btrfs-progs/delayed-ref.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2009 Oracle.  All rights reserved.
 */

#include "ctree.h"
#include "btrfs-list.h"
#include "delayed-ref.h"
#include "transaction.h"

/*
 * delayed back reference update tracking.  For subvolume trees
 * we queue up extent allocations and backref maintenance for
 * delayed processing.   This avoids deep call chains where we
 * add extents in the middle of btrfs_search_slot, and it allows
 * us to buffer up frequently modified backrefs in an rb tree instead
 * of hammering updates on the extent allocation tree.
 */

/*
 * compare two delayed tree backrefs with same bytenr and type
 */
static int comp_tree_refs(struct btrfs_delayed_tree_ref *ref1,
			  struct btrfs_delayed_tree_ref *ref2)
{
	if (ref1->node.type == BTRFS_TREE_BLOCK_REF_KEY) {
		if (ref1->root < ref2->root)
			return -1;
		if (ref1->root > ref2->root)
			return 1;
	} else {
		if (ref1->parent < ref2->parent)
			return -1;
		if (ref1->parent > ref2->parent)
			return 1;
	}
	return 0;
}

static int comp_refs(struct btrfs_delayed_ref_node *ref1,
		     struct btrfs_delayed_ref_node *ref2,
		     bool check_seq)
{
	int ret = 0;

	if (ref1->type < ref2->type)
		return -1;
	if (ref1->type > ref2->type)
		return 1;
	if (ref1->type == BTRFS_TREE_BLOCK_REF_KEY ||
	    ref1->type == BTRFS_SHARED_BLOCK_REF_KEY)
		ret = comp_tree_refs(btrfs_delayed_node_to_tree_ref(ref1),
				     btrfs_delayed_node_to_tree_ref(ref2));
	else
		BUG();

	if (ret)
		return ret;
	if (check_seq) {
		if (ref1->seq < ref2->seq)
			return -1;
		if (ref1->seq > ref2->seq)
			return 1;
	}
	return 0;
}

/* insert a new ref to head ref rbtree */
static struct btrfs_delayed_ref_head *htree_insert(struct rb_root *root,
						   struct rb_node *node)
{
	struct rb_node **p = &root->rb_node;
	struct rb_node *parent_node = NULL;
	struct btrfs_delayed_ref_head *entry;
	struct btrfs_delayed_ref_head *ins;
	u64 bytenr;

	ins = rb_entry(node, struct btrfs_delayed_ref_head, href_node);
	bytenr = ins->bytenr;
	while (*p) {
		parent_node = *p;
		entry = rb_entry(parent_node, struct btrfs_delayed_ref_head,
				 href_node);

		if (bytenr < entry->bytenr)
			p = &(*p)->rb_left;
		else if (bytenr > entry->bytenr)
			p = &(*p)->rb_right;
		else
			return entry;
	}

	rb_link_node(node, parent_node, p);
	rb_insert_color(node, root);
	return NULL;
}

static struct btrfs_delayed_ref_node* tree_insert(struct rb_root *root,
		struct btrfs_delayed_ref_node *ins)
{
	struct rb_node **p = &root->rb_node;
	struct rb_node *node = &ins->ref_node;
	struct rb_node *parent_node = NULL;
	struct btrfs_delayed_ref_node *entry;

	while (*p) {
		int comp;

		parent_node = *p;
		entry = rb_entry(parent_node, struct btrfs_delayed_ref_node,
				 ref_node);
		comp = comp_refs(ins, entry, true);
		if (comp < 0)
			p = &(*p)->rb_left;
		else if (comp > 0)
			p = &(*p)->rb_right;
		else
			return entry;
	}

	rb_link_node(node, parent_node, p);
	rb_insert_color(node, root);
	return NULL;
}

