linux/fs/btrfs/backref.c

/*
 * Copyright (C) 2011 STRATO.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include "ctree.h"
#include "disk-io.h"
#include "backref.h"

struct __data_ref {
	struct list_head list;
	u64 inum;
	u64 root;
	u64 extent_data_item_offset;
};

struct __shared_ref {
	struct list_head list;
	u64 disk_byte;
};

static int __inode_info(u64 inum, u64 ioff, u8 key_type,
			struct btrfs_root *fs_root, struct btrfs_path *path,
			struct btrfs_key *found_key)
{
	int ret;
	struct btrfs_key key;
	struct extent_buffer *eb;

	key.type = key_type;
	key.objectid = inum;
	key.offset = ioff;

	ret = btrfs_search_slot(NULL, fs_root, &key, path, 0, 0);
	if (ret < 0)
		return ret;

	eb = path->nodes[0];
	if (ret && path->slots[0] >= btrfs_header_nritems(eb)) {
		ret = btrfs_next_leaf(fs_root, path);
		if (ret)
			return ret;
		eb = path->nodes[0];
	}

	btrfs_item_key_to_cpu(eb, found_key, path->slots[0]);
	if (found_key->type != key.type || found_key->objectid != key.objectid)
		return 1;

	return 0;
}

/*
 * this makes the path point to (inum INODE_ITEM ioff)
 */
int inode_item_info(u64 inum, u64 ioff, struct btrfs_root *fs_root,
			struct btrfs_path *path)
{
	struct btrfs_key key;
	return __inode_info(inum, ioff, BTRFS_INODE_ITEM_KEY, fs_root, path,
				&key);
}

static int inode_ref_info(u64 inum, u64 ioff, struct btrfs_root *fs_root,
				struct btrfs_path *path,
				struct btrfs_key *found_key)
{
	return __inode_info(inum, ioff, BTRFS_INODE_REF_KEY, fs_root, path,
				found_key);
}

/*
 * this iterates to turn a btrfs_inode_ref into a full filesystem path. elements
 * of the path are separated by '/' and the path is guaranteed to be
 * 0-terminated. the path is only given within the current file system.
 * Therefore, it never starts with a '/'. the caller is responsible to provide
 * "size" bytes in "dest". the dest buffer will be filled backwards. finally,
 * the start point of the resulting string is returned. this pointer is within
 * dest, normally.
 * in case the path buffer would overflow, the pointer is decremented further
 * as if output was written to the buffer, though no more output is actually
 * generated. that way, the caller can determine how much space would be
 * required for the path to fit into the buffer. in that case, the returned
 * value will be smaller than dest. callers must check this!
 */
static char *iref_to_path(struct btrfs_root *fs_root, struct btrfs_path *path,
				struct btrfs_inode_ref *iref,
				struct extent_buffer *eb_in, u64 parent,
				char *dest, u32 size)
{
	u32 len;
	int slot;
	u64 next_inum;
	int ret;
	s64 bytes_left = size - 1;
	struct extent_buffer *eb = eb_in;
	struct btrfs_key found_key;

	if (bytes_left >= 0)
		dest[bytes_left] = '\0';

	while (1) {
		len = btrfs_inode_ref_name_len(eb, iref);
		bytes_left -= len;
		if (bytes_left >= 0)
			read_extent_buffer(eb, dest + bytes_left,
						(unsigned long)(iref + 1), len);
		if (eb != eb_in)
			free_extent_buffer(eb);
		ret = inode_ref_info(parent, 0, fs_root, path, &found_key);
		if (ret)
			break;
		next_inum = found_key.offset;

