1. 根目录:
2. fs
3. sysv
4. itree.c

/*
 *  linux/fs/sysv/itree.c
 *
 *  Handling of indirect blocks' trees.
 *  AV, Sep--Dec 2000
 */

#include <linux/buffer_head.h>
#include <linux/mount.h>
#include <linux/string.h>
#include "sysv.h"

enum {DIRECT = 10, DEPTH = 4};	/* Have triple indirect */

static inline void dirty_indirect(struct buffer_head *bh, struct inode *inode)
{
	mark_buffer_dirty_inode(bh, inode);
	if (IS_SYNC(inode))
		sync_dirty_buffer(bh);
}

static int block_to_path(struct inode *inode, long block, int offsets[DEPTH])
{
	struct super_block *sb = inode->i_sb;
	struct sysv_sb_info *sbi = SYSV_SB(sb);
	int ptrs_bits = sbi->s_ind_per_block_bits;
	unsigned long	indirect_blocks = sbi->s_ind_per_block,
			double_blocks = sbi->s_ind_per_block_2;
	int n = 0;

	if (block < 0) {
		printk("sysv_block_map: block < 0\n");
	} else if (block < DIRECT) {
		offsets[n++] = block;
	} else if ( (block -= DIRECT) < indirect_blocks) {
		offsets[n++] = DIRECT;
		offsets[n++] = block;
	} else if ((block -= indirect_blocks) < double_blocks) {
		offsets[n++] = DIRECT+1;
		offsets[n++] = block >> ptrs_bits;
		offsets[n++] = block & (indirect_blocks - 1);
	} else if (((block -= double_blocks) >> (ptrs_bits * 2)) < indirect_blocks) {
		offsets[n++] = DIRECT+2;
		offsets[n++] = block >> (ptrs_bits * 2);
		offsets[n++] = (block >> ptrs_bits) & (indirect_blocks - 1);
		offsets[n++] = block & (indirect_blocks - 1);
	} else {
		/* nothing */;
	}
	return n;
}

static inline int block_to_cpu(struct sysv_sb_info *sbi, sysv_zone_t nr)
{
	return sbi->s_block_base + fs32_to_cpu(sbi, nr);
}

typedef struct {
	sysv_zone_t     *p;
	sysv_zone_t     key;
	struct buffer_head *bh;
} Indirect;

static DEFINE_RWLOCK(pointers_lock);

static inline void add_chain(Indirect *p, struct buffer_head *bh, sysv_zone_t *v)
{
	p->key = *(p->p = v);
	p->bh = bh;
}

static inline int verify_chain(Indirect *from, Indirect *to)
{
	while (from <= to && from->key == *from->p)
		from++;
	return (from > to);
}

static inline sysv_zone_t *block_end(struct buffer_head *bh)
{
	return (sysv_zone_t*)((char*)bh->b_data + bh->b_size);
}

/*
 * Requires read_lock(&pointers_lock) or write_lock(&pointers_lock)
 */
static Indirect *get_branch(struct inode *inode,
			    int depth,
			    int offsets[],
			    Indirect chain[],
			    int *err)
{
	struct super_block *sb = inode->i_sb;
	Indirect *p = chain;
	struct buffer_head *bh;

	*err = 0;
	add_chain(chain, NULL, SYSV_I(inode)->i_data + *offsets);
	if (!p->key)
		goto no_block;
	while (--depth) {
		int block = block_to_cpu(SYSV_SB(sb), p->key);
		bh = sb_bread(sb, block);
		if (!bh)
			goto failure;
		if (!verify_chain(chain, p))
			goto changed;
		add_chain(++p, bh, (sysv_zone_t*)bh->b_data + *++offsets);
		if (!p->key)
			goto no_block;
	}
	return NULL;

changed:
	brelse(bh);
	*err = -EAGAIN;
	goto no_block;
failure:
	*err = -EIO;
no_block:
	return p;
}

static int alloc_branch(struct inode *inode,
			int num,
			int *offsets,
			Indirect *branch)
{
	int blocksize = inode->i_sb->s_blocksize;
	int n = 0;
	int i;

	branch[0].key = sysv_new_block(inode->i_sb);
	if (branch[0].key) for (n = 1; n < num; n++) {
		struct buffer_head *bh;
		int parent;
		/* Allocate the next block */
		branch[n].key = sysv_new_block(inode->i_sb);
		if (!branch[n].key)
			break;
		/*
		 * Get buffer_head for parent block, zero it out and set 
		 * the pointer to new one, then send parent to disk.
		 */
		parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key);
		bh = sb_getblk(inode->i_sb, parent);
		lock_buffer(bh);
		memset(bh->b_data, 0, blocksize);
		branch[n].bh = bh;
		branch[n].p = (sysv_zone_t*) bh->b_data + offsets[n];
		*branch[n].p = branch[n].key;
		set_buffer_uptodate(bh);
		unlock_buffer(bh);
		dirty_indirect(bh, inode);
	}
	if (n == num)
		return 0;

