ctree.h 74.1 KB
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/*
 * Copyright (C) 2007 Oracle.  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.
 */

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#ifndef __BTRFS_CTREE__
#define __BTRFS_CTREE__
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#include <linux/version.h>
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#include <linux/mm.h>
#include <linux/highmem.h>
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#include <linux/fs.h>
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#include <linux/completion.h>
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#include <linux/backing-dev.h>
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#include <linux/wait.h>
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#include <asm/kmap_types.h>
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#include "extent_io.h"
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#include "extent_map.h"
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#include "async-thread.h"
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struct btrfs_trans_handle;
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struct btrfs_transaction;
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extern struct kmem_cache *btrfs_trans_handle_cachep;
extern struct kmem_cache *btrfs_transaction_cachep;
extern struct kmem_cache *btrfs_bit_radix_cachep;
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extern struct kmem_cache *btrfs_path_cachep;
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struct btrfs_ordered_sum;
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#define BTRFS_MAGIC "_BHRfS_M"
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#define BTRFS_MAX_LEVEL 8
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#define BTRFS_COMPAT_EXTENT_TREE_V0

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/*
 * files bigger than this get some pre-flushing when they are added
 * to the ordered operations list.  That way we limit the total
 * work done by the commit
 */
#define BTRFS_ORDERED_OPERATIONS_FLUSH_LIMIT (8 * 1024 * 1024)

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/* holds pointers to all of the tree roots */
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#define BTRFS_ROOT_TREE_OBJECTID 1ULL
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/* stores information about which extents are in use, and reference counts */
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#define BTRFS_EXTENT_TREE_OBJECTID 2ULL
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/*
 * chunk tree stores translations from logical -> physical block numbering
 * the super block points to the chunk tree
 */
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#define BTRFS_CHUNK_TREE_OBJECTID 3ULL
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/*
 * stores information about which areas of a given device are in use.
 * one per device.  The tree of tree roots points to the device tree
 */
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#define BTRFS_DEV_TREE_OBJECTID 4ULL

/* one per subvolume, storing files and directories */
#define BTRFS_FS_TREE_OBJECTID 5ULL

/* directory objectid inside the root tree */
#define BTRFS_ROOT_TREE_DIR_OBJECTID 6ULL
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/* holds checksums of all the data extents */
#define BTRFS_CSUM_TREE_OBJECTID 7ULL

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/* orhpan objectid for tracking unlinked/truncated files */
#define BTRFS_ORPHAN_OBJECTID -5ULL

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/* does write ahead logging to speed up fsyncs */
#define BTRFS_TREE_LOG_OBJECTID -6ULL
#define BTRFS_TREE_LOG_FIXUP_OBJECTID -7ULL

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/* for space balancing */
#define BTRFS_TREE_RELOC_OBJECTID -8ULL
#define BTRFS_DATA_RELOC_TREE_OBJECTID -9ULL

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/*
 * extent checksums all have this objectid
 * this allows them to share the logging tree
 * for fsyncs
 */
#define BTRFS_EXTENT_CSUM_OBJECTID -10ULL

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/* dummy objectid represents multiple objectids */
#define BTRFS_MULTIPLE_OBJECTIDS -255ULL

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/*
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 * All files have objectids in this range.
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 */
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#define BTRFS_FIRST_FREE_OBJECTID 256ULL
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#define BTRFS_LAST_FREE_OBJECTID -256ULL
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#define BTRFS_FIRST_CHUNK_TREE_OBJECTID 256ULL
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/*
 * the device items go into the chunk tree.  The key is in the form
 * [ 1 BTRFS_DEV_ITEM_KEY device_id ]
 */
#define BTRFS_DEV_ITEMS_OBJECTID 1ULL

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/*
 * we can actually store much bigger names, but lets not confuse the rest
 * of linux
 */
#define BTRFS_NAME_LEN 255

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/* 32 bytes in various csum fields */
#define BTRFS_CSUM_SIZE 32
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/* csum types */
#define BTRFS_CSUM_TYPE_CRC32	0

static int btrfs_csum_sizes[] = { 4, 0 };

