drivers/md/raid5.h

   1 #ifndef _RAID5_H
   2 #define _RAID5_H
   3
   4 #include <linux/raid/xor.h>
   5 #include <linux/dmaengine.h>
   6
   7 /*
   8  *
   9  * Each stripe contains one buffer per device.  Each buffer can be in
  10  * one of a number of states stored in "flags".  Changes between
  11  * these states happen *almost* exclusively under the protection of the
  12  * STRIPE_ACTIVE flag.  Some very specific changes can happen in bi_end_io, and
  13  * these are not protected by STRIPE_ACTIVE.
  14  *
  15  * The flag bits that are used to represent these states are:
  16  *   R5_UPTODATE and R5_LOCKED
  17  *
  18  * State Empty == !UPTODATE, !LOCK
  19  *        We have no data, and there is no active request
  20  * State Want == !UPTODATE, LOCK
  21  *        A read request is being submitted for this block
  22  * State Dirty == UPTODATE, LOCK
  23  *        Some new data is in this buffer, and it is being written out
  24  * State Clean == UPTODATE, !LOCK
  25  *        We have valid data which is the same as on disc
  26  *
  27  * The possible state transitions are:
  28  *
  29  *  Empty -> Want   - on read or write to get old data for  parity calc
  30  *  Empty -> Dirty  - on compute_parity to satisfy write/sync request.
  31  *  Empty -> Clean  - on compute_block when computing a block for failed drive
  32  *  Want  -> Empty  - on failed read
  33  *  Want  -> Clean  - on successful completion of read request
  34  *  Dirty -> Clean  - on successful completion of write request
  35  *  Dirty -> Clean  - on failed write
  36  *  Clean -> Dirty  - on compute_parity to satisfy write/sync (RECONSTRUCT or RMW)
  37  *
  38  * The Want->Empty, Want->Clean, Dirty->Clean, transitions
  39  * all happen in b_end_io at interrupt time.
  40  * Each sets the Uptodate bit before releasing the Lock bit.
  41  * This leaves one multi-stage transition:
  42  *    Want->Dirty->Clean
  43  * This is safe because thinking that a Clean buffer is actually dirty
  44  * will at worst delay some action, and the stripe will be scheduled
  45  * for attention after the transition is complete.
  46  *
  47  * There is one possibility that is not covered by these states.  That
  48  * is if one drive has failed and there is a spare being rebuilt.  We
  49  * can't distinguish between a clean block that has been generated
  50  * from parity calculations, and a clean block that has been
  51  * successfully written to the spare ( or to parity when resyncing).
  52  * To distinguish these states we have a stripe bit STRIPE_INSYNC that
  53  * is set whenever a write is scheduled to the spare, or to the parity
  54  * disc if there is no spare.  A sync request clears this bit, and
  55  * when we find it set with no buffers locked, we know the sync is
  56  * complete.
  57  *
  58  * Buffers for the md device that arrive via make_request are attached
  59  * to the appropriate stripe in one of two lists linked on b_reqnext.
  60  * One list (bh_read) for read requests, one (bh_write) for write.
  61  * There should never be more than one buffer on the two lists
  62  * together, but we are not guaranteed of that so we allow for more.
  63  *
  64  * If a buffer is on the read list when the associated cache buffer is
  65  * Uptodate, the data is copied into the read buffer and it's b_end_io
  66  * routine is called.  This may happen in the end_request routine only
  67  * if the buffer has just successfully been read.  end_request should
  68  * remove the buffers from the list and then set the Uptodate bit on
  69  * the buffer.  Other threads may do this only if they first check
  70  * that the Uptodate bit is set.  Once they have checked that they may
  71  * take buffers off the read queue.
  72  *
  73  * When a buffer on the write list is committed for write it is copied
  74  * into the cache buffer, which is then marked dirty, and moved onto a
  75  * third list, the written list (bh_written).  Once both the parity
  76  * block and the cached buffer are successfully written, any buffer on
  77  * a written list can be returned with b_end_io.