	/* Allocation failed, free what we already allocated */
	for (i = 1; i < n; i++)
		bforget(branch[i].bh);
	for (i = 0; i < n; i++)
		sysv_free_block(inode->i_sb, branch[i].key);
	return -ENOSPC;
}

static inline int splice_branch(struct inode *inode,
				Indirect chain[],
				Indirect *where,
				int num)
{
	int i;

	/* Verify that place we are splicing to is still there and vacant */
	write_lock(&pointers_lock);
	if (!verify_chain(chain, where-1) || *where->p)
		goto changed;
	*where->p = where->key;
	write_unlock(&pointers_lock);

	inode->i_ctime = CURRENT_TIME_SEC;

	/* had we spliced it onto indirect block? */
	if (where->bh)
		dirty_indirect(where->bh, inode);

	if (IS_SYNC(inode))
		sysv_sync_inode(inode);
	else
		mark_inode_dirty(inode);
	return 0;

changed:
	write_unlock(&pointers_lock);
	for (i = 1; i < num; i++)
		bforget(where[i].bh);
	for (i = 0; i < num; i++)
		sysv_free_block(inode->i_sb, where[i].key);
	return -EAGAIN;
}

static int get_block(struct inode *inode, sector_t iblock, struct buffer_head *bh_result, int create)
{
	int err = -EIO;
	int offsets[DEPTH];
	Indirect chain[DEPTH];
	struct super_block *sb = inode->i_sb;
	Indirect *partial;
	int left;
	int depth = block_to_path(inode, iblock, offsets);

	if (depth == 0)
		goto out;

reread:
	read_lock(&pointers_lock);
	partial = get_branch(inode, depth, offsets, chain, &err);
	read_unlock(&pointers_lock);

	/* Simplest case - block found, no allocation needed */
	if (!partial) {
got_it:
		map_bh(bh_result, sb, block_to_cpu(SYSV_SB(sb),
					chain[depth-1].key));
		/* Clean up and exit */
		partial = chain+depth-1; /* the whole chain */
		goto cleanup;
	}

	/* Next simple case - plain lookup or failed read of indirect block */
	if (!create || err == -EIO) {
cleanup:
		while (partial > chain) {
			brelse(partial->bh);
			partial--;
		}
out:
		return err;
	}

	/*
	 * Indirect block might be removed by truncate while we were
	 * reading it. Handling of that case (forget what we've got and
	 * reread) is taken out of the main path.
	 */
	if (err == -EAGAIN)
		goto changed;

	left = (chain + depth) - partial;
	err = alloc_branch(inode, left, offsets+(partial-chain), partial);
	if (err)
		goto cleanup;

	if (splice_branch(inode, chain, partial, left) < 0)
		goto changed;

	set_buffer_new(bh_result);
	goto got_it;

changed:
	while (partial > chain) {
		brelse(partial->bh);
		partial--;
	}
	goto reread;
}

static inline int all_zeroes(sysv_zone_t *p, sysv_zone_t *q)
{
	while (p < q)
		if (*p++)
			return 0;
	return 1;
}

static Indirect *find_shared(struct inode *inode,
				int depth,
				int offsets[],
				Indirect chain[],
				sysv_zone_t *top)
{
	Indirect *partial, *p;
	int k, err;

	*top = 0;
	for (k = depth; k > 1 && !offsets[k-1]; k--)
		;

	write_lock(&pointers_lock);
	partial = get_branch(inode, k, offsets, chain, &err);
	if (!partial)
		partial = chain + k-1;
	/*
	 * If the branch acquired continuation since we've looked at it -
	 * fine, it should all survive and (new) top doesn't belong to us.
	 */
	if (!partial->key && *partial->p) {
		write_unlock(&pointers_lock);
		goto no_top;
	}
	for (p=partial; p>chain && all_zeroes((sysv_zone_t*)p->bh->b_data,p->p); p--)
		;
	/*
	 * OK, we've found the last block that must survive. The rest of our
	 * branch should be detached before unlocking. However, if that rest
	 * of branch is all ours and does not grow immediately from the inode
	 * it's easier to cheat and just decrement partial->p.
	 */
	if (p == chain + k - 1 && p > chain) {
		p->p--;
	} else {
		*top = *p->p;
		*p->p = 0;
	}
	write_unlock(&pointers_lock);

	while (partial > p) {
		brelse(partial->bh);
		partial--;
	}
no_top:
	return partial;
}

static inline void free_data(struct inode *inode, sysv_zone_t *p, sysv_zone_t *q)
{
	for ( ; p < q ; p++) {
		sysv_zone_t nr = *p;
		if (nr) {
			*p = 0;
			sysv_free_block(inode->i_sb, nr);
			mark_inode_dirty(inode);
		}
	}
}

static void free_branches(struct inode *inode, sysv_zone_t *p, sysv_zone_t *q, int depth)
{
	struct buffer_head * bh;
	struct super_block *sb = inode->i_sb;

