Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

[cris-mirror.git] / drivers / md / raid5.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _RAID5_H
#define _RAID5_H

#include <linux/raid/xor.h>
#include <linux/dmaengine.h>

/*
 *
 * Each stripe contains one buffer per device.  Each buffer can be in
 * one of a number of states stored in "flags".  Changes between
 * these states happen *almost* exclusively under the protection of the
 * STRIPE_ACTIVE flag.  Some very specific changes can happen in bi_end_io, and
 * these are not protected by STRIPE_ACTIVE.
 *
 * The flag bits that are used to represent these states are:
 *   R5_UPTODATE and R5_LOCKED
 *
 * State Empty == !UPTODATE, !LOCK
 *        We have no data, and there is no active request
 * State Want == !UPTODATE, LOCK
 *        A read request is being submitted for this block
 * State Dirty == UPTODATE, LOCK
 *        Some new data is in this buffer, and it is being written out
 * State Clean == UPTODATE, !LOCK
 *        We have valid data which is the same as on disc
 *
 * The possible state transitions are:
 *
 *  Empty -> Want   - on read or write to get old data for  parity calc
 *  Empty -> Dirty  - on compute_parity to satisfy write/sync request.
 *  Empty -> Clean  - on compute_block when computing a block for failed drive
 *  Want  -> Empty  - on failed read
 *  Want  -> Clean  - on successful completion of read request
 *  Dirty -> Clean  - on successful completion of write request
 *  Dirty -> Clean  - on failed write
 *  Clean -> Dirty  - on compute_parity to satisfy write/sync (RECONSTRUCT or RMW)
 *
 * The Want->Empty, Want->Clean, Dirty->Clean, transitions
 * all happen in b_end_io at interrupt time.
 * Each sets the Uptodate bit before releasing the Lock bit.
 * This leaves one multi-stage transition:
 *    Want->Dirty->Clean
 * This is safe because thinking that a Clean buffer is actually dirty
 * will at worst delay some action, and the stripe will be scheduled
 * for attention after the transition is complete.
 *
 * There is one possibility that is not covered by these states.  That
 * is if one drive has failed and there is a spare being rebuilt.  We
 * can't distinguish between a clean block that has been generated
 * from parity calculations, and a clean block that has been
 * successfully written to the spare ( or to parity when resyncing).
 * To distinguish these states we have a stripe bit STRIPE_INSYNC that
 * is set whenever a write is scheduled to the spare, or to the parity
 * disc if there is no spare.  A sync request clears this bit, and
 * when we find it set with no buffers locked, we know the sync is
 * complete.
 *
 * Buffers for the md device that arrive via make_request are attached
 * to the appropriate stripe in one of two lists linked on b_reqnext.
 * One list (bh_read) for read requests, one (bh_write) for write.
 * There should never be more than one buffer on the two lists
 * together, but we are not guaranteed of that so we allow for more.
 *
 * If a buffer is on the read list when the associated cache buffer is
 * Uptodate, the data is copied into the read buffer and it's b_end_io
 * routine is called.  This may happen in the end_request routine only
 * if the buffer has just successfully been read.  end_request should
 * remove the buffers from the list and then set the Uptodate bit on
 * the buffer.  Other threads may do this only if they first check
 * that the Uptodate bit is set.  Once they have checked that they may
 * take buffers off the read queue.
 *
 * When a buffer on the write list is committed for write it is copied
 * into the cache buffer, which is then marked dirty, and moved onto a
 * third list, the written list (bh_written).  Once both the parity
 * block and the cached buffer are successfully written, any buffer on
 * a written list can be returned with b_end_io.
 *
 * The write list and read list both act as fifos.  The read list,
 * write list and written list are protected by the device_lock.
 * The device_lock is only for list manipulations and will only be
