}
}

extern void drbd_flush_workqueue(struct drbd_work_queue *work_queue);

/* To get the ack_receiver out of the blocking network stack,
 * so it can change its sk_rcvtimeo from idle- to ping-timeout,
 * and send a ping, we need to send a signal.
 * Which signal we send is irrelevant. */
static inline void wake_ack_receiver(struct drbd_connection *connection)
{
	struct task_struct *task = connection->ack_receiver.task;
	if (task && get_t_state(&connection->ack_receiver) == RUNNING)
		send_sig(SIGXCPU, task, 1);
}

static inline void request_ping(struct drbd_connection *connection)
{
	set_bit(SEND_PING, &connection->flags);
	wake_ack_receiver(connection);
}

extern void *conn_prepare_command(struct drbd_connection *, struct drbd_socket *);
extern void *drbd_prepare_command(struct drbd_peer_device *, struct drbd_socket *);
extern int conn_send_command(struct drbd_connection *, struct drbd_socket *,
			     enum drbd_packet, unsigned int, void *,
			     unsigned int);
extern int drbd_send_command(struct drbd_peer_device *, struct drbd_socket *,
			     enum drbd_packet, unsigned int, void *,
			     unsigned int);

extern int drbd_send_ping(struct drbd_connection *connection);
extern int drbd_send_ping_ack(struct drbd_connection *connection);
extern int drbd_send_state_req(struct drbd_peer_device *, union drbd_state, union drbd_state);
extern int conn_send_state_req(struct drbd_connection *, union drbd_state, union drbd_state);

static inline void drbd_thread_stop(struct drbd_thread *thi)
{
	_drbd_thread_stop(thi, false, true);
}

static inline void drbd_thread_stop_nowait(struct drbd_thread *thi)
{
	_drbd_thread_stop(thi, false, false);
}

static inline void drbd_thread_restart_nowait(struct drbd_thread *thi)
{
	_drbd_thread_stop(thi, true, false);
}

/* counts how many answer packets packets we expect from our peer,
 * for either explicit application requests,
 * or implicit barrier packets as necessary.
 * increased:
 *  w_send_barrier
 *  _req_mod(req, QUEUE_FOR_NET_WRITE or QUEUE_FOR_NET_READ);
 *    it is much easier and equally valid to count what we queue for the
 *    worker, even before it actually was queued or send.
 *    (drbd_make_request_common; recovery path on read io-error)
 * decreased:
 *  got_BarrierAck (respective tl_clear, tl_clear_barrier)
 *  _req_mod(req, DATA_RECEIVED)
 *     [from receive_DataReply]
 *  _req_mod(req, WRITE_ACKED_BY_PEER or RECV_ACKED_BY_PEER or NEG_ACKED)
 *     [from got_BlockAck (P_WRITE_ACK, P_RECV_ACK)]
 *     for some reason it is NOT decreased in got_NegAck,
 *     but in the resulting cleanup code from report_params.
 *     we should try to remember the reason for that...
 *  _req_mod(req, SEND_FAILED or SEND_CANCELED)
 *  _req_mod(req, CONNECTION_LOST_WHILE_PENDING)
 *     [from tl_clear_barrier]
 */
static inline void inc_ap_pending(struct drbd_device *device)
{
	atomic_inc(&device->ap_pending_cnt);
}

#define dec_ap_pending(device) ((void)expect((device), __dec_ap_pending(device) >= 0))
static inline int __dec_ap_pending(struct drbd_device *device)
{
	int ap_pending_cnt = atomic_dec_return(&device->ap_pending_cnt);

	if (ap_pending_cnt == 0)
		wake_up(&device->misc_wait);
	return ap_pending_cnt;
}

/* counts how many resync-related answers we still expect from the peer
 *		     increase			decrease
 * C_SYNC_TARGET sends P_RS_DATA_REQUEST (and expects P_RS_DATA_REPLY)
 * C_SYNC_SOURCE sends P_RS_DATA_REPLY   (and expects P_WRITE_ACK with ID_SYNCER)
 *					   (or P_NEG_ACK with ID_SYNCER)
 */
static inline void inc_rs_pending(struct drbd_peer_device *peer_device)
{
	atomic_inc(&peer_device->device->rs_pending_cnt);
}

#define dec_rs_pending(peer_device) \
	((void)expect((peer_device), __dec_rs_pending(peer_device) >= 0))
static inline int __dec_rs_pending(struct drbd_peer_device *peer_device)
{
	return atomic_dec_return(&peer_device->device->rs_pending_cnt);
}

