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 /* SPDX-License-Identifier: GPL-2.0-or-later */
 /*
   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>.
 
 
 */
 
 #ifndef _DRBD_INT_H
 #define _DRBD_INT_H
 
 #include <crypto/hash.h>
 #include <linux/compiler.h>
 #include <linux/types.h>
 #include <linux/list.h>
 #include <linux/sched/signal.h>
 #include <linux/bitops.h>
 #include <linux/slab.h>
 #include <linux/ratelimit.h>
 #include <linux/tcp.h>
 #include <linux/mutex.h>
 #include <linux/major.h>
 #include <linux/blkdev.h>
 #include <linux/backing-dev.h>
 #include <linux/idr.h>
 #include <linux/dynamic_debug.h>
 #include <net/tcp.h>
 #include <linux/lru_cache.h>
 #include <linux/prefetch.h>
 #include <linux/drbd_genl_api.h>
 #include <linux/drbd.h>
 #include "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")))
 #else
 # define __protected_by(x)
 # define __protected_read_by(x)
 # define __protected_write_by(x)
 #endif
 
 /* shared module parameters, defined in drbd_main.c */
 #ifdef CONFIG_DRBD_FAULT_INJECTION
 extern int drbd_enable_faults;
 extern int drbd_fault_rate;
 #endif
 
 extern unsigned int drbd_minor_count;
 extern char drbd_usermode_helper[];
 extern int drbd_proc_details;
 
 
 /* This is used to stop/restart our threads.
  * Cannot use SIGTERM nor SIGKILL, since these
  * are sent out by init on runlevel changes
  * I choose SIGHUP for now.
  */
 #define DRBD_SIGKILL SIGHUP
 
 #define ID_IN_SYNC      (4711ULL)
 #define ID_OUT_OF_SYNC  (4712ULL)
 #define ID_SYNCER (-1ULL)
 
 #define UUID_NEW_BM_OFFSET ((u64)0x0001000000000000ULL)
 
 struct drbd_device;
 struct drbd_connection;
 
 #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 drbd_fault_rate &&
         (drbd_enable_faults & (1<<type)) &&
         _drbd_insert_fault(device, type);
 #else
     return 0;
 #endif
 }
 
 /* integer division, round _UP_ to the next integer */
 #define div_ceil(A, B) ((A)/(B) + ((A)%(B) ? 1 : 0))
 /* usual integer division */
 #define div_floor(A, B) ((A)/(B))
 
 extern struct ratelimit_state drbd_ratelimit_state;
 extern struct idr drbd_devices; /* RCU, updates: genl_lock() */
 extern struct list_head drbd_resources; /* RCU, updates: genl_lock() */
 
 extern const char *cmdname(enum drbd_packet cmd);
 
 /* for sending/receiving the bitmap,
  * possibly in some encoding scheme */
 struct bm_xfer_ctx {
     /* "const"
      * stores total bits and long words
      * of the bitmap, so we don't need to
      * call the accessor functions over and again. */
     unsigned long bm_bits;
     unsigned long bm_words;
     /* during xfer, current position within the bitmap */
     unsigned long bit_offset;
     unsigned long word_offset;
 
     /* statistics; index: (h->command == P_BITMAP) */
     unsigned packets[2];
     unsigned bytes[2];
 };
 
 extern void INFO_bm_xfer_stats(struct drbd_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_OP_DISCARD? */
     __EE_TRIM,
     /* explicit zero-out requested, or
      * our lower level cannot handle trim,
      * and we want to fall back to zeroout instead */
     __EE_ZEROOUT,
 
     /* In case a barrier failed,
      * we need to resubmit without the barrier flag. */
     __EE_RESUBMITTED,
 
     /* we may have several bios per peer request.
      * if any of those fail, we set this flag atomically
      * from the endio callback */
     __EE_WAS_ERROR,
 
     /* This ee has a pointer to a digest instead of a block id */
     __EE_HAS_DIGEST,
 
     /* Conflicting local requests need to be restarted after this request */
     __EE_RESTART_REQUESTS,
 
     /* The peer wants a write ACK for this (wire proto C) */
     __EE_SEND_WRITE_ACK,
 
     /* Is set when net_conf had two_primaries set while creating this peer_req */
     __EE_IN_INTERVAL_TREE,
 
     /* for debugfs: */
     /* has this been submitted, or does it still wait for something else? */
     __EE_SUBMITTED,
 
     /* this is/was a write request */
     __EE_WRITE,
 
     /* this is/was a write same request */
     __EE_WRITE_SAME,
 
     /* this originates from application on peer
      * (not some resync or verify or other DRBD internal request) */
     __EE_APPLICATION,
 
