drbd_int.h

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/*
  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]>.

  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 <linux/compiler.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/sched.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/crypto.h>
#include <linux/ratelimit.h>
#include <linux/tcp.h>
#include <linux/mutex.h>
#include <linux/major.h>
#include <linux/blkdev.h>
#include <linux/genhd.h>
#include <net/tcp.h>
#include <linux/lru_cache.h>
#include <linux/prefetch.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

#define __no_warn(lock, stmt) do { __acquire(lock); stmt; __release(lock); } while (0)

/* module parameter, defined in drbd_main.c */
extern unsigned int minor_count;
extern bool disable_sendpage;
extern bool allow_oos;
extern unsigned int cn_idx;

#ifdef CONFIG_DRBD_FAULT_INJECTION
extern int enable_faults;
extern int fault_rate;
extern int fault_devs;
#endif

extern char usermode_helper[];


/* I don't remember why XCPU ...
 * This is used to wake the asender,
 * and to interrupt sending the sending task
 * on disconnect.
 */
#define DRBD_SIG SIGXCPU

/* 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

/* All EEs on the free list should have ID_VACANT (== 0)
 * freshly allocated EEs get !ID_VACANT (== 1)
 * so if it says "cannot dereference null pointer at address 0x00000001",
 * it is most likely one of these :( */

#define ID_IN_SYNC      (4711ULL)
#define ID_OUT_OF_SYNC  (4712ULL)

#define ID_SYNCER (-1ULL)
#define ID_VACANT 0
#define is_syncer_block_id(id) ((id) == ID_SYNCER)
#define UUID_NEW_BM_OFFSET ((u64)0x0001000000000000ULL)

struct drbd_conf;


/* to shorten dev_warn(DEV, "msg"); and relatives statements */
#define DEV (disk_to_dev(mdev->vdisk))

#define D_ASSERT(exp)   if (!(exp)) \
     dev_err(DEV, "ASSERT( " #exp " ) in %s:%d\n", __FILE__, __LINE__)

#define ERR_IF(exp) if (({                      \
    int _b = (exp) != 0;                        \
    if (_b) dev_err(DEV, "ASSERT FAILED: %s: (%s) in %s:%d\n",  \
            __func__, #exp, __FILE__, __LINE__);        \
    _b;                             \
    }))

/* 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_conf *mdev, unsigned int type);

static inline int
drbd_insert_fault(struct drbd_conf *mdev, unsigned int type) {
#ifdef CONFIG_DRBD_FAULT_INJECTION
    return fault_rate &&
        (enable_faults & (1<<type)) &&
        _drbd_insert_fault(mdev, 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))

/* drbd_meta-data.c (still in drbd_main.c) */
/* 4th incarnation of the disk layout. */
#define DRBD_MD_MAGIC (DRBD_MAGIC+4)

extern struct drbd_conf **minor_table;
extern struct ratelimit_state drbd_ratelimit_state;

/* on the wire */
enum drbd_packets {
    /* receiver (data socket) */
    P_DATA            = 0x00,
    P_DATA_REPLY          = 0x01, /* Response to P_DATA_REQUEST */
    P_RS_DATA_REPLY       = 0x02, /* Response to P_RS_DATA_REQUEST */
    P_BARRIER         = 0x03,
    P_BITMAP          = 0x04,
    P_BECOME_SYNC_TARGET  = 0x05,
    P_BECOME_SYNC_SOURCE  = 0x06,
    P_UNPLUG_REMOTE       = 0x07, /* Used at various times to hint the peer */
    P_DATA_REQUEST        = 0x08, /* Used to ask for a data block */
    P_RS_DATA_REQUEST     = 0x09, /* Used to ask for a data block for resync */
    P_SYNC_PARAM          = 0x0a,
    P_PROTOCOL        = 0x0b,
    P_UUIDS           = 0x0c,
    P_SIZES           = 0x0d,
    P_STATE           = 0x0e,
    P_SYNC_UUID       = 0x0f,
    P_AUTH_CHALLENGE      = 0x10,
    P_AUTH_RESPONSE       = 0x11,
    P_STATE_CHG_REQ       = 0x12,

    /* asender (meta socket */
    P_PING            = 0x13,
    P_PING_ACK        = 0x14,
    P_RECV_ACK        = 0x15, /* Used in protocol B */
    P_WRITE_ACK       = 0x16, /* Used in protocol C */
    P_RS_WRITE_ACK        = 0x17, /* Is a P_WRITE_ACK, additionally call set_in_sync(). */
    P_DISCARD_ACK         = 0x18, /* Used in proto C, two-primaries conflict detection */
    P_NEG_ACK         = 0x19, /* Sent if local disk is unusable */
    P_NEG_DREPLY          = 0x1a, /* Local disk is broken... */
    P_NEG_RS_DREPLY       = 0x1b, /* Local disk is broken... */
    P_BARRIER_ACK         = 0x1c,
    P_STATE_CHG_REPLY     = 0x1d,

    /* "new" commands, no longer fitting into the ordering scheme above */

    P_OV_REQUEST          = 0x1e, /* data socket */
    P_OV_REPLY        = 0x1f,
    P_OV_RESULT       = 0x20, /* meta socket */
    P_CSUM_RS_REQUEST     = 0x21, /* data socket */
    P_RS_IS_IN_SYNC       = 0x22, /* meta socket */
    P_SYNC_PARAM89        = 0x23, /* data socket, protocol version 89 replacement for P_SYNC_PARAM */
    P_COMPRESSED_BITMAP   = 0x24, /* compressed or otherwise encoded bitmap transfer */
    /* P_CKPT_FENCE_REQ      = 0x25, * currently reserved for protocol D */
    /* P_CKPT_DISABLE_REQ    = 0x26, * currently reserved for protocol D */
    P_DELAY_PROBE         = 0x27, /* is used on BOTH sockets */
    P_OUT_OF_SYNC         = 0x28, /* Mark as out of sync (Outrunning), data socket */
    P_RS_CANCEL           = 0x29, /* meta: Used to cancel RS_DATA_REQUEST packet by SyncSource */

    P_MAX_CMD         = 0x2A,
    P_MAY_IGNORE          = 0x100, /* Flag to test if (cmd > P_MAY_IGNORE) ... */
    P_MAX_OPT_CMD         = 0x101,

    /* special command ids for handshake */

    P_HAND_SHAKE_M        = 0xfff1, /* First Packet on the MetaSock */
    P_HAND_SHAKE_S        = 0xfff2, /* First Packet on the Socket */

    P_HAND_SHAKE          = 0xfffe  /* FIXED for the next century! */
};

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

    if (cmd == P_HAND_SHAKE_M)
        return "HandShakeM";
    if (cmd == P_HAND_SHAKE_S)
        return "HandShakeS";
    if (cmd == P_HAND_SHAKE)
        return "HandShake";
    if (cmd >= P_MAX_CMD)
        return "Unknown";
    return cmdnames[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_conf *mdev,
        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
}

#ifndef __packed
#define __packed __attribute__((packed))
#endif

/* This is the layout for a packet on the wire.
 * The byteorder is the network byte order.
 *     (except block_id and barrier fields.
 *  these are pointers to local structs
 *  and have no relevance for the partner,
 *  which just echoes them as received.)
 *
 * NOTE that the payload starts at a long aligned offset,
 * regardless of 32 or 64 bit arch!
 */
struct p_header80 {
    u32   magic;
    u16   command;
    u16   length;   /* bytes of data after this header */
    u8    payload[0];
} __packed;

/* Header for big packets, Used for data packets exceeding 64kB */
struct p_header95 {
    u16   magic;    /* use DRBD_MAGIC_BIG here */
    u16   command;
    u32   length;   /* Use only 24 bits of that. Ignore the highest 8 bit. */
    u8    payload[0];
} __packed;

union p_header {
    struct p_header80 h80;
    struct p_header95 h95;
};

/*
 * short commands, packets without payload, plain p_header:
 *   P_PING
 *   P_PING_ACK
 *   P_BECOME_SYNC_TARGET
 *   P_BECOME_SYNC_SOURCE
 *   P_UNPLUG_REMOTE
 */

/*
 * commands with out-of-struct payload:
 *   P_BITMAP    (no additional fields)
 *   P_DATA, P_DATA_REPLY (see p_data)
 *   P_COMPRESSED_BITMAP (see receive_compressed_bitmap)
 */

