buffmgr.cpp

小型的操作系统开发的原代码

//***********************************************************************/
//    Author                    : Garry
//    Original Date             : Aug,25 2004
//    Module Name               : buffmgr.cpp
//    Module Funciton           : 
//                                This module countains the buffer manager
//                                implementation code.
//    Last modified Author      :
//    Last modified Date        :
//    Last modified Content     :
//                                1.
//                                2.
//    Lines number              :
//***********************************************************************/

#ifndef __STDAFX_H__
#include "..\INCLUDE\StdAfx.h"
#endif

//
//Create buffer routine,used by buffer manager to allocate a new buffer pool,and
//initializes the buffer control block.
//

//The following routine create a buffer pool by calling KMemAlloc.
static BOOL CreateBuffer1(__BUFFER_CONTROL_BLOCK* pControlBlock,DWORD dwPoolSize)
{
	BOOL                     bResult      = FALSE;
	LPVOID                   lpBufferPool = NULL;
	DWORD                    dwSize       = 0L;
	__FREE_BUFFER_HEADER*    pFreeHdr     = NULL;

	dwSize = RoundTo4k(dwPoolSize);
	lpBufferPool = KMemAlloc(dwPoolSize,KMEM_SIZE_TYPE_4K);
	if(NULL == lpBufferPool)                  //Fail to allocate memory.
		goto __TERMINAL;

	pControlBlock->dwPoolSize         = dwSize;  //Initialize the buffer control block.
	pControlBlock->dwFlags           |= CREATED_BY_SELF;
	pControlBlock->dwFlags           |= POOL_INITIALIZED;  //Set the pool initialized bit.
	pControlBlock->lpPoolStartAddress = lpBufferPool;
	pControlBlock->dwFreeSize = dwSize;

	pFreeHdr = (__FREE_BUFFER_HEADER*)lpBufferPool;
	pControlBlock->lpFreeBufferHeader = pFreeHdr;
	pFreeHdr->dwFlags = BUFFER_STATUS_FREE;
	pFreeHdr->lpNextBlock = NULL;
	pFreeHdr->lpPrevBlock = NULL; /*pControlBlock->lpFreeBufferHeader;*/
	pFreeHdr->dwBlockSize = dwSize - sizeof(__FREE_BUFFER_HEADER);
	pControlBlock->dwFreeSize = pFreeHdr->dwBlockSize;

	bResult = TRUE;

__TERMINAL:

	return bResult;
}

//
//The following routine create a buffer pool by using client created memory,and initialize
//the buffer control block.
//

static BOOL CreateBuffer2(__BUFFER_CONTROL_BLOCK* pControlBlock,
						  LPVOID lpBufferPool,
						  DWORD dwPoolSize)
{
	BOOL                     bResult      = FALSE;
	DWORD                    dwSize       = 0L;
	__FREE_BUFFER_HEADER*    pFreeHdr     = NULL;

	dwSize = dwPoolSize;

	pControlBlock->dwPoolSize         = dwSize;  //Initialize the buffer control block.
	pControlBlock->dwFlags           |= CREATED_BY_CLIENT;
	pControlBlock->dwFlags           |= POOL_INITIALIZED;  //Set the pool initialized bit.
	pControlBlock->lpPoolStartAddress = lpBufferPool;

	pFreeHdr = (__FREE_BUFFER_HEADER*)lpBufferPool;
	pControlBlock->lpFreeBufferHeader = pFreeHdr;
	pFreeHdr->dwFlags = BUFFER_STATUS_FREE;
	pFreeHdr->lpNextBlock = NULL;
	pFreeHdr->lpPrevBlock = NULL; /*pControlBlock->lpFreeBufferHeader;*/
	pFreeHdr->dwBlockSize = dwSize - sizeof(__FREE_BUFFER_HEADER);
	pControlBlock->dwFreeSize = pFreeHdr->dwBlockSize;

	bResult = TRUE;

	return bResult;
}

//
//The following is a helper function,it combines continuous free blocks into one
//big free block,and update the other free blocks's data structure,such as lpNextBlock,
//lpPrevBlock.
//

static VOID CombineFreeBlock(__BUFFER_CONTROL_BLOCK* lpControlBlock,  //The control block.
							 LPVOID                  lpStartCombine)  //The first block's
							                                          //address where to
																	  //start combine.
																	  //This function scans
																	  //the buffer pool
																	  //from this position
																	  //to end.
																	  //If this parameter
																	  //is NULL,then start
																	  //at the pool's original
																	  //address,which can
																	  //be get from
																	  //lpControlBlock's member.
{
	LPVOID                   lpEndAddr               = NULL;
	__FREE_BUFFER_HEADER*    lpFreeHeader            = NULL;
	__FREE_BUFFER_HEADER*    lpNextHeader            = NULL;
	__USED_BUFFER_HEADER*    lpUsedHeader            = NULL;
	DWORD	                 dwFlags                 = 0L;

	if(NULL == lpControlBlock)    //Parameters check.
	{
		return;
	}

	//ENTER_CRITICAL_SECTION();    //The following code must not be interrupted.
	__ENTER_CRITICAL_SECTION(NULL,dwFlags);