     /* If it contains only 0 bytes, send back P_RS_DEALLOCATED */
     __EE_RS_THIN_REQ,
 };
 #define EE_CALL_AL_COMPLETE_IO (1<<__EE_CALL_AL_COMPLETE_IO)
 #define EE_MAY_SET_IN_SYNC     (1<<__EE_MAY_SET_IN_SYNC)
 #define EE_TRIM                (1<<__EE_TRIM)
 #define EE_ZEROOUT             (1<<__EE_ZEROOUT)
 #define EE_RESUBMITTED         (1<<__EE_RESUBMITTED)
 #define EE_WAS_ERROR           (1<<__EE_WAS_ERROR)
 #define EE_HAS_DIGEST          (1<<__EE_HAS_DIGEST)
 #define EE_RESTART_REQUESTS (1<<__EE_RESTART_REQUESTS)
 #define EE_SEND_WRITE_ACK   (1<<__EE_SEND_WRITE_ACK)
 #define EE_IN_INTERVAL_TREE (1<<__EE_IN_INTERVAL_TREE)
 #define EE_SUBMITTED        (1<<__EE_SUBMITTED)
 #define EE_WRITE        (1<<__EE_WRITE)
 #define EE_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[];
 };
 extern struct fifo_buffer *fifo_alloc(unsigned int fifo_size);
 
 /* flag bits per connection */
 enum {
     NET_CONGESTED,      /* The data socket is congested */
     RESOLVE_CONFLICTS,  /* Set on one node, cleared on the peer! */
     SEND_PING,
     GOT_PING_ACK,       /* set when we receive a ping_ack packet, ping_wait gets woken */
     CONN_WD_ST_CHG_REQ, /* A cluster wide state change on the connection is active */
     CONN_WD_ST_CHG_OKAY,
     CONN_WD_ST_CHG_FAIL,
     CONN_DRY_RUN,       /* Expect disconnect after resync handshake. */
     CREATE_BARRIER,     /* next P_DATA is preceded by a P_BARRIER */
     STATE_SENT,     /* Do not change state/UUIDs while this is set */
     CALLBACK_PENDING,   /* Whether we have a call_usermodehelper(, UMH_WAIT_PROC)
                  * pending, from drbd worker context.
                  */
     DISCONNECT_SENT,
 
     DEVICE_WORK_PENDING,    /* tell worker that some device has pending work */
 };
 
 enum which_state { NOW, OLD = NOW, NEW };
 
 struct drbd_resource {
     char *name;
 #ifdef CONFIG_DEBUG_FS
     struct dentry *debugfs_res;
     struct dentry *debugfs_res_volumes;
     struct dentry *debugfs_res_connections;
     struct dentry *debugfs_res_in_flight_summary;
 #endif
     struct kref kref;
     struct idr devices;     /* volume number to device mapping */
     struct list_head connections;
     struct list_head resources;
     struct res_opts res_opts;
     struct mutex conf_update;   /* mutex for ready-copy-update of net_conf and disk_conf */
     struct mutex adm_mutex;     /* mutex to serialize administrative requests */
     spinlock_t req_lock;
 
     unsigned susp:1;        /* IO suspended by user */
     unsigned susp_nod:1;        /* IO suspended because no data */
     unsigned susp_fen:1;        /* IO suspended because fence peer handler runs */
 
     enum write_ordering_e write_ordering;
 
     cpumask_var_t cpu_mask;
 };
 
 struct drbd_thread_timing_details
 {
     unsigned long start_jif;
     void *cb_addr;
     const char *caller_fn;
     unsigned int line;
     unsigned int cb_nr;
 };
 
 struct drbd_connection {
     struct list_head connections;
     struct drbd_resource *resource;
 #ifdef CONFIG_DEBUG_FS
     struct dentry *debugfs_conn;
     struct dentry *debugfs_conn_callback_history;
     struct dentry *debugfs_conn_oldest_requests;
 #endif
     struct kref kref;
     struct idr peer_devices;    /* volume number to peer device mapping */
     enum drbd_conns cstate;     /* Only C_STANDALONE to C_WF_REPORT_PARAMS */
     struct mutex cstate_mutex;  /* Protects graceful disconnects */
     unsigned int connect_cnt;   /* Inc each time a connection is established */
 
     unsigned long flags;
     struct net_conf *net_conf;  /* content protected by rcu */
     wait_queue_head_t ping_wait;    /* Woken upon reception of a ping, and a state change */
 
     struct sockaddr_storage my_addr;
     int my_addr_len;
     struct sockaddr_storage peer_addr;
     int peer_addr_len;
 
     struct drbd_socket data;    /* data/barrier/cstate/parameter packets */
     struct drbd_socket meta;    /* ping/ack (metadata) packets */
     int agreed_pro_version;     /* actually used protocol version */
     u32 agreed_features;
     unsigned long last_received;    /* in jiffies, either socket */
     unsigned int ko_count;
 
     struct list_head transfer_log;  /* all requests not yet fully processed */
 
     struct crypto_shash *cram_hmac_tfm;
     struct crypto_shash *integrity_tfm;  /* checksums we compute, updates protected by connection->data->mutex */
     struct crypto_shash *peer_integrity_tfm;  /* checksums we verify, only accessed from receiver thread  */
     struct crypto_shash *csums_tfm;
     struct crypto_shash *verify_tfm;
     void *int_dig_in;
     void *int_dig_vv;
 
