cleanup: split internal.h into several internal header files

This patch cleanups the internal headers by splitting them into several
logical pieces.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 0 insertions, 725 deletions

diff --git a/include/linux_list.h b/include/linux_list.h
deleted file mode 100644
index 57b56d7..0000000
--- a/include/linux_list.h
+++ /dev/null
@@ -1,725 +0,0 @@
-#ifndef _LINUX_LIST_H
-#define _LINUX_LIST_H
-
-#undef offsetof
-#define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
-
-/**
- * container_of - cast a member of a structure out to the containing structure
- *
- * @ptr:	the pointer to the member.
- * @type:	the type of the container struct this is embedded in.
- * @member:	the name of the member within the struct.
- *
- */
-#define container_of(ptr, type, member) ({			\
-        const typeof( ((type *)0)->member ) *__mptr = (ptr);	\
-        (type *)( (char *)__mptr - offsetof(type,member) );})
-
-/*
- * Check at compile time that something is of a particular type.
- * Always evaluates to 1 so you may use it easily in comparisons.
- */
-#define typecheck(type,x) \
-({	type __dummy; \
-	typeof(x) __dummy2; \
-	(void)(&__dummy == &__dummy2); \
-	1; \
-})
-
-#define prefetch(x)		1
-
-/* empty define to make this work in userspace -HW */
-#ifndef smp_wmb
-#define smp_wmb()
-#endif
-
-/*
- * These are non-NULL pointers that will result in page faults
- * under normal circumstances, used to verify that nobody uses
- * non-initialized list entries.
- */
-#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)
-
-#define INIT_LIST_HEAD(ptr) do { \
-	(ptr)->next = (ptr); (ptr)->prev = (ptr); \
-} while (0)
-
-/*
- * Insert a new entry between two known consecutive entries.
- *
- * This is only for internal list manipulation where we know
- * the prev/next entries already!
- */
-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;
-}
-
-/**
- * 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.
- */
-static inline void list_add(struct list_head *new, struct list_head *head)
-{
-	__list_add(new, head, head->next);
-}
-
-/**
- * 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);
-}
-
-/*
- * Insert a new entry between two known consecutive entries.
- *
- * This is only for internal list manipulation where we know
- * the prev/next entries already!
- */
-static inline void __list_add_rcu(struct list_head * new,
-		struct list_head * prev, struct list_head * next)
-{
-	new->next = next;
-	new->prev = prev;
-	smp_wmb();
-	next->prev = new;
-	prev->next = new;
-}
-
-/**
- * list_add_rcu - add a new entry to rcu-protected list
- * @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.
- *
- * The caller must take whatever precautions are necessary
- * (such as holding appropriate locks) to avoid racing
- * with another list-mutation primitive, such as list_add_rcu()
- * or list_del_rcu(), running on this same list.
- * However, it is perfectly legal to run concurrently with
- * the _rcu list-traversal primitives, such as
- * list_for_each_entry_rcu().
- */
-static inline void list_add_rcu(struct list_head *new, struct list_head *head)
-{
-	__list_add_rcu(new, head, head->next);
-}
-
-/**
- * list_add_tail_rcu - add a new entry to rcu-protected list
- * @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.
- *
- * The caller must take whatever precautions are necessary
- * (such as holding appropriate locks) to avoid racing
- * with another list-mutation primitive, such as list_add_tail_rcu()
- * or list_del_rcu(), running on this same list.
- * However, it is perfectly legal to run concurrently with
- * the _rcu list-traversal primitives, such as
- * list_for_each_entry_rcu().
- */
-static inline void list_add_tail_rcu(struct list_head *new,
-					struct list_head *head)
-{
-	__list_add_rcu(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.
- */
-static inline void list_del(struct list_head *entry)
-{
-	__list_del(entry->prev, entry->next);
-	entry->next = LIST_POISON1;
-	entry->prev = LIST_POISON2;
-}
-
-/**
- * list_del_rcu - deletes entry from list without re-initialization
- * @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. It is useful for RCU based
- * lockfree traversal.
- *
- * In particular, it means that we can not poison the forward
- * pointers that may still be used for walking the list.
- *
- * The caller must take whatever precautions are necessary
- * (such as holding appropriate locks) to avoid racing
- * with another list-mutation primitive, such as list_del_rcu()
- * or list_add_rcu(), running on this same list.
- * However, it is perfectly legal to run concurrently with
- * the _rcu list-traversal primitives, such as
- * list_for_each_entry_rcu().
- *
- * Note that the caller is not permitted to immediately free
- * the newly deleted entry.  Instead, either synchronize_kernel()
- * or call_rcu() must be used to defer freeing until an RCU
- * grace period has elapsed.