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/* four bytes for CRC32 */
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#define BTRFS_EMPTY_DIR_SIZE 0
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#define BTRFS_FT_UNKNOWN	0
#define BTRFS_FT_REG_FILE	1
#define BTRFS_FT_DIR		2
#define BTRFS_FT_CHRDEV		3
#define BTRFS_FT_BLKDEV		4
#define BTRFS_FT_FIFO		5
#define BTRFS_FT_SOCK		6
#define BTRFS_FT_SYMLINK	7
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#define BTRFS_FT_XATTR		8
#define BTRFS_FT_MAX		9
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/*
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 * The key defines the order in the tree, and so it also defines (optimal)
 * block layout.
 *
 * objectid corresponds to the inode number.
 *
 * type tells us things about the object, and is a kind of stream selector.
 * so for a given inode, keys with type of 1 might refer to the inode data,
 * type of 2 may point to file data in the btree and type == 3 may point to
 * extents.
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 *
 * offset is the starting byte offset for this key in the stream.
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 *
 * btrfs_disk_key is in disk byte order.  struct btrfs_key is always
 * in cpu native order.  Otherwise they are identical and their sizes
 * should be the same (ie both packed)
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 */
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struct btrfs_disk_key {
	__le64 objectid;
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	u8 type;
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	__le64 offset;
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} __attribute__ ((__packed__));

struct btrfs_key {
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	u64 objectid;
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	u8 type;
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	u64 offset;
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} __attribute__ ((__packed__));

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struct btrfs_mapping_tree {
	struct extent_map_tree map_tree;
};

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#define BTRFS_UUID_SIZE 16
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struct btrfs_dev_item {
	/* the internal btrfs device id */
	__le64 devid;

	/* size of the device */
	__le64 total_bytes;

	/* bytes used */
	__le64 bytes_used;

	/* optimal io alignment for this device */
	__le32 io_align;

	/* optimal io width for this device */
	__le32 io_width;

	/* minimal io size for this device */
	__le32 sector_size;

	/* type and info about this device */
	__le64 type;

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	/* expected generation for this device */
	__le64 generation;

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	/*
	 * starting byte of this partition on the device,
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	 * to allow for stripe alignment in the future
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	 */
	__le64 start_offset;

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	/* grouping information for allocation decisions */
	__le32 dev_group;

	/* seek speed 0-100 where 100 is fastest */
	u8 seek_speed;

	/* bandwidth 0-100 where 100 is fastest */
	u8 bandwidth;

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	/* btrfs generated uuid for this device */
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	u8 uuid[BTRFS_UUID_SIZE];
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	/* uuid of FS who owns this device */
	u8 fsid[BTRFS_UUID_SIZE];
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} __attribute__ ((__packed__));

struct btrfs_stripe {
	__le64 devid;
	__le64 offset;
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	u8 dev_uuid[BTRFS_UUID_SIZE];
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} __attribute__ ((__packed__));

struct btrfs_chunk {
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	/* size of this chunk in bytes */
	__le64 length;

	/* objectid of the root referencing this chunk */
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	__le64 owner;
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	__le64 stripe_len;
	__le64 type;

	/* optimal io alignment for this chunk */
	__le32 io_align;

	/* optimal io width for this chunk */
	__le32 io_width;

	/* minimal io size for this chunk */
	__le32 sector_size;

	/* 2^16 stripes is quite a lot, a second limit is the size of a single
	 * item in the btree
	 */
	__le16 num_stripes;
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	/* sub stripes only matter for raid10 */
	__le16 sub_stripes;
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	struct btrfs_stripe stripe;
	/* additional stripes go here */
} __attribute__ ((__packed__));

static inline unsigned long btrfs_chunk_item_size(int num_stripes)
{
	BUG_ON(num_stripes == 0);
	return sizeof(struct btrfs_chunk) +
		sizeof(struct btrfs_stripe) * (num_stripes - 1);
}