 * held for a very short time.  It can be claimed from interrupts.
 *
 *
 * Stripes in the stripe cache can be on one of two lists (or on
 * neither).  The "inactive_list" contains stripes which are not
 * currently being used for any request.  They can freely be reused
 * for another stripe.  The "handle_list" contains stripes that need
 * to be handled in some way.  Both of these are fifo queues.  Each
 * stripe is also (potentially) linked to a hash bucket in the hash
 * table so that it can be found by sector number.  Stripes that are
 * not hashed must be on the inactive_list, and will normally be at
 * the front.  All stripes start life this way.
 *
 * The inactive_list, handle_list and hash bucket lists are all protected by the
 * device_lock.
 *  - stripes have a reference counter. If count==0, they are on a list.
 *  - If a stripe might need handling, STRIPE_HANDLE is set.
 *  - When refcount reaches zero, then if STRIPE_HANDLE it is put on
 *    handle_list else inactive_list
 *
 * This, combined with the fact that STRIPE_HANDLE is only ever
 * cleared while a stripe has a non-zero count means that if the
 * refcount is 0 and STRIPE_HANDLE is set, then it is on the
 * handle_list and if recount is 0 and STRIPE_HANDLE is not set, then
 * the stripe is on inactive_list.
 *
 * The possible transitions are:
 *  activate an unhashed/inactive stripe (get_active_stripe())
 *     lockdev check-hash unlink-stripe cnt++ clean-stripe hash-stripe unlockdev
 *  activate a hashed, possibly active stripe (get_active_stripe())
 *     lockdev check-hash if(!cnt++)unlink-stripe unlockdev
 *  attach a request to an active stripe (add_stripe_bh())
 *     lockdev attach-buffer unlockdev
 *  handle a stripe (handle_stripe())
 *     setSTRIPE_ACTIVE,  clrSTRIPE_HANDLE ...
 *              (lockdev check-buffers unlockdev) ..
 *              change-state ..
 *              record io/ops needed clearSTRIPE_ACTIVE schedule io/ops
 *  release an active stripe (release_stripe())
 *     lockdev if (!--cnt) { if  STRIPE_HANDLE, add to handle_list else add to inactive-list } unlockdev
 *
 * The refcount counts each thread that have activated the stripe,
 * plus raid5d if it is handling it, plus one for each active request
 * on a cached buffer, and plus one if the stripe is undergoing stripe
 * operations.
 *
 * The stripe operations are:
 * -copying data between the stripe cache and user application buffers
 * -computing blocks to save a disk access, or to recover a missing block
 * -updating the parity on a write operation (reconstruct write and
 *  read-modify-write)
 * -checking parity correctness
 * -running i/o to disk
 * These operations are carried out by raid5_run_ops which uses the async_tx
 * api to (optionally) offload operations to dedicated hardware engines.
 * When requesting an operation handle_stripe sets the pending bit for the
 * operation and increments the count.  raid5_run_ops is then run whenever
 * the count is non-zero.
 * There are some critical dependencies between the operations that prevent some
 * from being requested while another is in flight.
 * 1/ Parity check operations destroy the in cache version of the parity block,
 *    so we prevent parity dependent operations like writes and compute_blocks
 *    from starting while a check is in progress.  Some dma engines can perform
 *    the check without damaging the parity block, in these cases the parity
 *    block is re-marked up to date (assuming the check was successful) and is
 *    not re-read from disk.
 * 2/ When a write operation is requested we immediately lock the affected
 *    blocks, and mark them as not up to date.  This causes new read requests
 *    to be held off, as well as parity checks and compute block operations.
 * 3/ Once a compute block operation has been requested handle_stripe treats
 *    that block as if it is up to date.  raid5_run_ops guaruntees that any
 *    operation that is dependent on the compute block result is initiated after
 *    the compute block completes.
 */

