balloc.c

LINUX1.0内核源代码,学习LINUX编程的一定要看。

/*
 *  linux/fs/ext2/balloc.c
 *
 *  Copyright (C) 1992, 1993, 1994  Remy Card ([e-mail])
 *                                  Laboratoire MASI - Institut Blaise Pascal
 *                                  Universite Pierre et Marie Curie (Paris VI)
 *
 *  Enhanced block allocation by Stephen Tweedie ([e-mail]), 1993
 */

/*
 * balloc.c contains the blocks allocation and deallocation routines
 */

/*
 * The free blocks are managed by bitmaps.  A file system contains several
 * blocks groups.  Each group contains 1 bitmap block for blocks, 1 bitmap
 * block for inodes, N blocks for the inode table and data blocks.
 *
 * The file system contains group descriptors which are located after the
 * super block.  Each descriptor contains the number of the bitmap block and
 * the free blocks count in the block.  The descriptors are loaded in memory
 * when a file system is mounted (see ext2_read_super).
 */

#include <linux/fs.h>
#include <linux/ext2_fs.h>
#include <linux/stat.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/locks.h>

#include <asm/bitops.h>

#define clear_block(addr,size) \
	__asm__("cld\n\t" \
		"rep\n\t" \
		"stosl" \
		: \
		:"a" (0), "c" (size / 4), "D" ((long) (addr)) \
		:"cx", "di")

#define in_range(b, first, len)		((b) >= (first) && (b) <= (first) + (len) - 1)

static inline int find_first_zero_bit (unsigned long * addr, unsigned size)
{
	int res;

	if (!size)
		return 0;
	__asm__("
		cld
		movl $-1,%%eax
		repe; scasl
		je 1f
		subl $4,%%edi
		movl (%%edi),%%eax
		notl %%eax
		bsfl %%eax,%%edx
		jmp 2f
1:		xorl %%edx,%%edx
2:		subl %%ebx,%%edi
		shll $3,%%edi
		addl %%edi,%%edx"
		:"=d" (res)
		:"c" ((size + 31) >> 5), "D" (addr), "b" (addr)
		:"ax", "bx", "cx", "di");
	return res;
}

static inline int find_next_zero_bit (unsigned long * addr, int size,
				      int offset)
{
	unsigned long * p = ((unsigned long *) addr) + (offset >> 5);
	int set = 0, bit = offset & 31, res;
	
	if (bit) {
		/*
		 * Look for zero in first byte
		 */
		__asm__("
			bsfl %1,%0
			jne 1f
			movl $32, %0
1:			"
			: "=r" (set)
			: "r" (~(*p >> bit)));
		if (set < (32 - bit))
			return set + offset;
		set = 32 - bit;
		p++;
	}
	/*
	 * No zero yet, search remaining full bytes for a zero
	 */
	res = find_first_zero_bit (p, size - 32 * (p - addr));
	return (offset + set + res);
}

static inline char * find_first_zero_byte (char * addr, int size)
{
	char *res;

	if (!size)
		return 0;
	__asm__("
		cld
		mov $0,%%eax
		repnz; scasb
		jnz 1f
		dec %%edi
1:		"
		: "=D" (res)
		: "0" (addr), "c" (size)
		: "ax");
	return res;
}

static struct ext2_group_desc * get_group_desc (struct super_block * sb,
						unsigned int block_group,
						struct buffer_head ** bh)
{
	unsigned long group_desc;
	unsigned long desc;
	struct ext2_group_desc * gdp;

	if (block_group >= sb->u.ext2_sb.s_groups_count)
		ext2_panic (sb, "get_group_desc",
			    "block_group >= groups_count\n"
			    "block_group = %d, groups_count = %lu",
			    block_group, sb->u.ext2_sb.s_groups_count);