/* these defines must not be changed without changing the protocol version */
#define DP_HARDBARRIER        1 /* depricated */
#define DP_RW_SYNC        2 /* equals REQ_SYNC    */
#define DP_MAY_SET_IN_SYNC    4
#define DP_UNPLUG             8 /* not used anymore   */
#define DP_FUA               16 /* equals REQ_FUA     */
#define DP_FLUSH             32 /* equals REQ_FLUSH   */
#define DP_DISCARD           64 /* equals REQ_DISCARD */

struct p_data {
    union p_header head;
    u64     sector;    /* 64 bits sector number */
    u64     block_id;  /* to identify the request in protocol B&C */
    u32     seq_num;
    u32     dp_flags;
} __packed;

/*
 * commands which share a struct:
 *  p_block_ack:
 *   P_RECV_ACK (proto B), P_WRITE_ACK (proto C),
 *   P_DISCARD_ACK (proto C, two-primaries conflict detection)
 *  p_block_req:
 *   P_DATA_REQUEST, P_RS_DATA_REQUEST
 */
struct p_block_ack {
    struct p_header80 head;
    u64     sector;
    u64     block_id;
    u32     blksize;
    u32     seq_num;
} __packed;


struct p_block_req {
    struct p_header80 head;
    u64 sector;
    u64 block_id;
    u32 blksize;
    u32 pad;    /* to multiple of 8 Byte */
} __packed;

/*
 * commands with their own struct for additional fields:
 *   P_HAND_SHAKE
 *   P_BARRIER
 *   P_BARRIER_ACK
 *   P_SYNC_PARAM
 *   ReportParams
 */

struct p_handshake {
    struct p_header80 head; /* 8 bytes */
    u32 protocol_min;
    u32 feature_flags;
    u32 protocol_max;

    /* should be more than enough for future enhancements
     * for now, feature_flags and the reserverd array shall be zero.
     */

    u32 _pad;
    u64 reserverd[7];
} __packed;
/* 80 bytes, FIXED for the next century */

struct p_barrier {
    struct p_header80 head;
    u32 barrier;    /* barrier number _handle_ only */
    u32 pad;    /* to multiple of 8 Byte */
} __packed;

struct p_barrier_ack {
    struct p_header80 head;
    u32 barrier;
    u32 set_size;
} __packed;

struct p_rs_param {
    struct p_header80 head;
    u32 rate;

          /* Since protocol version 88 and higher. */
    char verify_alg[0];
} __packed;

struct p_rs_param_89 {
    struct p_header80 head;
    u32 rate;
        /* protocol version 89: */
    char verify_alg[SHARED_SECRET_MAX];
    char csums_alg[SHARED_SECRET_MAX];
} __packed;

struct p_rs_param_95 {
    struct p_header80 head;
    u32 rate;
    char verify_alg[SHARED_SECRET_MAX];
    char csums_alg[SHARED_SECRET_MAX];
    u32 c_plan_ahead;
    u32 c_delay_target;
    u32 c_fill_target;
    u32 c_max_rate;
} __packed;

enum drbd_conn_flags {
    CF_WANT_LOSE = 1,
    CF_DRY_RUN = 2,
};

struct p_protocol {
    struct p_header80 head;
    u32 protocol;
    u32 after_sb_0p;
    u32 after_sb_1p;
    u32 after_sb_2p;
    u32 conn_flags;
    u32 two_primaries;

              /* Since protocol version 87 and higher. */
    char integrity_alg[0];

} __packed;

struct p_uuids {
    struct p_header80 head;
    u64 uuid[UI_EXTENDED_SIZE];
} __packed;

struct p_rs_uuid {
    struct p_header80 head;
    u64     uuid;
} __packed;

struct p_sizes {
    struct p_header80 head;
    u64     d_size;  /* size of disk */
    u64     u_size;  /* user requested size */
    u64     c_size;  /* current exported size */
    u32     max_bio_size;  /* Maximal size of a BIO */
    u16     queue_order_type;  /* not yet implemented in DRBD*/
    u16     dds_flags; /* use enum dds_flags here. */
} __packed;

struct p_state {
    struct p_header80 head;
    u32     state;
} __packed;

struct p_req_state {
    struct p_header80 head;
    u32     mask;
    u32     val;
} __packed;

struct p_req_state_reply {
    struct p_header80 head;
    u32     retcode;
} __packed;

struct p_drbd06_param {
    u64   size;
    u32   state;
    u32   blksize;
    u32   protocol;
    u32   version;
    u32   gen_cnt[5];
    u32   bit_map_gen[5];
} __packed;

struct p_discard {
    struct p_header80 head;
    u64     block_id;
    u32     seq_num;
    u32     pad;
} __packed;

struct p_block_desc {
    struct p_header80 head;
    u64 sector;
    u32 blksize;
    u32 pad;    /* to multiple of 8 Byte */
} __packed;

/* Valid values for the encoding field.
 * Bump proto version when changing this. */
enum drbd_bitmap_code {
    /* RLE_VLI_Bytes = 0,
     * and other bit variants had been defined during
     * algorithm evaluation. */
    RLE_VLI_Bits = 2,
};

struct p_compressed_bm {
    struct p_header80 head;
    /* (encoding & 0x0f): actual encoding, see enum drbd_bitmap_code
     * (encoding & 0x80): polarity (set/unset) of first runlength
     * ((encoding >> 4) & 0x07): pad_bits, number of trailing zero bits
     * used to pad up to head.length bytes
     */
    u8 encoding;

    u8 code[0];
} __packed;

struct p_delay_probe93 {
    struct p_header80 head;
    u32     seq_num; /* sequence number to match the two probe packets */
    u32     offset;  /* usecs the probe got sent after the reference time point */
} __packed;

/* DCBP: Drbd Compressed Bitmap Packet ... */
static inline enum drbd_bitmap_code
DCBP_get_code(struct p_compressed_bm *p)
{
    return (enum drbd_bitmap_code)(p->encoding & 0x0f);
}

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

static inline int
DCBP_get_start(struct p_compressed_bm *p)
{
    return (p->encoding & 0x80) != 0;
}

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

static inline int
DCBP_get_pad_bits(struct p_compressed_bm *p)
{
    return (p->encoding >> 4) & 0x7;
}

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

/* one bitmap packet, including the p_header,
 * should fit within one _architecture independend_ page.
 * so we need to use the fixed size 4KiB page size
 * most architectures have used for a long time.
 */
#define BM_PACKET_PAYLOAD_BYTES (4096 - sizeof(struct p_header80))
#define BM_PACKET_WORDS (BM_PACKET_PAYLOAD_BYTES/sizeof(long))
#define BM_PACKET_VLI_BYTES_MAX (4096 - sizeof(struct p_compressed_bm))
#if (PAGE_SIZE < 4096)
/* drbd_send_bitmap / receive_bitmap would break horribly */
#error "PAGE_SIZE too small"
#endif

union p_polymorph {
        union p_header           header;
        struct p_handshake       handshake;
        struct p_data            data;
        struct p_block_ack       block_ack;
        struct p_barrier         barrier;
        struct p_barrier_ack     barrier_ack;
        struct p_rs_param_89     rs_param_89;
        struct p_rs_param_95     rs_param_95;
        struct p_protocol        protocol;
        struct p_sizes           sizes;
        struct p_uuids           uuids;
        struct p_state           state;
        struct p_req_state       req_state;
        struct p_req_state_reply req_state_reply;
        struct p_block_req       block_req;
    struct p_delay_probe93   delay_probe93;
    struct p_rs_uuid         rs_uuid;
    struct p_block_desc      block_desc;
} __packed;

/**********************************************************************/
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_conf *mdev;
    int reset_cpu_mask;
};

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

struct drbd_tl_epoch;
struct drbd_request {
    struct drbd_work w;
    struct drbd_conf *mdev;

    /* 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_endio_pri(). */
    struct bio *private_bio;

    struct hlist_node collision;
    sector_t sector;
    unsigned int size;
    unsigned int epoch; /* barrier_nr */

    /* barrier_nr: used to check on "completion" whether this req was in
     * the current epoch, and we therefore have to close it,
     * starting a new epoch...
     */

    struct list_head tl_requests; /* ring list in the transfer log */
    struct bio *master_bio;       /* master bio pointer */
    unsigned long rq_state; /* see comments above _req_mod() */
    unsigned long start_time;
};

struct drbd_tl_epoch {
    struct drbd_work w;
    struct list_head requests; /* requests before */
    struct drbd_tl_epoch *next; /* pointer to the next barrier */
    unsigned int br_number;  /* the barriers identifier. */
    int n_writes;   /* number of requests attached before this barrier */
};

struct drbd_request;

