raid5.h

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#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 distingush 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 {
    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 {
    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 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 */
    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 */
    enum check_states   check_state;
    enum reconstruct_states reconstruct_state;
    spinlock_t      stripe_lock;
    struct stripe_operations {
        int              target, target2;
        enum sum_check_flags zero_sum_result;
        #ifdef CONFIG_MULTICORE_RAID456
        unsigned long        request;
        wait_queue_head_t    wait_for_ops;
        #endif
    } 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;
        struct bio  *toread, *read, *towrite, *written;
        sector_t    sector;         /* sector of this page */
        unsigned long   flags;
    } 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 failed_num[2];
    int p_failed, q_failed;
    int dec_preread_active;
    unsigned long ops_request;

    struct bio *return_bi;
    struct md_rdev *blocked_rdev;
    int handle_bad_blocks;
};

/* 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 */
};

/*
 * Stripe state
 */
enum {
    STRIPE_ACTIVE,
    STRIPE_HANDLE,
    STRIPE_SYNC_REQUESTED,
    STRIPE_SYNCING,
    STRIPE_INSYNC,
    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,
};

/*
 * Operation request flags
 */
enum {
    STRIPE_OP_BIOFILL,
    STRIPE_OP_COMPUTE_BLK,
    STRIPE_OP_PREXOR,
    STRIPE_OP_BIODRAIN,
    STRIPE_OP_RECONSTRUCT,
    STRIPE_OP_CHECK,
};
/*
 * 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.
 */


struct disk_info {
    struct md_rdev  *rdev, *replacement;
};

struct r5conf {
    struct hlist_head   *stripe_hashtbl;
    struct mddev        *mddev;
    int         chunk_sectors;
    int         level, algorithm;
    int         max_degraded;
    int         raid_disks;
    int         max_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 */
    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    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   */
    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 */
    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 */

    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 */
        void        *scribble;   /* space for constructing buffer
                          * lists and performing address
                          * conversions
                          */
    } __percpu *percpu;
    size_t          scribble_len; /* size of scribble region must be
                           * associated with conf to handle
                           * cpu hotplug while reshaping
                           */
#ifdef CONFIG_HOTPLUG_CPU
    struct notifier_block   cpu_notify;
#endif

    /*
     * Free stripes pool
     */
    atomic_t        active_stripes;
    struct list_head    inactive_list;
    wait_queue_head_t   wait_for_stripe;
    wait_queue_head_t   wait_for_overlap;
    int         inactive_blocked;   /* release of inactive stripes blocked,
                             * waiting for 25% to be free
                             */
    int         pool_size; /* number of disks in stripeheads in pool */
    spinlock_t      device_lock;
    struct disk_info    *disks;

    /* 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;
};

/*
 * 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 int md_raid5_congested(struct mddev *mddev, int bits);
extern void md_raid5_kick_device(struct r5conf *conf);
extern int raid5_set_cache_size(struct mddev *mddev, int size);
#endif