Btrfs: pretend page cache & commit code

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.c

@@ -250,6 +250,7 @@ static int balance_level(struct ctree_root *root, struct ctree_path *path,
 		tree_block_release(root, mid_buf);
 		/* once for the root ptr */
 		tree_block_release(root, mid_buf);
+		clean_tree_block(root, mid_buf);
 		return free_extent(root, blocknr, 1);
 	}
 	parent = &parent_buf->node;
@@ -280,6 +281,7 @@ static int balance_level(struct ctree_root *root, struct ctree_path *path,
 		if (right->header.nritems == 0) {
 			u64 blocknr = right_buf->blocknr;
 			tree_block_release(root, right_buf);
+			clean_tree_block(root, right_buf);
 			right_buf = NULL;
 			right = NULL;
 			wret = del_ptr(root, path, level + 1, pslot + 1);
@@ -291,7 +293,7 @@ static int balance_level(struct ctree_root *root, struct ctree_path *path,
 		} else {
 			memcpy(parent->keys + pslot + 1, right->keys,
 				sizeof(struct key));
-			wret = write_tree_block(root, parent_buf);
+			wret = dirty_tree_block(root, parent_buf);
 			if (wret)
 				ret = wret;
 		}
@@ -316,6 +318,7 @@ static int balance_level(struct ctree_root *root, struct ctree_path *path,
 		/* we've managed to empty the middle node, drop it */
 		u64 blocknr = mid_buf->blocknr;
 		tree_block_release(root, mid_buf);
+		clean_tree_block(root, mid_buf);
 		mid_buf = NULL;
 		mid = NULL;
 		wret = del_ptr(root, path, level + 1, pslot);
@@ -327,7 +330,7 @@ static int balance_level(struct ctree_root *root, struct ctree_path *path,
 	} else {
 		/* update the parent key to reflect our changes */
 		memcpy(parent->keys + pslot, mid->keys, sizeof(struct key));
-		wret = write_tree_block(root, parent_buf);
+		wret = dirty_tree_block(root, parent_buf);
 		if (wret)
 			ret = wret;
 	}
@@ -458,7 +461,7 @@ static int fixup_low_keys(struct ctree_root *root,
 			break;
 		t = &path->nodes[i]->node;
 		memcpy(t->keys + tslot, key, sizeof(*key));
-		wret = write_tree_block(root, path->nodes[i]);
+		wret = dirty_tree_block(root, path->nodes[i]);
 		if (wret)
 			ret = wret;
 		if (tslot != 0)
@@ -508,11 +511,11 @@ static int push_node_left(struct ctree_root *root, struct tree_buffer *dst_buf,
 	src->header.nritems -= push_items;
 	dst->header.nritems += push_items;
 
-	wret = write_tree_block(root, src_buf);
+	wret = dirty_tree_block(root, src_buf);
 	if (wret < 0)
 		ret = wret;
 
-	wret = write_tree_block(root, dst_buf);
+	wret = dirty_tree_block(root, dst_buf);
 	if (wret < 0)
 		ret = wret;
 	return ret;
@@ -566,11 +569,11 @@ static int balance_node_right(struct ctree_root *root,
 	src->header.nritems -= push_items;
 	dst->header.nritems += push_items;
 
-	wret = write_tree_block(root, src_buf);
+	wret = dirty_tree_block(root, src_buf);
 	if (wret < 0)
 		ret = wret;
 
-	wret = write_tree_block(root, dst_buf);
+	wret = dirty_tree_block(root, dst_buf);
 	if (wret < 0)
 		ret = wret;
 	return ret;
@@ -612,7 +615,7 @@ static int insert_new_root(struct ctree_root *root,
 	tree_block_release(root, root->node);
 	root->node = t;
 	t->count++;
-	write_tree_block(root, t);
+	dirty_tree_block(root, t);
 	path->nodes[level] = t;
 	path->slots[level] = 0;
 	return 0;
@@ -652,7 +655,7 @@ static int insert_ptr(struct ctree_root *root,
 	lower->header.nritems++;
 	if (lower->keys[1].objectid == 0)
 			BUG();
-	write_tree_block(root, path->nodes[level]);
+	dirty_tree_block(root, path->nodes[level]);
 	return 0;
 }
 
