buffer.c

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/*
 * linux/fs/fat/buffer.c
 *
 *
 */

#include <linux/mm.h>
#include <linux/malloc.h>
#include <linux/string.h>
#include <linux/fs.h>
#include <linux/msdos_fs.h>
#include <linux/fat_cvf.h>

#if 0
#  define PRINTK(x) printk x
#else
#  define PRINTK(x)
#endif

struct buffer_head *fat_bread(struct super_block *sb, int block)
{
	return MSDOS_SB(sb)->cvf_format->cvf_bread(sb,block);
}
struct buffer_head *fat_getblk(struct super_block *sb, int block)
{
	return MSDOS_SB(sb)->cvf_format->cvf_getblk(sb,block);
}
void fat_brelse (struct super_block *sb, struct buffer_head *bh)
{
	if (bh) 
		MSDOS_SB(sb)->cvf_format->cvf_brelse(sb,bh);
}
void fat_mark_buffer_dirty (
	struct super_block *sb,
	struct buffer_head *bh)
{
	MSDOS_SB(sb)->cvf_format->cvf_mark_buffer_dirty(sb,bh);
}
void fat_set_uptodate (
	struct super_block *sb,
	struct buffer_head *bh,
	int val)
{
	MSDOS_SB(sb)->cvf_format->cvf_set_uptodate(sb,bh,val);
}
int fat_is_uptodate(struct super_block *sb, struct buffer_head *bh)
{
	return MSDOS_SB(sb)->cvf_format->cvf_is_uptodate(sb,bh);
}
void fat_ll_rw_block (
	struct super_block *sb,
	int opr,
	int nbreq,
	struct buffer_head *bh[32])
{
	MSDOS_SB(sb)->cvf_format->cvf_ll_rw_block(sb,opr,nbreq,bh);
}

struct buffer_head *default_fat_bread(struct super_block *sb, int block)
{
	return bread (sb->s_dev,block,512);
}
struct buffer_head *default_fat_getblk(struct super_block *sb, int block)
{
	return getblk (sb->s_dev,block,512);
}
void default_fat_brelse(struct super_block *sb, struct buffer_head *bh)
{
	brelse (bh);
}
void default_fat_mark_buffer_dirty (
	struct super_block *sb,
	struct buffer_head *bh)
{
	mark_buffer_dirty (bh);
}
void default_fat_set_uptodate (
	struct super_block *sb,
	struct buffer_head *bh,
	int val)
{
	mark_buffer_uptodate(bh, val);
}
int default_fat_is_uptodate (struct super_block *sb, struct buffer_head *bh)
{
	return buffer_uptodate(bh);
}
void default_fat_ll_rw_block (
	struct super_block *sb,
	int opr,
	int nbreq,
	struct buffer_head *bh[32])
{
	ll_rw_block(opr,nbreq,bh);
}

struct buffer_head *bigblock_fat_bread (
	struct super_block *sb,
	int block)
{
	struct buffer_head *ret = NULL;
	struct buffer_head *real;
	if (sb->s_blocksize == 1024){
		real = bread (sb->s_dev,block>>1,1024);
	} else {
		real = bread (sb->s_dev,block>>2,2048);
	}

	if (real != NULL) {
		ret = (struct buffer_head *)
			kmalloc (sizeof(struct buffer_head), GFP_KERNEL);
		if (ret != NULL) {
			/* #Specification: msdos / strategy / special device / dummy blocks
			 * Many special device (Scsi optical disk for one) use
			 * larger hardware sector size. This allows for higher
			 * capacity.

			 * Most of the time, the MS-DOS filesystem that sits
			 * on this device is totally unaligned. It use logically
			 * 512 bytes sector size, with logical sector starting
			 * in the middle of a hardware block. The bad news is
			 * that a hardware sector may hold data own by two
			 * different files. This means that the hardware sector
			 * must be read, patch and written almost all the time.

			 * Needless to say that it kills write performance
			 * on all OS.

			 * Internally the linux msdos fs is using 512 bytes
			 * logical sector. When accessing such a device, we
			 * allocate dummy buffer cache blocks, that we stuff
			 * with the information of a real one (1k large).

			 * This strategy is used to hide this difference to
			 * the core of the msdos fs. The slowdown is not
			 * hidden though!
			 */
			/*
			 * The memset is there only to catch errors. The msdos
			 * fs is only using b_data
			 */
			memset (ret,0,sizeof(*ret));
			ret->b_data = real->b_data;
			if (sb->s_blocksize == 2048) {
				if (block & 3) ret->b_data += (block & 3) << 9;
			}else{
				if (block & 1) ret->b_data += 512;
			}
			ret->b_next = real;
		}else{
			brelse (real);
		}
	}
	return ret;
}

void bigblock_fat_brelse (
	struct super_block *sb,
	struct buffer_head *bh)
{
	brelse (bh->b_next);
	/*
	 * We can free the dummy because a new one is allocated at
	 * each fat_getblk() and fat_bread().
	 */
	kfree (bh);
}

void bigblock_fat_mark_buffer_dirty (
	struct super_block *sb,
	struct buffer_head *bh)
{
	mark_buffer_dirty (bh->b_next);
}

void bigblock_fat_set_uptodate (
	struct super_block *sb,
	struct buffer_head *bh,
	int val)
{
	mark_buffer_uptodate(bh->b_next, val);
}

int bigblock_fat_is_uptodate (
	struct super_block *sb,
	struct buffer_head *bh)
{
	return buffer_uptodate(bh->b_next);
}

void bigblock_fat_ll_rw_block (
	struct super_block *sb,
	int opr,
	int nbreq,
	struct buffer_head *bh[32])
{
	struct buffer_head *tmp[32];
	int i;
	for (i=0; i<nbreq; i++)
		tmp[i] = bh[i]->b_next;
	ll_rw_block(opr,nbreq,tmp);
}