- */
-static inline void list_del_rcu(struct list_head *entry)
-{
-	__list_del(entry->prev, entry->next);
-	entry->prev = LIST_POISON2;
-}
-
-/**
- * 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_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_ checks that no other CPU might be
- * in the process of still modifying either member
- *
- * 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.
- *
- * @head: the list to test.
- */
-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 counter.
- * @head:	the head for your list.
- */
-#define list_for_each(pos, head) \
-	for (pos = (head)->next, prefetch(pos->next); pos != (head); \
-        	pos = pos->next, prefetch(pos->next))
-
-/**
- * __list_for_each	-	iterate over a list
- * @pos:	the &struct list_head to use as a loop counter.
- * @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 counter.
- * @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, prefetch(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 counter.
- * @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 counter.
- * @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),	\
-		     prefetch(pos->member.next))
-
-/**
- * list_for_each_entry_reverse - iterate backwards over list of given type.
- * @pos:	the type * to use as a loop counter.
- * @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),	\
-		     prefetch(pos->member.prev))
-
-/**
- * list_prepare_entry - prepare a pos entry for use as a start point 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.
- */
-#define list_prepare_entry(pos, head, member) \
-	((pos) ? : list_entry(head, typeof(*pos), member))
-
-/**
- * list_for_each_entry_continue -	iterate over list of given type
- *			continuing after existing point
- * @pos:	the type * to use as a loop counter.
- * @head:	the head for your list.
- * @member:	the name of the list_struct within the struct.
- */
-#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),	\
-		     prefetch(pos->member.next))
-
-/**
- * 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 counter.
- * @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_rcu	-	iterate over an rcu-protected list
- * @pos:	the &struct list_head to use as a loop counter.
- * @head:	the head for your list.
- *
- * This list-traversal primitive may safely run concurrently with
- * the _rcu list-mutation primitives such as list_add_rcu()
- * as long as the traversal is guarded by rcu_read_lock().
- */
-#define list_for_each_rcu(pos, head) \
-	for (pos = (head)->next, prefetch(pos->next); pos != (head); \
-        	pos = pos->next, ({ smp_read_barrier_depends(); 0;}), prefetch(pos->next))
-
-#define __list_for_each_rcu(pos, head) \
-	for (pos = (head)->next; pos != (head); \
-        	pos = pos->next, ({ smp_read_barrier_depends(); 0;}))
-
-/**
- * list_for_each_safe_rcu	-	iterate over an rcu-protected list safe
- *					against removal of list entry
- * @pos:	the &struct list_head to use as a loop counter.
- * @n:		another &struct list_head to use as temporary storage
- * @head:	the head for your list.
- *
- * This list-traversal primitive may safely run concurrently with
- * the _rcu list-mutation primitives such as list_add_rcu()
- * as long as the traversal is guarded by rcu_read_lock().
- */
-#define list_for_each_safe_rcu(pos, n, head) \
-	for (pos = (head)->next, n = pos->next; pos != (head); \
-		pos = n, ({ smp_read_barrier_depends(); 0;}), n = pos->next)
-
-/**
- * list_for_each_entry_rcu	-	iterate over rcu list of given type
- * @pos:	the type * to use as a loop counter.
- * @head:	the head for your list.
- * @member:	the name of the list_struct within the struct.
- *
- * This list-traversal primitive may safely run concurrently with
- * the _rcu list-mutation primitives such as list_add_rcu()
- * as long as the traversal is guarded by rcu_read_lock().
- */
-#define list_for_each_entry_rcu(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),	\
-		     ({ smp_read_barrier_depends(); 0;}),		\
-		     prefetch(pos->member.next))
-
-
-/**
- * list_for_each_continue_rcu	-	iterate over an rcu-protected list
- *			continuing after existing point.
- * @pos:	the &struct list_head to use as a loop counter.
- * @head:	the head for your list.
- *
- * This list-traversal primitive may safely run concurrently with
- * the _rcu list-mutation primitives such as list_add_rcu()
- * as long as the traversal is guarded by rcu_read_lock().
- */
-#define list_for_each_continue_rcu(pos, head) \
-	for ((pos) = (pos)->next, prefetch((pos)->next); (pos) != (head); \
-        	(pos) = (pos)->next, ({ smp_read_barrier_depends(); 0;}), prefetch((pos)->next))
-
-/*
- * Double linked lists with a single pointer list head.
- * Mostly useful for hash tables where the two pointer list head is
- * too wasteful.
- * You lose the ability to access the tail in O(1).
