buffer.c - platform/external/mtools - Gitiles

 /*  Copyright 1997,2001-2003 Alain Knaff.
  *  This file is part of mtools.
  *
  *  Mtools is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation, either version 3 of the License, or
  *  (at your option) any later version.
  *
  *  Mtools is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License
  *  along with Mtools.  If not, see <http://www.gnu.org/licenses/>.
  *
  * Buffer read/write module
  */

 #include "sysincludes.h"
 #include "msdos.h"
 #include "mtools.h"
 #include "buffer.h"

 typedef struct Buffer_t {
 	struct Stream_t head;

 	size_t size;     	/* size of read/write buffer */
 	int dirty;	       	/* is the buffer dirty? */

 	size_t sectorSize;	/* sector size: all operations happen
 				 * in multiples of this */
 	size_t cylinderSize;	/* cylinder size: preferred alignment,
 				 * but for efficiency, less data may be read */
 	int ever_dirty;	       	/* was the buffer ever dirty? */
 	size_t dirty_pos;
 	size_t dirty_end;
 	mt_off_t current;	/* first sector in buffer */
 	size_t cur_size;	/* the current size */
 	char *buf;		/* disk read/write buffer */
 } Buffer_t;

 /* Convert position relative to buffer to absolute position */
 static mt_off_t abs_pos(Buffer_t *Buffer, size_t rel) {
 	return Buffer->current + (mt_off_t) rel;
 }

 /* End of currently valid buffer */
 static mt_off_t cur_end(Buffer_t *Buffer) {
 	return abs_pos(Buffer, Buffer->cur_size);
 }

 /* distance from absolute position until next full cylinder. If position already
  * *is* on a full cylinder boundary, return size of full cylinder */
 static size_t pos_to_next_full_cyl(Buffer_t *Buffer, mt_off_t pos) {
 	return Buffer->cylinderSize -
 		(size_t) (pos % (mt_off_t) Buffer->cylinderSize);
 }

 /*
  * Flush a dirty buffer to disk.  Resets Buffer->dirty to zero.
  * All errors are fatal.
  */

 static int _buf_flush(Buffer_t *Buffer)
 {
 	ssize_t ret;

 #ifdef HAVE_ASSERT_H
 	assert(Buffer->head.Next != NULL);
 #endif

 	if (!Buffer->dirty)
 		return 0;
 #ifdef DEBUG
 	fprintf(stderr, "write %08x -- %02x %08x %08x\n",
 		Buffer,
 		(unsigned char) Buffer->buf[0],
 		Buffer->current + Buffer->dirty_pos,
 		Buffer->dirty_end - Buffer->dirty_pos);
 #endif

 	ret = force_pwrite(Buffer->head.Next,
 			   Buffer->buf + Buffer->dirty_pos,
 			   Buffer->current + (mt_off_t) Buffer->dirty_pos,
 			   Buffer->dirty_end - Buffer->dirty_pos);
 	if(ret < 0) {
 		perror("buffer_flush: write");
 		return -1;
 	}

 	if((size_t) ret != Buffer->dirty_end - Buffer->dirty_pos) {
 		fprintf(stderr,"buffer_flush: short write\n");
 		return -1;
 	}
 	Buffer->dirty = 0;
 	Buffer->dirty_end = 0;
 	Buffer->dirty_pos = 0;
 	return 0;
 }

 static int invalidate_buffer(Buffer_t *Buffer, mt_off_t start)
 {
 	if(_buf_flush(Buffer) < 0)
 		return -1;

 	/* start reading at the beginning of start's sector
 	 * don't start reading too early, or we might not even reach
 	 * start */
 	Buffer->current = ROUND_DOWN(start, (mt_off_t) Buffer->sectorSize);
 	Buffer->cur_size = 0;
 	return 0;
 }