     /* receiver side */
     struct drbd_epoch *current_epoch;
     spinlock_t epoch_lock;
     unsigned int epochs;
     atomic_t current_tle_nr;    /* transfer log epoch number */
     unsigned current_tle_writes;    /* writes seen within this tl epoch */
 
     unsigned long last_reconnect_jif;
     /* empty member on older kernels without blk_start_plug() */
     struct blk_plug receiver_plug;
     struct drbd_thread receiver;
     struct drbd_thread worker;
     struct drbd_thread ack_receiver;
     struct workqueue_struct *ack_sender;
 
     /* cached pointers,
      * so we can look up the oldest pending requests more quickly.
      * protected by resource->req_lock */
     struct drbd_request *req_next; /* DRBD 9: todo.req_next */
     struct drbd_request *req_ack_pending;
     struct drbd_request *req_not_net_done;
 
     /* sender side */
     struct drbd_work_queue sender_work;
 
 #define DRBD_THREAD_DETAILS_HIST    16
     unsigned int w_cb_nr; /* keeps counting up */
     unsigned int r_cb_nr; /* keeps counting up */
     struct drbd_thread_timing_details w_timing_details[DRBD_THREAD_DETAILS_HIST];
     struct drbd_thread_timing_details r_timing_details[DRBD_THREAD_DETAILS_HIST];
 
     struct {
         unsigned long last_sent_barrier_jif;
 
         /* whether this sender thread
          * has processed a single write yet. */
         bool seen_any_write_yet;
 
         /* Which barrier number to send with the next P_BARRIER */
         int current_epoch_nr;
 
         /* how many write requests have been sent
          * with req->epoch == current_epoch_nr.
          * If none, no P_BARRIER will be sent. */
         unsigned current_epoch_writes;
     } send;
 };
 
 static inline bool has_net_conf(struct drbd_connection *connection)
 {
     bool has_net_conf;
 
     rcu_read_lock();
     has_net_conf = rcu_dereference(connection->net_conf);
     rcu_read_unlock();
 
     return has_net_conf;
 }
 
 void __update_timing_details(
         struct drbd_thread_timing_details *tdp,
         unsigned int *cb_nr,
         void *cb,
         const char *fn, const unsigned int line);
 
 #define update_worker_timing_details(c, cb) \
     __update_timing_details(c->w_timing_details, &c->w_cb_nr, cb, __func__ , __LINE__ )
 #define update_receiver_timing_details(c, cb) \
     __update_timing_details(c->r_timing_details, &c->r_cb_nr, cb, __func__ , __LINE__ )
 
 struct submit_worker {
     struct workqueue_struct *wq;
     struct work_struct worker;
 
     /* protected by ..->resource->req_lock */
     struct list_head writes;
 };
 
 struct drbd_peer_device {
     struct list_head peer_devices;
     struct drbd_device *device;
     struct drbd_connection *connection;
     struct work_struct send_acks_work;
 #ifdef CONFIG_DEBUG_FS
     struct dentry *debugfs_peer_dev;
 #endif
 };
 
 struct drbd_device {
     struct drbd_resource *resource;
     struct list_head peer_devices;
     struct list_head pending_bitmap_io;
 
     unsigned long flush_jif;
 #ifdef CONFIG_DEBUG_FS
     struct dentry *debugfs_minor;
     struct dentry *debugfs_vol;
     struct dentry *debugfs_vol_oldest_requests;
     struct dentry *debugfs_vol_act_log_extents;
     struct dentry *debugfs_vol_resync_extents;
     struct dentry *debugfs_vol_data_gen_id;
     struct dentry *debugfs_vol_ed_gen_id;
 #endif
 
     unsigned int vnr;   /* volume number within the connection */
     unsigned int minor; /* device minor number */
 
     struct kref kref;
 
     /* things that are stored as / read from meta data on disk */
     unsigned long flags;
 
     /* configured by drbdsetup */
     struct drbd_backing_dev *ldev __protected_by(local);
 
     sector_t p_size;     /* partner's disk size */
     struct request_queue *rq_queue;
     struct gendisk      *vdisk;
 
     unsigned long last_reattach_jif;
     struct drbd_work resync_work;
     struct drbd_work unplug_work;
     struct timer_list resync_timer;
     struct timer_list md_sync_timer;
     struct timer_list start_resync_timer;
     struct timer_list request_timer;
 