  78  *
  79  * The write list and read list both act as fifos.  The read list,
  80  * write list and written list are protected by the device_lock.
  81  * The device_lock is only for list manipulations and will only be
  82  * held for a very short time.  It can be claimed from interrupts.
  83  *
  84  *
  85  * Stripes in the stripe cache can be on one of two lists (or on
  86  * neither).  The "inactive_list" contains stripes which are not
  87  * currently being used for any request.  They can freely be reused
  88  * for another stripe.  The "handle_list" contains stripes that need
  89  * to be handled in some way.  Both of these are fifo queues.  Each
  90  * stripe is also (potentially) linked to a hash bucket in the hash
  91  * table so that it can be found by sector number.  Stripes that are
  92  * not hashed must be on the inactive_list, and will normally be at
  93  * the front.  All stripes start life this way.
  94  *
  95  * The inactive_list, handle_list and hash bucket lists are all protected by the
  96  * device_lock.
  97  *  - stripes have a reference counter. If count==0, they are on a list.
  98  *  - If a stripe might need handling, STRIPE_HANDLE is set.
  99  *  - When refcount reaches zero, then if STRIPE_HANDLE it is put on
 100  *    handle_list else inactive_list
 101  *
 102  * This, combined with the fact that STRIPE_HANDLE is only ever
 103  * cleared while a stripe has a non-zero count means that if the
 104  * refcount is 0 and STRIPE_HANDLE is set, then it is on the
 105  * handle_list and if recount is 0 and STRIPE_HANDLE is not set, then
 106  * the stripe is on inactive_list.
 107  *
 108  * The possible transitions are:
 109  *  activate an unhashed/inactive stripe (get_active_stripe())
 110  *     lockdev check-hash unlink-stripe cnt++ clean-stripe hash-stripe unlockdev
 111  *  activate a hashed, possibly active stripe (get_active_stripe())
 112  *     lockdev check-hash if(!cnt++)unlink-stripe unlockdev
 113  *  attach a request to an active stripe (add_stripe_bh())
 114  *     lockdev attach-buffer unlockdev
 115  *  handle a stripe (handle_stripe())
 116  *     setSTRIPE_ACTIVE,  clrSTRIPE_HANDLE ...
 117  *              (lockdev check-buffers unlockdev) ..
 118  *              change-state ..
 119  *              record io/ops needed clearSTRIPE_ACTIVE schedule io/ops
 120  *  release an active stripe (release_stripe())
 121  *     lockdev if (!--cnt) { if  STRIPE_HANDLE, add to handle_list else add to inactive-list } unlockdev
 122  *
 123  * The refcount counts each thread that have activated the stripe,
 124  * plus raid5d if it is handling it, plus one for each active request
 125  * on a cached buffer, and plus one if the stripe is undergoing stripe
 126  * operations.
 127  *
 128  * The stripe operations are:
 129  * -copying data between the stripe cache and user application buffers
 130  * -computing blocks to save a disk access, or to recover a missing block
 131  * -updating the parity on a write operation (reconstruct write and
 132  *  read-modify-write)
 133  * -checking parity correctness
 134  * -running i/o to disk
 135  * These operations are carried out by raid5_run_ops which uses the async_tx
 136  * api to (optionally) offload operations to dedicated hardware engines.
 137  * When requesting an operation handle_stripe sets the pending bit for the
 138  * operation and increments the count.  raid5_run_ops is then run whenever
 139  * the count is non-zero.
 140  * There are some critical dependencies between the operations that prevent some
 141  * from being requested while another is in flight.
 142  * 1/ Parity check operations destroy the in cache version of the parity block,
 143  *    so we prevent parity dependent operations like writes and compute_blocks
 144  *    from starting while a check is in progress.  Some dma engines can perform
 145  *    the check without damaging the parity block, in these cases the parity
 146  *    block is re-marked up to date (assuming the check was successful) and is
 147  *    not re-read from disk.