/*
 * Operations state - intermediate states that are visible outside of
 *   STRIPE_ACTIVE.
 * In general _idle indicates nothing is running, _run indicates a data
 * processing operation is active, and _result means the data processing result
 * is stable and can be acted upon.  For simple operations like biofill and
 * compute that only have an _idle and _run state they are indicated with
 * sh->state flags (STRIPE_BIOFILL_RUN and STRIPE_COMPUTE_RUN)
 */
/**
 * enum check_states - handles syncing / repairing a stripe
 * @check_state_idle - check operations are quiesced
 * @check_state_run - check operation is running
 * @check_state_result - set outside lock when check result is valid
 * @check_state_compute_run - check failed and we are repairing
 * @check_state_compute_result - set outside lock when compute result is valid
 */
enum check_states {
        check_state_idle = 0,
        check_state_run, /* xor parity check */
        check_state_run_q, /* q-parity check */
        check_state_run_pq, /* pq dual parity check */
        check_state_check_result,
        check_state_compute_run, /* parity repair */
        check_state_compute_result,
};

/**
 * enum reconstruct_states - handles writing or expanding a stripe
 */
enum reconstruct_states {
        reconstruct_state_idle = 0,
        reconstruct_state_prexor_drain_run,     /* prexor-write */
        reconstruct_state_drain_run,            /* write */
        reconstruct_state_run,                  /* expand */
        reconstruct_state_prexor_drain_result,
        reconstruct_state_drain_result,
        reconstruct_state_result,
};

struct stripe_head {
        struct hlist_node       hash;
        struct list_head        lru;          /* inactive_list or handle_list */
        struct llist_node       release_list;
        struct r5conf           *raid_conf;
        short                   generation;     /* increments with every
                                                 * reshape */
        sector_t                sector;         /* sector of this row */
        short                   pd_idx;         /* parity disk index */
        short                   qd_idx;         /* 'Q' disk index for raid6 */
        short                   ddf_layout;/* use DDF ordering to calculate Q */
        short                   hash_lock_index;
        unsigned long           state;          /* state flags */
        atomic_t                count;        /* nr of active thread/requests */
        int                     bm_seq; /* sequence number for bitmap flushes */
        int                     disks;          /* disks in stripe */
        int                     overwrite_disks; /* total overwrite disks in stripe,
                                                  * this is only checked when stripe
                                                  * has STRIPE_BATCH_READY
                                                  */
        enum check_states       check_state;
        enum reconstruct_states reconstruct_state;
        spinlock_t              stripe_lock;
        int                     cpu;
        struct r5worker_group   *group;

        struct stripe_head      *batch_head; /* protected by stripe lock */
        spinlock_t              batch_lock; /* only header's lock is useful */
        struct list_head        batch_list; /* protected by head's batch lock*/

        union {
                struct r5l_io_unit      *log_io;
                struct ppl_io_unit      *ppl_io;
        };

        struct list_head        log_list;
        sector_t                log_start; /* first meta block on the journal */
        struct list_head        r5c; /* for r5c_cache->stripe_in_journal */

        struct page             *ppl_page; /* partial parity of this stripe */
        /**
         * struct stripe_operations
         * @target - STRIPE_OP_COMPUTE_BLK target
         * @target2 - 2nd compute target in the raid6 case
         * @zero_sum_result - P and Q verification flags
         * @request - async service request flags for raid_run_ops
         */
        struct stripe_operations {
                int                  target, target2;
                enum sum_check_flags zero_sum_result;
        } ops;
        struct r5dev {
                /* rreq and rvec are used for the replacement device when
                 * writing data to both devices.
                 */
                struct bio      req, rreq;
                struct bio_vec  vec, rvec;
                struct page     *page, *orig_page;
                struct bio      *toread, *read, *towrite, *written;
                sector_t        sector;                 /* sector of this page */
                unsigned long   flags;
                u32             log_checksum;
        } dev[1]; /* allocated with extra space depending of RAID geometry */
};

/* stripe_head_state - collects and tracks the dynamic state of a stripe_head
 *     for handle_stripe.
 */
struct stripe_head_state {
        /* 'syncing' means that we need to read all devices, either
         * to check/correct parity, or to reconstruct a missing device.
         * 'replacing' means we are replacing one or more drives and
         * the source is valid at this point so we don't need to
         * read all devices, just the replacement targets.
         */
        int syncing, expanding, expanded, replacing;
        int locked, uptodate, to_read, to_write, failed, written;
        int to_fill, compute, req_compute, non_overwrite;
        int injournal, just_cached;
        int failed_num[2];
        int p_failed, q_failed;
        int dec_preread_active;
        unsigned long ops_request;

        struct md_rdev *blocked_rdev;
        int handle_bad_blocks;
        int log_failed;
        int waiting_extra_page;
};