	group_desc = block_group / EXT2_DESC_PER_BLOCK(sb);
	desc = block_group % EXT2_DESC_PER_BLOCK(sb);
	if (!sb->u.ext2_sb.s_group_desc[group_desc])
		ext2_panic (sb, "get_group_desc",
			    "Group descriptor not loaded\n"
			    "block_group = %d, group_desc = %lu, desc = %lu",
			     block_group, group_desc, desc);
	gdp = (struct ext2_group_desc *) 
	      sb->u.ext2_sb.s_group_desc[group_desc]->b_data;
	if (bh)
		*bh = sb->u.ext2_sb.s_group_desc[group_desc];
	return gdp + desc;
}

static void read_block_bitmap (struct super_block * sb,
			       unsigned int block_group,
			       unsigned long bitmap_nr)
{
	struct ext2_group_desc * gdp;
	struct buffer_head * bh;
	
	gdp = get_group_desc (sb, block_group, NULL);
	bh = bread (sb->s_dev, gdp->bg_block_bitmap, sb->s_blocksize);
	if (!bh)
		ext2_panic (sb, "read_block_bitmap",
			    "Cannot read block bitmap\n"
			    "block_group = %d, block_bitmap = %lu",
			    block_group, gdp->bg_block_bitmap);
	sb->u.ext2_sb.s_block_bitmap_number[bitmap_nr] = block_group;
	sb->u.ext2_sb.s_block_bitmap[bitmap_nr] = bh;
}

/*
 * load_block_bitmap loads the block bitmap for a blocks group
 *
 * It maintains a cache for the last bitmaps loaded.  This cache is managed
 * with a LRU algorithm.
 *
 * Notes:
 * 1/ There is one cache per mounted file system.
 * 2/ If the file system contains less than EXT2_MAX_GROUP_LOADED groups,
 *    this function reads the bitmap without maintaining a LRU cache.
 */
static int load__block_bitmap (struct super_block * sb,
			       unsigned int block_group)
{
	int i, j;
	unsigned long block_bitmap_number;
	struct buffer_head * block_bitmap;

	if (block_group >= sb->u.ext2_sb.s_groups_count)
		ext2_panic (sb, "load_block_bitmap",
			    "block_group >= groups_count\n"
			    "block_group = %d, groups_count = %lu",
			    block_group, sb->u.ext2_sb.s_groups_count);

	if (sb->u.ext2_sb.s_groups_count <= EXT2_MAX_GROUP_LOADED) {
		if (sb->u.ext2_sb.s_block_bitmap[block_group]) {
			if (sb->u.ext2_sb.s_block_bitmap_number[block_group] !=
			    block_group)
				ext2_panic (sb, "load_block_bitmap",
					    "block_group != block_bitmap_number");
			else
				return block_group;
		} else {
			read_block_bitmap (sb, block_group, block_group);
			return block_group;
		}
	}

	for (i = 0; i < sb->u.ext2_sb.s_loaded_block_bitmaps &&
		    sb->u.ext2_sb.s_block_bitmap_number[i] != block_group; i++)
		;
	if (i < sb->u.ext2_sb.s_loaded_block_bitmaps &&
  	    sb->u.ext2_sb.s_block_bitmap_number[i] == block_group) {
		block_bitmap_number = sb->u.ext2_sb.s_block_bitmap_number[i];
		block_bitmap = sb->u.ext2_sb.s_block_bitmap[i];
		for (j = i; j > 0; j--) {
			sb->u.ext2_sb.s_block_bitmap_number[j] =
				sb->u.ext2_sb.s_block_bitmap_number[j - 1];
			sb->u.ext2_sb.s_block_bitmap[j] =
				sb->u.ext2_sb.s_block_bitmap[j - 1];
		}
		sb->u.ext2_sb.s_block_bitmap_number[0] = block_bitmap_number;
		sb->u.ext2_sb.s_block_bitmap[0] = block_bitmap;
	} else {
		if (sb->u.ext2_sb.s_loaded_block_bitmaps < EXT2_MAX_GROUP_LOADED)
			sb->u.ext2_sb.s_loaded_block_bitmaps++;
		else
			brelse (sb->u.ext2_sb.s_block_bitmap[EXT2_MAX_GROUP_LOADED - 1]);
		for (j = sb->u.ext2_sb.s_loaded_block_bitmaps - 1; j > 0;  j--) {
			sb->u.ext2_sb.s_block_bitmap_number[j] =
				sb->u.ext2_sb.s_block_bitmap_number[j - 1];
			sb->u.ext2_sb.s_block_bitmap[j] =
				sb->u.ext2_sb.s_block_bitmap[j - 1];
		}
		read_block_bitmap (sb, block_group, 0);
	}
	return 0;
}