/* These Tl_epoch_entries may be in one of 6 lists:
   active_ee .. data packet being written
   sync_ee   .. syncer block being written
   done_ee   .. block written, need to send P_WRITE_ACK
   read_ee   .. [RS]P_DATA_REQUEST being read
*/

struct drbd_epoch {
    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 drbd_wq_barrier {
    struct drbd_work w;
    struct completion done;
};

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

struct drbd_epoch_entry {
    struct drbd_work w;
    struct hlist_node collision;
    struct drbd_epoch *epoch; /* for writes */
    struct drbd_conf *mdev;
    struct page *pages;
    atomic_t pending_bios;
    unsigned int size;
    /* see comments on ee flag bits below */
    unsigned long flags;
    sector_t sector;
    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,

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

    /* we may have several bios per epoch entry.
     * 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,
};
#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_RESUBMITTED         (1<<__EE_RESUBMITTED)
#define EE_WAS_ERROR           (1<<__EE_WAS_ERROR)
#define EE_HAS_DIGEST          (1<<__EE_HAS_DIGEST)

/* global flag bits */
enum {
    CREATE_BARRIER,     /* next P_DATA is preceded by a P_BARRIER */
    SIGNAL_ASENDER,     /* whether asender wants to be interrupted */
    SEND_PING,      /* whether asender should send a ping asap */

    UNPLUG_REMOTE,      /* sending a "UnplugRemote" could help */
    MD_DIRTY,       /* current uuids and flags not yet on disk */
    DISCARD_CONCURRENT, /* Set on one node, cleared on the peer! */
    USE_DEGR_WFC_T,     /* degr-wfc-timeout instead of wfc-timeout. */
    CLUSTER_ST_CHANGE,  /* Cluster wide state change going on... */
    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 */
    SUSPEND_IO,     /* suspend application io */
    BITMAP_IO,      /* suspend application io;
                   once no more io in flight, start bitmap io */
    BITMAP_IO_QUEUED,       /* Started bitmap IO */
    GO_DISKLESS,        /* Disk is being detached, on io-error or admin request. */
    WAS_IO_ERROR,       /* Local disk failed returned IO error */
    FORCE_DETACH,       /* Force-detach from local disk, aborting any pending local IO */
    RESYNC_AFTER_NEG,       /* Resync after online grow after the attach&negotiate finished. */
    NET_CONGESTED,      /* The data socket is congested */

    CONFIG_PENDING,     /* serialization of (re)configuration requests.
                 * if set, also prevents the device from dying */
    DEVICE_DYING,       /* device became unconfigured,
                 * but worker thread is still handling the cleanup.
                 * reconfiguring (nl_disk_conf, nl_net_conf) is dissalowed,
                 * while this is set. */
    RESIZE_PENDING,     /* Size change detected locally, waiting for the response from
                 * the peer, if it changed there as well. */
    CONN_DRY_RUN,       /* Expect disconnect after resync handshake. */
    GOT_PING_ACK,       /* set when we receive a ping_ack packet, misc wait gets woken */
    NEW_CUR_UUID,       /* Create new current UUID when thawing IO */
    AL_SUSPENDED,       /* Activity logging is currently suspended. */
    AHEAD_TO_SYNC_SOURCE,   /* Ahead -> SyncSource queued */
    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.
                 */
};

struct drbd_bitmap; /* opaque for drbd_conf */

/* definition of bits in bm_flags to be used in drbd_bm_lock
 * and drbd_bitmap_io and friends. */
enum bm_flag {
    /* do we need to kfree, or vfree bm_pages? */
    BM_P_VMALLOCED = 0x10000, /* internal use only, will be masked out */

    /* 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;
    struct semaphore s; /* producers up it, worker down()s it */
    spinlock_t q_lock;  /* to protect the list. */
};

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

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

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

    s32 al_offset;  /* signed relative sector offset to al area */
    s32 bm_offset;  /* signed relative sector offset to bitmap */

    /* u32 al_nr_extents;      important for restoring the AL
     * is stored into  sync_conf.al_extents, which in turn
     * gets applied to act_log->nr_elements
     */
};

/* for sync_conf and other types... */
#define NL_PACKET(name, number, fields) struct name { fields };
#define NL_INTEGER(pn,pr,member) int member;
#define NL_INT64(pn,pr,member) __u64 member;
#define NL_BIT(pn,pr,member)   unsigned member:1;
#define NL_STRING(pn,pr,member,len) unsigned char member[len]; int member ## _len;
#include <linux/drbd_nl.h>

struct drbd_backing_dev {
    struct block_device *backing_bdev;
    struct block_device *md_bdev;
    struct drbd_md md;
    struct disk_conf dc; /* The user provided config... */
    sector_t known_size; /* last known size of that backing device */
};

struct drbd_md_io {
    unsigned int done;
    int error;
};

struct bm_io_work {
    struct drbd_work w;
    char *why;
    enum bm_flag flags;
    int (*io_fn)(struct drbd_conf *mdev);
    void (*done)(struct drbd_conf *mdev, int rv);
};

enum write_ordering_e {
    WO_none,
    WO_drain_io,
    WO_bdev_flush,
};

struct fifo_buffer {
    int *values;
    unsigned int head_index;
    unsigned int size;
};

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

    /* configured by drbdsetup */
    struct net_conf *net_conf; /* protected by get_net_conf() and put_net_conf() */
    struct syncer_conf sync_conf;
    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;

    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 */
    unsigned long last_received; /* in jiffies, either socket */
    unsigned int ko_count;
    struct drbd_work  resync_work,
              unplug_work,
              go_diskless,
              md_sync_work,
              start_resync_work;
    struct timer_list resync_timer;
    struct timer_list md_sync_timer;
    struct timer_list start_resync_timer;
    struct timer_list request_timer;
#ifdef DRBD_DEBUG_MD_SYNC
    struct {
        unsigned int line;
        const char* func;
    } last_md_mark_dirty;
#endif

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

    union drbd_state state;
    wait_queue_head_t misc_wait;
    wait_queue_head_t state_wait;  /* upon each state change. */
    wait_queue_head_t net_cnt_wait;
    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_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 replys for */
    atomic_t local_cnt;  /* Waiting for local completion */
    atomic_t net_cnt;    /* Users of net_conf */
    spinlock_t req_lock;
    struct drbd_tl_epoch *unused_spare_tle; /* for pre-allocation */
    struct drbd_tl_epoch *newest_tle;
    struct drbd_tl_epoch *oldest_tle;
    struct list_head out_of_sequence_requests;
    struct list_head barrier_acked_requests;
    struct hlist_head *tl_hash;
    unsigned int tl_hash_s;

    /* 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;

    /* where does the admin want us to start? (sector) */
    sector_t ov_start_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 crypto_hash *csums_tfm;
    struct crypto_hash *verify_tfm;

    unsigned long last_reattach_jif;
    unsigned long last_reconnect_jif;
    struct drbd_thread receiver;
    struct drbd_thread worker;
    struct drbd_thread asender;
    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 drbd_epoch *current_epoch;
    spinlock_t epoch_lock;
    unsigned int epochs;
    enum write_ordering_e write_ordering;
    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;   /* send ack */
    struct list_head read_ee;   /* IO in progress (any read) */
    struct list_head net_ee;    /* zero-copy network send in progress */
    struct hlist_head *ee_hash; /* is proteced by req_lock! */
    unsigned int ee_hash_s;