/* Flags for struct r5dev.flags */
enum r5dev_flags {
        R5_UPTODATE,    /* page contains current data */
        R5_LOCKED,      /* IO has been submitted on "req" */
        R5_DOUBLE_LOCKED,/* Cannot clear R5_LOCKED until 2 writes complete */
        R5_OVERWRITE,   /* towrite covers whole page */
/* and some that are internal to handle_stripe */
        R5_Insync,      /* rdev && rdev->in_sync at start */
        R5_Wantread,    /* want to schedule a read */
        R5_Wantwrite,
        R5_Overlap,     /* There is a pending overlapping request
                         * on this block */
        R5_ReadNoMerge, /* prevent bio from merging in block-layer */
        R5_ReadError,   /* seen a read error here recently */
        R5_ReWrite,     /* have tried to over-write the readerror */

        R5_Expanded,    /* This block now has post-expand data */
        R5_Wantcompute, /* compute_block in progress treat as
                         * uptodate
                         */
        R5_Wantfill,    /* dev->toread contains a bio that needs
                         * filling
                         */
        R5_Wantdrain,   /* dev->towrite needs to be drained */
        R5_WantFUA,     /* Write should be FUA */
        R5_SyncIO,      /* The IO is sync */
        R5_WriteError,  /* got a write error - need to record it */
        R5_MadeGood,    /* A bad block has been fixed by writing to it */
        R5_ReadRepl,    /* Will/did read from replacement rather than orig */
        R5_MadeGoodRepl,/* A bad block on the replacement device has been
                         * fixed by writing to it */
        R5_NeedReplace, /* This device has a replacement which is not
                         * up-to-date at this stripe. */
        R5_WantReplace, /* We need to update the replacement, we have read
                         * data in, and now is a good time to write it out.
                         */
        R5_Discard,     /* Discard the stripe */
        R5_SkipCopy,    /* Don't copy data from bio to stripe cache */
        R5_InJournal,   /* data being written is in the journal device.
                         * if R5_InJournal is set for parity pd_idx, all the
                         * data and parity being written are in the journal
                         * device
                         */
        R5_OrigPageUPTDODATE,   /* with write back cache, we read old data into
                                 * dev->orig_page for prexor. When this flag is
                                 * set, orig_page contains latest data in the
                                 * raid disk.
                                 */
};

/*
 * Stripe state
 */
enum {
        STRIPE_ACTIVE,
        STRIPE_HANDLE,
        STRIPE_SYNC_REQUESTED,
        STRIPE_SYNCING,
        STRIPE_INSYNC,
        STRIPE_REPLACED,
        STRIPE_PREREAD_ACTIVE,
        STRIPE_DELAYED,
        STRIPE_DEGRADED,
        STRIPE_BIT_DELAY,
        STRIPE_EXPANDING,
        STRIPE_EXPAND_SOURCE,
        STRIPE_EXPAND_READY,
        STRIPE_IO_STARTED,      /* do not count towards 'bypass_count' */
        STRIPE_FULL_WRITE,      /* all blocks are set to be overwritten */
        STRIPE_BIOFILL_RUN,
        STRIPE_COMPUTE_RUN,
        STRIPE_OPS_REQ_PENDING,
        STRIPE_ON_UNPLUG_LIST,
        STRIPE_DISCARD,
        STRIPE_ON_RELEASE_LIST,
        STRIPE_BATCH_READY,
        STRIPE_BATCH_ERR,
        STRIPE_BITMAP_PENDING,  /* Being added to bitmap, don't add
                                 * to batch yet.
                                 */
        STRIPE_LOG_TRAPPED,     /* trapped into log (see raid5-cache.c)
                                 * this bit is used in two scenarios:
                                 *
                                 * 1. write-out phase
                                 *  set in first entry of r5l_write_stripe
                                 *  clear in second entry of r5l_write_stripe
                                 *  used to bypass logic in handle_stripe
                                 *
                                 * 2. caching phase
                                 *  set in r5c_try_caching_write()
                                 *  clear when journal write is done
                                 *  used to initiate r5c_cache_data()
                                 *  also used to bypass logic in handle_stripe
                                 */
        STRIPE_R5C_CACHING,     /* the stripe is in caching phase
                                 * see more detail in the raid5-cache.c
                                 */
        STRIPE_R5C_PARTIAL_STRIPE,      /* in r5c cache (to-be/being handled or
                                         * in conf->r5c_partial_stripe_list)
                                         */
        STRIPE_R5C_FULL_STRIPE, /* in r5c cache (to-be/being handled or
                                 * in conf->r5c_full_stripe_list)
                                 */
        STRIPE_R5C_PREFLUSH,    /* need to flush journal device */
};