		/* regular exit ahead */
		if (parent == next_inum)
			break;

		slot = path->slots[0];
		eb = path->nodes[0];
		/* make sure we can use eb after releasing the path */
		if (eb != eb_in)
			atomic_inc(&eb->refs);
		btrfs_release_path(path);

		iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);
		parent = next_inum;
		--bytes_left;
		if (bytes_left >= 0)
			dest[bytes_left] = '/';
	}

	btrfs_release_path(path);

	if (ret)
		return ERR_PTR(ret);

	return dest + bytes_left;
}

/*
 * this makes the path point to (logical EXTENT_ITEM *)
 * returns BTRFS_EXTENT_FLAG_DATA for data, BTRFS_EXTENT_FLAG_TREE_BLOCK for
 * tree blocks and <0 on error.
 */
int extent_from_logical(struct btrfs_fs_info *fs_info, u64 logical,
			struct btrfs_path *path, struct btrfs_key *found_key)
{
	int ret;
	u64 flags;
	u32 item_size;
	struct extent_buffer *eb;
	struct btrfs_extent_item *ei;
	struct btrfs_key key;

	key.type = BTRFS_EXTENT_ITEM_KEY;
	key.objectid = logical;
	key.offset = (u64)-1;

	ret = btrfs_search_slot(NULL, fs_info->extent_root, &key, path, 0, 0);
	if (ret < 0)
		return ret;
	ret = btrfs_previous_item(fs_info->extent_root, path,
					0, BTRFS_EXTENT_ITEM_KEY);
	if (ret < 0)
		return ret;

	btrfs_item_key_to_cpu(path->nodes[0], found_key, path->slots[0]);
	if (found_key->type != BTRFS_EXTENT_ITEM_KEY ||
	    found_key->objectid > logical ||
	    found_key->objectid + found_key->offset <= logical)
		return -ENOENT;

	eb = path->nodes[0];
	item_size = btrfs_item_size_nr(eb, path->slots[0]);
	BUG_ON(item_size < sizeof(*ei));

	ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
	flags = btrfs_extent_flags(eb, ei);

	if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK)
		return BTRFS_EXTENT_FLAG_TREE_BLOCK;
	if (flags & BTRFS_EXTENT_FLAG_DATA)
		return BTRFS_EXTENT_FLAG_DATA;

	return -EIO;
}

/*
 * helper function to iterate extent inline refs. ptr must point to a 0 value
 * for the first call and may be modified. it is used to track state.
 * if more refs exist, 0 is returned and the next call to
 * __get_extent_inline_ref must pass the modified ptr parameter to get the
 * next ref. after the last ref was processed, 1 is returned.
 * returns <0 on error
 */
static int __get_extent_inline_ref(unsigned long *ptr, struct extent_buffer *eb,
				struct btrfs_extent_item *ei, u32 item_size,
				struct btrfs_extent_inline_ref **out_eiref,
				int *out_type)
{
	unsigned long end;
	u64 flags;
	struct btrfs_tree_block_info *info;

	if (!*ptr) {
		/* first call */
		flags = btrfs_extent_flags(eb, ei);
		if (flags & BTRFS_EXTENT_FLAG_TREE_BLOCK) {
			info = (struct btrfs_tree_block_info *)(ei + 1);
			*out_eiref =
				(struct btrfs_extent_inline_ref *)(info + 1);
		} else {
			*out_eiref = (struct btrfs_extent_inline_ref *)(ei + 1);
		}
		*ptr = (unsigned long)*out_eiref;
		if ((void *)*ptr >= (void *)ei + item_size)
			return -ENOENT;
	}

	end = (unsigned long)ei + item_size;
	*out_eiref = (struct btrfs_extent_inline_ref *)*ptr;
	*out_type = btrfs_extent_inline_ref_type(eb, *out_eiref);

	*ptr += btrfs_extent_inline_ref_size(*out_type);
	WARN_ON(*ptr > end);
	if (*ptr == end)
		return 1; /* last */

	return 0;
}

/*
 * reads the tree block backref for an extent. tree level and root are returned
 * through out_level and out_root. ptr must point to a 0 value for the first
 * call and may be modified (see __get_extent_inline_ref comment).
 * returns 0 if data was provided, 1 if there was no more data to provide or
 * <0 on error.
 */
int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
				struct btrfs_extent_item *ei, u32 item_size,
				u64 *out_root, u8 *out_level)
{
	int ret;
	int type;
	struct btrfs_tree_block_info *info;
	struct btrfs_extent_inline_ref *eiref;

	if (*ptr == (unsigned long)-1)
		return 1;