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#define BTRFS_FSID_SIZE 16
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#define BTRFS_HEADER_FLAG_WRITTEN	(1ULL << 0)
#define BTRFS_HEADER_FLAG_RELOC		(1ULL << 1)
#define BTRFS_SUPER_FLAG_SEEDING	(1ULL << 32)
#define BTRFS_SUPER_FLAG_METADUMP	(1ULL << 33)

#define BTRFS_BACKREF_REV_MAX		256
#define BTRFS_BACKREF_REV_SHIFT		56
#define BTRFS_BACKREF_REV_MASK		(((u64)BTRFS_BACKREF_REV_MAX - 1) << \
					 BTRFS_BACKREF_REV_SHIFT)

#define BTRFS_OLD_BACKREF_REV		0
#define BTRFS_MIXED_BACKREF_REV		1
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/*
 * every tree block (leaf or node) starts with this header.
 */
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struct btrfs_header {
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	/* these first four must match the super block */
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	u8 csum[BTRFS_CSUM_SIZE];
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	u8 fsid[BTRFS_FSID_SIZE]; /* FS specific uuid */
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	__le64 bytenr; /* which block this node is supposed to live in */
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	__le64 flags;
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	/* allowed to be different from the super from here on down */
	u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
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	__le64 generation;
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	__le64 owner;
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	__le32 nritems;
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	u8 level;
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} __attribute__ ((__packed__));

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#define BTRFS_NODEPTRS_PER_BLOCK(r) (((r)->nodesize - \
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				      sizeof(struct btrfs_header)) / \
				     sizeof(struct btrfs_key_ptr))
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#define __BTRFS_LEAF_DATA_SIZE(bs) ((bs) - sizeof(struct btrfs_header))
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#define BTRFS_LEAF_DATA_SIZE(r) (__BTRFS_LEAF_DATA_SIZE(r->leafsize))
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#define BTRFS_MAX_INLINE_DATA_SIZE(r) (BTRFS_LEAF_DATA_SIZE(r) - \
					sizeof(struct btrfs_item) - \
					sizeof(struct btrfs_file_extent_item))
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/*
 * this is a very generous portion of the super block, giving us
 * room to translate 14 chunks with 3 stripes each.
 */
#define BTRFS_SYSTEM_CHUNK_ARRAY_SIZE 2048
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#define BTRFS_LABEL_SIZE 256
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/*
 * the super block basically lists the main trees of the FS
 * it currently lacks any block count etc etc
 */
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struct btrfs_super_block {
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	u8 csum[BTRFS_CSUM_SIZE];
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	/* the first 4 fields must match struct btrfs_header */
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	u8 fsid[BTRFS_FSID_SIZE];    /* FS specific uuid */
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	__le64 bytenr; /* this block number */
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	__le64 flags;
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	/* allowed to be different from the btrfs_header from here own down */
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	__le64 magic;
	__le64 generation;
	__le64 root;
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	__le64 chunk_root;
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	__le64 log_root;
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	/* this will help find the new super based on the log root */
	__le64 log_root_transid;
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	__le64 total_bytes;
	__le64 bytes_used;
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	__le64 root_dir_objectid;
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	__le64 num_devices;
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	__le32 sectorsize;
	__le32 nodesize;
	__le32 leafsize;
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	__le32 stripesize;
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	__le32 sys_chunk_array_size;
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	__le64 chunk_root_generation;
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	__le64 compat_flags;
	__le64 compat_ro_flags;
	__le64 incompat_flags;
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	__le16 csum_type;
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	u8 root_level;
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	u8 chunk_root_level;
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	u8 log_root_level;
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	struct btrfs_dev_item dev_item;
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	char label[BTRFS_LABEL_SIZE];
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	/* future expansion */
	__le64 reserved[32];
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	u8 sys_chunk_array[BTRFS_SYSTEM_CHUNK_ARRAY_SIZE];
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} __attribute__ ((__packed__));

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/*
 * Compat flags that we support.  If any incompat flags are set other than the
 * ones specified below then we will fail to mount
 */
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#define BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF	(1ULL << 0)