@@ -698,10 +701,10 @@ static int split_node(struct ctree_root *root, struct ctree_path *path,
 	c->header.nritems = mid;
 	ret = 0;
 
-	wret = write_tree_block(root, t);
+	wret = dirty_tree_block(root, t);
 	if (wret)
 		ret = wret;
-	wret = write_tree_block(root, split_buffer);
+	wret = dirty_tree_block(root, split_buffer);
 	if (wret)
 		ret = wret;
 	wret = insert_ptr(root, path, split->keys, split_buffer->blocknr,
@@ -815,11 +818,11 @@ static int push_leaf_right(struct ctree_root *root, struct ctree_path *path,
 	}
 	left->header.nritems -= push_items;
 
-	write_tree_block(root, left_buf);
+	dirty_tree_block(root, left_buf);
-	write_tree_block(root, right_buf);
+	dirty_tree_block(root, right_buf);
 	memcpy(upper->node.keys + slot + 1,
 		&right->items[0].key, sizeof(struct key));
-	write_tree_block(root, upper);
+	dirty_tree_block(root, upper);
 	/* then fixup the leaf pointer in the path */
 	if (path->slots[0] >= left->header.nritems) {
 		path->slots[0] -= left->header.nritems;
@@ -909,10 +912,10 @@ static int push_leaf_left(struct ctree_root *root, struct ctree_path *path,
 		push_space = right->items[i].offset;
 	}
 
-	wret = write_tree_block(root, t);
+	wret = dirty_tree_block(root, t);
 	if (wret)
 		ret = wret;
-	wret = write_tree_block(root, right_buf);
+	wret = dirty_tree_block(root, right_buf);
 	if (wret)
 		ret = wret;
 
@@ -1019,10 +1022,10 @@ static int split_leaf(struct ctree_root *root, struct ctree_path *path,
 			  right_buffer->blocknr, path->slots[1] + 1, 1);
 	if (wret)
 		ret = wret;
-	wret = write_tree_block(root, right_buffer);
+	wret = dirty_tree_block(root, right_buffer);
 	if (wret)
 		ret = wret;
-	wret = write_tree_block(root, l_buf);
+	wret = dirty_tree_block(root, l_buf);
 	if (wret)
 		ret = wret;
 
@@ -1062,12 +1065,14 @@ int insert_item(struct ctree_root *root, struct key *key,
 	ret = search_slot(root, key, &path, data_size);
 	if (ret == 0) {
 		release_path(root, &path);
-		return -EEXIST;
+		ret = -EEXIST;
-	}
+		wret = commit_transaction(root);
-	if (ret < 0) {
+		if (wret)
-		release_path(root, &path);
+			ret = wret;
 		return ret;
 	}
+	if (ret < 0)
+		goto out;
 
 	slot_orig = path.slots[0];
 	leaf_buf = path.nodes[0];
@@ -1113,14 +1118,18 @@ int insert_item(struct ctree_root *root, struct key *key,
 	if (slot == 0)
 		ret = fixup_low_keys(root, &path, key, 1);
 
-	wret = write_tree_block(root, leaf_buf);
+	wret = dirty_tree_block(root, leaf_buf);
 	if (wret)
 		ret = wret;
 
 	if (leaf_free_space(leaf) < 0)
 		BUG();
 	check_leaf(&path, 0);
+out:
 	release_path(root, &path);
+	wret = commit_transaction(root);
+	if (wret)
+		ret = wret;
 	return ret;
 }
 
@@ -1160,7 +1169,7 @@ static int del_ptr(struct ctree_root *root, struct ctree_path *path, int level,
 		if (wret)
 			ret = wret;
 	}
-	wret = write_tree_block(root, parent);
+	wret = dirty_tree_block(root, parent);
 	if (wret)
 		ret = wret;
 	return ret;
@@ -1203,8 +1212,9 @@ int del_item(struct ctree_root *root, struct ctree_path *path)
 	if (leaf->header.nritems == 0) {
 		if (leaf_buf == root->node) {
 			leaf->header.flags = node_level(0);
-			write_tree_block(root, leaf_buf);
+			dirty_tree_block(root, leaf_buf);
 		} else {
+			clean_tree_block(root, leaf_buf);
 			wret = del_ptr(root, path, 1, path->slots[1]);
 			if (wret)
 				ret = wret;
@@ -1220,7 +1230,7 @@ int del_item(struct ctree_root *root, struct ctree_path *path)
 			if (wret)
 				ret = wret;
 		}
-		wret = write_tree_block(root, leaf_buf);
+		wret = dirty_tree_block(root, leaf_buf);
 		if (wret)
 			ret = wret;
 