 #undef OFFSET
 #define OFFSET ((size_t)(start - This->current))

 typedef enum position_t {
 	OUTSIDE,
 	APPEND,
 	INSIDE,
 	ERROR
 } position_t;

 static position_t isInBuffer(Buffer_t *This, mt_off_t start, size_t *len)
 {
 	if(start >= This->current && start < cur_end(This)) {
 		maximize(*len, This->cur_size - OFFSET);
 		return INSIDE;
 	} else if(start == cur_end(This) &&
 		  This->cur_size < This->size &&
 		  *len >= This->sectorSize) {
 		/* append to the buffer for this, three conditions have to
 		 * be met:
 		 *  1. The start falls exactly at the end of the currently
 		 *     loaded data
 		 *  2. There is still space
 		 *  3. We append at least one sector
 		 */
 		maximize(*len, This->size - This->cur_size);
 		*len = ROUND_DOWN(*len, This->sectorSize);
 		return APPEND;
 	} else {
 		if(invalidate_buffer(This, start) < 0)
 			return ERROR;
 		maximize(*len, This->cylinderSize - OFFSET);
 		maximize(*len, pos_to_next_full_cyl(This, This->current));
 		return OUTSIDE;
 	}
 }

 static ssize_t buf_pread(Stream_t *Stream, char *buf,
 			 mt_off_t start, size_t len)
 {
 	size_t length;
 	size_t offset;
 	char *disk_ptr;
 	ssize_t ret;
 	DeclareThis(Buffer_t);

 	if(!len)
 		return 0;

 	/*fprintf(stderr, "buf read %x   %x %x\n", Stream, start, len);*/
 	switch(isInBuffer(This, start, &len)) {
 		case OUTSIDE:
 		case APPEND:
 			/* always load until the end of the cylinder */
 			length = pos_to_next_full_cyl(This, cur_end(This));
 			maximize(length, This->size - This->cur_size);

 			/* read it! */
 			ret=PREADS(This->head.Next,
 				   This->buf + This->cur_size,
 				   This->current + (mt_off_t) This->cur_size,
 				   length);
 			if ( ret < 0 )
 				return ret;
 			This->cur_size += (size_t) ret;
 			if (This->current+(mt_off_t)This->cur_size < start) {
 				fprintf(stderr, "Short buffer fill\n");
 				exit(1);
 			}
 			break;
 		case INSIDE:
 			/* nothing to do */
 			break;
 		case ERROR:
 			return -1;
 	}

 	offset = OFFSET;
 	disk_ptr = This->buf + offset;
 	maximize(len, This->cur_size - offset);
 	memcpy(buf, disk_ptr, len);
 	return (ssize_t) len;
 }

 static ssize_t buf_pwrite(Stream_t *Stream, char *buf,
 			  mt_off_t start, size_t len)
 {
 	char *disk_ptr;
 	DeclareThis(Buffer_t);
 	size_t offset=0;

 	if(!len)
 		return 0;

 	This->ever_dirty = 1;

 #ifdef DEBUG
 	fprintf(stderr, "buf write %x   %02x %08x %08x -- %08x %08x -- %08x\n",
 		Stream, (unsigned char) This->buf[0],
 		start, len, This->current, This->cur_size, This->size);
 	fprintf(stderr, "%d %d %d %x %x\n",
 		start == This->current + This->cur_size,
 		This->cur_size < This->size,
 		len >= This->sectorSize, len, This->sectorSize);
 #endif
 	switch(isInBuffer(This, start, &len)) {
 		case OUTSIDE:
 #ifdef DEBUG
 			fprintf(stderr, "outside\n");
 #endif
 			if(start % (mt_off_t) This->cylinderSize ||
 			   len < This->sectorSize) {
 				size_t readSize;
 				ssize_t ret;
 				size_t bytes_read;

 				readSize = This->cylinderSize -
 					(size_t)(This->current % (mt_off_t) This->cylinderSize);

