text: /*
    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 <philipp.reisner@linbit.com>.
    Copyright (C) 2002-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
  
    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.
  
  */
  
  #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/genhd.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 "drbd_strings.h"
  #include "drbd_state.h"
  #include "drbd_protocol.h"
  
  #ifdef __CHECKER__
  # define __protected_by(x)       __attribute__((require_context(x,1,999,"rdwr")))
  # define __protected_read_by(x)  __attribute__((require_context(x,1,999,"read")))
  # define __protected_write_by(x) __attribute__((require_context(x,1,999,"write")))
  # define __must_hold(x)       __attribute__((context(x,1,1), require_context(x,1,999,"call")))
  #else
  # define __protected_by(x)
  # define __protected_read_by(x)
  # define __protected_write_by(x)
  # define __must_hold(x)
  #endif
  
  /* module parameter, defined in drbd_main.c */
  extern unsigned int minor_count;
  extern bool disable_sendpage;
  extern bool allow_oos;
  void tl_abort_disk_io(struct drbd_device *device);
  
  #ifdef CONFIG_DRBD_FAULT_INJECTION
  extern int enable_faults;
  extern int fault_rate;
  extern int fault_devs;
  #endif
  
  extern char usermode_helper[];
  
  
  /* 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;
  
  #define __drbd_printk_device(level, device, fmt, args...) \
  	dev_printk(level, disk_to_dev((device)->vdisk), fmt, ## args)
  #define __drbd_printk_peer_device(level, peer_device, fmt, args...) \
  	dev_printk(level, disk_to_dev((peer_device)->device->vdisk), fmt, ## args)
  #define __drbd_printk_resource(level, resource, fmt, args...) \
  	printk(level "drbd %s: " fmt, (resource)->name, ## args)
  #define __drbd_printk_connection(level, connection, fmt, args...) \
  	printk(level "drbd %s: " fmt, (connection)->resource->name, ## args)
  
  void drbd_printk_with_wrong_object_type(void);
  
  #define __drbd_printk_if_same_type(obj, type, func, level, fmt, args...) \
  	(__builtin_types_compatible_p(typeof(obj), type) || \
  	 __builtin_types_compatible_p(typeof(obj), const type)), \
  	func(level, (const type)(obj), fmt, ## args)
  
  #define drbd_printk(level, obj, fmt, args...) \
  	__builtin_choose_expr( \
  	  __drbd_printk_if_same_type(obj, struct drbd_device *, \
  			     __drbd_printk_device, level, fmt, ## args), \
  	  __builtin_choose_expr( \
  	    __drbd_printk_if_same_type(obj, struct drbd_resource *, \
  			       __drbd_printk_resource, level, fmt, ## args), \
  	    __builtin_choose_expr( \
  	      __drbd_printk_if_same_type(obj, struct drbd_connection *, \
  				 __drbd_printk_connection, level, fmt, ## args), \
  	      __builtin_choose_expr( \
  		__drbd_printk_if_same_type(obj, struct drbd_peer_device *, \
  				 __drbd_printk_peer_device, level, fmt, ## args), \
  		drbd_printk_with_wrong_object_type()))))
  
  #define drbd_dbg(obj, fmt, args...) \
  	drbd_printk(KERN_DEBUG, obj, fmt, ## args)
  #define drbd_alert(obj, fmt, args...) \
  	drbd_printk(KERN_ALERT, obj, fmt, ## args)
  #define drbd_err(obj, fmt, args...) \
  	drbd_printk(KERN_ERR, obj, fmt, ## args)
  #define drbd_warn(obj, fmt, args...) \
  	drbd_printk(KERN_WARNING, obj, fmt, ## args)
  #define drbd_info(obj, fmt, args...) \
  	drbd_printk(KERN_INFO, obj, fmt, ## args)
  #define drbd_emerg(obj, fmt, args...) \
  	drbd_printk(KERN_EMERG, obj, fmt, ## args)
  