@@ -1242,6 +1252,7 @@ int del_item(struct ctree_root *root, struct ctree_path *path)
 			}
 			if (leaf->header.nritems == 0) {
 				u64 blocknr = leaf_buf->blocknr;
+				clean_tree_block(root, leaf_buf);
 				wret = del_ptr(root, path, 1, slot);
 				if (wret)
 					ret = wret;
@@ -1254,6 +1265,9 @@ int del_item(struct ctree_root *root, struct ctree_path *path)
 			}
 		}
 	}
+	wret = commit_transaction(root);
+	if (wret)
+		ret = wret;
 	return ret;
 }
 

fs/btrfs/ctree.h

@@ -1,6 +1,8 @@
 #ifndef __CTREE__
 #define __CTREE__
 
+#include "list.h"
+
 #define CTREE_BLOCKSIZE 1024
 
 /*
@@ -53,6 +55,9 @@ struct ctree_root {
 	struct key current_insert;
 	int fp;
 	struct radix_tree_root cache_radix;
+	struct list_head trans;
+	struct list_head cache;
+	int cache_size;
 };
 
 /*

fs/btrfs/disk-io.c

@@ -11,6 +11,8 @@
 #include "disk-io.h"
 
 static int allocated_blocks = 0;
+int cache_size = 0;
+int cache_max = 10000;
 
 static int check_tree_block(struct ctree_root *root, struct tree_buffer *buf)
 {
@@ -21,6 +23,25 @@ static int check_tree_block(struct ctree_root *root, struct tree_buffer *buf)
 	return 0;
 }
 
+static int free_some_buffers(struct ctree_root *root)
+{
+	struct list_head *node, *next;
+	struct tree_buffer *b;
+	if (root->cache_size < cache_max)
+		return 0;
+	list_for_each_safe(node, next, &root->cache) {
+		b = list_entry(node, struct tree_buffer, cache);
+		if (b->count == 1) {
+			BUG_ON(!list_empty(&b->dirty));
+			list_del_init(&b->cache);
+			tree_block_release(root, b);
+			if (root->cache_size < cache_max)
+				return 0;
+		}
+	}
+	return 0;
+}
+
 struct tree_buffer *alloc_tree_block(struct ctree_root *root, u64 blocknr)
 {
 	struct tree_buffer *buf;
@@ -30,10 +51,14 @@ struct tree_buffer *alloc_tree_block(struct ctree_root *root, u64 blocknr)
 		return buf;
 	allocated_blocks++;
 	buf->blocknr = blocknr;
-	buf->count = 1;
+	buf->count = 2;
+	INIT_LIST_HEAD(&buf->dirty);
+	free_some_buffers(root);
 	radix_tree_preload(GFP_KERNEL);
 	ret = radix_tree_insert(&root->cache_radix, blocknr, buf);
 	radix_tree_preload_end();
+	list_add_tail(&buf->cache, &root->cache);
+	root->cache_size++;
 	if (ret) {
 		free(buf);
 		return NULL;
@@ -57,7 +82,6 @@ struct tree_buffer *find_tree_block(struct ctree_root *root, u64 blocknr)
 	return buf;
 }
 
-
 struct tree_buffer *read_tree_block(struct ctree_root *root, u64 blocknr)
 {
 	loff_t offset = blocknr * CTREE_BLOCKSIZE;
@@ -82,6 +106,24 @@ struct tree_buffer *read_tree_block(struct ctree_root *root, u64 blocknr)
 	return buf;
 }
 