#define BTRFS_FEATURE_COMPAT_SUPP		0ULL
#define BTRFS_FEATURE_COMPAT_RO_SUPP		0ULL
#define BTRFS_FEATURE_INCOMPAT_SUPP		\
	BTRFS_FEATURE_INCOMPAT_MIXED_BACKREF
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/*
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 * A leaf is full of items. offset and size tell us where to find
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 * the item in the leaf (relative to the start of the data area)
 */
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struct btrfs_item {
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	struct btrfs_disk_key key;
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	__le32 offset;
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	__le32 size;
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} __attribute__ ((__packed__));

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/*
 * leaves have an item area and a data area:
 * [item0, item1....itemN] [free space] [dataN...data1, data0]
 *
 * The data is separate from the items to get the keys closer together
 * during searches.
 */
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struct btrfs_leaf {
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	struct btrfs_header header;
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	struct btrfs_item items[];
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} __attribute__ ((__packed__));

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/*
 * all non-leaf blocks are nodes, they hold only keys and pointers to
 * other blocks
 */
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struct btrfs_key_ptr {
	struct btrfs_disk_key key;
	__le64 blockptr;
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	__le64 generation;
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} __attribute__ ((__packed__));

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struct btrfs_node {
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	struct btrfs_header header;
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	struct btrfs_key_ptr ptrs[];
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} __attribute__ ((__packed__));

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/*
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 * btrfs_paths remember the path taken from the root down to the leaf.
 * level 0 is always the leaf, and nodes[1...BTRFS_MAX_LEVEL] will point
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 * to any other levels that are present.
 *
 * The slots array records the index of the item or block pointer
 * used while walking the tree.
 */
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struct btrfs_path {
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	struct extent_buffer *nodes[BTRFS_MAX_LEVEL];
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	int slots[BTRFS_MAX_LEVEL];
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	/* if there is real range locking, this locks field will change */
	int locks[BTRFS_MAX_LEVEL];
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	int reada;
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	/* keep some upper locks as we walk down */
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	int lowest_level;
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	/*
	 * set by btrfs_split_item, tells search_slot to keep all locks
	 * and to force calls to keep space in the nodes
	 */
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	unsigned int search_for_split:1;
	unsigned int keep_locks:1;
	unsigned int skip_locking:1;
	unsigned int leave_spinning:1;
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	unsigned int search_commit_root:1;
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};
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/*
 * items in the extent btree are used to record the objectid of the
 * owner of the block and the number of references
 */
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struct btrfs_extent_item {
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	__le64 refs;
	__le64 generation;
	__le64 flags;
} __attribute__ ((__packed__));

struct btrfs_extent_item_v0 {
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	__le32 refs;
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} __attribute__ ((__packed__));

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#define BTRFS_MAX_EXTENT_ITEM_SIZE(r) ((BTRFS_LEAF_DATA_SIZE(r) >> 4) - \
					sizeof(struct btrfs_item))

#define BTRFS_EXTENT_FLAG_DATA		(1ULL << 0)
#define BTRFS_EXTENT_FLAG_TREE_BLOCK	(1ULL << 1)

/* following flags only apply to tree blocks */

/* use full backrefs for extent pointers in the block */
#define BTRFS_BLOCK_FLAG_FULL_BACKREF	(1ULL << 8)

struct btrfs_tree_block_info {
	struct btrfs_disk_key key;
	u8 level;
} __attribute__ ((__packed__));

struct btrfs_extent_data_ref {
	__le64 root;
	__le64 objectid;
	__le64 offset;
	__le32 count;
} __attribute__ ((__packed__));

struct btrfs_shared_data_ref {
	__le32 count;
} __attribute__ ((__packed__));

struct btrfs_extent_inline_ref {
	u8 type;
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	__le64 offset;
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} __attribute__ ((__packed__));

/* old style backrefs item */
struct btrfs_extent_ref_v0 {
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	__le64 root;
	__le64 generation;
	__le64 objectid;
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	__le32 count;
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} __attribute__ ((__packed__));

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/* dev extents record free space on individual devices.  The owner
 * field points back to the chunk allocation mapping tree that allocated
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 * the extent.  The chunk tree uuid field is a way to double check the owner
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 */
struct btrfs_dev_extent {
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	__le64 chunk_tree;
	__le64 chunk_objectid;
	__le64 chunk_offset;
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	__le64 length;
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	u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
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} __attribute__ ((__packed__));