    /* this one is protected by ee_lock, single thread */
    struct drbd_epoch_entry *last_write_w_barrier;

    int next_barrier_nr;
    struct hlist_head *app_reads_hash; /* is proteced by req_lock */
    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 page *md_io_page;    /* one page buffer for md_io */
    struct page *md_io_tmpp;    /* for logical_block_size != 512 */
    struct drbd_md_io md_io;
    atomic_t md_io_in_use;      /* protects the md_io, md_io_page and md_io_tmpp */
    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;
    int al_tr_pos;   /* position of the next transaction in the journal */
    struct crypto_hash *cram_hmac_tfm;
    struct crypto_hash *integrity_w_tfm; /* to be used by the worker thread */
    struct crypto_hash *integrity_r_tfm; /* to be used by the receiver thread */
    void *int_dig_out;
    void *int_dig_in;
    void *int_dig_vv;
    wait_queue_head_t seq_wait;
    atomic_t packet_seq;
    unsigned int peer_seq;
    spinlock_t peer_seq_lock;
    unsigned int minor;
    unsigned long comm_bm_set; /* communicated number of set bits. */
    cpumask_var_t cpu_mask;
    struct bm_io_work bm_io_work;
    u64 ed_uuid; /* UUID of the exposed data */
    struct mutex state_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 */
    int rs_in_flight; /* resync sectors in flight (to proxy, in proxy and from proxy) */
    int rs_planed;    /* resync sectors already planned */
    atomic_t ap_in_flight; /* App sectors in flight (waiting for ack) */
    unsigned int peer_max_bio_size;
    unsigned int local_max_bio_size;
};

static inline struct drbd_conf *minor_to_mdev(unsigned int minor)
{
    struct drbd_conf *mdev;

    mdev = minor < minor_count ? minor_table[minor] : NULL;

    return mdev;
}

static inline unsigned int mdev_to_minor(struct drbd_conf *mdev)
{
    return mdev->minor;
}

/* returns 1 if it was successful,
 * returns 0 if there was no data socket.
 * so wherever you are going to use the data.socket, e.g. do
 * if (!drbd_get_data_sock(mdev))
 *  return 0;
 *  CODE();
 * drbd_put_data_sock(mdev);
 */
static inline int drbd_get_data_sock(struct drbd_conf *mdev)
{
    mutex_lock(&mdev->data.mutex);
    /* drbd_disconnect() could have called drbd_free_sock()
     * while we were waiting in down()... */
    if (unlikely(mdev->data.socket == NULL)) {
        mutex_unlock(&mdev->data.mutex);
        return 0;
    }
    return 1;
}

static inline void drbd_put_data_sock(struct drbd_conf *mdev)
{
    mutex_unlock(&mdev->data.mutex);
}

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

/* drbd_main.c */

enum chg_state_flags {
    CS_HARD = 1,
    CS_VERBOSE = 2,
    CS_WAIT_COMPLETE = 4,
    CS_SERIALIZE    = 8,
    CS_ORDERED      = CS_WAIT_COMPLETE + CS_SERIALIZE,
};

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_conf *mdev);
extern enum drbd_state_rv drbd_change_state(struct drbd_conf *mdev,
                        enum chg_state_flags f,
                        union drbd_state mask,
                        union drbd_state val);
extern void drbd_force_state(struct drbd_conf *, union drbd_state,
            union drbd_state);
extern enum drbd_state_rv _drbd_request_state(struct drbd_conf *,
                          union drbd_state,
                          union drbd_state,
                          enum chg_state_flags);
extern enum drbd_state_rv __drbd_set_state(struct drbd_conf *, union drbd_state,
                       enum chg_state_flags,
                       struct completion *done);
extern void print_st_err(struct drbd_conf *, union drbd_state,
            union drbd_state, int);
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_conf *mdev);
extern void drbd_calc_cpu_mask(struct drbd_conf *mdev);
#else
#define drbd_thread_current_set_cpu(A) ({})
#define drbd_calc_cpu_mask(A) ({})
#endif
extern void drbd_free_resources(struct drbd_conf *mdev);
extern void tl_release(struct drbd_conf *mdev, unsigned int barrier_nr,
               unsigned int set_size);
extern void tl_clear(struct drbd_conf *mdev);
extern void _tl_add_barrier(struct drbd_conf *, struct drbd_tl_epoch *);
extern void drbd_free_sock(struct drbd_conf *mdev);
extern int drbd_send(struct drbd_conf *mdev, struct socket *sock,
            void *buf, size_t size, unsigned msg_flags);
extern int drbd_send_protocol(struct drbd_conf *mdev);
extern int drbd_send_uuids(struct drbd_conf *mdev);
extern int drbd_send_uuids_skip_initial_sync(struct drbd_conf *mdev);
extern int drbd_gen_and_send_sync_uuid(struct drbd_conf *mdev);
extern int drbd_send_sizes(struct drbd_conf *mdev, int trigger_reply, enum dds_flags flags);
extern int drbd_send_state(struct drbd_conf *mdev, union drbd_state s);
extern int drbd_send_current_state(struct drbd_conf *mdev);
extern int _drbd_send_cmd(struct drbd_conf *mdev, struct socket *sock,
            enum drbd_packets cmd, struct p_header80 *h,
            size_t size, unsigned msg_flags);
#define USE_DATA_SOCKET 1
#define USE_META_SOCKET 0
extern int drbd_send_cmd(struct drbd_conf *mdev, int use_data_socket,
            enum drbd_packets cmd, struct p_header80 *h,
            size_t size);
extern int drbd_send_cmd2(struct drbd_conf *mdev, enum drbd_packets cmd,
            char *data, size_t size);
extern int drbd_send_sync_param(struct drbd_conf *mdev, struct syncer_conf *sc);
extern int drbd_send_b_ack(struct drbd_conf *mdev, u32 barrier_nr,
            u32 set_size);
extern int drbd_send_ack(struct drbd_conf *mdev, enum drbd_packets cmd,
            struct drbd_epoch_entry *e);
extern int drbd_send_ack_rp(struct drbd_conf *mdev, enum drbd_packets cmd,
            struct p_block_req *rp);
extern int drbd_send_ack_dp(struct drbd_conf *mdev, enum drbd_packets cmd,
            struct p_data *dp, int data_size);
extern int drbd_send_ack_ex(struct drbd_conf *mdev, enum drbd_packets cmd,
                sector_t sector, int blksize, u64 block_id);
extern int drbd_send_oos(struct drbd_conf *mdev, struct drbd_request *req);
extern int drbd_send_block(struct drbd_conf *mdev, enum drbd_packets cmd,
               struct drbd_epoch_entry *e);
extern int drbd_send_dblock(struct drbd_conf *mdev, struct drbd_request *req);
extern int drbd_send_drequest(struct drbd_conf *mdev, int cmd,
                  sector_t sector, int size, u64 block_id);
extern int drbd_send_drequest_csum(struct drbd_conf *mdev,
                   sector_t sector,int size,
                   void *digest, int digest_size,
                   enum drbd_packets cmd);
extern int drbd_send_ov_request(struct drbd_conf *mdev,sector_t sector,int size);

extern int drbd_send_bitmap(struct drbd_conf *mdev);
extern int _drbd_send_bitmap(struct drbd_conf *mdev);
extern int drbd_send_sr_reply(struct drbd_conf *mdev, enum drbd_state_rv retcode);
extern void drbd_free_bc(struct drbd_backing_dev *ldev);
extern void drbd_mdev_cleanup(struct drbd_conf *mdev);
void drbd_print_uuids(struct drbd_conf *mdev, const char *text);

extern void drbd_md_sync(struct drbd_conf *mdev);
extern int  drbd_md_read(struct drbd_conf *mdev, struct drbd_backing_dev *bdev);
extern void drbd_uuid_set(struct drbd_conf *mdev, int idx, u64 val) __must_hold(local);
extern void _drbd_uuid_set(struct drbd_conf *mdev, int idx, u64 val) __must_hold(local);
extern void drbd_uuid_new_current(struct drbd_conf *mdev) __must_hold(local);
extern void _drbd_uuid_new_current(struct drbd_conf *mdev) __must_hold(local);
extern void drbd_uuid_set_bm(struct drbd_conf *mdev, u64 val) __must_hold(local);
extern void drbd_md_set_flag(struct drbd_conf *mdev, int flags) __must_hold(local);
extern void drbd_md_clear_flag(struct drbd_conf *mdev, int flags)__must_hold(local);
extern int drbd_md_test_flag(struct drbd_backing_dev *, int);
#ifndef DRBD_DEBUG_MD_SYNC
extern void drbd_md_mark_dirty(struct drbd_conf *mdev);
#else
#define drbd_md_mark_dirty(m)   drbd_md_mark_dirty_(m, __LINE__ , __func__ )
extern void drbd_md_mark_dirty_(struct drbd_conf *mdev,
        unsigned int line, const char *func);
#endif
extern void drbd_queue_bitmap_io(struct drbd_conf *mdev,
                 int (*io_fn)(struct drbd_conf *),
                 void (*done)(struct drbd_conf *, int),
                 char *why, enum bm_flag flags);
extern int drbd_bitmap_io(struct drbd_conf *mdev,
        int (*io_fn)(struct drbd_conf *),
        char *why, enum bm_flag flags);
extern int drbd_bmio_set_n_write(struct drbd_conf *mdev);
extern int drbd_bmio_clear_n_write(struct drbd_conf *mdev);
extern void drbd_go_diskless(struct drbd_conf *mdev);
extern void drbd_ldev_destroy(struct drbd_conf *mdev);