+int dirty_tree_block(struct ctree_root *root, struct tree_buffer *buf)
+{
+	if (!list_empty(&buf->dirty))
+		return 0;
+	list_add_tail(&buf->dirty, &root->trans);
+	buf->count++;
+	return 0;
+}
+
+int clean_tree_block(struct ctree_root *root, struct tree_buffer *buf)
+{
+	if (!list_empty(&buf->dirty)) {
+		list_del_init(&buf->dirty);
+		tree_block_release(root, buf);
+	}
+	return 0;
+}
+
 int write_tree_block(struct ctree_root *root, struct tree_buffer *buf)
 {
 	u64 blocknr = buf->blocknr;
@@ -96,9 +138,37 @@ int write_tree_block(struct ctree_root *root, struct tree_buffer *buf)
 	return 0;
 }
 
+static int __commit_transaction(struct ctree_root *root)
+{
+	struct tree_buffer *b;
+	int ret = 0;
+	int wret;
+	while(!list_empty(&root->trans)) {
+		b = list_entry(root->trans.next, struct tree_buffer, dirty);
+		list_del_init(&b->dirty);
+		wret = write_tree_block(root, b);
+		if (wret)
+			ret = wret;
+		tree_block_release(root, b);
+	}
+	return ret;
+}
+
+int commit_transaction(struct ctree_root *root)
+{
+	int ret;
+	ret = __commit_transaction(root);
+	if (!ret && root != root->extent_root)
+		ret = __commit_transaction(root->extent_root);
+	BUG_ON(ret);
+	return ret;
+}
+
 static int __setup_root(struct ctree_root *root, struct ctree_root *extent_root,
 			struct ctree_root_info *info, int fp)
 {
+	INIT_LIST_HEAD(&root->trans);
+	INIT_LIST_HEAD(&root->cache);
 	root->fp = fp;
 	root->node = NULL;
 	root->node = read_tree_block(root, info->tree_root);
@@ -157,8 +227,23 @@ int write_ctree_super(struct ctree_root *root, struct ctree_super_block *s)
 	return 0;
 }
 
+static int drop_cache(struct ctree_root *root)
+{
+	while(!list_empty(&root->cache)) {
+		struct tree_buffer *b = list_entry(root->cache.next,
+						   struct tree_buffer, cache);
+		list_del_init(&b->cache);
+		tree_block_release(root, b);
+	}
+	return 0;
+}
 int close_ctree(struct ctree_root *root)
 {
+	drop_cache(root->extent_root);
+	drop_cache(root);
+	BUG_ON(!list_empty(&root->trans));
+	BUG_ON(!list_empty(&root->extent_root->trans));
+
 	close(root->fp);
 	if (root->node)
 		tree_block_release(root, root->node);
@@ -182,6 +267,8 @@ void tree_block_release(struct ctree_root *root, struct tree_buffer *buf)
 		free(buf);
 		BUG_ON(allocated_blocks == 0);
 		allocated_blocks--;
+		BUG_ON(root->cache_size == 0);
+		root->cache_size--;
 	}
 }
 

fs/btrfs/disk-io.h

@@ -1,5 +1,6 @@
 #ifndef __DISKIO__
 #define __DISKIO__
+#include "list.h"
 
 struct tree_buffer {
 	u64 blocknr;
@@ -8,11 +9,16 @@ struct tree_buffer {
 		struct node node;
 		struct leaf leaf;
 	};
+	struct list_head dirty;
+	struct list_head cache;
 };
 
 struct tree_buffer *read_tree_block(struct ctree_root *root, u64 blocknr);
 struct tree_buffer *find_tree_block(struct ctree_root *root, u64 blocknr);
 int write_tree_block(struct ctree_root *root, struct tree_buffer *buf);
+int dirty_tree_block(struct ctree_root *root, struct tree_buffer *buf);
+int clean_tree_block(struct ctree_root *root, struct tree_buffer *buf);
+int commit_transaction(struct ctree_root *root);
 struct ctree_root *open_ctree(char *filename, struct ctree_super_block *s);
 int close_ctree(struct ctree_root *root);
 void tree_block_release(struct ctree_root *root, struct tree_buffer *buf);