/* counts how many answers we still need to send to the peer.
 * increased on
 *  receive_Data	unless protocol A;
 *			we need to send a P_RECV_ACK (proto B)
 *			or P_WRITE_ACK (proto C)
 *  receive_RSDataReply (recv_resync_read) we need to send a P_WRITE_ACK
 *  receive_DataRequest (receive_RSDataRequest) we need to send back P_DATA
 *  receive_Barrier_*	we need to send a P_BARRIER_ACK
 */
static inline void inc_unacked(struct drbd_device *device)
{
	atomic_inc(&device->unacked_cnt);
}

#define dec_unacked(device) ((void)expect(device, __dec_unacked(device) >= 0))
static inline int __dec_unacked(struct drbd_device *device)
{
	return atomic_dec_return(&device->unacked_cnt);
}

#define sub_unacked(device, n) ((void)expect(device, __sub_unacked(device) >= 0))
static inline int __sub_unacked(struct drbd_device *device, int n)
{
	return atomic_sub_return(n, &device->unacked_cnt);
}

static inline bool is_sync_target_state(enum drbd_conns connection_state)
{
	return	connection_state == C_SYNC_TARGET ||
		connection_state == C_PAUSED_SYNC_T;
}

static inline bool is_sync_source_state(enum drbd_conns connection_state)
{
	return	connection_state == C_SYNC_SOURCE ||
		connection_state == C_PAUSED_SYNC_S;
}

static inline bool is_sync_state(enum drbd_conns connection_state)
{
	return	is_sync_source_state(connection_state) ||
		is_sync_target_state(connection_state);
}

/**
 * get_ldev() - Increase the ref count on device->ldev. Returns 0 if there is no ldev
 * @_device:		DRBD device.
 * @_min_state:		Minimum device state required for success.
 *
 * You have to call put_ldev() when finished working with device->ldev.
 */
#define get_ldev_if_state(_device, _min_state)				\
	(_get_ldev_if_state((_device), (_min_state)) ?			\
	 ({ __acquire(x); true; }) : false)
#define get_ldev(_device) get_ldev_if_state(_device, D_INCONSISTENT)

static inline void put_ldev(struct drbd_device *device)
{
	enum drbd_disk_state disk_state = device->state.disk;
	/* We must check the state *before* the atomic_dec becomes visible,
	 * or we have a theoretical race where someone hitting zero,
	 * while state still D_FAILED, will then see D_DISKLESS in the
	 * condition below and calling into destroy, where he must not, yet. */
	int i = atomic_dec_return(&device->local_cnt);

	/* This may be called from some endio handler,
	 * so we must not sleep here. */

	__release(local);
	D_ASSERT(device, i >= 0);
	if (i == 0) {
		if (disk_state == D_DISKLESS)
			/* even internal references gone, safe to destroy */
			drbd_device_post_work(device, DESTROY_DISK);
		if (disk_state == D_FAILED)
			/* all application IO references gone. */
			if (!test_and_set_bit(GOING_DISKLESS, &device->flags))
				drbd_device_post_work(device, GO_DISKLESS);
		wake_up(&device->misc_wait);
	}
}

#ifndef __CHECKER__
static inline int _get_ldev_if_state(struct drbd_device *device, enum drbd_disk_state mins)
{
	int io_allowed;

	/* never get a reference while D_DISKLESS */
	if (device->state.disk == D_DISKLESS)
		return 0;

	atomic_inc(&device->local_cnt);
	io_allowed = (device->state.disk >= mins);
	if (!io_allowed)
		put_ldev(device);
	return io_allowed;
}
#else
extern int _get_ldev_if_state(struct drbd_device *device, enum drbd_disk_state mins);
#endif

/* this throttles on-the-fly application requests
 * according to max_buffers settings;
 * maybe re-implement using semaphores? */
static inline int drbd_get_max_buffers(struct drbd_device *device)
{
	struct net_conf *nc;
	int mxb;

	rcu_read_lock();
	nc = rcu_dereference(first_peer_device(device)->connection->net_conf);
	mxb = nc ? nc->max_buffers : 1000000;  /* arbitrary limit on open requests */
	rcu_read_unlock();

	return mxb;
}

static inline int drbd_state_is_stable(struct drbd_device *device)
{
	union drbd_dev_state s = device->state;

	/* DO NOT add a default clause, we want the compiler to warn us
	 * for any newly introduced state we may have forgotten to add here */

	switch ((enum drbd_conns)s.conn) {
	/* new io only accepted when there is no connection, ... */
	case C_STANDALONE:
	case C_WF_CONNECTION:
	/* ... or there is a well established connection. */
	case C_CONNECTED:
	case C_SYNC_SOURCE:
	case C_SYNC_TARGET:
	case C_VERIFY_S:
	case C_VERIFY_T:
	case C_PAUSED_SYNC_S:
	case C_PAUSED_SYNC_T:
	case C_AHEAD:
	case C_BEHIND:
		/* transitional states, IO allowed */
	case C_DISCONNECTING:
	case C_UNCONNECTED:
	case C_TIMEOUT:
	case C_BROKEN_PIPE:
	case C_NETWORK_FAILURE:
	case C_PROTOCOL_ERROR:
	case C_TEAR_DOWN:
	case C_WF_REPORT_PARAMS:
	case C_STARTING_SYNC_S:
	case C_STARTING_SYNC_T:
		break;