	while (1) {
		ret = __get_extent_inline_ref(ptr, eb, ei, item_size,
						&eiref, &type);
		if (ret < 0)
			return ret;

		if (type == BTRFS_TREE_BLOCK_REF_KEY ||
		    type == BTRFS_SHARED_BLOCK_REF_KEY)
			break;

		if (ret == 1)
			return 1;
	}

	/* we can treat both ref types equally here */
	info = (struct btrfs_tree_block_info *)(ei + 1);
	*out_root = btrfs_extent_inline_ref_offset(eb, eiref);
	*out_level = btrfs_tree_block_level(eb, info);

	if (ret == 1)
		*ptr = (unsigned long)-1;

	return 0;
}

static int __data_list_add(struct list_head *head, u64 inum,
				u64 extent_data_item_offset, u64 root)
{
	struct __data_ref *ref;

	ref = kmalloc(sizeof(*ref), GFP_NOFS);
	if (!ref)
		return -ENOMEM;

	ref->inum = inum;
	ref->extent_data_item_offset = extent_data_item_offset;
	ref->root = root;
	list_add_tail(&ref->list, head);

	return 0;
}

static int __data_list_add_eb(struct list_head *head, struct extent_buffer *eb,
				struct btrfs_extent_data_ref *dref)
{
	return __data_list_add(head, btrfs_extent_data_ref_objectid(eb, dref),
				btrfs_extent_data_ref_offset(eb, dref),
				btrfs_extent_data_ref_root(eb, dref));
}

static int __shared_list_add(struct list_head *head, u64 disk_byte)
{
	struct __shared_ref *ref;

	ref = kmalloc(sizeof(*ref), GFP_NOFS);
	if (!ref)
		return -ENOMEM;

	ref->disk_byte = disk_byte;
	list_add_tail(&ref->list, head);

	return 0;
}

static int __iter_shared_inline_ref_inodes(struct btrfs_fs_info *fs_info,
					   u64 logical, u64 inum,
					   u64 extent_data_item_offset,
					   u64 extent_offset,
					   struct btrfs_path *path,
					   struct list_head *data_refs,
					   iterate_extent_inodes_t *iterate,
					   void *ctx)
{
	u64 ref_root;
	u32 item_size;
	struct btrfs_key key;
	struct extent_buffer *eb;
	struct btrfs_extent_item *ei;
	struct btrfs_extent_inline_ref *eiref;
	struct __data_ref *ref;
	int ret;
	int type;
	int last;
	unsigned long ptr = 0;

	WARN_ON(!list_empty(data_refs));
	ret = extent_from_logical(fs_info, logical, path, &key);
	if (ret & BTRFS_EXTENT_FLAG_DATA)
		ret = -EIO;
	if (ret < 0)
		goto out;

	eb = path->nodes[0];
	ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
	item_size = btrfs_item_size_nr(eb, path->slots[0]);

	ret = 0;
	ref_root = 0;
	/*
	 * as done in iterate_extent_inodes, we first build a list of refs to
	 * iterate, then free the path and then iterate them to avoid deadlocks.
	 */
	do {
		last = __get_extent_inline_ref(&ptr, eb, ei, item_size,
						&eiref, &type);
		if (last < 0) {
			ret = last;
			goto out;
		}
		if (type == BTRFS_TREE_BLOCK_REF_KEY ||
		    type == BTRFS_SHARED_BLOCK_REF_KEY) {
			ref_root = btrfs_extent_inline_ref_offset(eb, eiref);
			ret = __data_list_add(data_refs, inum,
						extent_data_item_offset,
						ref_root);
		}
	} while (!ret && !last);

	btrfs_release_path(path);

	if (ref_root == 0) {
		printk(KERN_ERR "btrfs: failed to find tree block ref "
			"for shared data backref %llu\n", logical);
		WARN_ON(1);
		ret = -EIO;
	}

out:
	while (!list_empty(data_refs)) {
		ref = list_first_entry(data_refs, struct __data_ref, list);
		list_del(&ref->list);
		if (!ret)
			ret = iterate(ref->inum, extent_offset +
					ref->extent_data_item_offset,
					ref->root, ctx);
		kfree(ref);
	}

