balloc.c

elinux jffs初始版本 具体了解JFFS的文件系统！

/*
 *  linux/fs/ext2/balloc.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * 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 in_range(b, first, len)		((b) >= (first) && (b) <= (first) + (len) - 1)

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;

	/*
	 * This panic should never trigger on a bad filesystem: the caller
	 * should have verified the block/group number already.
	 */
	if (block_group >= sb->u.ext2_sb.s_groups_count)
		ext2_panic (sb, "get_group_desc",
			    "block_group >= groups_count - "
			    "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 - "
			    "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;
}

/*
 * Read the bitmap for a given block_group, reading into the specified 
 * slot in the superblock's bitmap cache.
 *
 * Return >=0 on success or a -ve error code.
 */

static int read_block_bitmap (struct super_block * sb,
			      unsigned int block_group,
			      unsigned long bitmap_nr)
{
	struct ext2_group_desc * gdp;
	struct buffer_head * bh;
	int retval = 0;
	
	gdp = get_group_desc (sb, block_group, NULL);
	bh = bread (sb->s_dev, gdp->bg_block_bitmap, sb->s_blocksize);
	if (!bh) {
		ext2_error (sb, "read_block_bitmap",
			    "Cannot read block bitmap - "
			    "block_group = %d, block_bitmap = %lu",
			    block_group, (unsigned long) gdp->bg_block_bitmap);
		retval = -EIO;
	}
	/*
	 * On IO error, just leave a zero in the superblock's block pointer for
	 * this group.  The IO will be retried next time.
	 */
	sb->u.ext2_sb.s_block_bitmap_number[bitmap_nr] = block_group;
	sb->u.ext2_sb.s_block_bitmap[bitmap_nr] = bh;
	return retval;
}

/*
 * 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.
 *
 * Return the slot used to store the bitmap, or a -ve error code.
 */
static int load__block_bitmap (struct super_block * sb,
			       unsigned int block_group)
{
	int i, j, retval = 0;
	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 - "
			    "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 {
			retval = read_block_bitmap (sb, block_group, block_group);
			if (retval < 0)
				return retval;
			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;

		/*
		 * There's still one special case here --- if block_bitmap == 0
		 * then our last attempt to read the bitmap failed and we have
		 * just ended up caching that failure.  Try again to read it.
		 */
		if (!block_bitmap)
			retval = read_block_bitmap (sb, block_group, 0);
	} 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];
		}
		retval = read_block_bitmap (sb, block_group, 0);
	}
	return retval;
}

/*
 * Load the block bitmap for a given block group.  First of all do a couple
 * of fast lookups for common cases and then pass the request onto the guts
 * of the bitmap loader.
 *
 * Return the slot number of the group in the superblock bitmap cache's on
 * success, or a -ve error code.
 *
 * There is still one inconsistancy here --- if the number of groups in this
 * filesystems is <= EXT2_MAX_GROUP_LOADED, then we have no way of 
 * differentiating between a group for which we have never performed a bitmap
 * IO request, and a group for which the last bitmap read request failed.
 */
static inline int load_block_bitmap (struct super_block * sb,
				     unsigned int block_group)
{
	int slot;
	
	/*
	 * Do the lookup for the slot.  First of all, check if we're asking
	 * for the same slot as last time, and did we succeed that last time?
	 */
	if (sb->u.ext2_sb.s_loaded_block_bitmaps > 0 &&
	    sb->u.ext2_sb.s_block_bitmap_number[0] == block_group &&
	    sb->u.ext2_sb.s_block_bitmap[block_group]) {
		slot = 0;
	}
	/*
	 * Or can we do a fast lookup based on a loaded group on a filesystem
	 * small enough to be mapped directly into the superblock?
	 */
	else 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]) {
		slot = block_group;
	} 
	/*
	 * If not, then do a full lookup for this block group.
	 */
	else {
		slot = load__block_bitmap (sb, block_group);
	}

	/*
	 * <0 means we just got an error
	 */
	if (slot < 0)
		return slot;
	
	/*
	 * If it's a valid slot, we may still have cached a previous IO error,
	 * in which case the bh in the superblock cache will be zero.
	 */
	if (!sb->u.ext2_sb.s_block_bitmap[slot])
		return -EIO;
	
	/*
	 * Must have been read in OK to get this far.
	 */
	return slot;
}

void ext2_free_blocks (const struct inode * inode, 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 super_block * sb;
	struct ext2_group_desc * gdp;
	struct ext2_super_block * es;

	sb = inode->i_sb;
	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 - "
			    "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_error (sb, "ext2_free_blocks",
			    "Freeing blocks across group boundary - "
			    "Block = %lu, count = %lu",
			    block, count);
		unlock_super (sb);
		return;
	}
	
	bitmap_nr = load_block_bitmap (sb, block_group);
	if (bitmap_nr < 0)
		goto error_return;
		
	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_error (sb, "ext2_free_blocks",
			    "Freeing blocks in system zones - "
			    "Block = %lu, count = %lu",
			    block, count);
		unlock_super (sb);
		return;
	}

	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 {
			if (sb->dq_op)
				sb->dq_op->free_block(inode, fs_to_dq_blocks(1, sb->s_blocksize));
			gdp->bg_free_blocks_count++;
			es->s_free_blocks_count++;
		}
	}
	
	mark_buffer_dirty(bh2, 1);
	mark_buffer_dirty(sb->u.ext2_sb.s_sbh, 1);

	mark_buffer_dirty(bh, 1);
	if (sb->s_flags & MS_SYNCHRONOUS) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}
	sb->s_dirt = 1;
error_return:
	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 (const struct inode * inode, unsigned long goal,
		    u32 * prealloc_count, u32 * prealloc_block, int * err)
{
	struct buffer_head * bh;
	struct buffer_head * bh2;
	char * p, * r;
	int i, j, k, tmp;
	int bitmap_nr;
	struct super_block * sb;
	struct ext2_group_desc * gdp;
	struct ext2_super_block * es;

	*err = -ENOSPC;
#ifdef EXT2FS_DEBUG