 				ret=PREADS(This->head.Next, This->buf,
 					   (mt_off_t)This->current, readSize);
 				/* read it! */
 				if ( ret < 0 )
 					return ret;
 				bytes_read = (size_t) ret;
 				if(bytes_read % This->sectorSize) {
 				  fprintf(stderr, "Weird: read size (%zd) not a multiple of sector size (%d)\n", bytes_read, (int) This->sectorSize);
 				    bytes_read -= bytes_read % This->sectorSize;
 				    if(bytes_read == 0) {
 					fprintf(stderr, "Nothing left\n");
 					exit(1);
 				    }
 				}
 				This->cur_size = bytes_read;
 				/* for dosemu. Autoextend size */
 				if(!This->cur_size) {
 					memset(This->buf,0,readSize);
 					This->cur_size = readSize;
 				}
 				offset = OFFSET;
 				break;
 			}
 			/* FALL THROUGH */
 		case APPEND:
 #ifdef DEBUG
 			fprintf(stderr, "append\n");
 #endif
 			len = ROUND_DOWN(len, This->sectorSize);
 			offset = OFFSET;
 			maximize(len, This->size - offset);
 			This->cur_size += len;
 			if(This->head.Next->Class->pre_allocate)
 				PRE_ALLOCATE(This->head.Next, cur_end(This));
 			break;
 		case INSIDE:
 			/* nothing to do */
 #ifdef DEBUG
 			fprintf(stderr, "inside\n");
 #endif
 			offset = OFFSET;
 			maximize(len, This->cur_size - offset);
 			break;
 		case ERROR:
 			return -1;
 #ifdef DEBUG
 		default:
 			fprintf(stderr, "Should not happen\n");
 			exit(1);
 #endif
 	}

 	disk_ptr = This->buf + offset;

 	/* extend if we write beyond end */
 	if(offset + len > This->cur_size) {
 		len -= (offset + len) % This->sectorSize;
 		This->cur_size = len + offset;
 	}

 	memcpy(disk_ptr, buf, len);
 	if(!This->dirty || offset < This->dirty_pos)
 		This->dirty_pos = ROUND_DOWN(offset, This->sectorSize);
 	if(!This->dirty || offset + len > This->dirty_end)
 		This->dirty_end = ROUND_UP(offset + len, This->sectorSize);

 	if(This->dirty_end > This->cur_size) {
 		fprintf(stderr,
 			"Internal error, dirty end too big dirty_end=%x cur_size=%x len=%x offset=%d sectorSize=%x\n",
 			(unsigned int) This->dirty_end,
 			(unsigned int) This->cur_size,
 			(unsigned int) len,
 			(int) offset, (int) This->sectorSize);
 		fprintf(stderr, "offset + len + grain - 1 = %x\n",
 				(int) (offset + len + This->sectorSize - 1));
 		fprintf(stderr, "ROUNDOWN(offset + len + grain - 1) = %x\n",
 				(int)ROUND_DOWN(offset + len + This->sectorSize - 1,
 								This->sectorSize));
 		fprintf(stderr, "This->dirty = %d\n", This->dirty);
 		exit(1);
 	}

 	This->dirty = 1;
 	return (ssize_t) len;
 }

 static int buf_flush(Stream_t *Stream)
 {
 	int ret;
 	DeclareThis(Buffer_t);

 	if (!This->ever_dirty)
 		return 0;
 	ret = _buf_flush(This);
 	if(ret == 0)
 		This->ever_dirty = 0;
 	return ret;
 }


 static int buf_free(Stream_t *Stream)
 {
 	DeclareThis(Buffer_t);

 	if(This->buf)
 		free(This->buf);
 	This->buf = 0;
 	return 0;
 }

 static Class_t BufferClass = {
 	0,
 	0,
 	buf_pread,
 	buf_pwrite,
 	buf_flush,
 	buf_free,
 	0, /* set_geom */
 	get_data_pass_through, /* get_data */
 	0, /* pre-allocate */
 	get_dosConvert_pass_through, /* dos convert */
 	0, /* discard */
 };

 Stream_t *buf_init(Stream_t *Next, size_t size,
 		   size_t cylinderSize,
 		   size_t sectorSize)
 {
 	Buffer_t *Buffer;

 #ifdef HAVE_ASSERT_H
 	assert(size != 0);
 	assert(cylinderSize != 0);
 	assert(sectorSize != 0);
 	assert(Next != NULL);
 #endif

 	if(size % cylinderSize != 0) {
 		fprintf(stderr, "size not multiple of cylinder size\n");
 		exit(1);
 	}
 	if(cylinderSize % sectorSize != 0) {
 		fprintf(stderr, "cylinder size not multiple of sector size\n");
 		exit(1);
 	}

 	Buffer = New(Buffer_t);
 	if(!Buffer)
 		return 0;
 	init_head(&Buffer->head, &BufferClass, Next);
 	Buffer->buf = malloc(size);
 	if ( !Buffer->buf){
 		Free(Buffer);
 		return 0;
 	}
 	Buffer->size = size;
 	Buffer->dirty = 0;
 	Buffer->cylinderSize = cylinderSize;
 	Buffer->sectorSize = sectorSize;