static inline int load_block_bitmap (struct super_block * sb,
				     unsigned int block_group)
{
	if (sb->u.ext2_sb.s_loaded_block_bitmaps > 0 &&
	    sb->u.ext2_sb.s_block_bitmap_number[0] == block_group)
		return 0;
	
	if (sb->u.ext2_sb.s_groups_count <= EXT2_MAX_GROUP_LOADED && 
	    sb->u.ext2_sb.s_block_bitmap_number[block_group] == block_group &&
	    sb->u.ext2_sb.s_block_bitmap[block_group]) 
		return block_group;

	return load__block_bitmap (sb, block_group);
}

void ext2_free_blocks (struct super_block * sb, unsigned long block,
		       unsigned long count)
{
	struct buffer_head * bh;
	struct buffer_head * bh2;
	unsigned long block_group;
	unsigned long bit;
	unsigned long i;
	int bitmap_nr;
	struct ext2_group_desc * gdp;
	struct ext2_super_block * es;

	if (!sb) {
		printk ("ext2_free_blocks: nonexistent device");
		return;
	}
	lock_super (sb);
	es = sb->u.ext2_sb.s_es;
	if (block < es->s_first_data_block || 
	    (block + count) > es->s_blocks_count) {
		ext2_error (sb, "ext2_free_blocks",
			    "Freeing blocks not in datazone\n"
			    "block = %lu, count = %lu", block, count);
		unlock_super (sb);
		return;
	}

	ext2_debug ("freeing block %lu\n", block);

	block_group = (block - es->s_first_data_block) /
		      EXT2_BLOCKS_PER_GROUP(sb);
	bit = (block - es->s_first_data_block) % EXT2_BLOCKS_PER_GROUP(sb);
	if (bit + count > EXT2_BLOCKS_PER_GROUP(sb))
		ext2_panic (sb, "ext2_free_blocks",
			    "Freeing blocks across group boundary\n"
			    "Block = %lu, count = %lu",
			    block, count);
	bitmap_nr = load_block_bitmap (sb, block_group);
	bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];
	gdp = get_group_desc (sb, block_group, &bh2);

	if (test_opt (sb, CHECK_STRICT) &&
	    (in_range (gdp->bg_block_bitmap, block, count) ||
	     in_range (gdp->bg_inode_bitmap, block, count) ||
	     in_range (block, gdp->bg_inode_table,
		       sb->u.ext2_sb.s_itb_per_group) ||
	     in_range (block + count - 1, gdp->bg_inode_table,
		       sb->u.ext2_sb.s_itb_per_group)))
		ext2_panic (sb, "ext2_free_blocks",
			    "Freeing blocks in system zones\n"
			    "Block = %lu, count = %lu",
			    block, count);

	for (i = 0; i < count; i++) {
		if (!clear_bit (bit + i, bh->b_data))
			ext2_warning (sb, "ext2_free_blocks",
				      "bit already cleared for block %lu", 
				      block);
		else {
			gdp->bg_free_blocks_count++;
			es->s_free_blocks_count++;
		}
	}
	
	bh2->b_dirt = 1;
	sb->u.ext2_sb.s_sbh->b_dirt = 1;

	bh->b_dirt = 1;
	if (sb->s_flags & MS_SYNC) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}
	sb->s_dirt = 1;
	unlock_super (sb);
	return;
}

/*
 * ext2_new_block uses a goal block to assist allocation.  If the goal is
 * free, or there is a free block within 32 blocks of the goal, that block
 * is allocated.  Otherwise a forward search is made for a free block; within 
 * each block group the search first looks for an entire free byte in the block
 * bitmap, and then for any free bit if that fails.
 */
int ext2_new_block (struct super_block * sb, unsigned long goal,
		    unsigned long * prealloc_count,