fs/ext2/balloc.c

/*
 *  linux/fs/ext2/balloc.c
 *
 *  Copyright (C) 1992, 1993, 1994  Remy Card (card@masi.ibp.fr)
 *                                  Laboratoire MASI - Institut Blaise Pascal
 *                                  Universite Pierre et Marie Curie (Paris VI)
 *
 *  Enhanced block allocation by Stephen Tweedie (sct@dcs.ed.ac.uk), 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,
		    unsigned long * prealloc_block)
{
	struct buffer_head * bh;
	struct buffer_head * bh2;
	char * p, * r;
	int i, j, k, tmp;
	unsigned long lmap;
	int bitmap_nr;
	struct ext2_group_desc * gdp;
	struct ext2_super_block * es;

#ifdef EXT2FS_DEBUG
	static int goal_hits = 0, goal_attempts = 0;
#endif
	if (!sb) {
		printk ("ext2_new_block: nonexistent device");
		return 0;
	}
	lock_super (sb);
	es = sb->u.ext2_sb.s_es;
	if (es->s_free_blocks_count <= es->s_r_blocks_count && !suser()) {
		unlock_super (sb);
		return 0;
	}

	ext2_debug ("goal=%lu.\n", goal);

repeat:
	/*
	 * First, test whether the goal block is free.
	 */
	if (goal < es->s_first_data_block || goal >= es->s_blocks_count)
		goal = es->s_first_data_block;
	i = (goal - es->s_first_data_block) / EXT2_BLOCKS_PER_GROUP(sb);
	gdp = get_group_desc (sb, i, &bh2);
	if (gdp->bg_free_blocks_count > 0) {
		j = ((goal - es->s_first_data_block) % EXT2_BLOCKS_PER_GROUP(sb));
#ifdef EXT2FS_DEBUG
		if (j)
			goal_attempts++;
#endif
		bitmap_nr = load_block_bitmap (sb, i);
		bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];

		ext2_debug ("goal is at %d:%d.\n", i, j);

		if (!test_bit(j, bh->b_data)) {
#ifdef EXT2FS_DEBUG
			goal_hits++;
			ext2_debug ("goal bit allocated.\n");
#endif
			goto got_block;
		}
		if (j) {
			/*
			 * The goal was occupied; search forward for a free 
			 * block within the next 32 blocks
			 */
			lmap = ((((unsigned long *) bh->b_data)[j >> 5]) >>
				((j & 31) + 1));
			if (j < EXT2_BLOCKS_PER_GROUP(sb) - 32)
				lmap |= (((unsigned long *) bh->b_data)[(j >> 5) + 1]) <<
				 (31 - (j & 31));
			else
				lmap |= 0xffffffff << (31 - (j & 31));
			if (lmap != 0xffffffffl) {
				__asm__ ("bsfl %1,%0"
					 : "=r" (k)
					 : "r" (~lmap));
				k++;
				if ((j + k) < EXT2_BLOCKS_PER_GROUP(sb)) {
					j += k;
					goto got_block;
				}
			}
		}
	
		ext2_debug ("Bit not found near goal\n");

		/*
		 * There has been no free block found in the near vicinity
		 * of the goal: do a search forward through the block groups,
		 * searching in each group first for an entire free byte in
		 * the bitmap and then for any free bit.
		 * 
		 * Search first in the remainder of the current group; then,
		 * cyclicly search throught the rest of the groups.
		 */
		p = ((char *) bh->b_data) + (j >> 3);
		r = find_first_zero_byte (p, 
					  (EXT2_BLOCKS_PER_GROUP(sb) - j + 7) >> 3);
		k = (r - ((char *) bh->b_data)) << 3;
		if (k < EXT2_BLOCKS_PER_GROUP(sb)) {
			j = k;
			goto search_back;
		}
		k = find_next_zero_bit ((unsigned long *) bh->b_data, 
					EXT2_BLOCKS_PER_GROUP(sb),
					j);
		if (k < EXT2_BLOCKS_PER_GROUP(sb)) {
			j = k;
			goto got_block;
		}
	}

	ext2_debug ("Bit not found in block group %d.\n", i);