     /* Used after attach while negotiating new disk state. */
     union drbd_state new_state_tmp;
 
     union drbd_dev_state state;
     wait_queue_head_t misc_wait;
     wait_queue_head_t state_wait;  /* upon each state change. */
     unsigned int send_cnt;
     unsigned int recv_cnt;
     unsigned int read_cnt;
     unsigned int writ_cnt;
     unsigned int al_writ_cnt;
     unsigned int bm_writ_cnt;
     atomic_t ap_bio_cnt;     /* Requests we need to complete */
     atomic_t ap_actlog_cnt;  /* Requests waiting for activity log */
     atomic_t ap_pending_cnt; /* AP data packets on the wire, ack expected */
     atomic_t rs_pending_cnt; /* RS request/data packets on the wire */
     atomic_t unacked_cnt;    /* Need to send replies for */
     atomic_t local_cnt;  /* Waiting for local completion */
     atomic_t suspend_cnt;
 
     /* Interval tree of pending local requests */
     struct rb_root read_requests;
     struct rb_root write_requests;
 
     /* for statistics and timeouts */
     /* [0] read, [1] write */
     struct list_head pending_master_completion[2];
     struct list_head pending_completion[2];
 
     /* use checksums for *this* resync */
     bool use_csums;
     /* blocks to resync in this run [unit BM_BLOCK_SIZE] */
     unsigned long rs_total;
     /* number of resync blocks that failed in this run */
     unsigned long rs_failed;
     /* Syncer's start time [unit jiffies] */
     unsigned long rs_start;
     /* cumulated time in PausedSyncX state [unit jiffies] */
     unsigned long rs_paused;
     /* skipped because csum was equal [unit BM_BLOCK_SIZE] */
     unsigned long rs_same_csum;
 #define DRBD_SYNC_MARKS 8
 #define DRBD_SYNC_MARK_STEP (3*HZ)
     /* block not up-to-date at mark [unit BM_BLOCK_SIZE] */
     unsigned long rs_mark_left[DRBD_SYNC_MARKS];
     /* marks's time [unit jiffies] */
     unsigned long rs_mark_time[DRBD_SYNC_MARKS];
     /* current index into rs_mark_{left,time} */
     int rs_last_mark;
     unsigned long rs_last_bcast; /* [unit jiffies] */
 
     /* where does the admin want us to start? (sector) */
     sector_t ov_start_sector;
     sector_t ov_stop_sector;
     /* where are we now? (sector) */
     sector_t ov_position;
     /* Start sector of out of sync range (to merge printk reporting). */
     sector_t ov_last_oos_start;
     /* size of out-of-sync range in sectors. */
     sector_t ov_last_oos_size;
     unsigned long ov_left; /* in bits */
 
     struct drbd_bitmap *bitmap;
     unsigned long bm_resync_fo; /* bit offset for drbd_bm_find_next */
 
     /* Used to track operations of resync... */
     struct lru_cache *resync;
     /* Number of locked elements in resync LRU */
     unsigned int resync_locked;
     /* resync extent number waiting for application requests */
     unsigned int resync_wenr;
 
     int open_cnt;
     u64 *p_uuid;
 
     struct list_head active_ee; /* IO in progress (P_DATA gets written to disk) */
     struct list_head sync_ee;   /* IO in progress (P_RS_DATA_REPLY gets written to disk) */
     struct list_head done_ee;   /* need to send P_WRITE_ACK */
     struct list_head read_ee;   /* [RS]P_DATA_REQUEST being read */
     struct list_head 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);
 extern void drbd_print_uuids(struct drbd_device *device, const char *text);
 extern void drbd_queue_unplug(struct drbd_device *device);
 
 extern void conn_md_sync(struct drbd_connection *connection);
 extern void drbd_md_write(struct drbd_device *device, void *buffer);
 extern void drbd_md_sync(struct drbd_device *device);
 extern int  drbd_md_read(struct drbd_device *device, struct drbd_backing_dev *bdev);
 extern void drbd_uuid_set(struct drbd_device *device, int idx, u64 val) __must_hold(local);
 extern void _drbd_uuid_set(struct drbd_device *device, int idx, u64 val) __must_hold(local);
 extern void drbd_uuid_new_current(struct drbd_device *device) __must_hold(local);
 extern void drbd_uuid_set_bm(struct drbd_device *device, u64 val) __must_hold(local);
 extern void drbd_uuid_move_history(struct drbd_device *device) __must_hold(local);
 extern void __drbd_uuid_set(struct drbd_device *device, int idx, u64 val) __must_hold(local);
 extern void drbd_md_set_flag(struct drbd_device *device, int flags) __must_hold(local);
 extern void drbd_md_clear_flag(struct drbd_device *device, int flags)__must_hold(local);
 extern int drbd_md_test_flag(struct drbd_backing_dev *, int);
 extern void drbd_md_mark_dirty(struct drbd_device *device);
 extern void drbd_queue_bitmap_io(struct drbd_device *device,
                  int (*io_fn)(struct drbd_device *),
                  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)))
 #define DRBD_MAX_SECTORS      DRBD_MAX_SECTORS_FIXED_BM
 /* 16 TB in units of sectors */
 #if BITS_PER_LONG == 32
 /* adjust by one page worth of bitmap,
  * so we won't wrap around in drbd_bm_find_next_bit.
  * you should use 64bit OS for that much storage, anyways. */
 #define DRBD_MAX_SECTORS_FLEX BM_BIT_TO_SECT(0xffff7fff)
 #else
 /* we allow up to 1 PiB now on 64bit architecture with "flexible" meta data */
 #define DRBD_MAX_SECTORS_FLEX (1UL << 51)
 /* corresponds to (1UL << 38) bits right now. */
 #endif
 