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struct btrfs_inode_ref {
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	__le64 index;
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	__le16 name_len;
	/* name goes here */
} __attribute__ ((__packed__));

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struct btrfs_timespec {
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	__le64 sec;
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	__le32 nsec;
} __attribute__ ((__packed__));

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enum btrfs_compression_type {
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	BTRFS_COMPRESS_NONE = 0,
	BTRFS_COMPRESS_ZLIB = 1,
	BTRFS_COMPRESS_LAST = 2,
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};
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struct btrfs_inode_item {
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	/* nfs style generation number */
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	__le64 generation;
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	/* transid that last touched this inode */
	__le64 transid;
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	__le64 size;
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	__le64 nbytes;
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	__le64 block_group;
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	__le32 nlink;
	__le32 uid;
	__le32 gid;
	__le32 mode;
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	__le64 rdev;
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	__le64 flags;
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	/* modification sequence number for NFS */
	__le64 sequence;

	/*
	 * a little future expansion, for more than this we can
	 * just grow the inode item and version it
	 */
	__le64 reserved[4];
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	struct btrfs_timespec atime;
	struct btrfs_timespec ctime;
	struct btrfs_timespec mtime;
	struct btrfs_timespec otime;
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} __attribute__ ((__packed__));

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struct btrfs_dir_log_item {
	__le64 end;
} __attribute__ ((__packed__));

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struct btrfs_dir_item {
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	struct btrfs_disk_key location;
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	__le64 transid;
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	__le16 data_len;
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	__le16 name_len;
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	u8 type;
} __attribute__ ((__packed__));

struct btrfs_root_item {
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	struct btrfs_inode_item inode;
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	__le64 generation;
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	__le64 root_dirid;
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	__le64 bytenr;
	__le64 byte_limit;
	__le64 bytes_used;
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	__le64 last_snapshot;
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	__le64 flags;
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	__le32 refs;
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	struct btrfs_disk_key drop_progress;
	u8 drop_level;
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	u8 level;
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} __attribute__ ((__packed__));
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/*
 * this is used for both forward and backward root refs
 */
struct btrfs_root_ref {
	__le64 dirid;
	__le64 sequence;
	__le16 name_len;
} __attribute__ ((__packed__));

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#define BTRFS_FILE_EXTENT_INLINE 0
#define BTRFS_FILE_EXTENT_REG 1
#define BTRFS_FILE_EXTENT_PREALLOC 2
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struct btrfs_file_extent_item {
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	/*
	 * transaction id that created this extent
	 */
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	__le64 generation;
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	/*
	 * max number of bytes to hold this extent in ram
	 * when we split a compressed extent we can't know how big
	 * each of the resulting pieces will be.  So, this is
	 * an upper limit on the size of the extent in ram instead of
	 * an exact limit.
	 */
	__le64 ram_bytes;

	/*
	 * 32 bits for the various ways we might encode the data,
	 * including compression and encryption.  If any of these
	 * are set to something a given disk format doesn't understand
	 * it is treated like an incompat flag for reading and writing,
	 * but not for stat.
	 */
	u8 compression;
	u8 encryption;
	__le16 other_encoding; /* spare for later use */

	/* are we inline data or a real extent? */
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	u8 type;
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	/*
	 * disk space consumed by the extent, checksum blocks are included
	 * in these numbers
	 */
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	__le64 disk_bytenr;
	__le64 disk_num_bytes;
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	/*
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	 * the logical offset in file blocks (no csums)
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	 * this extent record is for.  This allows a file extent to point
	 * into the middle of an existing extent on disk, sharing it
	 * between two snapshots (useful if some bytes in the middle of the
	 * extent have changed
	 */
	__le64 offset;
	/*
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	 * the logical number of file blocks (no csums included).  This
	 * always reflects the size uncompressed and without encoding.
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	 */
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	__le64 num_bytes;
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} __attribute__ ((__packed__));