 	Buffer->ever_dirty = 0;
 	Buffer->dirty_pos = 0;
 	Buffer->dirty_end = 0;
 	Buffer->current = 0L;
 	Buffer->cur_size = 0; /* buffer currently empty */

 	return &Buffer->head;
 }
	/* Copyright 1997,2001-2003 Alain Knaff.
	* This file is part of mtools.
	*
	* Mtools is free software: you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation, either version 3 of the License, or
	* (at your option) any later version.
	*
	* Mtools is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with Mtools. If not, see <http://www.gnu.org/licenses/>.
	*
	* Buffer read/write module
	*/

	#include "sysincludes.h"
	#include "msdos.h"
	#include "mtools.h"
	#include "buffer.h"

	typedef struct Buffer_t {
	struct Stream_t head;

	size_t size; /* size of read/write buffer */
	int dirty; /* is the buffer dirty? */

	size_t sectorSize; /* sector size: all operations happen
	* in multiples of this */
	size_t cylinderSize; /* cylinder size: preferred alignment,
	* but for efficiency, less data may be read */
	int ever_dirty; /* was the buffer ever dirty? */
	size_t dirty_pos;
	size_t dirty_end;
	mt_off_t current; /* first sector in buffer */
	size_t cur_size; /* the current size */
	char buf; / disk read/write buffer */
	} Buffer_t;

	/* Convert position relative to buffer to absolute position */
	static mt_off_t abs_pos(Buffer_t *Buffer, size_t rel) {
	return Buffer->current + (mt_off_t) rel;
	}

	/* End of currently valid buffer */
	static mt_off_t cur_end(Buffer_t *Buffer) {
	return abs_pos(Buffer, Buffer->cur_size);
	}

	/* distance from absolute position until next full cylinder. If position already
	* is on a full cylinder boundary, return size of full cylinder */
	static size_t pos_to_next_full_cyl(Buffer_t *Buffer, mt_off_t pos) {
	return Buffer->cylinderSize -
	(size_t) (pos % (mt_off_t) Buffer->cylinderSize);
	}

	/*
	* Flush a dirty buffer to disk. Resets Buffer->dirty to zero.
	* All errors are fatal.
	*/

	static int _buf_flush(Buffer_t *Buffer)
	{
	ssize_t ret;

	#ifdef HAVE_ASSERT_H
	assert(Buffer->head.Next != NULL);
	#endif

	if (!Buffer->dirty)
	return 0;
	#ifdef DEBUG
	fprintf(stderr, "write %08x -- %02x %08x %08x\n",
	Buffer,
	(unsigned char) Buffer->buf[0],
	Buffer->current + Buffer->dirty_pos,
	Buffer->dirty_end - Buffer->dirty_pos);
	#endif

	ret = force_pwrite(Buffer->head.Next,
	Buffer->buf + Buffer->dirty_pos,
	Buffer->current + (mt_off_t) Buffer->dirty_pos,
	Buffer->dirty_end - Buffer->dirty_pos);
	if(ret < 0) {
	perror("buffer_flush: write");
	return -1;
	}

	if((size_t) ret != Buffer->dirty_end - Buffer->dirty_pos) {
	fprintf(stderr,"buffer_flush: short write\n");
	return -1;
	}
	Buffer->dirty = 0;
	Buffer->dirty_end = 0;
	Buffer->dirty_pos = 0;
	return 0;
	}

	static int invalidate_buffer(Buffer_t *Buffer, mt_off_t start)
	{
	if(_buf_flush(Buffer) < 0)
	return -1;

	/* start reading at the beginning of start's sector
	* don't start reading too early, or we might not even reach
	* start */
	Buffer->current = ROUND_DOWN(start, (mt_off_t) Buffer->sectorSize);
	Buffer->cur_size = 0;
	return 0;
	}