#define STRIPE_EXPAND_SYNC_FLAGS \
        ((1 << STRIPE_EXPAND_SOURCE) |\
        (1 << STRIPE_EXPAND_READY) |\
        (1 << STRIPE_EXPANDING) |\
        (1 << STRIPE_SYNC_REQUESTED))
/*
 * Operation request flags
 */
enum {
        STRIPE_OP_BIOFILL,
        STRIPE_OP_COMPUTE_BLK,
        STRIPE_OP_PREXOR,
        STRIPE_OP_BIODRAIN,
        STRIPE_OP_RECONSTRUCT,
        STRIPE_OP_CHECK,
        STRIPE_OP_PARTIAL_PARITY,
};

/*
 * RAID parity calculation preferences
 */
enum {
        PARITY_DISABLE_RMW = 0,
        PARITY_ENABLE_RMW,
        PARITY_PREFER_RMW,
};

/*
 * Pages requested from set_syndrome_sources()
 */
enum {
        SYNDROME_SRC_ALL,
        SYNDROME_SRC_WANT_DRAIN,
        SYNDROME_SRC_WRITTEN,
};
/*
 * Plugging:
 *
 * To improve write throughput, we need to delay the handling of some
 * stripes until there has been a chance that several write requests
 * for the one stripe have all been collected.
 * In particular, any write request that would require pre-reading
 * is put on a "delayed" queue until there are no stripes currently
 * in a pre-read phase.  Further, if the "delayed" queue is empty when
 * a stripe is put on it then we "plug" the queue and do not process it
 * until an unplug call is made. (the unplug_io_fn() is called).
 *
 * When preread is initiated on a stripe, we set PREREAD_ACTIVE and add
 * it to the count of prereading stripes.
 * When write is initiated, or the stripe refcnt == 0 (just in case) we
 * clear the PREREAD_ACTIVE flag and decrement the count
 * Whenever the 'handle' queue is empty and the device is not plugged, we
 * move any strips from delayed to handle and clear the DELAYED flag and set
 * PREREAD_ACTIVE.
 * In stripe_handle, if we find pre-reading is necessary, we do it if
 * PREREAD_ACTIVE is set, else we set DELAYED which will send it to the delayed queue.
 * HANDLE gets cleared if stripe_handle leaves nothing locked.
 */

/* Note: disk_info.rdev can be set to NULL asynchronously by raid5_remove_disk.
 * There are three safe ways to access disk_info.rdev.
 * 1/ when holding mddev->reconfig_mutex
 * 2/ when resync/recovery/reshape is known to be happening - i.e. in code that
 *    is called as part of performing resync/recovery/reshape.
 * 3/ while holding rcu_read_lock(), use rcu_dereference to get the pointer
 *    and if it is non-NULL, increment rdev->nr_pending before dropping the RCU
 *    lock.
 * When .rdev is set to NULL, the nr_pending count checked again and if
 * it has been incremented, the pointer is put back in .rdev.
 */

struct disk_info {
        struct md_rdev  *rdev, *replacement;
        struct page     *extra_page; /* extra page to use in prexor */
};