 /* Estimate max bio size as 256 * PAGE_SIZE,
  * so for typical PAGE_SIZE of 4k, that is (1<<20) Byte.
  * Since we may live in a mixed-platform cluster,
  * we limit us to a platform agnostic constant here for now.
  * A followup commit may allow even bigger BIO sizes,
  * once we thought that through. */
 #define DRBD_MAX_BIO_SIZE (1U << 20)
 #if DRBD_MAX_BIO_SIZE > (BIO_MAX_VECS << PAGE_SHIFT)
 #error Architecture not supported: DRBD_MAX_BIO_SIZE > BIO_MAX_SIZE
 #endif
 #define DRBD_MAX_BIO_SIZE_SAFE (1U << 12)       /* Works always = 4k */
 
 #define DRBD_MAX_SIZE_H80_PACKET (1U << 15) /* Header 80 only allows packets up to 32KiB data */
 #define DRBD_MAX_BIO_SIZE_P95    (1U << 17) /* Protocol 95 to 99 allows bios up to 128KiB */
 
 /* For now, don't allow more than half of what we can "activate" in one
  * activity log transaction to be discarded in one go. We may need to rework
  * drbd_al_begin_io() to allow for even larger discard ranges */
 #define DRBD_MAX_BATCH_BIO_SIZE  (AL_UPDATES_PER_TRANSACTION/2*AL_EXTENT_SIZE)
 #define DRBD_MAX_BBIO_SECTORS    (DRBD_MAX_BATCH_BIO_SIZE >> 9)
 
 extern int  drbd_bm_init(struct drbd_device *device);
 extern int  drbd_bm_resize(struct drbd_device *device, sector_t sectors, int set_new_bits);
 extern void drbd_bm_cleanup(struct drbd_device *device);
 extern void drbd_bm_set_all(struct drbd_device *device);
 extern void drbd_bm_clear_all(struct drbd_device *device);
 /* set/clear/test only a few bits at a time */
 extern int  drbd_bm_set_bits(
         struct drbd_device *device, unsigned long s, unsigned long e);
 extern int  drbd_bm_clear_bits(
         struct drbd_device *device, unsigned long s, unsigned long e);
 extern int drbd_bm_count_bits(
     struct drbd_device *device, const unsigned long s, const unsigned long e);
 /* bm_set_bits variant for use while holding drbd_bm_lock,
  * may process the whole bitmap in one go */
 extern void _drbd_bm_set_bits(struct drbd_device *device,
         const unsigned long s, const unsigned long e);
 extern int  drbd_bm_test_bit(struct drbd_device *device, unsigned long bitnr);
 extern int  drbd_bm_e_weight(struct drbd_device *device, unsigned long enr);
 extern int  drbd_bm_read(struct drbd_device *device) __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;
 
 /* 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);
 
 /* drbd_req */
 extern void do_submit(struct work_struct *ws);
 extern void __drbd_make_request(struct drbd_device *, struct bio *);
 void drbd_submit_bio(struct bio *bio);
 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, enum req_op 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_shash *, struct bio *, void *);
 extern void drbd_csum_ee(struct crypto_shash *, struct drbd_peer_request *,
              void *);
 /* worker callbacks */
 extern int w_e_end_data_req(struct drbd_work *, int);
 extern int w_e_end_rsdata_req(struct drbd_work *, int);
 extern int w_e_end_csum_rs_req(struct drbd_work *, int);
 extern int w_e_end_ov_reply(struct drbd_work *, int);
 extern int w_e_end_ov_req(struct drbd_work *, int);
 extern int w_ov_finished(struct drbd_work *, int);
 extern int w_resync_timer(struct drbd_work *, int);
 extern int w_send_write_hint(struct drbd_work *, int);
 extern int w_send_dblock(struct drbd_work *, int);
 extern int w_send_read_req(struct drbd_work *, int);
 extern int w_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(struct timer_list *t);
 extern void start_resync_timer_fn(struct timer_list *t);
 
 extern void drbd_endio_write_sec_final(struct drbd_peer_request *peer_req);
 
