drivers/md/dm-snap.h

   1 /*
   2  * dm-snapshot.c
   3  *
   4  * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
   5  *
   6  * This file is released under the GPL.
   7  */
   8
   9 #ifndef DM_SNAPSHOT_H
  10 #define DM_SNAPSHOT_H
  11
  12 #include "dm.h"
  13 #include <linux/blkdev.h>
  14
  15 struct exception_table {
  16         uint32_t hash_mask;
  17         struct list_head *table;
  18 };
  19
  20 /*
  21  * The snapshot code deals with largish chunks of the disk at a
  22  * time. Typically 64k - 256k.
  23  */
  24 /* FIXME: can we get away with limiting these to a uint32_t ? */
  25 typedef sector_t chunk_t;
  26
  27 /*
  28  * An exception is used where an old chunk of data has been
  29  * replaced by a new one.
  30  */
  31 struct exception {
  32         struct list_head hash_list;
  33
  34         chunk_t old_chunk;
  35         chunk_t new_chunk;
  36 };
  37
  38 /*
  39  * Abstraction to handle the meta/layout of exception stores (the
  40  * COW device).
  41  */
  42 struct exception_store {
  43
  44         /*
  45          * Destroys this object when you've finished with it.
  46          */
  47         void (*destroy) (struct exception_store *store);
  48
  49         /*
  50          * The target shouldn't read the COW device until this is
  51          * called.
  52          */
  53         int (*read_metadata) (struct exception_store *store);
  54
  55         /*
  56          * Find somewhere to store the next exception.
  57          */
  58         int (*prepare_exception) (struct exception_store *store,
  59                                   struct exception *e);
  60
  61         /*
  62          * Update the metadata with this exception.
  63          */
  64         void (*commit_exception) (struct exception_store *store,
  65                                   struct exception *e,
  66                                   void (*callback) (void *, int success),
  67                                   void *callback_context);
  68
  69         /*
  70          * The snapshot is invalid, note this in the metadata.
  71          */
  72         void (*drop_snapshot) (struct exception_store *store);
  73
  74         /*
  75          * Return how full the snapshot is.
  76          */
  77         void (*fraction_full) (struct exception_store *store,
  78                                sector_t *numerator,
  79                                sector_t *denominator);
  80
  81         struct dm_snapshot *snap;
  82         void *context;
  83 };
  84
  85 struct dm_snapshot {
  86         struct rw_semaphore lock;
  87         struct dm_table *table;
  88
  89         struct dm_dev *origin;
  90         struct dm_dev *cow;
  91
  92         /* List of snapshots per Origin */
  93         struct list_head list;
  94
  95         /* Size of data blocks saved - must be a power of 2 */
  96         chunk_t chunk_size;
  97         chunk_t chunk_mask;
  98         chunk_t chunk_shift;
  99
 100         /* You can't use a snapshot if this is 0 (e.g. if full) */
 101         int valid;
 102
 103         /* Origin writes don't trigger exceptions until this is set */
 104         int active;
 105
 106         /* Used for display of table */
 107         char type;
 108
 109         /* The last percentage we notified */
 110         int last_percent;
 111
 112         struct exception_table pending;
 113         struct exception_table complete;
 114
 115         /* The on disk metadata handler */
 116         struct exception_store store;
 117
 118         struct kcopyd_client *kcopyd_client;
 119 };
 120
 121 /*
 122  * Used by the exception stores to load exceptions hen
 123  * initialising.
 124  */
 125 int dm_add_exception(struct dm_snapshot *s, chunk_t old, chunk_t new);
 126
 127 /*
 128  * Constructor and destructor for the default persistent
 129  * store.
 130  */
 131 int dm_create_persistent(struct exception_store *store, uint32_t chunk_size);
 132
 133 int dm_create_transient(struct exception_store *store,
 134                         struct dm_snapshot *s, int blocksize);
 135
 136 /*
 137  * Return the number of sectors in the device.
 138  */
 139 static inline sector_t get_dev_size(struct block_device *bdev)
 140 {
 141         return bdev->bd_inode->i_size >> SECTOR_SHIFT;
 142 }
 143
 144 static inline chunk_t sector_to_chunk(struct dm_snapshot *s, sector_t sector)
 145 {
 146         return (sector & ~s->chunk_mask) >> s->chunk_shift;
 147 }
 148
 149 static inline sector_t chunk_to_sector(struct dm_snapshot *s, chunk_t chunk)
 150 {
 151         return chunk << s->chunk_shift;
 152 }
 153
 154 static inline int bdev_equal(struct block_device *lhs, struct block_device *rhs)
 155 {
 156         /*
 157          * There is only ever one instance of a particular block
 158          * device so we can compare pointers safely.
 159          */
 160         return lhs == rhs;
 161 }
 162
 163 #endif