 148  * 2/ When a write operation is requested we immediately lock the affected
 149  *    blocks, and mark them as not up to date.  This causes new read requests
 150  *    to be held off, as well as parity checks and compute block operations.
 151  * 3/ Once a compute block operation has been requested handle_stripe treats
 152  *    that block as if it is up to date.  raid5_run_ops guaruntees that any
 153  *    operation that is dependent on the compute block result is initiated after
 154  *    the compute block completes.
 155  */
 156
 157 /*
 158  * Operations state - intermediate states that are visible outside of
 159  *   STRIPE_ACTIVE.
 160  * In general _idle indicates nothing is running, _run indicates a data
 161  * processing operation is active, and _result means the data processing result
 162  * is stable and can be acted upon.  For simple operations like biofill and
 163  * compute that only have an _idle and _run state they are indicated with
 164  * sh->state flags (STRIPE_BIOFILL_RUN and STRIPE_COMPUTE_RUN)
 165  */
 166 /**
 167  * enum check_states - handles syncing / repairing a stripe
 168  * @check_state_idle - check operations are quiesced
 169  * @check_state_run - check operation is running
 170  * @check_state_result - set outside lock when check result is valid
 171  * @check_state_compute_run - check failed and we are repairing
 172  * @check_state_compute_result - set outside lock when compute result is valid
 173  */
 174 enum check_states {
 175         check_state_idle = 0,
 176         check_state_run, /* xor parity check */
 177         check_state_run_q, /* q-parity check */
 178         check_state_run_pq, /* pq dual parity check */
 179         check_state_check_result,
 180         check_state_compute_run, /* parity repair */
 181         check_state_compute_result,
 182 };
 183
 184 /**
 185  * enum reconstruct_states - handles writing or expanding a stripe
 186  */
 187 enum reconstruct_states {
 188         reconstruct_state_idle = 0,
 189         reconstruct_state_prexor_drain_run,     /* prexor-write */
 190         reconstruct_state_drain_run,            /* write */
 191         reconstruct_state_run,                  /* expand */
 192         reconstruct_state_prexor_drain_result,
 193         reconstruct_state_drain_result,
 194         reconstruct_state_result,
 195 };
 196
 197 struct stripe_head {
 198         struct hlist_node       hash;
 199         struct list_head        lru;          /* inactive_list or handle_list */
 200         struct llist_node       release_list;
 201         struct r5conf           *raid_conf;
 202         short                   generation;     /* increments with every
 203                                                  * reshape */
 204         sector_t                sector;         /* sector of this row */
 205         short                   pd_idx;         /* parity disk index */
 206         short                   qd_idx;         /* 'Q' disk index for raid6 */
 207         short                   ddf_layout;/* use DDF ordering to calculate Q */
 208         short                   hash_lock_index;
 209         unsigned long           state;          /* state flags */
 210         atomic_t                count;        /* nr of active thread/requests */
 211         int                     bm_seq; /* sequence number for bitmap flushes */
 212         int                     disks;          /* disks in stripe */
 213         enum check_states       check_state;
 214         enum reconstruct_states reconstruct_state;
 215         spinlock_t              stripe_lock;
 216         int                     cpu;
 217         struct r5worker_group   *group;
 218         /**
 219          * struct stripe_operations
 220          * @target - STRIPE_OP_COMPUTE_BLK target
 221          * @target2 - 2nd compute target in the raid6 case
 222          * @zero_sum_result - P and Q verification flags
 223          * @request - async service request flags for raid_run_ops
 224          */
 225         struct stripe_operations {
 226                 int                  target, target2;
 227                 enum sum_check_flags zero_sum_result;
 228         } ops;
 229         struct r5dev {
 230                 /* rreq and rvec are used for the replacement device when
 231                  * writing data to both devices.
