bitmap.h

   1 /*
   2  * bitmap.h: Copyright (C) Peter T. Breuer (ptb@ot.uc3m.es) 2003
   3  *
   4  * additions: Copyright (C) 2003-2004, Paul Clements, SteelEye Technology, Inc.
   5  */
   6 #ifndef BITMAP_H
   7 #define BITMAP_H 1
   8
   9 #define BITMAP_MAJOR_LO 3
  10 /* version 4 insists the bitmap is in little-endian order
  11  * with version 3, it is host-endian which is non-portable
  12  */
  13 #define BITMAP_MAJOR_HI 4
  14 #define BITMAP_MAJOR_HOSTENDIAN 3
  15
  16 #define BITMAP_MINOR 39
  17
  18 /*
  19  * in-memory bitmap:
  20  *
  21  * Use 16 bit block counters to track pending writes to each "chunk".
  22  * The 2 high order bits are special-purpose, the first is a flag indicating
  23  * whether a resync is needed.  The second is a flag indicating whether a
  24  * resync is active.
  25  * This means that the counter is actually 14 bits:
  26  *
  27  * +--------+--------+------------------------------------------------+
  28  * | resync | resync |               counter                          |
  29  * | needed | active |                                                |
  30  * |  (0-1) |  (0-1) |              (0-16383)                         |
  31  * +--------+--------+------------------------------------------------+
  32  *
  33  * The "resync needed" bit is set when:
  34  *    a '1' bit is read from storage at startup.
  35  *    a write request fails on some drives
  36  *    a resync is aborted on a chunk with 'resync active' set
  37  * It is cleared (and resync-active set) when a resync starts across all drives
  38  * of the chunk.
  39  *
  40  *
  41  * The "resync active" bit is set when:
  42  *    a resync is started on all drives, and resync_needed is set.
  43  *       resync_needed will be cleared (as long as resync_active wasn't already set).
  44  * It is cleared when a resync completes.
  45  *
  46  * The counter counts pending write requests, plus the on-disk bit.
  47  * When the counter is '1' and the resync bits are clear, the on-disk
  48  * bit can be cleared aswell, thus setting the counter to 0.
  49  * When we set a bit, or in the counter (to start a write), if the fields is
  50  * 0, we first set the disk bit and set the counter to 1.
  51  *
  52  * If the counter is 0, the on-disk bit is clear and the stipe is clean
  53  * Anything that dirties the stipe pushes the counter to 2 (at least)
  54  * and sets the on-disk bit (lazily).
  55  * If a periodic sweep find the counter at 2, it is decremented to 1.
  56  * If the sweep find the counter at 1, the on-disk bit is cleared and the
  57  * counter goes to zero.
  58  *
  59  * Also, we'll hijack the "map" pointer itself and use it as two 16 bit block
  60  * counters as a fallback when "page" memory cannot be allocated:
  61  *
  62  * Normal case (page memory allocated):
  63  *
  64  *     page pointer (32-bit)
  65  *
  66  *     [ ] ------+
  67  *               |
  68  *               +-------> [   ][   ]..[   ] (4096 byte page == 2048 counters)
  69  *                          c1   c2    c2048
  70  *
  71  * Hijacked case (page memory allocation failed):
  72  *
  73  *     hijacked page pointer (32-bit)
  74  *
  75  *     [                  ][              ] (no page memory allocated)
  76  *      counter #1 (16-bit) counter #2 (16-bit)
  77  *
  78  */
  79
  80 #ifdef __KERNEL__
  81
  82 #define PAGE_BITS (PAGE_SIZE << 3)
  83 #define PAGE_BIT_SHIFT (PAGE_SHIFT + 3)
  84
  85 typedef __u16 bitmap_counter_t;
  86 #define COUNTER_BITS 16
  87 #define COUNTER_BIT_SHIFT 4
  88 #define COUNTER_BYTE_RATIO (COUNTER_BITS / 8)
  89 #define COUNTER_BYTE_SHIFT (COUNTER_BIT_SHIFT - 3)
  90
  91 #define NEEDED_MASK ((bitmap_counter_t) (1 << (COUNTER_BITS - 1)))
  92 #define RESYNC_MASK ((bitmap_counter_t) (1 << (COUNTER_BITS - 2)))