	if (depth--) {
		for ( ; p < q ; p++) {
			int block;
			sysv_zone_t nr = *p;
			if (!nr)
				continue;
			*p = 0;
			block = block_to_cpu(SYSV_SB(sb), nr);
			bh = sb_bread(sb, block);
			if (!bh)
				continue;
			free_branches(inode, (sysv_zone_t*)bh->b_data,
					block_end(bh), depth);
			bforget(bh);
			sysv_free_block(sb, nr);
			mark_inode_dirty(inode);
		}
	} else
		free_data(inode, p, q);
}

void sysv_truncate (struct inode * inode)
{
	sysv_zone_t *i_data = SYSV_I(inode)->i_data;
	int offsets[DEPTH];
	Indirect chain[DEPTH];
	Indirect *partial;
	sysv_zone_t nr = 0;
	int n;
	long iblock;
	unsigned blocksize;

	if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode) ||
	    S_ISLNK(inode->i_mode)))
		return;

	blocksize = inode->i_sb->s_blocksize;
	iblock = (inode->i_size + blocksize-1)
					>> inode->i_sb->s_blocksize_bits;

	block_truncate_page(inode->i_mapping, inode->i_size, get_block);

	n = block_to_path(inode, iblock, offsets);
	if (n == 0)
		return;

	if (n == 1) {
		free_data(inode, i_data+offsets[0], i_data + DIRECT);
		goto do_indirects;
	}

	partial = find_shared(inode, n, offsets, chain, &nr);
	/* Kill the top of shared branch (already detached) */
	if (nr) {
		if (partial == chain)
			mark_inode_dirty(inode);
		else
			dirty_indirect(partial->bh, inode);
		free_branches(inode, &nr, &nr+1, (chain+n-1) - partial);
	}
	/* Clear the ends of indirect blocks on the shared branch */
	while (partial > chain) {
		free_branches(inode, partial->p + 1, block_end(partial->bh),
				(chain+n-1) - partial);
		dirty_indirect(partial->bh, inode);
		brelse (partial->bh);
		partial--;
	}
do_indirects:
	/* Kill the remaining (whole) subtrees (== subtrees deeper than...) */
	while (n < DEPTH) {
		nr = i_data[DIRECT + n - 1];
		if (nr) {
			i_data[DIRECT + n - 1] = 0;
			mark_inode_dirty(inode);
			free_branches(inode, &nr, &nr+1, n);
		}
		n++;
	}
	inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
	if (IS_SYNC(inode))
		sysv_sync_inode (inode);
	else
		mark_inode_dirty(inode);
}

static unsigned sysv_nblocks(struct super_block *s, loff_t size)
{
	struct sysv_sb_info *sbi = SYSV_SB(s);
	int ptrs_bits = sbi->s_ind_per_block_bits;
	unsigned blocks, res, direct = DIRECT, i = DEPTH;
	blocks = (size + s->s_blocksize - 1) >> s->s_blocksize_bits;
	res = blocks;
	while (--i && blocks > direct) {
		blocks = ((blocks - direct - 1) >> ptrs_bits) + 1;
		res += blocks;
		direct = 1;
	}
	return blocks;
}

int sysv_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
{
	struct super_block *s = dentry->d_sb;
	generic_fillattr(dentry->d_inode, stat);
	stat->blocks = (s->s_blocksize / 512) * sysv_nblocks(s, stat->size);
	stat->blksize = s->s_blocksize;
	return 0;
}

static int sysv_writepage(struct page *page, struct writeback_control *wbc)
{
	return block_write_full_page(page,get_block,wbc);
}

static int sysv_readpage(struct file *file, struct page *page)
{
	return block_read_full_page(page,get_block);
}

int sysv_prepare_chunk(struct page *page, loff_t pos, unsigned len)
{
	return __block_write_begin(page, pos, len, get_block);
}

static void sysv_write_failed(struct address_space *mapping, loff_t to)
{
	struct inode *inode = mapping->host;

	if (to > inode->i_size) {
		truncate_pagecache(inode, inode->i_size);
		sysv_truncate(inode);
	}
}

static int sysv_write_begin(struct file *file, struct address_space *mapping,
			loff_t pos, unsigned len, unsigned flags,
			struct page **pagep, void **fsdata)
{
	int ret;

	ret = block_write_begin(mapping, pos, len, flags, pagep, get_block);
	if (unlikely(ret))
		sysv_write_failed(mapping, pos + len);

	return ret;
}

static sector_t sysv_bmap(struct address_space *mapping, sector_t block)
{
	return generic_block_bmap(mapping,block,get_block);
}

const struct address_space_operations sysv_aops = {
	.readpage = sysv_readpage,
	.writepage = sysv_writepage,
	.write_begin = sysv_write_begin,
	.write_end = generic_write_end,
	.bmap = sysv_bmap
};