/* Meta data layout
   We reserve a 128MB Block (4k aligned)
   * either at the end of the backing device
   * or on a separate meta data device. */

#define MD_RESERVED_SECT (128LU << 11)  /* 128 MB, unit sectors */
/* The following numbers are sectors */
#define MD_AL_OFFSET 8      /* 8 Sectors after start of meta area */
#define MD_AL_MAX_SIZE 64   /* = 32 kb LOG  ~ 3776 extents ~ 14 GB Storage */
/* Allows up to about 3.8TB */
#define MD_BM_OFFSET (MD_AL_OFFSET + MD_AL_MAX_SIZE)

/* Since the smalles IO unit is usually 512 byte */
#define MD_SECTOR_SHIFT  9
#define MD_SECTOR_SIZE   (1<<MD_SECTOR_SHIFT)

/* activity log */
#define AL_EXTENTS_PT ((MD_SECTOR_SIZE-12)/8-1) /* 61 ; Extents per 512B sector */
#define AL_EXTENT_SHIFT 22       /* One extent represents 4M Storage */
#define AL_EXTENT_SIZE (1<<AL_EXTENT_SHIFT)

#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)

#define BM_BLOCK_SHIFT  12           /* 4k per bit */
#define BM_BLOCK_SIZE    (1<<BM_BLOCK_SHIFT)
/* (9+3) : 512 bytes @ 8 bits; representing 16M storage
 * per sector of on disk bitmap */
#define BM_EXT_SHIFT     (BM_BLOCK_SHIFT + MD_SECTOR_SHIFT + 3)  /* = 24 */
#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))

/* how much _storage_ sectors we have per bitmap sector */
#define BM_EXT_TO_SECT(x)   ((sector_t)(x) << (BM_EXT_SHIFT-9))
#define BM_SECT_PER_EXT     BM_EXT_TO_SECT(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))
#define BM_WORDS_PER_AL_EXT (1 << (AL_EXTENT_SHIFT-BM_BLOCK_SHIFT-LN2_BPL))

#define BM_BLOCKS_PER_BM_EXT_B (BM_EXT_SHIFT - BM_BLOCK_SHIFT)
#define BM_BLOCKS_PER_BM_EXT_MASK  ((1<<BM_BLOCKS_PER_BM_EXT_B) - 1)

/* 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)
#define DRBD_MAX_SECTORS_BM \
      ((MD_RESERVED_SECT - MD_BM_OFFSET) * (1LL<<(BM_EXT_SHIFT-9)))
#if DRBD_MAX_SECTORS_BM < DRBD_MAX_SECTORS_32
#define DRBD_MAX_SECTORS      DRBD_MAX_SECTORS_BM
#define DRBD_MAX_SECTORS_FLEX DRBD_MAX_SECTORS_BM
#elif !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_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

/* Sector shift value for the "hash" functions of tl_hash and ee_hash tables.
 * With a value of 8 all IO in one 128K block make it to the same slot of the
 * hash table. */
#define HT_SHIFT 8
#define DRBD_MAX_BIO_SIZE (1U<<(9+HT_SHIFT))
#define DRBD_MAX_BIO_SIZE_SAFE (1U << 12)       /* Works always = 4k */

#define DRBD_MAX_SIZE_H80_PACKET (1U << 15) /* The old header only allows packets up to 32Kib data */

/* Number of elements in the app_reads_hash */
#define APP_R_HSIZE 15

extern int  drbd_bm_init(struct drbd_conf *mdev);
extern int  drbd_bm_resize(struct drbd_conf *mdev, sector_t sectors, int set_new_bits);
extern void drbd_bm_cleanup(struct drbd_conf *mdev);
extern void drbd_bm_set_all(struct drbd_conf *mdev);
extern void drbd_bm_clear_all(struct drbd_conf *mdev);
/* set/clear/test only a few bits at a time */
extern int  drbd_bm_set_bits(
        struct drbd_conf *mdev, unsigned long s, unsigned long e);
extern int  drbd_bm_clear_bits(
        struct drbd_conf *mdev, unsigned long s, unsigned long e);
extern int drbd_bm_count_bits(
    struct drbd_conf *mdev, 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_conf *mdev,
        const unsigned long s, const unsigned long e);
extern int  drbd_bm_test_bit(struct drbd_conf *mdev, unsigned long bitnr);
extern int  drbd_bm_e_weight(struct drbd_conf *mdev, unsigned long enr);
extern int  drbd_bm_write_page(struct drbd_conf *mdev, unsigned int idx) __must_hold(local);
extern int  drbd_bm_read(struct drbd_conf *mdev) __must_hold(local);
extern int  drbd_bm_write(struct drbd_conf *mdev) __must_hold(local);
extern int drbd_bm_write_all(struct drbd_conf *mdev) __must_hold(local);
extern int  drbd_bm_write_copy_pages(struct drbd_conf *mdev) __must_hold(local);
extern unsigned long drbd_bm_ALe_set_all(struct drbd_conf *mdev,
        unsigned long al_enr);
extern size_t        drbd_bm_words(struct drbd_conf *mdev);
extern unsigned long drbd_bm_bits(struct drbd_conf *mdev);
extern sector_t      drbd_bm_capacity(struct drbd_conf *mdev);

#define DRBD_END_OF_BITMAP  (~(unsigned long)0)
extern unsigned long drbd_bm_find_next(struct drbd_conf *mdev, 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_conf *mdev, unsigned long bm_fo);
extern unsigned long _drbd_bm_find_next_zero(struct drbd_conf *mdev, unsigned long bm_fo);
extern unsigned long _drbd_bm_total_weight(struct drbd_conf *mdev);
extern unsigned long drbd_bm_total_weight(struct drbd_conf *mdev);
extern int drbd_bm_rs_done(struct drbd_conf *mdev);
/* for receive_bitmap */
extern void drbd_bm_merge_lel(struct drbd_conf *mdev, size_t offset,
        size_t number, unsigned long *buffer);
/* for _drbd_send_bitmap */
extern void drbd_bm_get_lel(struct drbd_conf *mdev, size_t offset,
        size_t number, unsigned long *buffer);

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

extern struct kmem_cache *drbd_request_cache;
extern struct kmem_cache *drbd_ee_cache;    /* epoch entries */
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);

extern rwlock_t global_state_lock;

extern struct drbd_conf *drbd_new_device(unsigned int minor);
extern void drbd_free_mdev(struct drbd_conf *mdev);

extern int proc_details;

/* drbd_req */
extern void drbd_make_request(struct request_queue *q, struct bio *bio);
extern int drbd_read_remote(struct drbd_conf *mdev, struct drbd_request *req);
extern int drbd_merge_bvec(struct request_queue *q, struct bvec_merge_data *bvm, struct bio_vec *bvec);
extern int is_valid_ar_handle(struct drbd_request *, sector_t);


/* drbd_nl.c */
extern void drbd_suspend_io(struct drbd_conf *mdev);
extern void drbd_resume_io(struct drbd_conf *mdev);
extern char *ppsize(char *buf, unsigned long long size);
extern sector_t drbd_new_dev_size(struct drbd_conf *, struct drbd_backing_dev *, int);
enum determine_dev_size { dev_size_error = -1, unchanged = 0, shrunk = 1, grew = 2 };
extern enum determine_dev_size drbd_determine_dev_size(struct drbd_conf *, enum dds_flags) __must_hold(local);
extern void resync_after_online_grow(struct drbd_conf *);
extern void drbd_reconsider_max_bio_size(struct drbd_conf *mdev);
extern enum drbd_state_rv drbd_set_role(struct drbd_conf *mdev,
                    enum drbd_role new_role,
                    int force);
extern enum drbd_disk_state drbd_try_outdate_peer(struct drbd_conf *mdev);
extern void drbd_try_outdate_peer_async(struct drbd_conf *mdev);
extern int drbd_khelper(struct drbd_conf *mdev, char *cmd);