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struct btrfs_csum_item {
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	u8 csum;
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} __attribute__ ((__packed__));

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/* different types of block groups (and chunks) */
#define BTRFS_BLOCK_GROUP_DATA     (1 << 0)
#define BTRFS_BLOCK_GROUP_SYSTEM   (1 << 1)
#define BTRFS_BLOCK_GROUP_METADATA (1 << 2)
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#define BTRFS_BLOCK_GROUP_RAID0    (1 << 3)
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#define BTRFS_BLOCK_GROUP_RAID1    (1 << 4)
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#define BTRFS_BLOCK_GROUP_DUP	   (1 << 5)
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#define BTRFS_BLOCK_GROUP_RAID10   (1 << 6)
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struct btrfs_block_group_item {
	__le64 used;
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	__le64 chunk_objectid;
	__le64 flags;
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} __attribute__ ((__packed__));

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struct btrfs_space_info {
	u64 flags;
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	u64 total_bytes;	/* total bytes in the space */
	u64 bytes_used;		/* total bytes used on disk */
	u64 bytes_pinned;	/* total bytes pinned, will be freed when the
				   transaction finishes */
	u64 bytes_reserved;	/* total bytes the allocator has reserved for
				   current allocations */
	u64 bytes_readonly;	/* total bytes that are read only */

	/* delalloc accounting */
	u64 bytes_delalloc;	/* number of bytes reserved for allocation,
				   this space is not necessarily reserved yet
				   by the allocator */
	u64 bytes_may_use;	/* number of bytes that may be used for
				   delalloc */

	int full;		/* indicates that we cannot allocate any more
				   chunks for this space */
	int force_alloc;	/* set if we need to force a chunk alloc for
				   this space */

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	struct list_head list;
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	/* for block groups in our same type */
	struct list_head block_groups;
	spinlock_t lock;
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	struct rw_semaphore groups_sem;
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	atomic_t caching_threads;
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};

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/*
 * free clusters are used to claim free space in relatively large chunks,
 * allowing us to do less seeky writes.  They are used for all metadata
 * allocations and data allocations in ssd mode.
 */
struct btrfs_free_cluster {
	spinlock_t lock;
	spinlock_t refill_lock;
	struct rb_root root;

	/* largest extent in this cluster */
	u64 max_size;

	/* first extent starting offset */
	u64 window_start;

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	/* if this cluster simply points at a bitmap in the block group */
	bool points_to_bitmap;

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	struct btrfs_block_group_cache *block_group;
	/*
	 * when a cluster is allocated from a block group, we put the
	 * cluster onto a list in the block group so that it can
	 * be freed before the block group is freed.
	 */
	struct list_head block_group_list;
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};

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enum btrfs_caching_type {
	BTRFS_CACHE_NO		= 0,
	BTRFS_CACHE_STARTED	= 1,
	BTRFS_CACHE_FINISHED	= 2,
};

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struct btrfs_caching_control {
	struct list_head list;
	struct mutex mutex;
	wait_queue_head_t wait;
	struct btrfs_block_group_cache *block_group;
	u64 progress;
	atomic_t count;
};

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struct btrfs_block_group_cache {
	struct btrfs_key key;
	struct btrfs_block_group_item item;
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	struct btrfs_fs_info *fs_info;
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	spinlock_t lock;
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	u64 pinned;
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	u64 reserved;
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	u64 flags;
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	u64 sectorsize;
	int extents_thresh;
	int free_extents;
	int total_bitmaps;
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	int ro;
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	int dirty;

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	/* cache tracking stuff */
	int cached;
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	struct btrfs_caching_control *caching_ctl;
	u64 last_byte_to_unpin;
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	struct btrfs_space_info *space_info;

	/* free space cache stuff */
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	spinlock_t tree_lock;
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	struct rb_root free_space_offset;
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	u64 free_space;
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	/* block group cache stuff */
	struct rb_node cache_node;