fs/btrfs/list.h

@@ -0,0 +1,418 @@
+#ifndef _LINUX_LIST_H
+#define _LINUX_LIST_H
+
+#define LIST_POISON1  ((void *) 0x00100100)
+#define LIST_POISON2  ((void *) 0x00200200)
+
+/*
+ * Simple doubly linked list implementation.
+ *
+ * Some of the internal functions ("__xxx") are useful when
+ * manipulating whole lists rather than single entries, as
+ * sometimes we already know the next/prev entries and we can
+ * generate better code by using them directly rather than
+ * using the generic single-entry routines.
+ */
+
+struct list_head {
+	struct list_head *next, *prev;
+};
+
+#define LIST_HEAD_INIT(name) { &(name), &(name) }
+
+#define LIST_HEAD(name) \
+	struct list_head name = LIST_HEAD_INIT(name)
+
+static inline void INIT_LIST_HEAD(struct list_head *list)
+{
+	list->next = list;
+	list->prev = list;
+}
+
+/*
+ * Insert a new entry between two known consecutive entries.
+ *
+ * This is only for internal list manipulation where we know
+ * the prev/next entries already!
+ */
+#ifndef CONFIG_DEBUG_LIST
+static inline void __list_add(struct list_head *new,
+			      struct list_head *prev,
+			      struct list_head *next)
+{
+	next->prev = new;
+	new->next = next;
+	new->prev = prev;
+	prev->next = new;
+}
+#else
+extern void __list_add(struct list_head *new,
+			      struct list_head *prev,
+			      struct list_head *next);
+#endif
+
+/**
+ * list_add - add a new entry
+ * @new: new entry to be added
+ * @head: list head to add it after
+ *
+ * Insert a new entry after the specified head.
+ * This is good for implementing stacks.
+ */
+#ifndef CONFIG_DEBUG_LIST
+static inline void list_add(struct list_head *new, struct list_head *head)
+{
+	__list_add(new, head, head->next);
+}
+#else
+extern void list_add(struct list_head *new, struct list_head *head);
+#endif
+
+
+/**
+ * list_add_tail - add a new entry
+ * @new: new entry to be added
+ * @head: list head to add it before
+ *
+ * Insert a new entry before the specified head.
+ * This is useful for implementing queues.
+ */
+static inline void list_add_tail(struct list_head *new, struct list_head *head)
+{
+	__list_add(new, head->prev, head);
+}
+
+/*
+ * Delete a list entry by making the prev/next entries
+ * point to each other.
+ *
+ * This is only for internal list manipulation where we know
+ * the prev/next entries already!
+ */
+static inline void __list_del(struct list_head * prev, struct list_head * next)
+{
+	next->prev = prev;
+	prev->next = next;
+}
+
+/**
+ * list_del - deletes entry from list.
+ * @entry: the element to delete from the list.
+ * Note: list_empty on entry does not return true after this, the entry is
+ * in an undefined state.
+ */
+#ifndef CONFIG_DEBUG_LIST
+static inline void list_del(struct list_head *entry)
+{
+	__list_del(entry->prev, entry->next);
+	entry->next = LIST_POISON1;
+	entry->prev = LIST_POISON2;
+}
+#else
+extern void list_del(struct list_head *entry);
+#endif
+
+/**
+ * list_replace - replace old entry by new one
+ * @old : the element to be replaced
+ * @new : the new element to insert
+ * Note: if 'old' was empty, it will be overwritten.
+ */
+static inline void list_replace(struct list_head *old,
+				struct list_head *new)
+{
+	new->next = old->next;
+	new->next->prev = new;
+	new->prev = old->prev;
+	new->prev->next = new;
+}
+
+static inline void list_replace_init(struct list_head *old,
+					struct list_head *new)
+{
+	list_replace(old, new);
+	INIT_LIST_HEAD(old);
+}
+/**
+ * list_del_init - deletes entry from list and reinitialize it.
+ * @entry: the element to delete from the list.
+ */
+static inline void list_del_init(struct list_head *entry)
+{
+	__list_del(entry->prev, entry->next);
+	INIT_LIST_HEAD(entry);
+}
+
+/**
+ * list_move - delete from one list and add as another's head
+ * @list: the entry to move
+ * @head: the head that will precede our entry
+ */
+static inline void list_move(struct list_head *list, struct list_head *head)
+{
+        __list_del(list->prev, list->next);
+        list_add(list, head);
+}
+
+/**
+ * list_move_tail - delete from one list and add as another's tail