/*
 * find an head entry based on bytenr. This returns the delayed ref
 * head if it was able to find one, or NULL if nothing was in that spot.
 * If return_bigger is given, the next bigger entry is returned if no exact
 * match is found.
 */
static struct btrfs_delayed_ref_head *
find_ref_head(struct rb_root *root, u64 bytenr,
	      int return_bigger)
{
	struct rb_node *n;
	struct btrfs_delayed_ref_head *entry;

	n = root->rb_node;
	entry = NULL;
	while (n) {
		entry = rb_entry(n, struct btrfs_delayed_ref_head, href_node);

		if (bytenr < entry->bytenr)
			n = n->rb_left;
		else if (bytenr > entry->bytenr)
			n = n->rb_right;
		else
			return entry;
	}
	if (entry && return_bigger) {
		if (bytenr > entry->bytenr) {
			n = rb_next(&entry->href_node);
			if (!n)
				n = rb_first(root);
			entry = rb_entry(n, struct btrfs_delayed_ref_head,
					 href_node);
			return entry;
		}
		return entry;
	}
	return NULL;
}

static inline void drop_delayed_ref(struct btrfs_trans_handle *trans,
				    struct btrfs_delayed_ref_root *delayed_refs,
				    struct btrfs_delayed_ref_head *head,
				    struct btrfs_delayed_ref_node *ref)
{
	rb_erase(&ref->ref_node, &head->ref_tree);
	RB_CLEAR_NODE(&ref->ref_node);
	if (!list_empty(&ref->add_list))
		list_del(&ref->add_list);
	ref->in_tree = 0;
	btrfs_put_delayed_ref(ref);
	if (trans->delayed_ref_updates)
		trans->delayed_ref_updates--;
}

static bool merge_ref(struct btrfs_trans_handle *trans,
		      struct btrfs_delayed_ref_root *delayed_refs,
		      struct btrfs_delayed_ref_head *head,
		      struct btrfs_delayed_ref_node *ref,
		      u64 seq)
{
	struct btrfs_delayed_ref_node *next;
	struct rb_node *node = rb_next(&ref->ref_node);
	bool done = false;

	while (!done && node) {
		int mod;

		next = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
		node = rb_next(node);
		if (seq && next->seq >= seq)
			break;
		if (comp_refs(ref, next, false))
			break;

		if (ref->action == next->action) {
			mod = next->ref_mod;
		} else {
			if (ref->ref_mod < next->ref_mod) {
				__swap(ref, next);
				done = true;
			}
			mod = -next->ref_mod;
		}

		drop_delayed_ref(trans, delayed_refs, head, next);
		ref->ref_mod += mod;
		if (ref->ref_mod == 0) {
			drop_delayed_ref(trans, delayed_refs, head, ref);
			done = true;
		} else {
			/*
			 * Can't have multiples of the same ref on a tree block.
			 */
			WARN_ON(ref->type == BTRFS_TREE_BLOCK_REF_KEY ||
				ref->type == BTRFS_SHARED_BLOCK_REF_KEY);
		}
	}

	return done;
}

void btrfs_merge_delayed_refs(struct btrfs_trans_handle *trans,
			      struct btrfs_delayed_ref_root *delayed_refs,
			      struct btrfs_delayed_ref_head *head)
{
	struct btrfs_delayed_ref_node *ref;
	struct rb_node *node;

	if (RB_EMPTY_ROOT(&head->ref_tree))
		return;

	/* We don't have too many refs to merge for data. */
	if (head->is_data)
		return;

again:
	for (node = rb_first(&head->ref_tree); node; node = rb_next(node)) {
		ref = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
		if (merge_ref(trans, delayed_refs, head, ref, 0))
			goto again;
	}
}

struct btrfs_delayed_ref_head *
btrfs_select_ref_head(struct btrfs_trans_handle *trans)
{
	struct btrfs_delayed_ref_root *delayed_refs;
	struct btrfs_delayed_ref_head *head;
	u64 start;
	bool loop = false;

	delayed_refs = &trans->delayed_refs;