	/* for block groups in the same raid type */
	struct list_head list;
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	/* usage count */
	atomic_t count;
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	/* List of struct btrfs_free_clusters for this block group.
	 * Today it will only have one thing on it, but that may change
	 */
	struct list_head cluster_list;
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};
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struct reloc_control;
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struct btrfs_device;
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struct btrfs_fs_devices;
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struct btrfs_fs_info {
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	u8 fsid[BTRFS_FSID_SIZE];
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	u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
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	struct btrfs_root *extent_root;
	struct btrfs_root *tree_root;
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	struct btrfs_root *chunk_root;
	struct btrfs_root *dev_root;
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	struct btrfs_root *fs_root;
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	struct btrfs_root *csum_root;
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	/* the log root tree is a directory of all the other log roots */
	struct btrfs_root *log_root_tree;
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	struct radix_tree_root fs_roots_radix;
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	/* block group cache stuff */
	spinlock_t block_group_cache_lock;
	struct rb_root block_group_cache_tree;

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	struct extent_io_tree freed_extents[2];
	struct extent_io_tree *pinned_extents;
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	/* logical->physical extent mapping */
	struct btrfs_mapping_tree mapping_tree;

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	u64 generation;
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	u64 last_trans_committed;
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	/*
	 * this is updated to the current trans every time a full commit
	 * is required instead of the faster short fsync log commits
	 */
	u64 last_trans_log_full_commit;
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	u64 open_ioctl_trans;
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	unsigned long mount_opt;
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	u64 max_extent;
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	u64 max_inline;
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	u64 alloc_start;
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	struct btrfs_transaction *running_transaction;
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	wait_queue_head_t transaction_throttle;
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	wait_queue_head_t transaction_wait;
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	wait_queue_head_t async_submit_wait;
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	struct btrfs_super_block super_copy;
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	struct btrfs_super_block super_for_commit;
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	struct block_device *__bdev;
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	struct super_block *sb;
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	struct inode *btree_inode;
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	struct backing_dev_info bdi;
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	struct mutex trans_mutex;
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	struct mutex tree_log_mutex;
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	struct mutex transaction_kthread_mutex;
	struct mutex cleaner_mutex;
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	struct mutex chunk_mutex;
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	struct mutex drop_mutex;
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	struct mutex volume_mutex;
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	struct mutex tree_reloc_mutex;
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	/*
	 * this protects the ordered operations list only while we are
	 * processing all of the entries on it.  This way we make
	 * sure the commit code doesn't find the list temporarily empty
	 * because another function happens to be doing non-waiting preflush
	 * before jumping into the main commit.
	 */
	struct mutex ordered_operations_mutex;
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	struct rw_semaphore extent_commit_sem;
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	struct list_head trans_list;
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	struct list_head hashers;
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	struct list_head dead_roots;
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	struct list_head caching_block_groups;
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	atomic_t nr_async_submits;
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	atomic_t async_submit_draining;
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	atomic_t nr_async_bios;
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	atomic_t async_delalloc_pages;
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	/*
	 * this is used by the balancing code to wait for all the pending
	 * ordered extents
	 */
	spinlock_t ordered_extent_lock;
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	/*
	 * all of the data=ordered extents pending writeback
	 * these can span multiple transactions and basically include
	 * every dirty data page that isn't from nodatacow
	 */
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	struct list_head ordered_extents;
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	/*
	 * all of the inodes that have delalloc bytes.  It is possible for
	 * this list to be empty even when there is still dirty data=ordered
	 * extents waiting to finish IO.
	 */
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	struct list_head delalloc_inodes;
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	/*
	 * special rename and truncate targets that must be on disk before
	 * we're allowed to commit.  This is basically the ext3 style
	 * data=ordered list.
	 */
	struct list_head ordered_operations;