/*
 * Stripe cache
 */

#define NR_STRIPES              256
#define STRIPE_SIZE             PAGE_SIZE
#define STRIPE_SHIFT            (PAGE_SHIFT - 9)
#define STRIPE_SECTORS          (STRIPE_SIZE>>9)
#define IO_THRESHOLD            1
#define BYPASS_THRESHOLD        1
#define NR_HASH                 (PAGE_SIZE / sizeof(struct hlist_head))
#define HASH_MASK               (NR_HASH - 1)
#define MAX_STRIPE_BATCH        8

/* bio's attached to a stripe+device for I/O are linked together in bi_sector
 * order without overlap.  There may be several bio's per stripe+device, and
 * a bio could span several devices.
 * When walking this list for a particular stripe+device, we must never proceed
 * beyond a bio that extends past this device, as the next bio might no longer
 * be valid.
 * This function is used to determine the 'next' bio in the list, given the
 * sector of the current stripe+device
 */
static inline struct bio *r5_next_bio(struct bio *bio, sector_t sector)
{
        int sectors = bio_sectors(bio);

        if (bio->bi_iter.bi_sector + sectors < sector + STRIPE_SECTORS)
                return bio->bi_next;
        else
                return NULL;
}

/* NOTE NR_STRIPE_HASH_LOCKS must remain below 64.
 * This is because we sometimes take all the spinlocks
 * and creating that much locking depth can cause
 * problems.
 */
#define NR_STRIPE_HASH_LOCKS 8
#define STRIPE_HASH_LOCKS_MASK (NR_STRIPE_HASH_LOCKS - 1)

struct r5worker {
        struct work_struct work;
        struct r5worker_group *group;
        struct list_head temp_inactive_list[NR_STRIPE_HASH_LOCKS];
        bool working;
};

struct r5worker_group {
        struct list_head handle_list;
        struct list_head loprio_list;
        struct r5conf *conf;
        struct r5worker *workers;
        int stripes_cnt;
};

/*
 * r5c journal modes of the array: write-back or write-through.
 * write-through mode has identical behavior as existing log only
 * implementation.
 */
enum r5c_journal_mode {
        R5C_JOURNAL_MODE_WRITE_THROUGH = 0,
        R5C_JOURNAL_MODE_WRITE_BACK = 1,
};

enum r5_cache_state {
        R5_INACTIVE_BLOCKED,    /* release of inactive stripes blocked,
                                 * waiting for 25% to be free
                                 */
        R5_ALLOC_MORE,          /* It might help to allocate another
                                 * stripe.
                                 */
        R5_DID_ALLOC,           /* A stripe was allocated, don't allocate
                                 * more until at least one has been
                                 * released.  This avoids flooding
                                 * the cache.
                                 */
        R5C_LOG_TIGHT,          /* log device space tight, need to
                                 * prioritize stripes at last_checkpoint
                                 */
        R5C_LOG_CRITICAL,       /* log device is running out of space,
                                 * only process stripes that are already
                                 * occupying the log
                                 */
        R5C_EXTRA_PAGE_IN_USE,  /* a stripe is using disk_info.extra_page
                                 * for prexor
                                 */
};

#define PENDING_IO_MAX 512
#define PENDING_IO_ONE_FLUSH 128
struct r5pending_data {
        struct list_head sibling;
        sector_t sector; /* stripe sector */
        struct bio_list bios;
};

struct r5conf {
        struct hlist_head       *stripe_hashtbl;
        /* only protect corresponding hash list and inactive_list */
        spinlock_t              hash_locks[NR_STRIPE_HASH_LOCKS];
        struct mddev            *mddev;
        int                     chunk_sectors;
        int                     level, algorithm, rmw_level;
        int                     max_degraded;
        int                     raid_disks;
        int                     max_nr_stripes;
        int                     min_nr_stripes;