 232                  */
 233                 struct bio      req, rreq;
 234                 struct bio_vec  vec, rvec;
 235                 struct page     *page, *orig_page;
 236                 struct bio      *toread, *read, *towrite, *written;
 237                 sector_t        sector;                 /* sector of this page */
 238                 unsigned long   flags;
 239         } dev[1]; /* allocated with extra space depending of RAID geometry */
 240 };
 241
 242 /* stripe_head_state - collects and tracks the dynamic state of a stripe_head
 243  *     for handle_stripe.
 244  */
 245 struct stripe_head_state {
 246         /* 'syncing' means that we need to read all devices, either
 247          * to check/correct parity, or to reconstruct a missing device.
 248          * 'replacing' means we are replacing one or more drives and
 249          * the source is valid at this point so we don't need to
 250          * read all devices, just the replacement targets.
 251          */
 252         int syncing, expanding, expanded, replacing;
 253         int locked, uptodate, to_read, to_write, failed, written;
 254         int to_fill, compute, req_compute, non_overwrite;
 255         int failed_num[2];
 256         int p_failed, q_failed;
 257         int dec_preread_active;
 258         unsigned long ops_request;
 259
 260         struct bio *return_bi;
 261         struct md_rdev *blocked_rdev;
 262         int handle_bad_blocks;
 263 };
 264
 265 /* Flags for struct r5dev.flags */
 266 enum r5dev_flags {
 267         R5_UPTODATE,    /* page contains current data */
 268         R5_LOCKED,      /* IO has been submitted on "req" */
 269         R5_DOUBLE_LOCKED,/* Cannot clear R5_LOCKED until 2 writes complete */
 270         R5_OVERWRITE,   /* towrite covers whole page */
 271 /* and some that are internal to handle_stripe */
 272         R5_Insync,      /* rdev && rdev->in_sync at start */
 273         R5_Wantread,    /* want to schedule a read */
 274         R5_Wantwrite,
 275         R5_Overlap,     /* There is a pending overlapping request
 276                          * on this block */
 277         R5_ReadNoMerge, /* prevent bio from merging in block-layer */
 278         R5_ReadError,   /* seen a read error here recently */
 279         R5_ReWrite,     /* have tried to over-write the readerror */
 280
 281         R5_Expanded,    /* This block now has post-expand data */
 282         R5_Wantcompute, /* compute_block in progress treat as
 283                          * uptodate
 284                          */
 285         R5_Wantfill,    /* dev->toread contains a bio that needs
 286                          * filling
 287                          */
 288         R5_Wantdrain,   /* dev->towrite needs to be drained */
 289         R5_WantFUA,     /* Write should be FUA */
 290         R5_SyncIO,      /* The IO is sync */
 291         R5_WriteError,  /* got a write error - need to record it */
 292         R5_MadeGood,    /* A bad block has been fixed by writing to it */
 293         R5_ReadRepl,    /* Will/did read from replacement rather than orig */
 294         R5_MadeGoodRepl,/* A bad block on the replacement device has been
 295                          * fixed by writing to it */
 296         R5_NeedReplace, /* This device has a replacement which is not
 297                          * up-to-date at this stripe. */
 298         R5_WantReplace, /* We need to update the replacement, we have read
 299                          * data in, and now is a good time to write it out.