		/* Allow IO in BM exchange states with new protocols */
	case C_WF_BITMAP_S:
		if (first_peer_device(device)->connection->agreed_pro_version < 96)
			return 0;
		break;

		/* no new io accepted in these states */
	case C_WF_BITMAP_T:
	case C_WF_SYNC_UUID:
	case C_MASK:
		/* not "stable" */
		return 0;
	}

	switch ((enum drbd_disk_state)s.disk) {
	case D_DISKLESS:
	case D_INCONSISTENT:
	case D_OUTDATED:
	case D_CONSISTENT:
	case D_UP_TO_DATE:
	case D_FAILED:
		/* disk state is stable as well. */
		break;

	/* no new io accepted during transitional states */
	case D_ATTACHING:
	case D_NEGOTIATING:
	case D_UNKNOWN:
	case D_MASK:
		/* not "stable" */
		return 0;
	}

	return 1;
}

static inline int drbd_suspended(struct drbd_device *device)
{
	struct drbd_resource *resource = device->resource;

	return resource->susp || resource->susp_fen || resource->susp_nod;
}

static inline bool may_inc_ap_bio(struct drbd_device *device)
{
	int mxb = drbd_get_max_buffers(device);

	if (drbd_suspended(device))
		return false;
	if (atomic_read(&device->suspend_cnt))
		return false;

	/* to avoid potential deadlock or bitmap corruption,
	 * in various places, we only allow new application io
	 * to start during "stable" states. */

	/* no new io accepted when attaching or detaching the disk */
	if (!drbd_state_is_stable(device))
		return false;

	/* since some older kernels don't have atomic_add_unless,
	 * and we are within the spinlock anyways, we have this workaround.  */
	if (atomic_read(&device->ap_bio_cnt) > mxb)
		return false;
	if (test_bit(BITMAP_IO, &device->flags))
		return false;
	return true;
}

static inline bool inc_ap_bio_cond(struct drbd_device *device)
{
	bool rv = false;

	spin_lock_irq(&device->resource->req_lock);
	rv = may_inc_ap_bio(device);
	if (rv)
		atomic_inc(&device->ap_bio_cnt);
	spin_unlock_irq(&device->resource->req_lock);

	return rv;
}

static inline void inc_ap_bio(struct drbd_device *device)
{
	/* we wait here
	 *    as long as the device is suspended
	 *    until the bitmap is no longer on the fly during connection
	 *    handshake as long as we would exceed the max_buffer limit.
	 *
	 * to avoid races with the reconnect code,
	 * we need to atomic_inc within the spinlock. */

	wait_event(device->misc_wait, inc_ap_bio_cond(device));
}

static inline void dec_ap_bio(struct drbd_device *device)
{
	int mxb = drbd_get_max_buffers(device);
	int ap_bio = atomic_dec_return(&device->ap_bio_cnt);

	D_ASSERT(device, ap_bio >= 0);

	if (ap_bio == 0 && test_bit(BITMAP_IO, &device->flags)) {
		if (!test_and_set_bit(BITMAP_IO_QUEUED, &device->flags))
			drbd_queue_work(&first_peer_device(device)->
				connection->sender_work,
				&device->bm_io_work.w);
	}

	/* this currently does wake_up for every dec_ap_bio!
	 * maybe rather introduce some type of hysteresis?
	 * e.g. (ap_bio == mxb/2 || ap_bio == 0) ? */
	if (ap_bio < mxb)
		wake_up(&device->misc_wait);
}

static inline bool verify_can_do_stop_sector(struct drbd_device *device)
{
	return first_peer_device(device)->connection->agreed_pro_version >= 97 &&
		first_peer_device(device)->connection->agreed_pro_version != 100;
}

static inline int drbd_set_ed_uuid(struct drbd_device *device, u64 val)
{
	int changed = device->ed_uuid != val;
	device->ed_uuid = val;
	return changed;
}

static inline int drbd_queue_order_type(struct drbd_device *device)
{
	/* sorry, we currently have no working implementation
	 * of distributed TCQ stuff */
#ifndef QUEUE_ORDERED_NONE
#define QUEUE_ORDERED_NONE 0
#endif
	return QUEUE_ORDERED_NONE;
}

static inline struct drbd_connection *first_connection(struct drbd_resource *resource)
{
	return list_first_entry_or_null(&resource->connections,
				struct drbd_connection, connections);
}

#endif