include/linux/raid/raid5.h

   1 #ifndef _RAID5_H
   2 #define _RAID5_H
   3
   4 #include <linux/raid/md.h>
   5 #include <linux/raid/xor.h>
   6
   7 /*
   8  *
   9  * Each stripe contains one buffer per disc.  Each buffer can be in
  10  * one of a number of states stored in "flags".  Changes between
  11  * these states happen *almost* exclusively under a per-stripe
  12  * spinlock.  Some very specific changes can happen in bi_end_io, and
  13  * these are not protected by the spin lock.
  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.(RECONSTRUCT_WRITE)
  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 distingush 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 is
  80  * protected by the device_lock.  The write and written lists are
  81  * protected by the stripe lock.  The device_lock, which can be
  82  * claimed while the stipe lock is held, is only for list
  83  * manipulations and will only be held for a very short time.  It can
  84  * be claimed from interrupts.
  85  *
  86  *
  87  * Stripes in the stripe cache can be on one of two lists (or on
  88  * neither).  The "inactive_list" contains stripes which are not
  89  * currently being used for any request.  They can freely be reused
  90  * for another stripe.  The "handle_list" contains stripes that need
  91  * to be handled in some way.  Both of these are fifo queues.  Each
  92  * stripe is also (potentially) linked to a hash bucket in the hash
  93  * table so that it can be found by sector number.  Stripes that are
  94  * not hashed must be on the inactive_list, and will normally be at
  95  * the front.  All stripes start life this way.
  96  *
  97  * The inactive_list, handle_list and hash bucket lists are all protected by the
  98  * device_lock.
  99  *  - stripes on the inactive_list never have their stripe_lock held.
 100  *  - stripes have a reference counter. If count==0, they are on a list.
 101  *  - If a stripe might need handling, STRIPE_HANDLE is set.
 102  *  - When refcount reaches zero, then if STRIPE_HANDLE it is put on
 103  *    handle_list else inactive_list
 104  *
 105  * This, combined with the fact that STRIPE_HANDLE is only ever
 106  * cleared while a stripe has a non-zero count means that if the
 107  * refcount is 0 and STRIPE_HANDLE is set, then it is on the
 108  * handle_list and if recount is 0 and STRIPE_HANDLE is not set, then
 109  * the stripe is on inactive_list.
 110  *
 111  * The possible transitions are:
 112  *  activate an unhashed/inactive stripe (get_active_stripe())
 113  *     lockdev check-hash unlink-stripe cnt++ clean-stripe hash-stripe unlockdev
 114  *  activate a hashed, possibly active stripe (get_active_stripe())
 115  *     lockdev check-hash if(!cnt++)unlink-stripe unlockdev
 116  *  attach a request to an active stripe (add_stripe_bh())
 117  *     lockdev attach-buffer unlockdev
 118  *  handle a stripe (handle_stripe())
 119  *     lockstripe clrSTRIPE_HANDLE ... (lockdev check-buffers unlockdev) .. change-state .. record io needed unlockstripe schedule io
 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.