  93 #define COUNTER_MAX ((bitmap_counter_t) RESYNC_MASK - 1)
  94 #define NEEDED(x) (((bitmap_counter_t) x) & NEEDED_MASK)
  95 #define RESYNC(x) (((bitmap_counter_t) x) & RESYNC_MASK)
  96 #define COUNTER(x) (((bitmap_counter_t) x) & COUNTER_MAX)
  97
  98 /* how many counters per page? */
  99 #define PAGE_COUNTER_RATIO (PAGE_BITS / COUNTER_BITS)
 100 /* same, except a shift value for more efficient bitops */
 101 #define PAGE_COUNTER_SHIFT (PAGE_BIT_SHIFT - COUNTER_BIT_SHIFT)
 102 /* same, except a mask value for more efficient bitops */
 103 #define PAGE_COUNTER_MASK  (PAGE_COUNTER_RATIO - 1)
 104
 105 #define BITMAP_BLOCK_SIZE 512
 106 #define BITMAP_BLOCK_SHIFT 9
 107
 108 /* how many blocks per chunk? (this is variable) */
 109 #define CHUNK_BLOCK_RATIO(bitmap) ((bitmap)->chunksize >> BITMAP_BLOCK_SHIFT)
 110 #define CHUNK_BLOCK_SHIFT(bitmap) ((bitmap)->chunkshift - BITMAP_BLOCK_SHIFT)
 111 #define CHUNK_BLOCK_MASK(bitmap) (CHUNK_BLOCK_RATIO(bitmap) - 1)
 112
 113 /* when hijacked, the counters and bits represent even larger "chunks" */
 114 /* there will be 1024 chunks represented by each counter in the page pointers */
 115 #define PAGEPTR_BLOCK_RATIO(bitmap) \
 116                         (CHUNK_BLOCK_RATIO(bitmap) << PAGE_COUNTER_SHIFT >> 1)
 117 #define PAGEPTR_BLOCK_SHIFT(bitmap) \
 118                         (CHUNK_BLOCK_SHIFT(bitmap) + PAGE_COUNTER_SHIFT - 1)
 119 #define PAGEPTR_BLOCK_MASK(bitmap) (PAGEPTR_BLOCK_RATIO(bitmap) - 1)
 120
 121 /*
 122  * on-disk bitmap:
 123  *
 124  * Use one bit per "chunk" (block set). We do the disk I/O on the bitmap
 125  * file a page at a time. There's a superblock at the start of the file.
 126  */
 127
 128 /* map chunks (bits) to file pages - offset by the size of the superblock */
 129 #define CHUNK_BIT_OFFSET(chunk) ((chunk) + (sizeof(bitmap_super_t) << 3))
 130
 131 #endif
 132
 133 /*
 134  * bitmap structures:
 135  */
 136
 137 #define BITMAP_MAGIC 0x6d746962
 138
 139 /* use these for bitmap->flags and bitmap->sb->state bit-fields */
 140 enum bitmap_state {
 141         BITMAP_ACTIVE = 0x001, /* the bitmap is in use */
 142         BITMAP_STALE  = 0x002  /* the bitmap file is out of date or had -EIO */
 143 };
 144
 145 /* the superblock at the front of the bitmap file -- little endian */
 146 typedef struct bitmap_super_s {
 147         __u32 magic;        /*  0  BITMAP_MAGIC */
 148         __u32 version;      /*  4  the bitmap major for now, could change... */
 149         __u8  uuid[16];     /*  8  128 bit uuid - must match md device uuid */
 150         __u64 events;       /* 24  event counter for the bitmap (1)*/
 151         __u64 events_cleared;/*32  event counter when last bit cleared (2) */
 152         __u64 sync_size;    /* 40  the size of the md device's sync range(3) */
 153         __u32 state;        /* 48  bitmap state information */
 154         __u32 chunksize;    /* 52  the bitmap chunk size in bytes */
 155         __u32 daemon_sleep; /* 56  seconds between disk flushes */
 156         __u32 write_behind; /* 60  number of outstanding write-behind writes */
 157
 158         __u8  pad[256 - 64]; /* set to zero */
 159 } bitmap_super_t;
 160
 161 /* notes:
 162  * (1) This event counter is updated before the eventcounter in the md superblock
 163  *    When a bitmap is loaded, it is only accepted if this event counter is equal
 164  *    to, or one greater than, the event counter in the superblock.
 165  * (2) This event counter is updated when the other one is *if*and*only*if* the
 166  *    array is not degraded.  As bits are not cleared when the array is degraded,
 167  *    this represents the last time that any bits were cleared.
 168  *    If a device is being added that has an event count with this value or
 169  *    higher, it is accepted as conforming to the bitmap.