 /* drbd_receiver.c */
 extern int drbd_issue_discard_or_zero_out(struct drbd_device *device,
         sector_t start, unsigned int nr_sectors, int flags);
 extern int drbd_receiver(struct drbd_thread *thi);
 extern int drbd_ack_receiver(struct drbd_thread *thi);
 extern void drbd_send_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 *, blk_opf_t, 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 *);
 
 /* sets the number of 512 byte sectors of our virtual device */
 void drbd_set_my_capacity(struct drbd_device *device, sector_t size);
 
 /*
  * used to submit our private bio
  */
 static inline void drbd_submit_bio_noacct(struct drbd_device *device,
                          int fault_type, struct bio *bio)
 {
     __release(local);
     if (!bio->bi_bdev) {
         drbd_err(device, "drbd_submit_bio_noacct: bio->bi_bdev == NULL\n");
         bio->bi_status = BLK_STS_IOERR;
         bio_endio(bio);
         return;
     }
 
     if (drbd_insert_fault(device, fault_type))
         bio_io_error(bio);
     else
         submit_bio_noacct(bio);
 }
 
 void drbd_bump_write_ordering(struct drbd_resource *resource, struct drbd_backing_dev *bdev,
                   enum write_ordering_e wo);
 
 /* drbd_proc.c */
 extern struct proc_dir_entry *drbd_proc;
 int drbd_seq_show(struct seq_file *seq, void *v);
 
 /* drbd_actlog.c */
 extern bool drbd_al_begin_io_prepare(struct drbd_device *device, struct drbd_interval *i);
 extern int drbd_al_begin_io_nonblock(struct drbd_device *device, struct drbd_interval *i);
 extern void drbd_al_begin_io_commit(struct drbd_device *device);
 extern bool drbd_al_begin_io_fastpath(struct drbd_device *device, struct drbd_interval *i);
 extern void drbd_al_begin_io(struct drbd_device *device, struct drbd_interval *i);
 extern void drbd_al_complete_io(struct drbd_device *device, struct drbd_interval *i);
 extern void drbd_rs_complete_io(struct drbd_device *device, sector_t sector);
 extern int drbd_rs_begin_io(struct drbd_device *device, sector_t sector);
 extern int drbd_try_rs_begin_io(struct drbd_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 int notify_resource_state(struct sk_buff *,
                   unsigned int,
                   struct drbd_resource *,
                   struct resource_info *,
                   enum drbd_notification_type);
 extern int notify_device_state(struct sk_buff *,
                 unsigned int,
                 struct drbd_device *,
                 struct device_info *,
                 enum drbd_notification_type);
 extern int notify_connection_state(struct sk_buff *,
                     unsigned int,
                     struct drbd_connection *,
                     struct connection_info *,
                     enum drbd_notification_type);
 extern int notify_peer_device_state(struct sk_buff *,
                      unsigned int,
                      struct drbd_peer_device *,
                      struct peer_device_info *,
                      enum drbd_notification_type);
 extern void notify_helper(enum drbd_notification_type, struct drbd_device *,
               struct drbd_connection *, const char *, int);
 
 /*
  * inline helper functions
  *************************/
 
 /* see also page_chain_add and friends in drbd_receiver.c */
 static inline struct page *page_chain_next(struct page *page)
 {
     return (struct page *)page_private(page);
 }
 #define page_chain_for_each(page) \
     for (; page && ({ prefetch(page_chain_next(page)); 1; }); \
             page = page_chain_next(page))
 #define page_chain_for_each_safe(page, n) \
     for (; page && ({ n = page_chain_next(page); 1; }); page = n)
 
 
 static inline 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;
         }
         fallthrough;    /* for DRBD_META_IO_ERROR or DRBD_FORCE_DETACH */
     case EP_DETACH:
     case EP_CALL_HELPER:
         /* Remember whether we saw a READ or WRITE error.
          *
          * Recovery of the affected area for WRITE failure is covered
          * by the activity log.
          * READ errors may fall outside that area though. Certain READ
          * errors can be "healed" by writing good data to the affected
          * blocks, which triggers block re-allocation in lower layers.
          *
          * If we can not write the bitmap after a READ error,
          * we may need to trigger a full sync (see w_go_diskless()).
          *
          * Force-detach is not really an IO error, but rather a
          * desperate measure to try to deal with a completely
          * unresponsive lower level IO stack.
          * Still it should be treated as a WRITE error.
          *
          * Meta IO error is always WRITE error:
          * we read meta data only once during attach,
          * which will fail in case of errors.
          */
         set_bit(WAS_IO_ERROR, &device->flags);
         if (df == DRBD_READ_ERROR)
             set_bit(WAS_READ_ERROR, &device->flags);
         if (df == DRBD_FORCE_DETACH)
             set_bit(FORCE_DETACH, &device->flags);
         if (device->state.disk > D_FAILED) {
             _drbd_set_state(_NS(device, disk, D_FAILED), CS_HARD, NULL);
             drbd_err(device,
                 "Local IO failed in %s. Detaching...\n", where);
         }
         break;
     }
 }
 