again:
	start = delayed_refs->run_delayed_start;
	head = find_ref_head(&delayed_refs->href_root, start, 1);
	if (!head && !loop) {
		delayed_refs->run_delayed_start = 0;
		start = 0;
		loop = true;
		head = find_ref_head(&delayed_refs->href_root, start, 1);
		if (!head)
			return NULL;
	} else if (!head && loop) {
		return NULL;
	}

	while (head->processing) {
		struct rb_node *node;

		node = rb_next(&head->href_node);
		if (!node) {
			if (loop)
				return NULL;
			delayed_refs->run_delayed_start = 0;
			start = 0;
			loop = true;
			goto again;
		}
		head = rb_entry(node, struct btrfs_delayed_ref_head,
				href_node);
	}

	head->processing = 1;
	WARN_ON(delayed_refs->num_heads_ready == 0);
	delayed_refs->num_heads_ready--;
	delayed_refs->run_delayed_start = head->bytenr +
		head->num_bytes;
	return head;
}

/*
 * Helper to insert the ref_node to the tail or merge with tail.
 *
 * Return 0 for insert.
 * Return >0 for merge.
 */
static int insert_delayed_ref(struct btrfs_trans_handle *trans,
			      struct btrfs_delayed_ref_root *root,
			      struct btrfs_delayed_ref_head *href,
			      struct btrfs_delayed_ref_node *ref)
{
	struct btrfs_delayed_ref_node *exist;
	int mod;
	int ret = 0;

	exist = tree_insert(&href->ref_tree, ref);
	if (!exist)
		goto inserted;

	/* Now we are sure we can merge */
	ret = 1;
	if (exist->action == ref->action) {
		mod = ref->ref_mod;
	} else {
		/* Need to change action */
		if (exist->ref_mod < ref->ref_mod) {
			exist->action = ref->action;
			mod = -exist->ref_mod;
			exist->ref_mod = ref->ref_mod;
			if (ref->action == BTRFS_ADD_DELAYED_REF)
				list_add_tail(&exist->add_list,
					      &href->ref_add_list);
			else if (ref->action == BTRFS_DROP_DELAYED_REF) {
				ASSERT(!list_empty(&exist->add_list));
				list_del(&exist->add_list);
			} else {
				ASSERT(0);
			}
		} else
			mod = -ref->ref_mod;
	}
	exist->ref_mod += mod;

	/* remove existing tail if its ref_mod is zero */
	if (exist->ref_mod == 0)
		drop_delayed_ref(trans, root, href, exist);
	return ret;
inserted:
	if (ref->action == BTRFS_ADD_DELAYED_REF)
		list_add_tail(&ref->add_list, &href->ref_add_list);
	trans->delayed_ref_updates++;
	return ret;
}

/*
 * helper function to update the accounting in the head ref
 * existing and update must have the same bytenr
 */
static noinline void
update_existing_head_ref(struct btrfs_delayed_ref_root *delayed_refs,
			 struct btrfs_delayed_ref_head *existing,
			 struct btrfs_delayed_ref_head *update,
			 int *old_ref_mod_ret)
{
	int old_ref_mod;

	BUG_ON(existing->is_data != update->is_data);

	if (update->must_insert_reserved) {
		/* if the extent was freed and then
		 * reallocated before the delayed ref
		 * entries were processed, we can end up
		 * with an existing head ref without
		 * the must_insert_reserved flag set.
		 * Set it again here
		 */
		existing->must_insert_reserved = update->must_insert_reserved;

		/*
		 * update the num_bytes so we make sure the accounting
		 * is done correctly
		 */
		existing->num_bytes = update->num_bytes;