 170  * (3)This is the number of sectors represented by the bitmap, and is the range that
 171  *    resync happens across.  For raid1 and raid5/6 it is the size of individual
 172  *    devices.  For raid10 it is the size of the array.
 173  */
 174
 175 #ifdef __KERNEL__
 176
 177 /* the in-memory bitmap is represented by bitmap_pages */
 178 struct bitmap_page {
 179         /*
 180          * map points to the actual memory page
 181          */
 182         char *map;
 183         /*
 184          * in emergencies (when map cannot be alloced), hijack the map
 185          * pointer and use it as two counters itself
 186          */
 187         unsigned int hijacked;
 188         /*
 189          * count of dirty bits on the page
 190          */
 191         int count;
 192 };
 193
 194 /* keep track of bitmap file pages that have pending writes on them */
 195 struct page_list {
 196         struct list_head list;
 197         struct page *page;
 198 };
 199
 200 /* the main bitmap structure - one per mddev */
 201 struct bitmap {
 202         struct bitmap_page *bp;
 203         unsigned long pages; /* total number of pages in the bitmap */
 204         unsigned long missing_pages; /* number of pages not yet allocated */
 205
 206         mddev_t *mddev; /* the md device that the bitmap is for */
 207
 208         int counter_bits; /* how many bits per block counter */
 209
 210         /* bitmap chunksize -- how much data does each bit represent? */
 211         unsigned long chunksize;
 212         unsigned long chunkshift; /* chunksize = 2^chunkshift (for bitops) */
 213         unsigned long chunks; /* total number of data chunks for the array */
 214
 215         /* We hold a count on the chunk currently being synced, and drop
 216          * it when the last block is started.  If the resync is aborted
 217          * midway, we need to be able to drop that count, so we remember
 218          * the counted chunk..
 219          */
 220         unsigned long syncchunk;
 221
 222         __u64   events_cleared;
 223
 224         /* bitmap spinlock */
 225         spinlock_t lock;
 226
 227         struct file *file; /* backing disk file */
 228         struct page *sb_page; /* cached copy of the bitmap file superblock */
 229         struct page **filemap; /* list of cache pages for the file */
 230         unsigned long *filemap_attr; /* attributes associated w/ filemap pages */
 231         unsigned long file_pages; /* number of pages in the file */
 232
 233         unsigned long flags;
 234
 235         /*
 236          * the bitmap daemon - periodically wakes up and sweeps the bitmap
 237          * file, cleaning up bits and flushing out pages to disk as necessary
 238          */
 239         mdk_thread_t *daemon;
 240         unsigned long daemon_sleep; /* how many seconds between updates? */
 241
 242         /*
 243          * bitmap write daemon - this daemon performs writes to the bitmap file
 244          * this thread is only needed because of a limitation in ext3 (jbd)
 245          * that does not allow a task to have two journal transactions ongoing
 246          * simultaneously (even if the transactions are for two different
 247          * filesystems) -- in the case of bitmap, that would be the filesystem
 248          * that the bitmap file resides on and the filesystem that is mounted
 249          * on the md device -- see current->journal_info in jbd/transaction.c
 250          */
 251         mdk_thread_t *write_daemon;
 252         mdk_thread_t *writeback_daemon;
 253         spinlock_t write_lock;
 254         struct semaphore write_ready;
 255         struct semaphore write_done;
 256         unsigned long writes_pending;
 257         wait_queue_head_t write_wait;
 258         struct list_head write_pages;
 259         struct list_head complete_pages;
 260         mempool_t *write_pool;
 261 };
 262
 263 /* the bitmap API */
 264
 265 /* these are used only by md/bitmap */
 266 int  bitmap_create(mddev_t *mddev);
 267 void bitmap_destroy(mddev_t *mddev);
 268 int  bitmap_active(struct bitmap *bitmap);
 269
 270 char *file_path(struct file *file, char *buf, int count);
 271 void bitmap_print_sb(struct bitmap *bitmap);
 272 int bitmap_update_sb(struct bitmap *bitmap);
 273
 274 int  bitmap_setallbits(struct bitmap *bitmap);
 275
 276 /* these are exported */
 277 void bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors);
 278 void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long sectors,
 279                      int success);
 280 int bitmap_start_sync(struct bitmap *bitmap, sector_t offset, int *blocks);
 281 void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, int *blocks, int aborted);
 282 void bitmap_close_sync(struct bitmap *bitmap);
 283
 284 int bitmap_unplug(struct bitmap *bitmap);
 285 #endif
 286
 287 #endif