 300                          */
 301         R5_Discard,     /* Discard the stripe */
 302         R5_SkipCopy,    /* Don't copy data from bio to stripe cache */
 303 };
 304
 305 /*
 306  * Stripe state
 307  */
 308 enum {
 309         STRIPE_ACTIVE,
 310         STRIPE_HANDLE,
 311         STRIPE_SYNC_REQUESTED,
 312         STRIPE_SYNCING,
 313         STRIPE_INSYNC,
 314         STRIPE_REPLACED,
 315         STRIPE_PREREAD_ACTIVE,
 316         STRIPE_DELAYED,
 317         STRIPE_DEGRADED,
 318         STRIPE_BIT_DELAY,
 319         STRIPE_EXPANDING,
 320         STRIPE_EXPAND_SOURCE,
 321         STRIPE_EXPAND_READY,
 322         STRIPE_IO_STARTED,      /* do not count towards 'bypass_count' */
 323         STRIPE_FULL_WRITE,      /* all blocks are set to be overwritten */
 324         STRIPE_BIOFILL_RUN,
 325         STRIPE_COMPUTE_RUN,
 326         STRIPE_OPS_REQ_PENDING,
 327         STRIPE_ON_UNPLUG_LIST,
 328         STRIPE_DISCARD,
 329         STRIPE_ON_RELEASE_LIST,
 330 };
 331
 332 /*
 333  * Operation request flags
 334  */
 335 enum {
 336         STRIPE_OP_BIOFILL,
 337         STRIPE_OP_COMPUTE_BLK,
 338         STRIPE_OP_PREXOR,
 339         STRIPE_OP_BIODRAIN,
 340         STRIPE_OP_RECONSTRUCT,
 341         STRIPE_OP_CHECK,
 342 };
 343 /*
 344  * Plugging:
 345  *
 346  * To improve write throughput, we need to delay the handling of some
 347  * stripes until there has been a chance that several write requests
 348  * for the one stripe have all been collected.
 349  * In particular, any write request that would require pre-reading
 350  * is put on a "delayed" queue until there are no stripes currently
 351  * in a pre-read phase.  Further, if the "delayed" queue is empty when
 352  * a stripe is put on it then we "plug" the queue and do not process it
 353  * until an unplug call is made. (the unplug_io_fn() is called).
 354  *
 355  * When preread is initiated on a stripe, we set PREREAD_ACTIVE and add
 356  * it to the count of prereading stripes.
 357  * When write is initiated, or the stripe refcnt == 0 (just in case) we
 358  * clear the PREREAD_ACTIVE flag and decrement the count
 359  * Whenever the 'handle' queue is empty and the device is not plugged, we
 360  * move any strips from delayed to handle and clear the DELAYED flag and set
 361  * PREREAD_ACTIVE.
 362  * In stripe_handle, if we find pre-reading is necessary, we do it if
 363  * PREREAD_ACTIVE is set, else we set DELAYED which will send it to the delayed queue.
 364  * HANDLE gets cleared if stripe_handle leaves nothing locked.
 365  */
 366
 367
 368 struct disk_info {
 369         struct md_rdev  *rdev, *replacement;
 370 };
 371
 372 /* NOTE NR_STRIPE_HASH_LOCKS must remain below 64.
 373  * This is because we sometimes take all the spinlocks
 374  * and creating that much locking depth can cause
 375  * problems.
 376  */
 377 #define NR_STRIPE_HASH_LOCKS 8
 378 #define STRIPE_HASH_LOCKS_MASK (NR_STRIPE_HASH_LOCKS - 1)
 379
 380 struct r5worker {
 381         struct work_struct work;
 382         struct r5worker_group *group;
 383         struct list_head temp_inactive_list[NR_STRIPE_HASH_LOCKS];
 384         bool working;
 385 };
 386
 387 struct r5worker_group {
 388         struct list_head handle_list;
 389         struct r5conf *conf;
 390         struct r5worker *workers;
 391         int stripes_cnt;
 392 };
 393
 394 struct r5conf {
 395         struct hlist_head       *stripe_hashtbl;
 396         /* only protect corresponding hash list and inactive_list */
 397         spinlock_t              hash_locks[NR_STRIPE_HASH_LOCKS];
 398         struct mddev            *mddev;
 399         int                     chunk_sectors;
 400         int                     level, algorithm;
 401         int                     max_degraded;
 402         int                     raid_disks;
 403         int                     max_nr_stripes;
 404
 405         /* reshape_progress is the leading edge of a 'reshape'
 406          * It has value MaxSector when no reshape is happening
 407          * If delta_disks < 0, it is the last sector we started work on,
 408          * else is it the next sector to work on.