  #define dynamic_drbd_dbg(device, fmt, args...) \
  	dynamic_dev_dbg(disk_to_dev(device->vdisk), fmt, ## args)
  
  #define D_ASSERT(device, exp)	do { \
  	if (!(exp)) \
  		drbd_err(device, "ASSERT( " #exp " ) in %s:%d\n", __FILE__, __LINE__); \
  	} while (0)
  
  /**
   * expect  -  Make an assertion
   *
   * Unlike the assert macro, this macro returns a boolean result.
   */
  #define expect(exp) ({								\
  		bool _bool = (exp);						\
  		if (!_bool)							\
  			drbd_err(device, "ASSERTION %s FAILED in %s\n",		\
  			        #exp, __func__);				\
  		_bool;								\
  		})
  
  /* 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 fault_rate &&
  		(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_device *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;
  };
  
  /* Prototype declaration of function defined in drbd_receiver.c */
  int drbdd_init(struct drbd_thread *);
  int drbd_asender(struct drbd_thread *);
  
  /* 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;
  	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;
  	};
  };
  
  /* 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_DISCARD? */
  	__EE_IS_TRIM,
  
  	/* 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,
  
  	/* 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_IS_TRIM             (1<<__EE_IS_TRIM)
  #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_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 block_device *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;
  	char *why;
  	enum bm_flag flags;
  	int (*io_fn)(struct drbd_device *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[0];
  };
  extern struct fifo_buffer *fifo_alloc(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.
  				 * If set, bdi_write_congested() returns true,
  				 * so shrink_page_list() would not recurse into,
  				 * and potentially deadlock on, this drbd worker.
  				 */
  	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_ahash *integrity_tfm;  /* checksums we compute, updates protected by connection->data->mutex */
  	struct crypto_ahash *peer_integrity_tfm;  /* checksums we verify, only accessed from receiver thread  */
  	struct crypto_ahash *csums_tfm;
  	struct crypto_ahash *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;
  	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 __protected_by(local);
  
  	sector_t p_size;     /* partner's disk size */
  	struct request_queue *rq_queue;
  	struct block_device *this_bdev;
  	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 net_ee;    /* zero-copy network send in progress */
  
  	int next_barrier_nr;
  	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);
  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);
  void drbd_print_uuids(struct drbd_device *device, const char *text);
  
  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 *),
  				 void (*done)(struct drbd_device *, int),
  				 char *why, enum bm_flag flags);
  extern int drbd_bitmap_io(struct drbd_device *device,
  		int (*io_fn)(struct drbd_device *),
  		char *why, enum bm_flag flags);
  extern int drbd_bitmap_io_from_worker(struct drbd_device *device,
  		int (*io_fn)(struct drbd_device *),
  		char *why, enum bm_flag flags);
  extern int drbd_bmio_set_n_write(struct drbd_device *device) __must_hold(local);
  extern int drbd_bmio_clear_n_write(struct drbd_device *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)))
  #if !defined(CONFIG_LBDAF) && BITS_PER_LONG == 32
  #define DRBD_MAX_SECTORS      DRBD_MAX_SECTORS_32
  #define DRBD_MAX_SECTORS_FLEX DRBD_MAX_SECTORS_32
  #else
  #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
  #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_PAGES << 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) __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) __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) __must_hold(local);
  extern int  drbd_bm_write_copy_pages(struct drbd_device *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;
  
  /* drbd's page pool, used to buffer data received from the peer,
   * or data requested by the peer.
   *
   * This does not have an emergency reserve.
   *
   * When allocating from this pool, it first takes pages from the pool.
   * Only if the pool is depleted will try to allocate from the system.
   *
   * The assumption is that pages taken from this pool will be processed,
   * and given back, "quickly", and then can be recycled, so we can avoid
   * frequent calls to alloc_page(), and still will be able to make progress even
   * under memory pressure.
   */
  extern struct page *drbd_pp_pool;
  extern spinlock_t   drbd_pp_lock;
  extern int	    drbd_pp_vacant;
  extern wait_queue_head_t drbd_pp_wait;
  
