ialloc.c

elinux jffs初始版本 具体了解JFFS的文件系统！

/*
 *  linux/fs/ext2/ialloc.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card ([e-mail])
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  BSD ufs-inspired inode and directory allocation by 
 *  Stephen Tweedie ([e-mail]), 1993
 */

/*
 * ialloc.c contains the inodes allocation and deallocation routines
 */

/*
 * The free inodes 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/sched.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/locks.h>

#include <asm/bitops.h>

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 - "
			    "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 inode allocation 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_inode_bitmap (struct super_block * sb,
			      unsigned long block_group,
			      unsigned int 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_inode_bitmap, sb->s_blocksize);
	if (!bh) {
		ext2_error (sb, "read_inode_bitmap",
			    "Cannot read inode bitmap - "
			    "block_group = %lu, inode_bitmap = %lu",
			    block_group, (unsigned long) gdp->bg_inode_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_inode_bitmap_number[bitmap_nr] = block_group;
	sb->u.ext2_sb.s_inode_bitmap[bitmap_nr] = bh;
	return retval;
}

/*
 * load_inode_bitmap loads the inode 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_inode_bitmap (struct super_block * sb,
			      unsigned int block_group)
{
	int i, j, retval = 0;
	unsigned long inode_bitmap_number;
	struct buffer_head * inode_bitmap;

	if (block_group >= sb->u.ext2_sb.s_groups_count)
		ext2_panic (sb, "load_inode_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_loaded_inode_bitmaps > 0 &&
	    sb->u.ext2_sb.s_inode_bitmap_number[0] == block_group)
		return 0;
	if (sb->u.ext2_sb.s_groups_count <= EXT2_MAX_GROUP_LOADED) {
		if (sb->u.ext2_sb.s_inode_bitmap[block_group]) {
			if (sb->u.ext2_sb.s_inode_bitmap_number[block_group] != block_group)
				ext2_panic (sb, "load_inode_bitmap",
					    "block_group != inode_bitmap_number");
			else
				return block_group;
		} else {
			retval = read_inode_bitmap (sb, block_group, block_group);
			if (retval < 0)
				return retval;
			return block_group;
		}
	}

	for (i = 0; i < sb->u.ext2_sb.s_loaded_inode_bitmaps &&
		    sb->u.ext2_sb.s_inode_bitmap_number[i] != block_group;
	     i++)
		;
	if (i < sb->u.ext2_sb.s_loaded_inode_bitmaps &&
  	    sb->u.ext2_sb.s_inode_bitmap_number[i] == block_group) {
		inode_bitmap_number = sb->u.ext2_sb.s_inode_bitmap_number[i];
		inode_bitmap = sb->u.ext2_sb.s_inode_bitmap[i];
		for (j = i; j > 0; j--) {
			sb->u.ext2_sb.s_inode_bitmap_number[j] =
				sb->u.ext2_sb.s_inode_bitmap_number[j - 1];
			sb->u.ext2_sb.s_inode_bitmap[j] =
				sb->u.ext2_sb.s_inode_bitmap[j - 1];
		}
		sb->u.ext2_sb.s_inode_bitmap_number[0] = inode_bitmap_number;
		sb->u.ext2_sb.s_inode_bitmap[0] = inode_bitmap;

		/*
		 * There's still one special case here --- if inode_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 (!inode_bitmap)
			retval = read_inode_bitmap (sb, block_group, 0);
	} else {
		if (sb->u.ext2_sb.s_loaded_inode_bitmaps < EXT2_MAX_GROUP_LOADED)
			sb->u.ext2_sb.s_loaded_inode_bitmaps++;
		else
			brelse (sb->u.ext2_sb.s_inode_bitmap[EXT2_MAX_GROUP_LOADED - 1]);
		for (j = sb->u.ext2_sb.s_loaded_inode_bitmaps - 1; j > 0; j--) {
			sb->u.ext2_sb.s_inode_bitmap_number[j] =
				sb->u.ext2_sb.s_inode_bitmap_number[j - 1];
			sb->u.ext2_sb.s_inode_bitmap[j] =
				sb->u.ext2_sb.s_inode_bitmap[j - 1];
		}
		retval = read_inode_bitmap (sb, block_group, 0);
	}
	return retval;
}

void ext2_free_inode (struct inode * inode)
{
	struct super_block * sb;
	struct buffer_head * bh;
	struct buffer_head * bh2;
	unsigned long block_group;
	unsigned long bit;
	int bitmap_nr;
	struct ext2_group_desc * gdp;
	struct ext2_super_block * es;

	if (!inode)
		return;
	if (!inode->i_dev) {
		printk ("ext2_free_inode: inode has no device\n");
		return;
	}
	if (inode->i_count > 1) {
		printk ("ext2_free_inode: inode has count=%ld\n",
			inode->i_count);
		return;
	}
	if (inode->i_nlink) {
		printk ("ext2_free_inode: inode has nlink=%d\n",
			inode->i_nlink);
		return;
	}
	if (!inode->i_sb) {
		printk("ext2_free_inode: inode on nonexistent device\n");
		return;
	}

	ext2_debug ("freeing inode %lu\n", inode->i_ino);

	sb = inode->i_sb;
	lock_super (sb);
	if (inode->i_ino < EXT2_FIRST_INO(sb) ||
	    inode->i_ino > sb->u.ext2_sb.s_es->s_inodes_count) {
		ext2_error (sb, "free_inode",
			    "reserved inode or nonexistent inode");
		unlock_super (sb);
		return;
	}
	es = sb->u.ext2_sb.s_es;
	block_group = (inode->i_ino - 1) / EXT2_INODES_PER_GROUP(sb);
	bit = (inode->i_ino - 1) % EXT2_INODES_PER_GROUP(sb);
	bitmap_nr = load_inode_bitmap (sb, block_group);
	if (bitmap_nr < 0) {
		unlock_super (sb);
		return;
	}
	
	bh = sb->u.ext2_sb.s_inode_bitmap[bitmap_nr];
	if (!clear_bit (bit, bh->b_data))
		ext2_warning (sb, "ext2_free_inode",
			      "bit already cleared for inode %lu", inode->i_ino);
	else {
		gdp = get_group_desc (sb, block_group, &bh2);
		gdp->bg_free_inodes_count++;
		if (S_ISDIR(inode->i_mode))
			gdp->bg_used_dirs_count--;
		mark_buffer_dirty(bh2, 1);
		es->s_free_inodes_count++;
		mark_buffer_dirty(sb->u.ext2_sb.s_sbh, 1);
		inode->i_dirt = 0;
	}
	mark_buffer_dirty(bh, 1);
	if (sb->s_flags & MS_SYNCHRONOUS) {
		ll_rw_block (WRITE, 1, &bh);
		wait_on_buffer (bh);
	}
	if (sb->dq_op)
		sb->dq_op->free_inode (inode, 1);
	sb->s_dirt = 1;
	clear_inode (inode);
	unlock_super (sb);
}

/*
 * This function increments the inode version number
 *
 * This may be used one day by the NFS server
 */
static void inc_inode_version (struct inode * inode,
			       struct ext2_group_desc *gdp,
			       int mode)
{
	inode->u.ext2_i.i_version++;
	inode->i_dirt = 1;

	return;
}

/*
 * There are two policies for allocating an inode.  If the new inode is
 * a directory, then a forward search is made for a block group with both
 * free space and a low directory-to-inode ratio; if that fails, then of
 * the groups with above-average free space, that group with the fewest
 * directories already is chosen.
 *
 * For other inodes, search forward from the parent directory\'s block