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	/*
	 * there is a pool of worker threads for checksumming during writes
	 * and a pool for checksumming after reads.  This is because readers
	 * can run with FS locks held, and the writers may be waiting for
	 * those locks.  We don't want ordering in the pending list to cause
	 * deadlocks, and so the two are serviced separately.
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	 *
	 * A third pool does submit_bio to avoid deadlocking with the other
	 * two
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	 */
	struct btrfs_workers workers;
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	struct btrfs_workers delalloc_workers;
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	struct btrfs_workers endio_workers;
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	struct btrfs_workers endio_meta_workers;
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	struct btrfs_workers endio_meta_write_workers;
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	struct btrfs_workers endio_write_workers;
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	struct btrfs_workers submit_workers;
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	/*
	 * fixup workers take dirty pages that didn't properly go through
	 * the cow mechanism and make them safe to write.  It happens
	 * for the sys_munmap function call path
	 */
	struct btrfs_workers fixup_workers;
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	struct task_struct *transaction_kthread;
	struct task_struct *cleaner_kthread;
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	int thread_pool_size;
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	struct kobject super_kobj;
	struct completion kobj_unregister;
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	int do_barriers;
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	int closing;
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	int log_root_recovering;
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	u64 total_pinned;
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	/* protected by the delalloc lock, used to keep from writing
	 * metadata until there is a nice batch
	 */
	u64 dirty_metadata_bytes;
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	struct list_head dirty_cowonly_roots;

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	struct btrfs_fs_devices *fs_devices;
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	/*
	 * the space_info list is almost entirely read only.  It only changes
	 * when we add a new raid type to the FS, and that happens
	 * very rarely.  RCU is used to protect it.
	 */
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	struct reloc_control *reloc_ctl;

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	spinlock_t new_trans_lock;
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	u64 delalloc_bytes;
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	/* data_alloc_cluster is only used in ssd mode */
	struct btrfs_free_cluster data_alloc_cluster;

	/* all metadata allocations go through this cluster */
	struct btrfs_free_cluster meta_alloc_cluster;
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	spinlock_t ref_cache_lock;
	u64 total_ref_cache_size;

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	u64 avail_data_alloc_bits;
	u64 avail_metadata_alloc_bits;
	u64 avail_system_alloc_bits;
	u64 data_alloc_profile;
	u64 metadata_alloc_profile;
	u64 system_alloc_profile;
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	unsigned data_chunk_allocations;
	unsigned metadata_ratio;

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};
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/*
 * in ram representation of the tree.  extent_root is used for all allocations
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struct btrfs_root {
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	struct extent_buffer *node;
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	/* the node lock is held while changing the node pointer */
	spinlock_t node_lock;

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	struct extent_buffer *commit_root;
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	struct btrfs_root *log_root;
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	struct btrfs_root *reloc_root;
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	struct btrfs_root_item root_item;
	struct btrfs_key root_key;
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	struct btrfs_fs_info *fs_info;
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	struct extent_io_tree dirty_log_pages;

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	struct kobject root_kobj;
	struct completion kobj_unregister;
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	struct mutex objectid_mutex;
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	struct mutex log_mutex;
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	wait_queue_head_t log_writer_wait;
	wait_queue_head_t log_commit_wait[2];
	atomic_t log_writers;
	atomic_t log_commit[2];
	unsigned long log_transid;
	unsigned long log_batch;
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	u64 objectid;
	u64 last_trans;
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	/* data allocations are done in sectorsize units */
	u32 sectorsize;

	/* node allocations are done in nodesize units */
	u32 nodesize;

	/* leaf allocations are done in leafsize units */
	u32 leafsize;

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	u32 stripesize;

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	u32 type;
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	u64 highest_inode;
	u64 last_inode_alloc;
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	int ref_cows;
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	int track_dirty;
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	u64 defrag_trans_start;
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	struct btrfs_key defrag_progress;
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	struct btrfs_key defrag_max;
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	int defrag_running;
	int defrag_level;
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	char *name;
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	int in_sysfs;
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	/* the dirty list is only used by non-reference counted roots */
	struct list_head dirty_list;
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	struct list_head root_list;

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	struct list_head orphan_list;
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	spinlock_t inode_lock;
	/* red-black tree that keeps track of in-memory inodes */
	struct rb_root inode_tree;

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	/*
	 * right now this just gets used so that a root has its own devid
	 * for stat.  It may be used for more later
	 */
	struct super_block anon_super;
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};

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/*
 * inode items have the data typically returned from stat and store other
 * info about object characteristics.  There is one for every file and dir in
 * the FS
 */