/*
 * extmem.h
 * Zhaonian Zou
 * Harbin Institute of Technology
 * Jun 22, 2011
 */

#ifndef EXTMEM_H
#define EXTMEM_H

#define BLOCK_AVAILABLE 0
#define BLOCK_UNAVAILABLE 1

typedef struct tagBuffer {
    unsigned long numIO;    // 外存 I/O 次数
    size_t bufSize;         // 缓冲区大小（单位：字节）
    size_t blkSize;         // 块的大小（单位：字节）
    size_t numAllBlk;       // 缓冲区内可存放的最多块数
    size_t numFreeBlk;      // 缓冲区内可用的块数
    unsigned char *data;    // 缓冲区内存区域
} Buffer;

/* Initialize a buffer with the specified buffer size and block size.
 * If the initialization fails, the return value is NULL;
 * otherwise the pointer to the buffer.
 */
Buffer *initBuffer(size_t bufSize, size_t blkSize, Buffer *buf);

/* Free the memory used by a buffer. */
void freeBuffer(Buffer *buf);

/* Apply for a new block from a buffer.
 * If no free blocks are available in the buffer,
 * then the return value is NULL; otherwise the pointer to the block.
 */
unsigned char *getNewBlockInBuffer(Buffer *buf);

/* Set a block in a buffer to be available. */
void freeBlockInBuffer(unsigned char *blk, Buffer *buf);

/* Drop a block on the disk */
int dropBlockOnDisk(unsigned int addr);

/* Read a block from the hard disk to the buffer by the address of the block. */
unsigned char *readBlockFromDisk(unsigned int addr, Buffer *buf);

/* Read a block in the buffer to the hard disk by the address of the block. */
int writeBlockToDisk(unsigned char *blkPtr, unsigned int addr, Buffer *buf);

#endif // EXTMEM_H