	return ret;
}

static int __iter_shared_inline_ref(struct btrfs_fs_info *fs_info,
				    u64 logical, u64 orig_extent_item_objectid,
				    u64 extent_offset, struct btrfs_path *path,
				    struct list_head *data_refs,
				    iterate_extent_inodes_t *iterate,
				    void *ctx)
{
	u64 disk_byte;
	struct btrfs_key key;
	struct btrfs_file_extent_item *fi;
	struct extent_buffer *eb;
	int slot;
	int nritems;
	int ret;
	int found = 0;

	eb = read_tree_block(fs_info->tree_root, logical,
				fs_info->tree_root->leafsize, 0);
	if (!eb)
		return -EIO;

	/*
	 * from the shared data ref, we only have the leaf but we need
	 * the key. thus, we must look into all items and see that we
	 * find one (some) with a reference to our extent item.
	 */
	nritems = btrfs_header_nritems(eb);
	for (slot = 0; slot < nritems; ++slot) {
		btrfs_item_key_to_cpu(eb, &key, slot);
		if (key.type != BTRFS_EXTENT_DATA_KEY)
			continue;
		fi = btrfs_item_ptr(eb, slot, struct btrfs_file_extent_item);
		if (!fi) {
			free_extent_buffer(eb);
			return -EIO;
		}
		disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
		if (disk_byte != orig_extent_item_objectid) {
			if (found)
				break;
			else
				continue;
		}
		++found;
		ret = __iter_shared_inline_ref_inodes(fs_info, logical,
							key.objectid,
							key.offset,
							extent_offset, path,
							data_refs,
							iterate, ctx);
		if (ret)
			break;
	}

	if (!found) {
		printk(KERN_ERR "btrfs: failed to follow shared data backref "
			"to parent %llu\n", logical);
		WARN_ON(1);
		ret = -EIO;
	}

	free_extent_buffer(eb);
	return ret;
}

/*
 * calls iterate() for every inode that references the extent identified by
 * the given parameters. will use the path given as a parameter and return it
 * released.
 * when the iterator function returns a non-zero value, iteration stops.
 */
int iterate_extent_inodes(struct btrfs_fs_info *fs_info,
				struct btrfs_path *path,
				u64 extent_item_objectid,
				u64 extent_offset,
				iterate_extent_inodes_t *iterate, void *ctx)
{
	unsigned long ptr = 0;
	int last;
	int ret;
	int type;
	u64 logical;
	u32 item_size;
	struct btrfs_extent_inline_ref *eiref;
	struct btrfs_extent_data_ref *dref;
	struct extent_buffer *eb;
	struct btrfs_extent_item *ei;
	struct btrfs_key key;
	struct list_head data_refs = LIST_HEAD_INIT(data_refs);
	struct list_head shared_refs = LIST_HEAD_INIT(shared_refs);
	struct __data_ref *ref_d;
	struct __shared_ref *ref_s;

	eb = path->nodes[0];
	ei = btrfs_item_ptr(eb, path->slots[0], struct btrfs_extent_item);
	item_size = btrfs_item_size_nr(eb, path->slots[0]);

	/* first we iterate the inline refs, ... */
	do {
		last = __get_extent_inline_ref(&ptr, eb, ei, item_size,
						&eiref, &type);
		if (last == -ENOENT) {
			ret = 0;
			break;
		}
		if (last < 0) {
			ret = last;
			break;
		}

		if (type == BTRFS_EXTENT_DATA_REF_KEY) {
			dref = (struct btrfs_extent_data_ref *)(&eiref->offset);
			ret = __data_list_add_eb(&data_refs, eb, dref);
		} else if (type == BTRFS_SHARED_DATA_REF_KEY) {
			logical = btrfs_extent_inline_ref_offset(eb, eiref);
			ret = __shared_list_add(&shared_refs, logical);
		}
	} while (!ret && !last);