	/*
	 * Now search the rest of the groups.  We assume that 
	 * i and gdp correctly point to the last group visited.
	 */
	for (k = 0; k < sb->u.ext2_sb.s_groups_count; k++) {
		i++;
		if (i >= sb->u.ext2_sb.s_groups_count)
			i = 0;
		gdp = get_group_desc (sb, i, &bh2);
		if (gdp->bg_free_blocks_count > 0)
			break;
	}
	if (k >= sb->u.ext2_sb.s_groups_count) {
		unlock_super (sb);
		return 0;
	}
	bitmap_nr = load_block_bitmap (sb, i);
	bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];
	r = find_first_zero_byte (bh->b_data, 
				  EXT2_BLOCKS_PER_GROUP(sb) >> 3);
	j = (r - bh->b_data) << 3;
	if (j < EXT2_BLOCKS_PER_GROUP(sb))
		goto search_back;
	else
		j = find_first_zero_bit ((unsigned long *) bh->b_data,
					 EXT2_BLOCKS_PER_GROUP(sb));
	if (j >= EXT2_BLOCKS_PER_GROUP(sb)) {
		ext2_error (sb, "ext2_new_block",
			    "Free blocks count corrupted for block group %d", i);
		unlock_super (sb);
		return 0;
	}

search_back:
	/* 
	 * We have succeeded in finding a free byte in the block
	 * bitmap.  Now search backwards up to 7 bits to find the
	 * start of this group of free blocks.
	 */
	for (k = 0; k < 7 && j > 0 && !test_bit (j - 1, bh->b_data); k++, j--);
	
got_block:

	ext2_debug ("using block group %d(%d)\n", i, gdp->bg_free_blocks_count);

	tmp = j + i * EXT2_BLOCKS_PER_GROUP(sb) + es->s_first_data_block;

	if (test_opt (sb, CHECK_STRICT) &&
	    (tmp == gdp->bg_block_bitmap ||
	     tmp == gdp->bg_inode_bitmap ||
	     in_range (tmp, gdp->bg_inode_table, sb->u.ext2_sb.s_itb_per_group)))
		ext2_panic (sb, "ext2_new_block",
			    "Allocating block in system zone\n"
			    "block = %u", tmp);

	if (set_bit (j, bh->b_data)) {
		ext2_warning (sb, "ext2_new_block",
			      "bit already set for block %d", j);
		goto repeat;
	}

	ext2_debug ("found bit %d\n", j);

	/*
	 * Do block preallocation now if required.
	 */
#ifdef EXT2_PREALLOCATE
	if (prealloc_block) {
		*prealloc_count = 0;
		*prealloc_block = tmp + 1;
		for (k = 1;
		     k < 8 && (j + k) < EXT2_BLOCKS_PER_GROUP(sb); k++) {
			if (set_bit (j + k, bh->b_data))
				break;
			(*prealloc_count)++;
		}	
		gdp->bg_free_blocks_count -= *prealloc_count;
		es->s_free_blocks_count -= *prealloc_count;
		ext2_debug ("Preallocated a further %lu bits.\n",
			    *prealloc_count);
	}
#endif

	j = tmp;

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

	if (j >= es->s_blocks_count) {
		ext2_error (sb, "ext2_new_block",
			    "block >= blocks count\n"
			    "block_group = %d, block=%d", i, j);
		unlock_super (sb);
		return 0;
	}
	if (!(bh = getblk (sb->s_dev, j, sb->s_blocksize))) {
		ext2_error (sb, "ext2_new_block", "cannot get block %d", j);
		unlock_super (sb);
		return 0;
	}
	clear_block (bh->b_data, sb->s_blocksize);
	bh->b_uptodate = 1;
	bh->b_dirt = 1;
	brelse (bh);

	ext2_debug ("allocating block %d. "
		    "Goal hits %d of %d.\n", j, goal_hits, goal_attempts);

	gdp->bg_free_blocks_count--;
	bh2->b_dirt = 1;
	es->s_free_blocks_count--;
	sb->u.ext2_sb.s_sbh->b_dirt = 1;
	sb->s_dirt = 1;
	unlock_super (sb);
	return j;
}

unsigned long ext2_count_free_blocks (struct super_block * sb)
{
#ifdef EXT2FS_DEBUG
	struct ext2_super_block * es;
	unsigned long desc_count, bitmap_count, x;
	int bitmap_nr;
	struct ext2_group_desc * gdp;
	int i;
	