	#undef OFFSET
	#define OFFSET ((size_t)(start - This->current))

	typedef enum position_t {
	OUTSIDE,
	APPEND,
	INSIDE,
	ERROR
	} position_t;

	static position_t isInBuffer(Buffer_t This, mt_off_t start, size_t len)
	{
	if(start >= This->current && start < cur_end(This)) {
	maximize(*len, This->cur_size - OFFSET);
	return INSIDE;
	} else if(start == cur_end(This) &&
	This->cur_size < This->size &&
	*len >= This->sectorSize) {
	/* append to the buffer for this, three conditions have to
	* be met:
	* 1. The start falls exactly at the end of the currently
	* loaded data
	* 2. There is still space
	* 3. We append at least one sector
	*/
	maximize(*len, This->size - This->cur_size);
	len = ROUND_DOWN(len, This->sectorSize);
	return APPEND;
	} else {
	if(invalidate_buffer(This, start) < 0)
	return ERROR;
	maximize(*len, This->cylinderSize - OFFSET);
	maximize(*len, pos_to_next_full_cyl(This, This->current));
	return OUTSIDE;
	}
	}

	static ssize_t buf_pread(Stream_t Stream, char buf,
	mt_off_t start, size_t len)
	{
	size_t length;
	size_t offset;
	char *disk_ptr;
	ssize_t ret;
	DeclareThis(Buffer_t);

	if(!len)
	return 0;

	/fprintf(stderr, "buf read %x %x %x\n", Stream, start, len);/
	switch(isInBuffer(This, start, &len)) {
	case OUTSIDE:
	case APPEND:
	/* always load until the end of the cylinder */
	length = pos_to_next_full_cyl(This, cur_end(This));
	maximize(length, This->size - This->cur_size);

	/* read it! */
	ret=PREADS(This->head.Next,
	This->buf + This->cur_size,
	This->current + (mt_off_t) This->cur_size,
	length);
	if ( ret < 0 )
	return ret;
	This->cur_size += (size_t) ret;
	if (This->current+(mt_off_t)This->cur_size < start) {
	fprintf(stderr, "Short buffer fill\n");
	exit(1);
	}
	break;
	case INSIDE:
	/* nothing to do */
	break;
	case ERROR:
	return -1;
	}

	offset = OFFSET;
	disk_ptr = This->buf + offset;
	maximize(len, This->cur_size - offset);
	memcpy(buf, disk_ptr, len);
	return (ssize_t) len;
	}

	static ssize_t buf_pwrite(Stream_t Stream, char buf,
	mt_off_t start, size_t len)
	{
	char *disk_ptr;
	DeclareThis(Buffer_t);
	size_t offset=0;

	if(!len)
	return 0;

	This->ever_dirty = 1;

	#ifdef DEBUG
	fprintf(stderr, "buf write %x %02x %08x %08x -- %08x %08x -- %08x\n",
	Stream, (unsigned char) This->buf[0],
	start, len, This->current, This->cur_size, This->size);
	fprintf(stderr, "%d %d %d %x %x\n",
	start == This->current + This->cur_size,
	This->cur_size < This->size,
	len >= This->sectorSize, len, This->sectorSize);
	#endif
	switch(isInBuffer(This, start, &len)) {
	case OUTSIDE:
	#ifdef DEBUG
	fprintf(stderr, "outside\n");
	#endif
	if(start % (mt_off_t) This->cylinderSize \|\|
	len < This->sectorSize) {
	size_t readSize;
	ssize_t ret;
	size_t bytes_read;

	readSize = This->cylinderSize -
	(size_t)(This->current % (mt_off_t) This->cylinderSize);

	ret=PREADS(This->head.Next, This->buf,
	(mt_off_t)This->current, readSize);
	/* read it! */
	if ( ret < 0 )
	return ret;
	bytes_read = (size_t) ret;
	if(bytes_read % This->sectorSize) {
	fprintf(stderr, "Weird: read size (%zd) not a multiple of sector size (%d)\n", bytes_read, (int) This->sectorSize);
	bytes_read -= bytes_read % This->sectorSize;
	if(bytes_read == 0) {
	fprintf(stderr, "Nothing left\n");
	exit(1);
	}
	}
	This->cur_size = bytes_read;
	/* for dosemu. Autoextend size */
	if(!This->cur_size) {
	memset(This->buf,0,readSize);
	This->cur_size = readSize;
	}
	offset = OFFSET;
	break;
	}
	/* FALL THROUGH */
	case APPEND:
	#ifdef DEBUG
	fprintf(stderr, "append\n");
	#endif
	len = ROUND_DOWN(len, This->sectorSize);
	offset = OFFSET;
	maximize(len, This->size - offset);
	This->cur_size += len;
	if(This->head.Next->Class->pre_allocate)
	PRE_ALLOCATE(This->head.Next, cur_end(This));
	break;
	case INSIDE:
	/* nothing to do */
	#ifdef DEBUG
	fprintf(stderr, "inside\n");
	#endif
	offset = OFFSET;
	maximize(len, This->cur_size - offset);
	break;
	case ERROR:
	return -1;
	#ifdef DEBUG
	default:
	fprintf(stderr, "Should not happen\n");
	exit(1);
	#endif
	}