 /**
  * drbd_chk_io_error: Handle the on_io_error setting, should be called from all io completion handlers
  * @device:  DRBD device.
  * @error:   Error code passed to the IO completion callback
  * @forcedetach: Force detach. I.e. the error happened while accessing the meta data
  *
  * See also drbd_main.c:after_state_ch() if (os.disk > D_FAILED && ns.disk == D_FAILED)
  */
 #define drbd_chk_io_error(m,e,f) drbd_chk_io_error_(m,e,f, __func__)
 static inline void drbd_chk_io_error_(struct drbd_device *device,
     int error, enum drbd_force_detach_flags forcedetach, const char *where)
 {
     if (error) {
         unsigned long flags;
         spin_lock_irqsave(&device->resource->req_lock, flags);
         __drbd_chk_io_error_(device, forcedetach, where);
         spin_unlock_irqrestore(&device->resource->req_lock, flags);
     }
 }
 
 
 /**
  * drbd_md_first_sector() - Returns the first sector number of the meta data area
  * @bdev:   Meta data block device.
  *
  * BTW, for internal meta data, this happens to be the maximum capacity
  * we could agree upon with our peer node.
  */
 static inline sector_t drbd_md_first_sector(struct drbd_backing_dev *bdev)
 {
     switch (bdev->md.meta_dev_idx) {
     case DRBD_MD_INDEX_INTERNAL:
     case DRBD_MD_INDEX_FLEX_INT:
         return bdev->md.md_offset + bdev->md.bm_offset;
     case DRBD_MD_INDEX_FLEX_EXT:
     default:
         return bdev->md.md_offset;
     }
 }
 
 /**
  * drbd_md_last_sector() - Return the last sector number of the meta data area
  * @bdev:   Meta data block device.
  */
 static inline sector_t drbd_md_last_sector(struct drbd_backing_dev *bdev)
 {
     switch (bdev->md.meta_dev_idx) {
     case DRBD_MD_INDEX_INTERNAL:
     case DRBD_MD_INDEX_FLEX_INT:
         return bdev->md.md_offset + MD_4kB_SECT -1;
     case DRBD_MD_INDEX_FLEX_EXT:
     default:
         return bdev->md.md_offset + bdev->md.md_size_sect -1;
     }
 }
 
 /* Returns the number of 512 byte sectors of the device */
 static inline sector_t drbd_get_capacity(struct block_device *bdev)
 {
     return bdev ? bdev_nr_sectors(bdev) : 0;
 }
 
 /**
  * drbd_get_max_capacity() - Returns the capacity we announce to out peer
  * @bdev:   Meta data block device.
  *
  * returns the capacity we announce to out peer.  we clip ourselves at the
  * various MAX_SECTORS, because if we don't, current implementation will
  * oops sooner or later
  */
 static inline sector_t drbd_get_max_capacity(struct drbd_backing_dev *bdev)
 {
     sector_t s;
 
     switch (bdev->md.meta_dev_idx) {
     case DRBD_MD_INDEX_INTERNAL:
     case DRBD_MD_INDEX_FLEX_INT:
         s = drbd_get_capacity(bdev->backing_bdev)
             ? min_t(sector_t, DRBD_MAX_SECTORS_FLEX,
                 drbd_md_first_sector(bdev))
             : 0;
         break;
     case DRBD_MD_INDEX_FLEX_EXT:
         s = min_t(sector_t, DRBD_MAX_SECTORS_FLEX,
                 drbd_get_capacity(bdev->backing_bdev));
         /* clip at maximum size the meta device can support */
         s = min_t(sector_t, s,
             BM_EXT_TO_SECT(bdev->md.md_size_sect
                      - bdev->md.bm_offset));
         break;
     default:
         s = min_t(sector_t, DRBD_MAX_SECTORS,
                 drbd_get_capacity(bdev->backing_bdev));
     }
     return s;
 }
 
 /**
  * drbd_md_ss() - Return the sector number of our meta data super block
  * @bdev:   Meta data block device.
  */
 static inline sector_t drbd_md_ss(struct drbd_backing_dev *bdev)
 {
     const int meta_dev_idx = bdev->md.meta_dev_idx;
 
     if (meta_dev_idx == DRBD_MD_INDEX_FLEX_EXT)
         return 0;
 
     /* Since drbd08, internal meta data is always "flexible".
      * position: last 4k aligned block of 4k size */
     if (meta_dev_idx == DRBD_MD_INDEX_INTERNAL ||
         meta_dev_idx == DRBD_MD_INDEX_FLEX_INT)
         return (drbd_get_capacity(bdev->backing_bdev) & ~7ULL) - 8;
 