	}

	if (update->extent_op) {
		if (!existing->extent_op) {
			existing->extent_op = update->extent_op;
		} else {
			if (update->extent_op->update_key) {
				memcpy(&existing->extent_op->key,
				       &update->extent_op->key,
				       sizeof(update->extent_op->key));
				existing->extent_op->update_key = true;
			}
			if (update->extent_op->update_flags) {
				existing->extent_op->flags_to_set |=
					update->extent_op->flags_to_set;
				existing->extent_op->update_flags = true;
			}
			btrfs_free_delayed_extent_op(update->extent_op);
		}
	}
	/*
	 * update the reference mod on the head to reflect this new operation,
	 * only need the lock for this case cause we could be processing it
	 * currently, for refs we just added we know we're a-ok.
	 */
	old_ref_mod = existing->total_ref_mod;
	if (old_ref_mod_ret)
		*old_ref_mod_ret = old_ref_mod;
	existing->ref_mod += update->ref_mod;
	existing->total_ref_mod += update->ref_mod;

}

static void init_delayed_ref_head(struct btrfs_delayed_ref_head *head_ref,
				  void *qrecord,
				  u64 bytenr, u64 num_bytes, u64 ref_root,
				  u64 reserved, int action, bool is_data,
				  bool is_system)
{
	int count_mod = 1;
	int must_insert_reserved = 0;

	/* If reserved is provided, it must be a data extent. */
	BUG_ON(!is_data && reserved);

	/*
	 * The head node stores the sum of all the mods, so dropping a ref
	 * should drop the sum in the head node by one.
	 */
	if (action == BTRFS_UPDATE_DELAYED_HEAD)
		count_mod = 0;
	else if (action == BTRFS_DROP_DELAYED_REF)
		count_mod = -1;

	/*
	 * BTRFS_ADD_DELAYED_EXTENT means that we need to update the reserved
	 * accounting when the extent is finally added, or if a later
	 * modification deletes the delayed ref without ever inserting the
	 * extent into the extent allocation tree.  ref->must_insert_reserved
	 * is the flag used to record that accounting mods are required.
	 *
	 * Once we record must_insert_reserved, switch the action to
	 * BTRFS_ADD_DELAYED_REF because other special casing is not required.
	 */
	if (action == BTRFS_ADD_DELAYED_EXTENT)
		must_insert_reserved = 1;
	else
		must_insert_reserved = 0;

	head_ref->refs = 1;
	head_ref->bytenr = bytenr;
	head_ref->num_bytes = num_bytes;
	head_ref->ref_mod = count_mod;
	head_ref->must_insert_reserved = must_insert_reserved;
	head_ref->is_data = is_data;
	head_ref->is_system = is_system;
	head_ref->ref_tree = RB_ROOT;
	INIT_LIST_HEAD(&head_ref->ref_add_list);
	RB_CLEAR_NODE(&head_ref->href_node);
	head_ref->processing = 0;
	head_ref->total_ref_mod = count_mod;
}

/*
 * helper function to actually insert a head node into the rbtree.
 * this does all the dirty work in terms of maintaining the correct
 * overall modification count.
 */
static noinline struct btrfs_delayed_ref_head *
add_delayed_ref_head(struct btrfs_trans_handle *trans,
		     struct btrfs_delayed_ref_head *head_ref,
		     void *qrecord,
		     int action, int *qrecord_inserted_ret,
		     int *old_ref_mod, int *new_ref_mod)
{
	struct btrfs_delayed_ref_head *existing;
	struct btrfs_delayed_ref_root *delayed_refs;

	delayed_refs = &trans->delayed_refs;

	existing = htree_insert(&delayed_refs->href_root, &head_ref->href_node);
	if (existing) {
		update_existing_head_ref(delayed_refs, existing, head_ref, old_ref_mod);
		/*
		 * we've updated the existing ref, free the newly
		 * allocated ref
		 */
		kfree(head_ref);
		head_ref = existing;
	} else {
		if (old_ref_mod)
			*old_ref_mod = 0;
		delayed_refs->num_heads++;
		delayed_refs->num_heads_ready++;
		trans->delayed_ref_updates++;
	}
	if (new_ref_mod)
		*new_ref_mod = head_ref->total_ref_mod;