 409          */
 410         sector_t                reshape_progress;
 411         /* reshape_safe is the trailing edge of a reshape.  We know that
 412          * before (or after) this address, all reshape has completed.
 413          */
 414         sector_t                reshape_safe;
 415         int                     previous_raid_disks;
 416         int                     prev_chunk_sectors;
 417         int                     prev_algo;
 418         short                   generation; /* increments with every reshape */
 419         seqcount_t              gen_lock;       /* lock against generation changes */
 420         unsigned long           reshape_checkpoint; /* Time we last updated
 421                                                      * metadata */
 422         long long               min_offset_diff; /* minimum difference between
 423                                                   * data_offset and
 424                                                   * new_data_offset across all
 425                                                   * devices.  May be negative,
 426                                                   * but is closest to zero.
 427                                                   */
 428
 429         struct list_head        handle_list; /* stripes needing handling */
 430         struct list_head        hold_list; /* preread ready stripes */
 431         struct list_head        delayed_list; /* stripes that have plugged requests */
 432         struct list_head        bitmap_list; /* stripes delaying awaiting bitmap update */
 433         struct bio              *retry_read_aligned; /* currently retrying aligned bios   */
 434         struct bio              *retry_read_aligned_list; /* aligned bios retry list  */
 435         atomic_t                preread_active_stripes; /* stripes with scheduled io */
 436         atomic_t                active_aligned_reads;
 437         atomic_t                pending_full_writes; /* full write backlog */
 438         int                     bypass_count; /* bypassed prereads */
 439         int                     bypass_threshold; /* preread nice */
 440         int                     skip_copy; /* Don't copy data from bio to stripe cache */
 441         struct list_head        *last_hold; /* detect hold_list promotions */
 442
 443         atomic_t                reshape_stripes; /* stripes with pending writes for reshape */
 444         /* unfortunately we need two cache names as we temporarily have
 445          * two caches.
 446          */
 447         int                     active_name;
 448         char                    cache_name[2][32];
 449         struct kmem_cache               *slab_cache; /* for allocating stripes */
 450
 451         int                     seq_flush, seq_write;
 452         int                     quiesce;
 453
 454         int                     fullsync;  /* set to 1 if a full sync is needed,
 455                                             * (fresh device added).
 456                                             * Cleared when a sync completes.
 457                                             */
 458         int                     recovery_disabled;
 459         /* per cpu variables */
 460         struct raid5_percpu {
 461                 struct page     *spare_page; /* Used when checking P/Q in raid6 */
 462                 void            *scribble;   /* space for constructing buffer
 463                                               * lists and performing address
 464                                               * conversions
 465                                               */
 466         } __percpu *percpu;
 467         size_t                  scribble_len; /* size of scribble region must be
 468                                                * associated with conf to handle
 469                                                * cpu hotplug while reshaping
 470                                                */
 471 #ifdef CONFIG_HOTPLUG_CPU
 472         struct notifier_block   cpu_notify;
 473 #endif
 474
 475         /*
 476          * Free stripes pool
 477          */
 478         atomic_t                active_stripes;
 479         struct list_head        inactive_list[NR_STRIPE_HASH_LOCKS];
 480         atomic_t                empty_inactive_list_nr;
 481         struct llist_head       released_stripes;
 482         wait_queue_head_t       wait_for_stripe;
 483         wait_queue_head_t       wait_for_overlap;
 484         int                     inactive_blocked;       /* release of inactive stripes blocked,
 485                                                          * waiting for 25% to be free
 486                                                          */
 487         int                     pool_size; /* number of disks in stripeheads in pool */
 488         spinlock_t              device_lock;
 489         struct disk_info        *disks;
 490
 491         /* When taking over an array from a different personality, we store
 492          * the new thread here until we fully activate the array.
