rom/filesys/SFS/FS/cachebuffers.h

   1 #ifndef _CACHEBUFFERS_H
   2 #define _CACHEBUFFERS_H
   3
   4 #include <exec/nodes.h>
   5 #include <exec/types.h>
   6
   7 struct CacheBuffer {
   8   /* Keep the below two structures in this order.  There is no support for linking
   9      structures in two different lists properly, so to find the start of the CacheBuffer
  10      structure in the case of the 2nd MinNode we substract a few bytes from it. */
  11
  12   struct MinNode node;               // LRU link
  13   struct MinNode hashnode;           // Linked chain of blocks with same hash value
  14
  15   UBYTE locked;                      // 0 if unlocked.
  16   UBYTE bits;                        /* Bit 0: Set means this block is original.
  17                                         Bit 1: Set means this block is the latest version.
  18                                         Bit 2: Set means that this block has an empty original.
  19                                         Bit 3: Set means that this block was checksummed correctly. */
  20   UWORD id;                          // a 2-byte id code used to check if this really IS a cachebuffer...
  21
  22   ULONG blckno;                      // Partition Blocknumber, or zero if this block isn't in use
  23
  24   void *data;                        /* Make sure this is LONGWORD aligned! */
  25
  26   UBYTE attached_data[0];
  27 };
  28
  29 #define CB_ORIGINAL (1)
  30 #define CB_LATEST   (2)
  31 #define CB_EMPTY    (4)
  32 #define CB_CHECKSUM (8)
  33
  34 /*
  35   CB_ORIGINAL          : This CacheBuffer contains a block exactly like it is currently on disk.
  36
  37   CB_LATEST            : This CacheBuffer contains the latest version of a block (ie, including
  38                          modifications made during a transaction).
  39
  40   CB_LATEST | CB_EMPTY : Same as CB_LATEST, but the block has no original version (it was based
  41                          on an as of yet unallocated block).
  42
  43   Other combinations of CB_LATEST, CB_ORIGINAL and CB_EMPTY are invalid.
  44
  45   An exception to this rule could be none set at all, which would indicate an unused cachebuffer.
  46 */
  47
  48 #endif // _CACHEBUFFERS_H