  /* 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;
  
  /* 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;
  /* to allocate from that set */
  extern struct bio *bio_alloc_drbd(gfp_t gfp_mask);
  
  /* And a bio_set for cloning */
  extern struct bio_set *drbd_io_bio_set;
  
  extern struct mutex resources_mutex;
  
  extern int conn_lowest_minor(struct drbd_connection *connection);
  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);
  
  extern int proc_details;
  
  /* drbd_req */
  extern void do_submit(struct work_struct *ws);
  extern void __drbd_make_request(struct drbd_device *, struct bio *, unsigned long);
  extern blk_qc_t drbd_make_request(struct request_queue *q, struct bio *bio);
  extern int drbd_read_remote(struct drbd_device *device, struct drbd_request *req);
  extern int is_valid_ar_handle(struct drbd_request *, sector_t);
  
  
  /* 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_device *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, int op);
  extern void drbd_ov_out_of_sync_found(struct drbd_device *, sector_t, int);
  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_device *device);
  
  static inline void ov_out_of_sync_print(struct drbd_device *device)
  {
  	if (device->ov_last_oos_size) {
  		drbd_err(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_ahash *, struct bio *, void *);
  extern void drbd_csum_ee(struct crypto_ahash *, 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_e_reissue(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 int w_start_resync(struct drbd_work *, int);
  
  extern void resync_timer_fn(unsigned long data);
  extern void start_resync_timer_fn(unsigned long data);
  
  extern void drbd_endio_write_sec_final(struct drbd_peer_request *peer_req);
  
  /* drbd_receiver.c */
  extern int drbd_receiver(struct drbd_thread *thi);
  extern int drbd_ack_receiver(struct drbd_thread *thi);
  extern void drbd_send_ping_wf(struct work_struct *ws);
  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_device *device, sector_t sector,
  		bool throttle_if_app_is_waiting);
  extern int drbd_submit_peer_request(struct drbd_device *,
  				    struct drbd_peer_request *, const unsigned,
  				    const unsigned, const int);
  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 *, struct drbd_peer_request *,
  				 int);
  #define drbd_free_peer_req(m,e) __drbd_free_peer_req(m, e, 0)
  #define drbd_free_net_peer_req(m,e) __drbd_free_peer_req(m, e, 1)
  extern struct page *drbd_alloc_pages(struct drbd_peer_device *, unsigned int, bool);
  extern void drbd_set_recv_tcq(struct drbd_device *device, int tcq_enabled);
  extern void _drbd_clear_done_ee(struct drbd_device *device, struct list_head *to_be_freed);
  extern int drbd_connected(struct drbd_peer_device *);
  
  static inline void drbd_tcp_cork(struct socket *sock)
  {
  	int val = 1;
  	(void) kernel_setsockopt(sock, SOL_TCP, TCP_CORK,
  			(char*)&val, sizeof(val));
  }
  
  static inline void drbd_tcp_uncork(struct socket *sock)
  {
  	int val = 0;
  	(void) kernel_setsockopt(sock, SOL_TCP, TCP_CORK,
  			(char*)&val, sizeof(val));
  }
  
  static inline void drbd_tcp_nodelay(struct socket *sock)
  {
  	int val = 1;
  	(void) kernel_setsockopt(sock, SOL_TCP, TCP_NODELAY,
  			(char*)&val, sizeof(val));
  }
  
  static inline void drbd_tcp_quickack(struct socket *sock)
  {
  	int val = 2;
  	(void) kernel_setsockopt(sock, SOL_TCP, TCP_QUICKACK,
  			(char*)&val, sizeof(val));
  }
  
  /* sets the number of 512 byte sectors of our virtual device */
  static inline void drbd_set_my_capacity(struct drbd_device *device,
  					sector_t size)
  {
  	/* set_capacity(device->this_bdev->bd_disk, size); */
  	set_capacity(device->vdisk, size);
  	device->this_bdev->bd_inode->i_size = (loff_t)size << 9;
  }
  