	return head_ref;
}

/*
 * init_delayed_ref_common - Initialize the structure which represents a
 *			     modification to a an extent.
 *
 * @fs_info:    Internal to the mounted filesystem mount structure.
 *
 * @ref:	The structure which is going to be initialized.
 *
 * @bytenr:	The logical address of the extent for which a modification is
 *		going to be recorded.
 *
 * @num_bytes:  Size of the extent whose modification is being recorded.
 *
 * @ref_root:	The id of the root where this modification has originated, this
 *		can be either one of the well-known metadata trees or the
 *		subvolume id which references this extent.
 *
 * @action:	Can be one of BTRFS_ADD_DELAYED_REF/BTRFS_DROP_DELAYED_REF or
 *		BTRFS_ADD_DELAYED_EXTENT
 *
 * @ref_type:	Holds the type of the extent which is being recorded, can be
 *		one of BTRFS_SHARED_BLOCK_REF_KEY/BTRFS_TREE_BLOCK_REF_KEY
 *		when recording a metadata extent or BTRFS_SHARED_DATA_REF_KEY/
 *		BTRFS_EXTENT_DATA_REF_KEY when recording data extent
 */
static void init_delayed_ref_common(struct btrfs_fs_info *fs_info,
				    struct btrfs_delayed_ref_node *ref,
				    u64 bytenr, u64 num_bytes, u64 ref_root,
				    int action, u8 ref_type)
{
	if (action == BTRFS_ADD_DELAYED_EXTENT)
		action = BTRFS_ADD_DELAYED_REF;

	ref->refs = 1;
	ref->bytenr = bytenr;
	ref->num_bytes = num_bytes;
	ref->ref_mod = 1;
	ref->action = action;
	ref->is_head = 0;
	ref->in_tree = 1;
	ref->seq = 0;
	ref->type = ref_type;
	RB_CLEAR_NODE(&ref->ref_node);
	INIT_LIST_HEAD(&ref->add_list);
}

/*
 * add a delayed tree ref.  This does all of the accounting required
 * to make sure the delayed ref is eventually processed before this
 * transaction commits.
 */
int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info,
			       struct btrfs_trans_handle *trans,
			       u64 bytenr, u64 num_bytes, u64 parent,
			       u64 ref_root, int level, int action,
			       struct btrfs_delayed_extent_op *extent_op,
			       int *old_ref_mod, int *new_ref_mod)
{
	struct btrfs_delayed_tree_ref *ref;
	struct btrfs_delayed_ref_head *head_ref;
	struct btrfs_delayed_ref_root *delayed_refs;
	bool is_system = (ref_root == BTRFS_CHUNK_TREE_OBJECTID);
	int ret;
	u8 ref_type;

	BUG_ON(extent_op && extent_op->is_data);
	ref = kmalloc(sizeof(*ref), GFP_NOFS);
	if (!ref)
		return -ENOMEM;

	if (parent)
		ref_type = BTRFS_SHARED_BLOCK_REF_KEY;
	else
		ref_type = BTRFS_TREE_BLOCK_REF_KEY;
	init_delayed_ref_common(fs_info, &ref->node, bytenr, num_bytes,
				ref_root, action, ref_type);
	ref->root = ref_root;
	ref->parent = parent;
	ref->level = level;

	head_ref = kmalloc(sizeof(*head_ref), GFP_NOFS);
	if (!head_ref)
		goto free_ref;

	init_delayed_ref_head(head_ref, NULL, bytenr, num_bytes,
			      ref_root, 0, action, false, is_system);
	head_ref->extent_op = extent_op;

	delayed_refs = &trans->delayed_refs;

	head_ref = add_delayed_ref_head(trans, head_ref, NULL, action, NULL,
			old_ref_mod, new_ref_mod);

	ret = insert_delayed_ref(trans, delayed_refs, head_ref, &ref->node);

	if (ret > 0)
		kfree(ref);

	return 0;

free_ref:
	kfree(ref);

	return -ENOMEM;
}