	/* ... then we proceed to in-tree references and ... */
	while (!ret) {
		++path->slots[0];
		if (path->slots[0] > btrfs_header_nritems(eb)) {
			ret = btrfs_next_leaf(fs_info->extent_root, path);
			if (ret) {
				if (ret == 1)
					ret = 0; /* we're done */
				break;
			}
			eb = path->nodes[0];
		}
		btrfs_item_key_to_cpu(eb, &key, path->slots[0]);
		if (key.objectid != extent_item_objectid)
			break;
		if (key.type == BTRFS_EXTENT_DATA_REF_KEY) {
			dref = btrfs_item_ptr(eb, path->slots[0],
						struct btrfs_extent_data_ref);
			ret = __data_list_add_eb(&data_refs, eb, dref);
		} else if (key.type == BTRFS_SHARED_DATA_REF_KEY) {
			ret = __shared_list_add(&shared_refs, key.offset);
		}
	}

	btrfs_release_path(path);

	/*
	 * ... only at the very end we can process the refs we found. this is
	 * because the iterator function we call is allowed to make tree lookups
	 * and we have to avoid deadlocks. additionally, we need more tree
	 * lookups ourselves for shared data refs.
	 */
	while (!list_empty(&data_refs)) {
		ref_d = list_first_entry(&data_refs, struct __data_ref, list);
		list_del(&ref_d->list);
		if (!ret)
			ret = iterate(ref_d->inum, extent_offset +
					ref_d->extent_data_item_offset,
					ref_d->root, ctx);
		kfree(ref_d);
	}

	while (!list_empty(&shared_refs)) {
		ref_s = list_first_entry(&shared_refs, struct __shared_ref,
					list);
		list_del(&ref_s->list);
		if (!ret)
			ret = __iter_shared_inline_ref(fs_info,
							ref_s->disk_byte,
							extent_item_objectid,
							extent_offset, path,
							&data_refs,
							iterate, ctx);
		kfree(ref_s);
	}

	return ret;
}

int iterate_inodes_from_logical(u64 logical, struct btrfs_fs_info *fs_info,
				struct btrfs_path *path,
				iterate_extent_inodes_t *iterate, void *ctx)
{
	int ret;
	u64 offset;
	struct btrfs_key found_key;

	ret = extent_from_logical(fs_info, logical, path,
					&found_key);
	if (ret & BTRFS_EXTENT_FLAG_TREE_BLOCK)
		ret = -EINVAL;
	if (ret < 0)
		return ret;

	offset = logical - found_key.objectid;
	ret = iterate_extent_inodes(fs_info, path, found_key.objectid,
					offset, iterate, ctx);

	return ret;
}

static int iterate_irefs(u64 inum, struct btrfs_root *fs_root,
				struct btrfs_path *path,
				iterate_irefs_t *iterate, void *ctx)
{
	int ret;
	int slot;
	u32 cur;
	u32 len;
	u32 name_len;
	u64 parent = 0;
	int found = 0;
	struct extent_buffer *eb;
	struct btrfs_item *item;
	struct btrfs_inode_ref *iref;
	struct btrfs_key found_key;

	while (1) {
		ret = inode_ref_info(inum, parent ? parent+1 : 0, fs_root, path,
					&found_key);
		if (ret < 0)
			break;
		if (ret) {
			ret = found ? 0 : -ENOENT;
			break;
		}
		++found;

		parent = found_key.offset;
		slot = path->slots[0];
		eb = path->nodes[0];
		/* make sure we can use eb after releasing the path */
		atomic_inc(&eb->refs);
		btrfs_release_path(path);

		item = btrfs_item_nr(eb, slot);
		iref = btrfs_item_ptr(eb, slot, struct btrfs_inode_ref);

		for (cur = 0; cur < btrfs_item_size(eb, item); cur += len) {
			name_len = btrfs_inode_ref_name_len(eb, iref);
			/* path must be released before calling iterate()! */
			ret = iterate(parent, iref, eb, ctx);
			if (ret) {
				free_extent_buffer(eb);
				break;
			}
			len = sizeof(*iref) + name_len;
			iref = (struct btrfs_inode_ref *)((char *)iref + len);
		}
		free_extent_buffer(eb);
	}