        /* reshape_progress is the leading edge of a 'reshape'
         * It has value MaxSector when no reshape is happening
         * If delta_disks < 0, it is the last sector we started work on,
         * else is it the next sector to work on.
         */
        sector_t                reshape_progress;
        /* reshape_safe is the trailing edge of a reshape.  We know that
         * before (or after) this address, all reshape has completed.
         */
        sector_t                reshape_safe;
        int                     previous_raid_disks;
        int                     prev_chunk_sectors;
        int                     prev_algo;
        short                   generation; /* increments with every reshape */
        seqcount_t              gen_lock;       /* lock against generation changes */
        unsigned long           reshape_checkpoint; /* Time we last updated
                                                     * metadata */
        long long               min_offset_diff; /* minimum difference between
                                                  * data_offset and
                                                  * new_data_offset across all
                                                  * devices.  May be negative,
                                                  * but is closest to zero.
                                                  */

        struct list_head        handle_list; /* stripes needing handling */
        struct list_head        loprio_list; /* low priority stripes */
        struct list_head        hold_list; /* preread ready stripes */
        struct list_head        delayed_list; /* stripes that have plugged requests */
        struct list_head        bitmap_list; /* stripes delaying awaiting bitmap update */
        struct bio              *retry_read_aligned; /* currently retrying aligned bios   */
        unsigned int            retry_read_offset; /* sector offset into retry_read_aligned */
        struct bio              *retry_read_aligned_list; /* aligned bios retry list  */
        atomic_t                preread_active_stripes; /* stripes with scheduled io */
        atomic_t                active_aligned_reads;
        atomic_t                pending_full_writes; /* full write backlog */
        int                     bypass_count; /* bypassed prereads */
        int                     bypass_threshold; /* preread nice */
        int                     skip_copy; /* Don't copy data from bio to stripe cache */
        struct list_head        *last_hold; /* detect hold_list promotions */

        atomic_t                reshape_stripes; /* stripes with pending writes for reshape */
        /* unfortunately we need two cache names as we temporarily have
         * two caches.
         */
        int                     active_name;
        char                    cache_name[2][32];
        struct kmem_cache       *slab_cache; /* for allocating stripes */
        struct mutex            cache_size_mutex; /* Protect changes to cache size */

        int                     seq_flush, seq_write;
        int                     quiesce;

        int                     fullsync;  /* set to 1 if a full sync is needed,
                                            * (fresh device added).
                                            * Cleared when a sync completes.
                                            */
        int                     recovery_disabled;
        /* per cpu variables */
        struct raid5_percpu {
                struct page     *spare_page; /* Used when checking P/Q in raid6 */
                struct flex_array *scribble;   /* space for constructing buffer
                                              * lists and performing address
                                              * conversions
                                              */
        } __percpu *percpu;
        int scribble_disks;
        int scribble_sectors;
        struct hlist_node node;

        /*
         * Free stripes pool
         */
        atomic_t                active_stripes;
        struct list_head        inactive_list[NR_STRIPE_HASH_LOCKS];

        atomic_t                r5c_cached_full_stripes;
        struct list_head        r5c_full_stripe_list;
        atomic_t                r5c_cached_partial_stripes;
        struct list_head        r5c_partial_stripe_list;
        atomic_t                r5c_flushing_full_stripes;
        atomic_t                r5c_flushing_partial_stripes;

        atomic_t                empty_inactive_list_nr;
        struct llist_head       released_stripes;
        wait_queue_head_t       wait_for_quiescent;
        wait_queue_head_t       wait_for_stripe;
        wait_queue_head_t       wait_for_overlap;
        unsigned long           cache_state;
        struct shrinker         shrinker;
        int                     pool_size; /* number of disks in stripeheads in pool */
        spinlock_t              device_lock;
        struct disk_info        *disks;
        struct bio_set          *bio_split;