/* drbd_worker.c */
extern int drbd_worker(struct drbd_thread *thi);
extern int drbd_alter_sa(struct drbd_conf *mdev, int na);
extern void drbd_start_resync(struct drbd_conf *mdev, enum drbd_conns side);
extern void resume_next_sg(struct drbd_conf *mdev);
extern void suspend_other_sg(struct drbd_conf *mdev);
extern int drbd_resync_finished(struct drbd_conf *mdev);
/* maybe rather drbd_main.c ? */
extern void *drbd_md_get_buffer(struct drbd_conf *mdev);
extern void drbd_md_put_buffer(struct drbd_conf *mdev);
extern int drbd_md_sync_page_io(struct drbd_conf *mdev,
                struct drbd_backing_dev *bdev, sector_t sector, int rw);
extern void wait_until_done_or_disk_failure(struct drbd_conf *mdev, struct drbd_backing_dev *bdev,
                        unsigned int *done);
extern void drbd_ov_oos_found(struct drbd_conf*, sector_t, int);
extern void drbd_rs_controller_reset(struct drbd_conf *mdev);

static inline void ov_oos_print(struct drbd_conf *mdev)
{
    if (mdev->ov_last_oos_size) {
        dev_err(DEV, "Out of sync: start=%llu, size=%lu (sectors)\n",
             (unsigned long long)mdev->ov_last_oos_start,
             (unsigned long)mdev->ov_last_oos_size);
    }
    mdev->ov_last_oos_size=0;
}


extern void drbd_csum_bio(struct drbd_conf *, struct crypto_hash *, struct bio *, void *);
extern void drbd_csum_ee(struct drbd_conf *, struct crypto_hash *, struct drbd_epoch_entry *, void *);
/* worker callbacks */
extern int w_req_cancel_conflict(struct drbd_conf *, struct drbd_work *, int);
extern int w_read_retry_remote(struct drbd_conf *, struct drbd_work *, int);
extern int w_e_end_data_req(struct drbd_conf *, struct drbd_work *, int);
extern int w_e_end_rsdata_req(struct drbd_conf *, struct drbd_work *, int);
extern int w_e_end_csum_rs_req(struct drbd_conf *, struct drbd_work *, int);
extern int w_e_end_ov_reply(struct drbd_conf *, struct drbd_work *, int);
extern int w_e_end_ov_req(struct drbd_conf *, struct drbd_work *, int);
extern int w_ov_finished(struct drbd_conf *, struct drbd_work *, int);
extern int w_resync_timer(struct drbd_conf *, struct drbd_work *, int);
extern int w_resume_next_sg(struct drbd_conf *, struct drbd_work *, int);
extern int w_send_write_hint(struct drbd_conf *, struct drbd_work *, int);
extern int w_send_dblock(struct drbd_conf *, struct drbd_work *, int);
extern int w_send_barrier(struct drbd_conf *, struct drbd_work *, int);
extern int w_send_read_req(struct drbd_conf *, struct drbd_work *, int);
extern int w_prev_work_done(struct drbd_conf *, struct drbd_work *, int);
extern int w_e_reissue(struct drbd_conf *, struct drbd_work *, int);
extern int w_restart_disk_io(struct drbd_conf *, struct drbd_work *, int);
extern int w_send_oos(struct drbd_conf *, struct drbd_work *, int);
extern int w_start_resync(struct drbd_conf *, struct drbd_work *, int);

extern void resync_timer_fn(unsigned long data);
extern void start_resync_timer_fn(unsigned long data);

/* drbd_receiver.c */
extern int drbd_rs_should_slow_down(struct drbd_conf *mdev, sector_t sector);
extern int drbd_submit_ee(struct drbd_conf *mdev, struct drbd_epoch_entry *e,
        const unsigned rw, const int fault_type);
extern int drbd_release_ee(struct drbd_conf *mdev, struct list_head *list);
extern struct drbd_epoch_entry *drbd_alloc_ee(struct drbd_conf *mdev,
                        u64 id,
                        sector_t sector,
                        unsigned int data_size,
                        gfp_t gfp_mask) __must_hold(local);
extern void drbd_free_some_ee(struct drbd_conf *mdev, struct drbd_epoch_entry *e,
        int is_net);
#define drbd_free_ee(m,e)   drbd_free_some_ee(m, e, 0)
#define drbd_free_net_ee(m,e)   drbd_free_some_ee(m, e, 1)
extern void drbd_wait_ee_list_empty(struct drbd_conf *mdev,
        struct list_head *head);
extern void _drbd_wait_ee_list_empty(struct drbd_conf *mdev,
        struct list_head *head);
extern void drbd_set_recv_tcq(struct drbd_conf *mdev, int tcq_enabled);
extern void _drbd_clear_done_ee(struct drbd_conf *mdev, struct list_head *to_be_freed);
extern void drbd_flush_workqueue(struct drbd_conf *mdev);
extern void drbd_free_tl_hash(struct drbd_conf *mdev);

/* yes, there is kernel_setsockopt, but only since 2.6.18. we don't need to
 * mess with get_fs/set_fs, we know we are KERNEL_DS always. */
static inline int drbd_setsockopt(struct socket *sock, int level, int optname,
            char __user *optval, int optlen)
{
    int err;
    if (level == SOL_SOCKET)
        err = sock_setsockopt(sock, level, optname, optval, optlen);
    else
        err = sock->ops->setsockopt(sock, level, optname, optval,
                        optlen);
    return err;
}

static inline void drbd_tcp_cork(struct socket *sock)
{
    int __user val = 1;
    (void) drbd_setsockopt(sock, SOL_TCP, TCP_CORK,
            (char __user *)&val, sizeof(val));
}

static inline void drbd_tcp_uncork(struct socket *sock)
{
    int __user val = 0;
    (void) drbd_setsockopt(sock, SOL_TCP, TCP_CORK,
            (char __user *)&val, sizeof(val));
}

static inline void drbd_tcp_nodelay(struct socket *sock)
{
    int __user val = 1;
    (void) drbd_setsockopt(sock, SOL_TCP, TCP_NODELAY,
            (char __user *)&val, sizeof(val));
}

static inline void drbd_tcp_quickack(struct socket *sock)
{
    int __user val = 2;
    (void) drbd_setsockopt(sock, SOL_TCP, TCP_QUICKACK,
            (char __user *)&val, sizeof(val));
}

void drbd_bump_write_ordering(struct drbd_conf *mdev, enum write_ordering_e wo);

/* drbd_proc.c */
extern struct proc_dir_entry *drbd_proc;
extern const struct file_operations drbd_proc_fops;
extern const char *drbd_conn_str(enum drbd_conns s);
extern const char *drbd_role_str(enum drbd_role s);

/* drbd_actlog.c */
extern void drbd_al_begin_io(struct drbd_conf *mdev, sector_t sector);
extern void drbd_al_complete_io(struct drbd_conf *mdev, sector_t sector);
extern void drbd_rs_complete_io(struct drbd_conf *mdev, sector_t sector);
extern int drbd_rs_begin_io(struct drbd_conf *mdev, sector_t sector);
extern int drbd_try_rs_begin_io(struct drbd_conf *mdev, sector_t sector);
extern void drbd_rs_cancel_all(struct drbd_conf *mdev);
extern int drbd_rs_del_all(struct drbd_conf *mdev);
extern void drbd_rs_failed_io(struct drbd_conf *mdev,
        sector_t sector, int size);
extern int drbd_al_read_log(struct drbd_conf *mdev, struct drbd_backing_dev *);
extern void drbd_advance_rs_marks(struct drbd_conf *mdev, unsigned long still_to_go);
extern void __drbd_set_in_sync(struct drbd_conf *mdev, sector_t sector,
        int size, const char *file, const unsigned int line);
#define drbd_set_in_sync(mdev, sector, size) \
    __drbd_set_in_sync(mdev, sector, size, __FILE__, __LINE__)
extern int __drbd_set_out_of_sync(struct drbd_conf *mdev, sector_t sector,
        int size, const char *file, const unsigned int line);
#define drbd_set_out_of_sync(mdev, sector, size) \
    __drbd_set_out_of_sync(mdev, sector, size, __FILE__, __LINE__)
extern void drbd_al_apply_to_bm(struct drbd_conf *mdev);
extern void drbd_al_shrink(struct drbd_conf *mdev);


/* drbd_nl.c */

void drbd_nl_cleanup(void);
int __init drbd_nl_init(void);
void drbd_bcast_state(struct drbd_conf *mdev, union drbd_state);
void drbd_bcast_sync_progress(struct drbd_conf *mdev);
void drbd_bcast_ee(struct drbd_conf *mdev,
        const char *reason, const int dgs,
        const char* seen_hash, const char* calc_hash,
        const struct drbd_epoch_entry* e);