	lpFreeHeader = (NULL == lpStartCombine) ? (__FREE_BUFFER_HEADER*)(lpControlBlock->lpPoolStartAddress) : 
	                                          (__FREE_BUFFER_HEADER*)lpStartCombine;

    lpEndAddr = (LPVOID)((DWORD)lpControlBlock->lpPoolStartAddress + lpControlBlock->dwPoolSize);

	lpNextHeader = lpFreeHeader ? (__FREE_BUFFER_HEADER*)((DWORD)lpFreeHeader + 
		                          sizeof(__FREE_BUFFER_HEADER) + 
								  lpFreeHeader->dwBlockSize) : NULL;

	while(TRUE)
	{
		if(lpEndAddr == (LPVOID)lpNextHeader)  //Now,seek to the end of the buffer pool.
			break;

		if(lpFreeHeader->dwFlags & BUFFER_STATUS_USED)  //The current block is used.
		{
			lpFreeHeader = lpNextHeader;
			lpNextHeader = (__FREE_BUFFER_HEADER*)((DWORD)lpFreeHeader + 
				                                   sizeof(__USED_BUFFER_HEADER) + 
												   lpFreeHeader->dwBlockSize); //Skip the current block.
			continue;   //Continue to check next block.
		}

		if(lpNextHeader->dwFlags & BUFFER_STATUS_USED) //If the next block is used,then
			                                           //skip two blocks.
		{
			lpFreeHeader = (__FREE_BUFFER_HEADER*)((DWORD)lpNextHeader + 
				                                   sizeof(__FREE_BUFFER_HEADER) + 
												   lpNextHeader->dwBlockSize);

			if((LPVOID)lpFreeHeader == lpEndAddr)  //Seek to the end of the buffer pool.
				break;

			lpNextHeader = (__FREE_BUFFER_HEADER*)((DWORD)lpFreeHeader +
				                                   sizeof(__FREE_BUFFER_HEADER) + 
												   lpFreeHeader->dwBlockSize);
			//lpNextHeader = NULL;
			continue;
		}
		else  //The next block is free too,so we combine the two blocks,and update the
			  //free block list.
		{
			if(NULL == lpNextHeader->lpPrevBlock) //The next block is the first free block.
			{
				lpNextHeader->lpNextBlock->lpPrevBlock = NULL;
				lpControlBlock->lpFreeBufferHeader = lpNextHeader->lpNextBlock;
			}
			else  //The next block is not the first block.
			{
				if(NULL == lpNextHeader->lpNextBlock) //Is the last block.
				{
					lpNextHeader->lpPrevBlock->lpNextBlock = NULL;
				}
				else  //Not the last block.
				{
					lpNextHeader->lpNextBlock->lpPrevBlock = lpNextHeader->lpPrevBlock;
					lpNextHeader->lpPrevBlock->lpNextBlock = lpNextHeader->lpNextBlock;
				}
			}

			lpFreeHeader->dwBlockSize += sizeof(__FREE_BUFFER_HEADER);  //Combine the two block.
			lpFreeHeader->dwBlockSize += lpNextHeader->dwBlockSize;

			lpNextHeader = (__FREE_BUFFER_HEADER*)((DWORD)lpFreeHeader + 
				                                   sizeof(__FREE_BUFFER_HEADER) + 
												   lpFreeHeader->dwBlockSize);

		}
	}

	//LEAVE_CRITICAL_SECTION();
	__LEAVE_CRITICAL_SECTION(NULL,dwFlags);
}

//
//Allocate buffer routine,this routine allocates a buffer from buffer pool,according
//the size of the client request,and returns the start address of the buffer.
//

static LPVOID Allocate(__BUFFER_CONTROL_BLOCK* pControlBlock,DWORD dwSize)
{
	LPVOID                   lpBuffer         = NULL;
	__FREE_BUFFER_HEADER*    lpFreeHeader     = NULL;
	__FREE_BUFFER_HEADER*    lpTmpHeader      = NULL;
	__USED_BUFFER_HEADER*    lpUsedHeader     = NULL;
	DWORD                    dwBoundrySize    = 0L;
	BOOL                     bFind            = FALSE;
	DWORD                    dwFlags          = 0L;

	if((NULL == pControlBlock) || (0 == dwSize))  //Parameters check.
		goto __TERMINAL;

__BEGIN:

	if(dwSize < MIN_BUFFER_SIZE)
		dwSize = MIN_BUFFER_SIZE;

	dwBoundrySize = dwSize + MIN_BUFFER_SIZE + sizeof(__FREE_BUFFER_HEADER);

	//ENTER_CRITICAL_SECTION();    //The following operation must not be interrupted.
	__ENTER_CRITICAL_SECTION(NULL,dwFlags);

	lpFreeHeader = pControlBlock->lpFreeBufferHeader;
	while(lpFreeHeader)
	{
		if(lpFreeHeader->dwBlockSize < dwSize)   //The current block is not fitable.
		{
			lpFreeHeader = lpFreeHeader->lpNextBlock;
			continue;