	disk_ptr = This->buf + offset;

	/* extend if we write beyond end */
	if(offset + len > This->cur_size) {
	len -= (offset + len) % This->sectorSize;
	This->cur_size = len + offset;
	}

	memcpy(disk_ptr, buf, len);
	if(!This->dirty \|\| offset < This->dirty_pos)
	This->dirty_pos = ROUND_DOWN(offset, This->sectorSize);
	if(!This->dirty \|\| offset + len > This->dirty_end)
	This->dirty_end = ROUND_UP(offset + len, This->sectorSize);

	if(This->dirty_end > This->cur_size) {
	fprintf(stderr,
	"Internal error, dirty end too big dirty_end=%x cur_size=%x len=%x offset=%d sectorSize=%x\n",
	(unsigned int) This->dirty_end,
	(unsigned int) This->cur_size,
	(unsigned int) len,
	(int) offset, (int) This->sectorSize);
	fprintf(stderr, "offset + len + grain - 1 = %x\n",
	(int) (offset + len + This->sectorSize - 1));
	fprintf(stderr, "ROUNDOWN(offset + len + grain - 1) = %x\n",
	(int)ROUND_DOWN(offset + len + This->sectorSize - 1,
	This->sectorSize));
	fprintf(stderr, "This->dirty = %d\n", This->dirty);
	exit(1);
	}

	This->dirty = 1;
	return (ssize_t) len;
	}

	static int buf_flush(Stream_t *Stream)
	{
	int ret;
	DeclareThis(Buffer_t);

	if (!This->ever_dirty)
	return 0;
	ret = _buf_flush(This);
	if(ret == 0)
	This->ever_dirty = 0;
	return ret;
	}


	static int buf_free(Stream_t *Stream)
	{
	DeclareThis(Buffer_t);

	if(This->buf)
	free(This->buf);
	This->buf = 0;
	return 0;
	}

	static Class_t BufferClass = {
	0,
	0,
	buf_pread,
	buf_pwrite,
	buf_flush,
	buf_free,
	0, /* set_geom */
	get_data_pass_through, /* get_data */
	0, /* pre-allocate */
	get_dosConvert_pass_through, /* dos convert */
	0, /* discard */
	};

	Stream_t buf_init(Stream_t Next, size_t size,
	size_t cylinderSize,
	size_t sectorSize)
	{
	Buffer_t *Buffer;

	#ifdef HAVE_ASSERT_H
	assert(size != 0);
	assert(cylinderSize != 0);
	assert(sectorSize != 0);
	assert(Next != NULL);
	#endif

	if(size % cylinderSize != 0) {
	fprintf(stderr, "size not multiple of cylinder size\n");
	exit(1);
	}
	if(cylinderSize % sectorSize != 0) {
	fprintf(stderr, "cylinder size not multiple of sector size\n");
	exit(1);
	}

	Buffer = New(Buffer_t);
	if(!Buffer)
	return 0;
	init_head(&Buffer->head, &BufferClass, Next);
	Buffer->buf = malloc(size);
	if ( !Buffer->buf){
	Free(Buffer);
	return 0;
	}
	Buffer->size = size;
	Buffer->dirty = 0;
	Buffer->cylinderSize = cylinderSize;
	Buffer->sectorSize = sectorSize;

	Buffer->ever_dirty = 0;
	Buffer->dirty_pos = 0;
	Buffer->dirty_end = 0;
	Buffer->current = 0L;
	Buffer->cur_size = 0; /* buffer currently empty */

	return &Buffer->head;
	}