        /* When taking over an array from a different personality, we store
         * the new thread here until we fully activate the array.
         */
        struct md_thread        *thread;
        struct list_head        temp_inactive_list[NR_STRIPE_HASH_LOCKS];
        struct r5worker_group   *worker_groups;
        int                     group_cnt;
        int                     worker_cnt_per_group;
        struct r5l_log          *log;
        void                    *log_private;

        spinlock_t              pending_bios_lock;
        bool                    batch_bio_dispatch;
        struct r5pending_data   *pending_data;
        struct list_head        free_list;
        struct list_head        pending_list;
        int                     pending_data_cnt;
        struct r5pending_data   *next_pending_data;
};


/*
 * Our supported algorithms
 */
#define ALGORITHM_LEFT_ASYMMETRIC       0 /* Rotating Parity N with Data Restart */
#define ALGORITHM_RIGHT_ASYMMETRIC      1 /* Rotating Parity 0 with Data Restart */
#define ALGORITHM_LEFT_SYMMETRIC        2 /* Rotating Parity N with Data Continuation */
#define ALGORITHM_RIGHT_SYMMETRIC       3 /* Rotating Parity 0 with Data Continuation */

/* Define non-rotating (raid4) algorithms.  These allow
 * conversion of raid4 to raid5.
 */
#define ALGORITHM_PARITY_0              4 /* P or P,Q are initial devices */
#define ALGORITHM_PARITY_N              5 /* P or P,Q are final devices. */

/* DDF RAID6 layouts differ from md/raid6 layouts in two ways.
 * Firstly, the exact positioning of the parity block is slightly
 * different between the 'LEFT_*' modes of md and the "_N_*" modes
 * of DDF.
 * Secondly, or order of datablocks over which the Q syndrome is computed
 * is different.
 * Consequently we have different layouts for DDF/raid6 than md/raid6.
 * These layouts are from the DDFv1.2 spec.
 * Interestingly DDFv1.2-Errata-A does not specify N_CONTINUE but
 * leaves RLQ=3 as 'Vendor Specific'
 */

#define ALGORITHM_ROTATING_ZERO_RESTART 8 /* DDF PRL=6 RLQ=1 */
#define ALGORITHM_ROTATING_N_RESTART    9 /* DDF PRL=6 RLQ=2 */
#define ALGORITHM_ROTATING_N_CONTINUE   10 /*DDF PRL=6 RLQ=3 */

/* For every RAID5 algorithm we define a RAID6 algorithm
 * with exactly the same layout for data and parity, and
 * with the Q block always on the last device (N-1).
 * This allows trivial conversion from RAID5 to RAID6
 */
#define ALGORITHM_LEFT_ASYMMETRIC_6     16
#define ALGORITHM_RIGHT_ASYMMETRIC_6    17
#define ALGORITHM_LEFT_SYMMETRIC_6      18
#define ALGORITHM_RIGHT_SYMMETRIC_6     19
#define ALGORITHM_PARITY_0_6            20
#define ALGORITHM_PARITY_N_6            ALGORITHM_PARITY_N

static inline int algorithm_valid_raid5(int layout)
{
        return (layout >= 0) &&
                (layout <= 5);
}
static inline int algorithm_valid_raid6(int layout)
{
        return (layout >= 0 && layout <= 5)
                ||
                (layout >= 8 && layout <= 10)
                ||
                (layout >= 16 && layout <= 20);
}

static inline int algorithm_is_DDF(int layout)
{
        return layout >= 8 && layout <= 10;
}

extern void md_raid5_kick_device(struct r5conf *conf);
extern int raid5_set_cache_size(struct mddev *mddev, int size);
extern sector_t raid5_compute_blocknr(struct stripe_head *sh, int i, int previous);
extern void raid5_release_stripe(struct stripe_head *sh);
extern sector_t raid5_compute_sector(struct r5conf *conf, sector_t r_sector,
                                     int previous, int *dd_idx,
                                     struct stripe_head *sh);
extern struct stripe_head *
raid5_get_active_stripe(struct r5conf *conf, sector_t sector,
                        int previous, int noblock, int noquiesce);
extern int raid5_calc_degraded(struct r5conf *conf);
extern int r5c_journal_mode_set(struct mddev *mddev, int journal_mode);
#endif