	lock_super (sb);
	es = sb->u.ext2_sb.s_es;
	desc_count = 0;
	bitmap_count = 0;
	gdp = NULL;
	for (i = 0; i < sb->u.ext2_sb.s_groups_count; i++) {
		gdp = get_group_desc (sb, i, NULL);
		desc_count += gdp->bg_free_blocks_count;
		bitmap_nr = load_block_bitmap (sb, i);
		x = ext2_count_free (sb->u.ext2_sb.s_block_bitmap[bitmap_nr],
				     sb->s_blocksize);
		printk ("group %d: stored = %d, counted = %lu\n",
			i, gdp->bg_free_blocks_count, x);
		bitmap_count += x;
	}
	printk("ext2_count_free_blocks: stored = %lu, computed = %lu, %lu\n",
	       es->s_free_blocks_count, desc_count, bitmap_count);
	unlock_super (sb);
	return bitmap_count;
#else
	return sb->u.ext2_sb.s_es->s_free_blocks_count;
#endif
}

static inline int block_in_use (unsigned long block,
				struct super_block * sb,
				unsigned char * map)
{
	return test_bit ((block - sb->u.ext2_sb.s_es->s_first_data_block) %
			 EXT2_BLOCKS_PER_GROUP(sb), map);
}

void ext2_check_blocks_bitmap (struct super_block * sb)
{
	struct buffer_head * bh;
	struct ext2_super_block * es;
	unsigned long desc_count, bitmap_count, x;
	unsigned long desc_blocks;
	int bitmap_nr;
	struct ext2_group_desc * gdp;
	int i, j;

	lock_super (sb);
	es = sb->u.ext2_sb.s_es;
	desc_count = 0;
	bitmap_count = 0;
	gdp = NULL;
	desc_blocks = (sb->u.ext2_sb.s_groups_count + EXT2_DESC_PER_BLOCK(sb) - 1) /
		      EXT2_DESC_PER_BLOCK(sb);
	for (i = 0; i < sb->u.ext2_sb.s_groups_count; i++) {
		gdp = get_group_desc (sb, i, NULL);
		desc_count += gdp->bg_free_blocks_count;
		bitmap_nr = load_block_bitmap (sb, i);
		bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];

		if (!test_bit (0, bh->b_data))
			ext2_error (sb, "ext2_check_blocks_bitmap",
				    "Superblock in group %d is marked free", i);

		for (j = 0; j < desc_blocks; j++)
			if (!test_bit (j + 1, bh->b_data))
				ext2_error (sb, "ext2_check_blocks_bitmap",
					    "Descriptor block #%d in group "
					    "%d is marked free", j, i);

		if (!block_in_use (gdp->bg_block_bitmap, sb, bh->b_data))
			ext2_error (sb, "ext2_check_blocks_bitmap",
				    "Block bitmap for group %d is marked free",
				    i);

		if (!block_in_use (gdp->bg_inode_bitmap, sb, bh->b_data))
			ext2_error (sb, "ext2_check_blocks_bitmap",
				    "Inode bitmap for group %d is marked free",
				    i);

		for (j = 0; j < sb->u.ext2_sb.s_itb_per_group; j++)
			if (!block_in_use (gdp->bg_inode_table + j, sb, bh->b_data))
				ext2_error (sb, "ext2_check_blocks_bitmap",
					    "Block #%d of the inode table in "
					    "group %d is marked free", j, i);

		x = ext2_count_free (bh, sb->s_blocksize);
		if (gdp->bg_free_blocks_count != x)
			ext2_error (sb, "ext2_check_blocks_bitmap",
				    "Wrong free blocks count for group %d, "
				    "stored = %d, counted = %lu", i,
				    gdp->bg_free_blocks_count, x);
		bitmap_count += x;
	}
	if (es->s_free_blocks_count != bitmap_count)
		ext2_error (sb, "ext2_check_blocks_bitmap",
			    "Wrong free blocks count in super block, "
			    "stored = %lu, counted = %lu",
			    es->s_free_blocks_count, bitmap_count);
	unlock_super (sb);
}