#define role_MASK R_MASK
#define peer_MASK R_MASK
#define disk_MASK D_MASK
#define pdsk_MASK D_MASK
#define conn_MASK C_MASK
#define susp_MASK 1
#define user_isp_MASK 1
#define aftr_isp_MASK 1
#define susp_nod_MASK 1
#define susp_fen_MASK 1

#define NS(T, S) \
    ({ union drbd_state mask; mask.i = 0; mask.T = T##_MASK; mask; }), \
    ({ union drbd_state val; val.i = 0; val.T = (S); val; })
#define NS2(T1, S1, T2, S2) \
    ({ union drbd_state mask; mask.i = 0; mask.T1 = T1##_MASK; \
      mask.T2 = T2##_MASK; mask; }), \
    ({ union drbd_state val; val.i = 0; val.T1 = (S1); \
      val.T2 = (S2); val; })
#define NS3(T1, S1, T2, S2, T3, S3) \
    ({ union drbd_state mask; mask.i = 0; mask.T1 = T1##_MASK; \
      mask.T2 = T2##_MASK; mask.T3 = T3##_MASK; mask; }), \
    ({ union drbd_state val;  val.i = 0; val.T1 = (S1); \
      val.T2 = (S2); val.T3 = (S3); val; })

#define _NS(D, T, S) \
    D, ({ union drbd_state __ns; __ns.i = D->state.i; __ns.T = (S); __ns; })
#define _NS2(D, T1, S1, T2, S2) \
    D, ({ union drbd_state __ns; __ns.i = D->state.i; __ns.T1 = (S1); \
    __ns.T2 = (S2); __ns; })
#define _NS3(D, T1, S1, T2, S2, T3, S3) \
    D, ({ union drbd_state __ns; __ns.i = D->state.i; __ns.T1 = (S1); \
    __ns.T2 = (S2); __ns.T3 = (S3); __ns; })

/*
 * 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_ee_has_active_page(struct drbd_epoch_entry *e)
{
    struct page *page = e->pages;
    page_chain_for_each(page) {
        if (page_count(page) > 1)
            return 1;
    }
    return 0;
}

static inline void drbd_state_lock(struct drbd_conf *mdev)
{
    wait_event(mdev->misc_wait,
           !test_and_set_bit(CLUSTER_ST_CHANGE, &mdev->flags));
}

static inline void drbd_state_unlock(struct drbd_conf *mdev)
{
    clear_bit(CLUSTER_ST_CHANGE, &mdev->flags);
    wake_up(&mdev->misc_wait);
}

static inline enum drbd_state_rv
_drbd_set_state(struct drbd_conf *mdev, union drbd_state ns,
        enum chg_state_flags flags, struct completion *done)
{
    enum drbd_state_rv rv;

    read_lock(&global_state_lock);
    rv = __drbd_set_state(mdev, ns, flags, done);
    read_unlock(&global_state_lock);

    return rv;
}

static inline int drbd_request_state(struct drbd_conf *mdev,
                     union drbd_state mask,
                     union drbd_state val)
{
    return _drbd_request_state(mdev, mask, val, CS_VERBOSE + CS_ORDERED);
}

enum drbd_force_detach_flags {
    DRBD_IO_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_conf *mdev,
        enum drbd_force_detach_flags forcedetach,
        const char *where)
{
    switch (mdev->ldev->dc.on_io_error) {
    case EP_PASS_ON:
        if (forcedetach == DRBD_IO_ERROR) {
            if (__ratelimit(&drbd_ratelimit_state))
                dev_err(DEV, "Local IO failed in %s.\n", where);
            if (mdev->state.disk > D_INCONSISTENT)
                _drbd_set_state(_NS(mdev, disk, D_INCONSISTENT), CS_HARD, NULL);
            break;
        }
        /* NOTE fall through to detach case if forcedetach set */
    case EP_DETACH:
    case EP_CALL_HELPER:
        set_bit(WAS_IO_ERROR, &mdev->flags);
        if (forcedetach == DRBD_FORCE_DETACH)
            set_bit(FORCE_DETACH, &mdev->flags);
        if (mdev->state.disk > D_FAILED) {
            _drbd_set_state(_NS(mdev, disk, D_FAILED), CS_HARD, NULL);
            dev_err(DEV,
                "Local IO failed in %s. Detaching...\n", where);
        }
        break;
    }
}

#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_conf *mdev,
    int error, enum drbd_force_detach_flags forcedetach, const char *where)
{
    if (error) {
        unsigned long flags;
        spin_lock_irqsave(&mdev->req_lock, flags);
        __drbd_chk_io_error_(mdev, forcedetach, where);
        spin_unlock_irqrestore(&mdev->req_lock, flags);
    }
}


static inline sector_t drbd_md_first_sector(struct drbd_backing_dev *bdev)
{
    switch (bdev->dc.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;
    }
}

static inline sector_t drbd_md_last_sector(struct drbd_backing_dev *bdev)
{
    switch (bdev->dc.meta_dev_idx) {
    case DRBD_MD_INDEX_INTERNAL:
    case DRBD_MD_INDEX_FLEX_INT:
        return bdev->md.md_offset + MD_AL_OFFSET - 1;
    case DRBD_MD_INDEX_FLEX_EXT:
    default:
        return bdev->md.md_offset + bdev->md.md_size_sect;
    }
}

/* 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;
}

static inline sector_t drbd_get_max_capacity(struct drbd_backing_dev *bdev)
{
    sector_t s;
    switch (bdev->dc.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;
}

static inline sector_t drbd_md_ss__(struct drbd_conf *mdev,
                    struct drbd_backing_dev *bdev)
{
    switch (bdev->dc.meta_dev_idx) {
    default: /* external, some index */
        return MD_RESERVED_SECT * bdev->dc.meta_dev_idx;
    case DRBD_MD_INDEX_INTERNAL:
        /* with drbd08, internal meta data is always "flexible" */
    case DRBD_MD_INDEX_FLEX_INT:
        /* sizeof(struct md_on_disk_07) == 4k
         * position: last 4k aligned block of 4k size */
        if (!bdev->backing_bdev) {
            if (__ratelimit(&drbd_ratelimit_state)) {
                dev_err(DEV, "bdev->backing_bdev==NULL\n");
                dump_stack();
            }
            return 0;
        }
        return (drbd_get_capacity(bdev->backing_bdev) & ~7ULL)
            - MD_AL_OFFSET;
    case DRBD_MD_INDEX_FLEX_EXT:
        return 0;
    }
}

static inline void
drbd_queue_work_front(struct drbd_work_queue *q, struct drbd_work *w)
{
    unsigned long flags;
    spin_lock_irqsave(&q->q_lock, flags);
    list_add(&w->list, &q->q);
    up(&q->s); /* within the spinlock,
              see comment near end of drbd_worker() */
    spin_unlock_irqrestore(&q->q_lock, flags);
}

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);
    up(&q->s); /* within the spinlock,
              see comment near end of drbd_worker() */
    spin_unlock_irqrestore(&q->q_lock, flags);
}

static inline void wake_asender(struct drbd_conf *mdev)
{
    if (test_bit(SIGNAL_ASENDER, &mdev->flags))
        force_sig(DRBD_SIG, mdev->asender.task);
}

static inline void request_ping(struct drbd_conf *mdev)
{
    set_bit(SEND_PING, &mdev->flags);
    wake_asender(mdev);
}

static inline int drbd_send_short_cmd(struct drbd_conf *mdev,
    enum drbd_packets cmd)
{
    struct p_header80 h;
    return drbd_send_cmd(mdev, USE_DATA_SOCKET, cmd, &h, sizeof(h));
}

static inline int drbd_send_ping(struct drbd_conf *mdev)
{
    struct p_header80 h;
    return drbd_send_cmd(mdev, USE_META_SOCKET, P_PING, &h, sizeof(h));
}

static inline int drbd_send_ping_ack(struct drbd_conf *mdev)
{
    struct p_header80 h;
    return drbd_send_cmd(mdev, USE_META_SOCKET, P_PING_ACK, &h, sizeof(h));
}

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_conf *mdev)
{
    atomic_inc(&mdev->ap_pending_cnt);
}

#define ERR_IF_CNT_IS_NEGATIVE(which)               \
    if (atomic_read(&mdev->which) < 0)          \
        dev_err(DEV, "in %s:%d: " #which " = %d < 0 !\n",   \
            __func__ , __LINE__ ,           \
            atomic_read(&mdev->which))