 493          */
 494         struct md_thread        *thread;
 495         struct list_head        temp_inactive_list[NR_STRIPE_HASH_LOCKS];
 496         struct r5worker_group   *worker_groups;
 497         int                     group_cnt;
 498         int                     worker_cnt_per_group;
 499 };
 500
 501 /*
 502  * Our supported algorithms
 503  */
 504 #define ALGORITHM_LEFT_ASYMMETRIC       0 /* Rotating Parity N with Data Restart */
 505 #define ALGORITHM_RIGHT_ASYMMETRIC      1 /* Rotating Parity 0 with Data Restart */
 506 #define ALGORITHM_LEFT_SYMMETRIC        2 /* Rotating Parity N with Data Continuation */
 507 #define ALGORITHM_RIGHT_SYMMETRIC       3 /* Rotating Parity 0 with Data Continuation */
 508
 509 /* Define non-rotating (raid4) algorithms.  These allow
 510  * conversion of raid4 to raid5.
 511  */
 512 #define ALGORITHM_PARITY_0              4 /* P or P,Q are initial devices */
 513 #define ALGORITHM_PARITY_N              5 /* P or P,Q are final devices. */
 514
 515 /* DDF RAID6 layouts differ from md/raid6 layouts in two ways.
 516  * Firstly, the exact positioning of the parity block is slightly
 517  * different between the 'LEFT_*' modes of md and the "_N_*" modes
 518  * of DDF.
 519  * Secondly, or order of datablocks over which the Q syndrome is computed
 520  * is different.
 521  * Consequently we have different layouts for DDF/raid6 than md/raid6.
 522  * These layouts are from the DDFv1.2 spec.
 523  * Interestingly DDFv1.2-Errata-A does not specify N_CONTINUE but
 524  * leaves RLQ=3 as 'Vendor Specific'
 525  */
 526
 527 #define ALGORITHM_ROTATING_ZERO_RESTART 8 /* DDF PRL=6 RLQ=1 */
 528 #define ALGORITHM_ROTATING_N_RESTART    9 /* DDF PRL=6 RLQ=2 */
 529 #define ALGORITHM_ROTATING_N_CONTINUE   10 /*DDF PRL=6 RLQ=3 */
 530
 531
 532 /* For every RAID5 algorithm we define a RAID6 algorithm
 533  * with exactly the same layout for data and parity, and
 534  * with the Q block always on the last device (N-1).
 535  * This allows trivial conversion from RAID5 to RAID6
 536  */
 537 #define ALGORITHM_LEFT_ASYMMETRIC_6     16
 538 #define ALGORITHM_RIGHT_ASYMMETRIC_6    17
 539 #define ALGORITHM_LEFT_SYMMETRIC_6      18
 540 #define ALGORITHM_RIGHT_SYMMETRIC_6     19
 541 #define ALGORITHM_PARITY_0_6            20
 542 #define ALGORITHM_PARITY_N_6            ALGORITHM_PARITY_N
 543
 544 static inline int algorithm_valid_raid5(int layout)
 545 {
 546         return (layout >= 0) &&
 547                 (layout <= 5);
 548 }
 549 static inline int algorithm_valid_raid6(int layout)
 550 {
 551         return (layout >= 0 && layout <= 5)
 552                 ||
 553                 (layout >= 8 && layout <= 10)
 554                 ||
 555                 (layout >= 16 && layout <= 20);
 556 }
 557
 558 static inline int algorithm_is_DDF(int layout)
 559 {
 560         return layout >= 8 && layout <= 10;
 561 }
 562
 563 extern int md_raid5_congested(struct mddev *mddev, int bits);
 564 extern void md_raid5_kick_device(struct r5conf *conf);
 565 extern int raid5_set_cache_size(struct mddev *mddev, int size);
 566 #endif