+ * @list: the entry to move
+ * @head: the head that will follow our entry
+ */
+static inline void list_move_tail(struct list_head *list,
+				  struct list_head *head)
+{
+        __list_del(list->prev, list->next);
+        list_add_tail(list, head);
+}
+
+/**
+ * list_is_last - tests whether @list is the last entry in list @head
+ * @list: the entry to test
+ * @head: the head of the list
+ */
+static inline int list_is_last(const struct list_head *list,
+				const struct list_head *head)
+{
+	return list->next == head;
+}
+
+/**
+ * list_empty - tests whether a list is empty
+ * @head: the list to test.
+ */
+static inline int list_empty(const struct list_head *head)
+{
+	return head->next == head;
+}
+
+/**
+ * list_empty_careful - tests whether a list is empty and not being modified
+ * @head: the list to test
+ *
+ * Description:
+ * tests whether a list is empty _and_ checks that no other CPU might be
+ * in the process of modifying either member (next or prev)
+ *
+ * NOTE: using list_empty_careful() without synchronization
+ * can only be safe if the only activity that can happen
+ * to the list entry is list_del_init(). Eg. it cannot be used
+ * if another CPU could re-list_add() it.
+ */
+static inline int list_empty_careful(const struct list_head *head)
+{
+	struct list_head *next = head->next;
+	return (next == head) && (next == head->prev);
+}
+
+static inline void __list_splice(struct list_head *list,
+				 struct list_head *head)
+{
+	struct list_head *first = list->next;
+	struct list_head *last = list->prev;
+	struct list_head *at = head->next;
+
+	first->prev = head;
+	head->next = first;
+
+	last->next = at;
+	at->prev = last;
+}
+
+/**
+ * list_splice - join two lists
+ * @list: the new list to add.
+ * @head: the place to add it in the first list.
+ */
+static inline void list_splice(struct list_head *list, struct list_head *head)
+{
+	if (!list_empty(list))
+		__list_splice(list, head);
+}
+
+/**
+ * list_splice_init - join two lists and reinitialise the emptied list.
+ * @list: the new list to add.
+ * @head: the place to add it in the first list.
+ *
+ * The list at @list is reinitialised
+ */
+static inline void list_splice_init(struct list_head *list,
+				    struct list_head *head)
+{
+	if (!list_empty(list)) {
+		__list_splice(list, head);
+		INIT_LIST_HEAD(list);
+	}
+}
+
+/**
+ * list_entry - get the struct for this entry
+ * @ptr:	the &struct list_head pointer.
+ * @type:	the type of the struct this is embedded in.
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_entry(ptr, type, member) \
+	container_of(ptr, type, member)
+
+/**
+ * list_for_each	-	iterate over a list
+ * @pos:	the &struct list_head to use as a loop cursor.
+ * @head:	the head for your list.
+ */
+#define list_for_each(pos, head) \
+	for (pos = (head)->next; prefetch(pos->next), pos != (head); \
+        	pos = pos->next)
+
+/**
+ * __list_for_each	-	iterate over a list
+ * @pos:	the &struct list_head to use as a loop cursor.
+ * @head:	the head for your list.
+ *
+ * This variant differs from list_for_each() in that it's the
+ * simplest possible list iteration code, no prefetching is done.
+ * Use this for code that knows the list to be very short (empty
+ * or 1 entry) most of the time.
+ */
+#define __list_for_each(pos, head) \
+	for (pos = (head)->next; pos != (head); pos = pos->next)
+
+/**
+ * list_for_each_prev	-	iterate over a list backwards
+ * @pos:	the &struct list_head to use as a loop cursor.
+ * @head:	the head for your list.
+ */
+#define list_for_each_prev(pos, head) \
+	for (pos = (head)->prev; prefetch(pos->prev), pos != (head); \
+        	pos = pos->prev)
+
+/**
+ * list_for_each_safe - iterate over a list safe against removal of list entry
+ * @pos:	the &struct list_head to use as a loop cursor.
+ * @n:		another &struct list_head to use as temporary storage
+ * @head:	the head for your list.
+ */
+#define list_for_each_safe(pos, n, head) \
+	for (pos = (head)->next, n = pos->next; pos != (head); \
+		pos = n, n = pos->next)
+
+/**