#define dec_ap_pending(mdev)    do {                \
    typecheck(struct drbd_conf *, mdev);            \
    if (atomic_dec_and_test(&mdev->ap_pending_cnt))     \
        wake_up(&mdev->misc_wait);          \
    ERR_IF_CNT_IS_NEGATIVE(ap_pending_cnt); } while (0)

/* 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_conf *mdev)
{
    atomic_inc(&mdev->rs_pending_cnt);
}

#define dec_rs_pending(mdev)    do {                \
    typecheck(struct drbd_conf *, mdev);            \
    atomic_dec(&mdev->rs_pending_cnt);          \
    ERR_IF_CNT_IS_NEGATIVE(rs_pending_cnt); } while (0)

/* 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_conf *mdev)
{
    atomic_inc(&mdev->unacked_cnt);
}

#define dec_unacked(mdev)   do {                \
    typecheck(struct drbd_conf *, mdev);            \
    atomic_dec(&mdev->unacked_cnt);             \
    ERR_IF_CNT_IS_NEGATIVE(unacked_cnt); } while (0)

#define sub_unacked(mdev, n)    do {                \
    typecheck(struct drbd_conf *, mdev);            \
    atomic_sub(n, &mdev->unacked_cnt);          \
    ERR_IF_CNT_IS_NEGATIVE(unacked_cnt); } while (0)


static inline void put_net_conf(struct drbd_conf *mdev)
{
    if (atomic_dec_and_test(&mdev->net_cnt))
        wake_up(&mdev->net_cnt_wait);
}

static inline int get_net_conf(struct drbd_conf *mdev)
{
    int have_net_conf;

    atomic_inc(&mdev->net_cnt);
    have_net_conf = mdev->state.conn >= C_UNCONNECTED;
    if (!have_net_conf)
        put_net_conf(mdev);
    return have_net_conf;
}

#define get_ldev(M) __cond_lock(local, _get_ldev_if_state(M,D_INCONSISTENT))
#define get_ldev_if_state(M,MINS) __cond_lock(local, _get_ldev_if_state(M,MINS))

static inline void put_ldev(struct drbd_conf *mdev)
{
    int i = atomic_dec_return(&mdev->local_cnt);

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

    __release(local);
    D_ASSERT(i >= 0);
    if (i == 0) {
        if (mdev->state.disk == D_DISKLESS)
            /* even internal references gone, safe to destroy */
            drbd_ldev_destroy(mdev);
        if (mdev->state.disk == D_FAILED)
            /* all application IO references gone. */
            drbd_go_diskless(mdev);
        wake_up(&mdev->misc_wait);
    }
}

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

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

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

/* you must have an "get_ldev" reference */
static inline void drbd_get_syncer_progress(struct drbd_conf *mdev,
        unsigned long *bits_left, unsigned int *per_mil_done)
{
    /* this is to break it at compile time when we change that, in case we
     * want to support more than (1<<32) bits on a 32bit arch. */
    typecheck(unsigned long, mdev->rs_total);

    /* note: both rs_total and rs_left are in bits, i.e. in
     * units of BM_BLOCK_SIZE.
     * for the percentage, we don't care. */

    if (mdev->state.conn == C_VERIFY_S || mdev->state.conn == C_VERIFY_T)
        *bits_left = mdev->ov_left;
    else
        *bits_left = drbd_bm_total_weight(mdev) - mdev->rs_failed;
    /* >> 10 to prevent overflow,
     * +1 to prevent division by zero */
    if (*bits_left > mdev->rs_total) {
        /* doh. maybe a logic bug somewhere.
         * may also be just a race condition
         * between this and a disconnect during sync.
         * for now, just prevent in-kernel buffer overflow.
         */
        smp_rmb();
        dev_warn(DEV, "cs:%s rs_left=%lu > rs_total=%lu (rs_failed %lu)\n",
                drbd_conn_str(mdev->state.conn),
                *bits_left, mdev->rs_total, mdev->rs_failed);
        *per_mil_done = 0;
    } else {
        /* Make sure the division happens in long context.
         * We allow up to one petabyte storage right now,
         * at a granularity of 4k per bit that is 2**38 bits.
         * After shift right and multiplication by 1000,
         * this should still fit easily into a 32bit long,
         * so we don't need a 64bit division on 32bit arch.
         * Note: currently we don't support such large bitmaps on 32bit
         * arch anyways, but no harm done to be prepared for it here.
         */
        unsigned int shift = mdev->rs_total > UINT_MAX ? 16 : 10;
        unsigned long left = *bits_left >> shift;
        unsigned long total = 1UL + (mdev->rs_total >> shift);
        unsigned long tmp = 1000UL - left * 1000UL/total;
        *per_mil_done = tmp;
    }
}


/* 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_conf *mdev)
{
    int mxb = 1000000; /* arbitrary limit on open requests */
    if (get_net_conf(mdev)) {
        mxb = mdev->net_conf->max_buffers;
        put_net_conf(mdev);
    }
    return mxb;
}

static inline int drbd_state_is_stable(struct drbd_conf *mdev)
{
    union drbd_state s = mdev->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 (mdev->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 tansitional states */
    case D_ATTACHING:
    case D_NEGOTIATING:
    case D_UNKNOWN:
    case D_MASK:
        /* not "stable" */
        return 0;
    }

    return 1;
}

static inline int is_susp(union drbd_state s)
{
    return s.susp || s.susp_nod || s.susp_fen;
}

static inline bool may_inc_ap_bio(struct drbd_conf *mdev)
{
    int mxb = drbd_get_max_buffers(mdev);

    if (is_susp(mdev->state))
        return false;
    if (test_bit(SUSPEND_IO, &mdev->flags))
        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(mdev))
        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(&mdev->ap_bio_cnt) > mxb)
        return false;
    if (test_bit(BITMAP_IO, &mdev->flags))
        return false;
    return true;
}

static inline bool inc_ap_bio_cond(struct drbd_conf *mdev, int count)
{
    bool rv = false;

    spin_lock_irq(&mdev->req_lock);
    rv = may_inc_ap_bio(mdev);
    if (rv)
        atomic_add(count, &mdev->ap_bio_cnt);
    spin_unlock_irq(&mdev->req_lock);

    return rv;
}

static inline void inc_ap_bio(struct drbd_conf *mdev, int count)
{
    /* 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 exeed the max_buffer limit.
     *
     * to avoid races with the reconnect code,
     * we need to atomic_inc within the spinlock. */

    wait_event(mdev->misc_wait, inc_ap_bio_cond(mdev, count));
}

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

    D_ASSERT(ap_bio >= 0);

    if (ap_bio == 0 && test_bit(BITMAP_IO, &mdev->flags)) {
        if (!test_and_set_bit(BITMAP_IO_QUEUED, &mdev->flags))
            drbd_queue_work(&mdev->data.work, &mdev->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(&mdev->misc_wait);
}

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

static inline int seq_cmp(u32 a, u32 b)
{
    /* we assume wrap around at 32bit.
     * for wrap around at 24bit (old atomic_t),
     * we'd have to
     *  a <<= 8; b <<= 8;
     */
    return (s32)(a) - (s32)(b);
}
#define seq_lt(a, b) (seq_cmp((a), (b)) < 0)
#define seq_gt(a, b) (seq_cmp((a), (b)) > 0)
#define seq_ge(a, b) (seq_cmp((a), (b)) >= 0)
#define seq_le(a, b) (seq_cmp((a), (b)) <= 0)
/* CAUTION: please no side effects in arguments! */
#define seq_max(a, b) ((u32)(seq_gt((a), (b)) ? (a) : (b)))

static inline void update_peer_seq(struct drbd_conf *mdev, unsigned int new_seq)
{
    unsigned int m;
    spin_lock(&mdev->peer_seq_lock);
    m = seq_max(mdev->peer_seq, new_seq);
    mdev->peer_seq = m;
    spin_unlock(&mdev->peer_seq_lock);
    if (m == new_seq)
        wake_up(&mdev->seq_wait);
}

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

static inline int drbd_queue_order_type(struct drbd_conf *mdev)
{
    /* 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 void drbd_md_flush(struct drbd_conf *mdev)
{
    int r;

    if (test_bit(MD_NO_FUA, &mdev->flags))
        return;

    r = blkdev_issue_flush(mdev->ldev->md_bdev, GFP_KERNEL, NULL);
    if (r) {
        set_bit(MD_NO_FUA, &mdev->flags);
        dev_err(DEV, "meta data flush failed with status %d, disabling md-flushes\n", r);
    }
}

#endif