 126  */
 127
 128 struct stripe_head {
 129         struct stripe_head      *hash_next, **hash_pprev; /* hash pointers */
 130         struct list_head        lru;                    /* inactive_list or handle_list */
 131         struct raid5_private_data       *raid_conf;
 132         sector_t                sector;                 /* sector of this row */
 133         int                     pd_idx;                 /* parity disk index */
 134         unsigned long           state;                  /* state flags */
 135         atomic_t                count;                  /* nr of active thread/requests */
 136         spinlock_t              lock;
 137         struct r5dev {
 138                 struct bio      req;
 139                 struct bio_vec  vec;
 140                 struct page     *page;
 141                 struct bio      *toread, *towrite, *written;
 142                 sector_t        sector;                 /* sector of this page */
 143                 unsigned long   flags;
 144         } dev[1]; /* allocated with extra space depending of RAID geometry */
 145 };
 146 /* Flags */
 147 #define R5_UPTODATE     0       /* page contains current data */
 148 #define R5_LOCKED       1       /* IO has been submitted on "req" */
 149 #define R5_OVERWRITE    2       /* towrite covers whole page */
 150 /* and some that are internal to handle_stripe */
 151 #define R5_Insync       3       /* rdev && rdev->in_sync at start */
 152 #define R5_Wantread     4       /* want to schedule a read */
 153 #define R5_Wantwrite    5
 154 #define R5_Syncio       6       /* this io need to be accounted as resync io */
 155 #define R5_Overlap      7       /* There is a pending overlapping request on this block */
 156
 157 /*
 158  * Write method
 159  */
 160 #define RECONSTRUCT_WRITE       1
 161 #define READ_MODIFY_WRITE       2
 162 /* not a write method, but a compute_parity mode */
 163 #define CHECK_PARITY            3
 164
 165 /*
 166  * Stripe state
 167  */
 168 #define STRIPE_ERROR            1
 169 #define STRIPE_HANDLE           2
 170 #define STRIPE_SYNCING          3
 171 #define STRIPE_INSYNC           4
 172 #define STRIPE_PREREAD_ACTIVE   5
 173 #define STRIPE_DELAYED          6
 174
 175 /*
 176  * Plugging:
 177  *
 178  * To improve write throughput, we need to delay the handling of some
 179  * stripes until there has been a chance that several write requests
 180  * for the one stripe have all been collected.
 181  * In particular, any write request that would require pre-reading
 182  * is put on a "delayed" queue until there are no stripes currently
 183  * in a pre-read phase.  Further, if the "delayed" queue is empty when
 184  * a stripe is put on it then we "plug" the queue and do not process it
 185  * until an unplug call is made. (the unplug_io_fn() is called).
 186  *
 187  * When preread is initiated on a stripe, we set PREREAD_ACTIVE and add
 188  * it to the count of prereading stripes.
 189  * When write is initiated, or the stripe refcnt == 0 (just in case) we
 190  * clear the PREREAD_ACTIVE flag and decrement the count
 191  * Whenever the delayed queue is empty and the device is not plugged, we
 192  * move any strips from delayed to handle and clear the DELAYED flag and set PREREAD_ACTIVE.
 193  * In stripe_handle, if we find pre-reading is necessary, we do it if
 194  * PREREAD_ACTIVE is set, else we set DELAYED which will send it to the delayed queue.
 195  * HANDLE gets cleared if stripe_handle leave nothing locked.
 196  */
 197
 198
 199 struct disk_info {
 200         mdk_rdev_t      *rdev;
 201 };
 202
 203 struct raid5_private_data {
 204         struct stripe_head      **stripe_hashtbl;
 205         mddev_t                 *mddev;
 206         struct disk_info        *spare;
 207         int                     chunk_size, level, algorithm;
 208         int                     raid_disks, working_disks, failed_disks;
 209         int                     max_nr_stripes;
 210
 211         struct list_head        handle_list; /* stripes needing handling */
 212         struct list_head        delayed_list; /* stripes that have plugged requests */
 213         atomic_t                preread_active_stripes; /* stripes with scheduled io */
 214
 215         char                    cache_name[20];
 216         kmem_cache_t            *slab_cache; /* for allocating stripes */
 217         /*
 218          * Free stripes pool
 219          */
 220         atomic_t                active_stripes;
 221         struct list_head        inactive_list;
 222         wait_queue_head_t       wait_for_stripe;
 223         wait_queue_head_t       wait_for_overlap;
 224         int                     inactive_blocked;       /* release of inactive stripes blocked,
 225                                                          * waiting for 25% to be free
 226                                                          */
 227         spinlock_t              device_lock;
 228         struct disk_info        disks[0];
 229 };
 230
 231 typedef struct raid5_private_data raid5_conf_t;
 232
 233 #define mddev_to_conf(mddev) ((raid5_conf_t *) mddev->private)
 234
 235 /*
 236  * Our supported algorithms
 237  */
 238 #define ALGORITHM_LEFT_ASYMMETRIC       0
 239 #define ALGORITHM_RIGHT_ASYMMETRIC      1
 240 #define ALGORITHM_LEFT_SYMMETRIC        2
 241 #define ALGORITHM_RIGHT_SYMMETRIC       3
 242
 243 #endif