     /* external, some index; this is the old fixed size layout */
     return MD_128MB_SECT * bdev->md.meta_dev_idx;
 }
 
 static inline void
 drbd_queue_work(struct drbd_work_queue *q, struct drbd_work *w)
 {
     unsigned long flags;
     spin_lock_irqsave(&q->q_lock, flags);
     list_add_tail(&w->list, &q->q);
     spin_unlock_irqrestore(&q->q_lock, flags);
     wake_up(&q->q_wait);
 }
 
 static inline void
 drbd_queue_work_if_unqueued(struct drbd_work_queue *q, struct drbd_work *w)
 {
     unsigned long flags;
     spin_lock_irqsave(&q->q_lock, flags);
     if (list_empty_careful(&w->list))
         list_add_tail(&w->list, &q->q);
     spin_unlock_irqrestore(&q->q_lock, flags);
     wake_up(&q->q_wait);
 }
 
 static inline void
 drbd_device_post_work(struct drbd_device *device, int work_bit)
 {
     if (!test_and_set_bit(work_bit, &device->flags)) {
         struct drbd_connection *connection =
             first_peer_device(device)->connection;
         struct drbd_work_queue *q = &connection->sender_work;
         if (!test_and_set_bit(DEVICE_WORK_PENDING, &connection->flags))
             wake_up(&q->q_wait);
     }
 }
 
 extern void drbd_flush_workqueue(struct drbd_work_queue *work_queue);
 
 /* To get the ack_receiver out of the blocking network stack,
  * so it can change its sk_rcvtimeo from idle- to ping-timeout,
  * and send a ping, we need to send a signal.
  * Which signal we send is irrelevant. */
 static inline void wake_ack_receiver(struct drbd_connection *connection)
 {
     struct task_struct *task = connection->ack_receiver.task;
     if (task && get_t_state(&connection->ack_receiver) == RUNNING)
         send_sig(SIGXCPU, task, 1);
 }
 
 static inline void request_ping(struct drbd_connection *connection)
 {
     set_bit(SEND_PING, &connection->flags);
     wake_ack_receiver(connection);
 }
 
 extern void *conn_prepare_command(struct drbd_connection *, struct drbd_socket *);
 extern void *drbd_prepare_command(struct drbd_peer_device *, struct drbd_socket *);
 extern int conn_send_command(struct drbd_connection *, struct drbd_socket *,
                  enum drbd_packet, unsigned int, void *,
                  unsigned int);
 extern int drbd_send_command(struct drbd_peer_device *, struct drbd_socket *,
                  enum drbd_packet, unsigned int, void *,
                  unsigned int);
 
 extern int drbd_send_ping(struct drbd_connection *connection);
 extern int drbd_send_ping_ack(struct drbd_connection *connection);
 extern int drbd_send_state_req(struct drbd_peer_device *, union drbd_state, union drbd_state);
 extern int conn_send_state_req(struct drbd_connection *, union drbd_state, union drbd_state);
 
 static inline void drbd_thread_stop(struct drbd_thread *thi)
 {
     _drbd_thread_stop(thi, false, true);
 }
 
 static inline void drbd_thread_stop_nowait(struct drbd_thread *thi)
 {
     _drbd_thread_stop(thi, false, false);
 }
 
 static inline void drbd_thread_restart_nowait(struct drbd_thread *thi)
 {
     _drbd_thread_stop(thi, true, false);
 }
 
 /* counts how many answer packets packets we expect from our peer,
  * for either explicit application requests,
  * or implicit barrier packets as necessary.
  * increased:
  *  w_send_barrier
  *  _req_mod(req, QUEUE_FOR_NET_WRITE or QUEUE_FOR_NET_READ);
  *    it is much easier and equally valid to count what we queue for the
  *    worker, even before it actually was queued or send.
  *    (drbd_make_request_common; recovery path on read io-error)
  * decreased:
  *  got_BarrierAck (respective tl_clear, tl_clear_barrier)
  *  _req_mod(req, DATA_RECEIVED)
  *     [from receive_DataReply]
  *  _req_mod(req, WRITE_ACKED_BY_PEER or RECV_ACKED_BY_PEER or NEG_ACKED)
  *     [from got_BlockAck (P_WRITE_ACK, P_RECV_ACK)]
  *     for some reason it is NOT decreased in got_NegAck,
  *     but in the resulting cleanup code from report_params.
  *     we should try to remember the reason for that...
  *  _req_mod(req, SEND_FAILED or SEND_CANCELED)
  *  _req_mod(req, CONNECTION_LOST_WHILE_PENDING)
  *     [from tl_clear_barrier]
  */
 static inline void inc_ap_pending(struct drbd_device *device)
 {
     atomic_inc(&device->ap_pending_cnt);
 }
 
 #define 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

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