	btrfs_release_path(path);

	return ret;
}

/*
 * returns 0 if the path could be dumped (probably truncated)
 * returns <0 in case of an error
 */
static int inode_to_path(u64 inum, struct btrfs_inode_ref *iref,
				struct extent_buffer *eb, void *ctx)
{
	struct inode_fs_paths *ipath = ctx;
	char *fspath;
	char *fspath_min;
	int i = ipath->fspath->elem_cnt;
	const int s_ptr = sizeof(char *);
	u32 bytes_left;

	bytes_left = ipath->fspath->bytes_left > s_ptr ?
					ipath->fspath->bytes_left - s_ptr : 0;

	fspath_min = (char *)ipath->fspath->val + (i + 1) * s_ptr;
	fspath = iref_to_path(ipath->fs_root, ipath->btrfs_path, iref, eb,
				inum, fspath_min, bytes_left);
	if (IS_ERR(fspath))
		return PTR_ERR(fspath);

	if (fspath > fspath_min) {
		ipath->fspath->val[i] = (u64)(unsigned long)fspath;
		++ipath->fspath->elem_cnt;
		ipath->fspath->bytes_left = fspath - fspath_min;
	} else {
		++ipath->fspath->elem_missed;
		ipath->fspath->bytes_missing += fspath_min - fspath;
		ipath->fspath->bytes_left = 0;
	}

	return 0;
}

/*
 * this dumps all file system paths to the inode into the ipath struct, provided
 * is has been created large enough. each path is zero-terminated and accessed
 * from ipath->fspath->val[i].
 * when it returns, there are ipath->fspath->elem_cnt number of paths available
 * in ipath->fspath->val[]. when the allocated space wasn't sufficient, the
 * number of missed paths in recored in ipath->fspath->elem_missed, otherwise,
 * it's zero. ipath->fspath->bytes_missing holds the number of bytes that would
 * have been needed to return all paths.
 */
int paths_from_inode(u64 inum, struct inode_fs_paths *ipath)
{
	return iterate_irefs(inum, ipath->fs_root, ipath->btrfs_path,
				inode_to_path, ipath);
}

/*
 * allocates space to return multiple file system paths for an inode.
 * total_bytes to allocate are passed, note that space usable for actual path
 * information will be total_bytes - sizeof(struct inode_fs_paths).
 * the returned pointer must be freed with free_ipath() in the end.
 */
struct btrfs_data_container *init_data_container(u32 total_bytes)
{
	struct btrfs_data_container *data;
	size_t alloc_bytes;

	alloc_bytes = max_t(size_t, total_bytes, sizeof(*data));
	data = kmalloc(alloc_bytes, GFP_NOFS);
	if (!data)
		return ERR_PTR(-ENOMEM);

	if (total_bytes >= sizeof(*data)) {
		data->bytes_left = total_bytes - sizeof(*data);
		data->bytes_missing = 0;
	} else {
		data->bytes_missing = sizeof(*data) - total_bytes;
		data->bytes_left = 0;
	}

	data->elem_cnt = 0;
	data->elem_missed = 0;

	return data;
}

/*
 * allocates space to return multiple file system paths for an inode.
 * total_bytes to allocate are passed, note that space usable for actual path
 * information will be total_bytes - sizeof(struct inode_fs_paths).
 * the returned pointer must be freed with free_ipath() in the end.
 */
struct inode_fs_paths *init_ipath(s32 total_bytes, struct btrfs_root *fs_root,
					struct btrfs_path *path)
{
	struct inode_fs_paths *ifp;
	struct btrfs_data_container *fspath;

	fspath = init_data_container(total_bytes);
	if (IS_ERR(fspath))
		return (void *)fspath;

	ifp = kmalloc(sizeof(*ifp), GFP_NOFS);
	if (!ifp) {
		kfree(fspath);
		return ERR_PTR(-ENOMEM);
	}

	ifp->btrfs_path = path;
	ifp->fspath = fspath;
	ifp->fs_root = fs_root;

	return ifp;
}

void free_ipath(struct inode_fs_paths *ipath)
{
	kfree(ipath);
}