+ * list_for_each_entry	-	iterate over list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_for_each_entry(pos, head, member)				\
+	for (pos = list_entry((head)->next, typeof(*pos), member);	\
+	     prefetch(pos->member.next), &pos->member != (head); 	\
+	     pos = list_entry(pos->member.next, typeof(*pos), member))
+
+/**
+ * list_for_each_entry_reverse - iterate backwards over list of given type.
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_for_each_entry_reverse(pos, head, member)			\
+	for (pos = list_entry((head)->prev, typeof(*pos), member);	\
+	     prefetch(pos->member.prev), &pos->member != (head); 	\
+	     pos = list_entry(pos->member.prev, typeof(*pos), member))
+
+/**
+ * list_prepare_entry - prepare a pos entry for use in list_for_each_entry_continue
+ * @pos:	the type * to use as a start point
+ * @head:	the head of the list
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Prepares a pos entry for use as a start point in list_for_each_entry_continue.
+ */
+#define list_prepare_entry(pos, head, member) \
+	((pos) ? : list_entry(head, typeof(*pos), member))
+
+/**
+ * list_for_each_entry_continue - continue iteration over list of given type
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Continue to iterate over list of given type, continuing after
+ * the current position.
+ */
+#define list_for_each_entry_continue(pos, head, member) 		\
+	for (pos = list_entry(pos->member.next, typeof(*pos), member);	\
+	     prefetch(pos->member.next), &pos->member != (head);	\
+	     pos = list_entry(pos->member.next, typeof(*pos), member))
+
+/**
+ * list_for_each_entry_from - iterate over list of given type from the current point
+ * @pos:	the type * to use as a loop cursor.
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Iterate over list of given type, continuing from current position.
+ */
+#define list_for_each_entry_from(pos, head, member) 			\
+	for (; prefetch(pos->member.next), &pos->member != (head);	\
+	     pos = list_entry(pos->member.next, typeof(*pos), member))
+
+/**
+ * list_for_each_entry_safe - iterate over list of given type safe against removal of list entry
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ */
+#define list_for_each_entry_safe(pos, n, head, member)			\
+	for (pos = list_entry((head)->next, typeof(*pos), member),	\
+		n = list_entry(pos->member.next, typeof(*pos), member);	\
+	     &pos->member != (head); 					\
+	     pos = n, n = list_entry(n->member.next, typeof(*n), member))
+
+/**
+ * list_for_each_entry_safe_continue
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Iterate over list of given type, continuing after current point,
+ * safe against removal of list entry.
+ */
+#define list_for_each_entry_safe_continue(pos, n, head, member) 		\
+	for (pos = list_entry(pos->member.next, typeof(*pos), member), 		\
+		n = list_entry(pos->member.next, typeof(*pos), member);		\
+	     &pos->member != (head);						\
+	     pos = n, n = list_entry(n->member.next, typeof(*n), member))
+
+/**
+ * list_for_each_entry_safe_from
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Iterate over list of given type from current point, safe against
+ * removal of list entry.
+ */
+#define list_for_each_entry_safe_from(pos, n, head, member) 			\
+	for (n = list_entry(pos->member.next, typeof(*pos), member);		\
+	     &pos->member != (head);						\
+	     pos = n, n = list_entry(n->member.next, typeof(*n), member))
+
+/**
+ * list_for_each_entry_safe_reverse
+ * @pos:	the type * to use as a loop cursor.
+ * @n:		another type * to use as temporary storage
+ * @head:	the head for your list.
+ * @member:	the name of the list_struct within the struct.
+ *
+ * Iterate backwards over list of given type, safe against removal
+ * of list entry.
+ */
+#define list_for_each_entry_safe_reverse(pos, n, head, member)		\
+	for (pos = list_entry((head)->prev, typeof(*pos), member),	\
+		n = list_entry(pos->member.prev, typeof(*pos), member);	\
+	     &pos->member != (head); 					\
+	     pos = n, n = list_entry(n->member.prev, typeof(*n), member))
+
+#endif