  /*
   * used to submit our private bio
   */
  static inline void drbd_generic_make_request(struct drbd_device *device,
  					     int fault_type, struct bio *bio)
  {
  	__release(local);
  	if (!bio->bi_bdev) {
  		drbd_err(device, "drbd_generic_make_request: 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
  		generic_make_request(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;
  extern const struct file_operations drbd_proc_fops;
  
  /* 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_device *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_device *device,
  		sector_t sector, int size);
  extern void drbd_advance_rs_marks(struct drbd_device *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_device *device, sector_t sector, int size,
  		enum update_sync_bits_mode mode);
  #define drbd_set_in_sync(device, sector, size) \
  	__drbd_change_sync(device, sector, size, SET_IN_SYNC)
  #define drbd_set_out_of_sync(device, sector, size) \
  	__drbd_change_sync(device, sector, size, SET_OUT_OF_SYNC)
  #define drbd_rs_failed_io(device, sector, size) \
  	__drbd_change_sync(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 void notify_resource_state(struct sk_buff *,
  				  unsigned int,
  				  struct drbd_resource *,
  				  struct resource_info *,
  				  enum drbd_notification_type);
  extern void notify_device_state(struct sk_buff *,
  				unsigned int,
  				struct drbd_device *,
  				struct device_info *,
  				enum drbd_notification_type);
  extern void notify_connection_state(struct sk_buff *,
  				    unsigned int,
  				    struct drbd_connection *,
  				    struct connection_info *,
  				    enum drbd_notification_type);
  extern void 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 int drbd_peer_req_has_active_page(struct drbd_peer_request *peer_req)
  {
  	struct page *page = peer_req->pages;
  	page_chain_for_each(page) {
  		if (page_count(page) > 1)
  			return 1;
  	}
  	return 0;
  }
  
  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 (__ratelimit(&drbd_ratelimit_state))
  				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;
  		}
  		/* NOTE fall through 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 ? get_capacity(bdev->bd_disk) : 0; */
  	return bdev ? i_size_read(bdev->bd_inode) >> 9 : 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)
  		force_sig(SIGXCPU, task);
  }
  
  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 ERR_IF_CNT_IS_NEGATIVE(which, func, line)			\
  	if (atomic_read(&device->which) < 0)				\
  		drbd_err(device, "in %s:%d: " #which " = %d < 0 !\n",	\
  			func, line,					\
  			atomic_read(&device->which))
  
  #define dec_ap_pending(device) _dec_ap_pending(device, __func__, __LINE__)
  static inline void _dec_ap_pending(struct drbd_device *device, const char *func, int line)
  {
  	if (atomic_dec_and_test(&device->ap_pending_cnt))
  		wake_up(&device->misc_wait);
  	ERR_IF_CNT_IS_NEGATIVE(ap_pending_cnt, func, line);
  }
  
  /* 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_device *device)
  {
  	atomic_inc(&device->rs_pending_cnt);
  }
  
  #define dec_rs_pending(device) _dec_rs_pending(device, __func__, __LINE__)
  static inline void _dec_rs_pending(struct drbd_device *device, const char *func, int line)
  {
  	atomic_dec(&device->rs_pending_cnt);
  	ERR_IF_CNT_IS_NEGATIVE(rs_pending_cnt, func, line);
  }
  
  /* 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) _dec_unacked(device, __func__, __LINE__)
  static inline void _dec_unacked(struct drbd_device *device, const char *func, int line)
  {
  	atomic_dec(&device->unacked_cnt);
  	ERR_IF_CNT_IS_NEGATIVE(unacked_cnt, func, line);
  }
  
  #define sub_unacked(device, n) _sub_unacked(device, n, __func__, __LINE__)
  static inline void _sub_unacked(struct drbd_device *device, int n, const char *func, int line)
  {
  	atomic_sub(n, &device->unacked_cnt);
  	ERR_IF_CNT_IS_NEGATIVE(unacked_cnt, func, line);
  }
  
  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
  