- */
-
-struct hlist_head {
-	struct hlist_node *first;
-};
-
-struct hlist_node {
-	struct hlist_node *next, **pprev;
-};
-
-#define HLIST_HEAD_INIT { .first = NULL }
-#define HLIST_HEAD(name) struct hlist_head name = {  .first = NULL }
-#define INIT_HLIST_HEAD(ptr) ((ptr)->first = NULL)
-#define INIT_HLIST_NODE(ptr) ((ptr)->next = NULL, (ptr)->pprev = NULL)
-
-static inline int hlist_unhashed(const struct hlist_node *h)
-{
-	return !h->pprev;
-}
-
-static inline int hlist_empty(const struct hlist_head *h)
-{
-	return !h->first;
-}
-
-static inline void __hlist_del(struct hlist_node *n)
-{
-	struct hlist_node *next = n->next;
-	struct hlist_node **pprev = n->pprev;
-	*pprev = next;
-	if (next)
-		next->pprev = pprev;
-}
-
-static inline void hlist_del(struct hlist_node *n)
-{
-	__hlist_del(n);
-	n->next = LIST_POISON1;
-	n->pprev = LIST_POISON2;
-}
-
-/**
- * hlist_del_rcu - deletes entry from hash list without re-initialization
- * @n: the element to delete from the hash list.
- *
- * Note: list_unhashed() on entry does not return true after this,
- * the entry is in an undefined state. It is useful for RCU based
- * lockfree traversal.
- *
- * In particular, it means that we can not poison the forward
- * pointers that may still be used for walking the hash list.
- *
- * The caller must take whatever precautions are necessary
- * (such as holding appropriate locks) to avoid racing
- * with another list-mutation primitive, such as hlist_add_head_rcu()
- * or hlist_del_rcu(), running on this same list.
- * However, it is perfectly legal to run concurrently with
- * the _rcu list-traversal primitives, such as
- * hlist_for_each_entry().
- */
-static inline void hlist_del_rcu(struct hlist_node *n)
-{
-	__hlist_del(n);
-	n->pprev = LIST_POISON2;
-}
-
-static inline void hlist_del_init(struct hlist_node *n)
-{
-	if (n->pprev)  {
-		__hlist_del(n);
-		INIT_HLIST_NODE(n);
-	}
-}
-
-#define hlist_del_rcu_init hlist_del_init
-
-static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
-{
-	struct hlist_node *first = h->first;
-	n->next = first;
-	if (first)
-		first->pprev = &n->next;
-	h->first = n;
-	n->pprev = &h->first;
-}
-
-
-/**
- * hlist_add_head_rcu - adds the specified element to the specified hlist,
- * while permitting racing traversals.
- * @n: the element to add to the hash list.
- * @h: the list to add to.
- *
- * The caller must take whatever precautions are necessary
- * (such as holding appropriate locks) to avoid racing
- * with another list-mutation primitive, such as hlist_add_head_rcu()
- * or hlist_del_rcu(), running on this same list.
- * However, it is perfectly legal to run concurrently with
- * the _rcu list-traversal primitives, such as
- * hlist_for_each_entry(), but only if smp_read_barrier_depends()
- * is used to prevent memory-consistency problems on Alpha CPUs.
- * Regardless of the type of CPU, the list-traversal primitive
- * must be guarded by rcu_read_lock().
- *
- * OK, so why don't we have an hlist_for_each_entry_rcu()???
- */
-static inline void hlist_add_head_rcu(struct hlist_node *n,
-					struct hlist_head *h)
-{
-	struct hlist_node *first = h->first;
-	n->next = first;
-	n->pprev = &h->first;
-	smp_wmb();
-	if (first)
-		first->pprev = &n->next;
-	h->first = n;
-}
-
-/* next must be != NULL */
-static inline void hlist_add_before(struct hlist_node *n,
-					struct hlist_node *next)
-{
-	n->pprev = next->pprev;
-	n->next = next;
-	next->pprev = &n->next;
-	*(n->pprev) = n;
-}
-
-static inline void hlist_add_after(struct hlist_node *n,
-					struct hlist_node *next)
-{
-	next->next = n->next;
-	n->next = next;
-	next->pprev = &n->next;
-
-	if(next->next)
-		next->next->pprev  = &next->next;
-}
-
-#define hlist_entry(ptr, type, member) container_of(ptr,type,member)
-
-#define hlist_for_each(pos, head) \
-	for (pos = (head)->first; pos && ({ prefetch(pos->next); 1; }); \
-	     pos = pos->next)
-
-#define hlist_for_each_safe(pos, n, head) \
-	for (pos = (head)->first; pos && ({ n = pos->next; 1; }); \
-	     pos = n)
-
-/**
- * hlist_for_each_entry	- iterate over list of given type
- * @tpos:	the type * to use as a loop counter.
- * @pos:	the &struct hlist_node to use as a loop counter.
- * @head:	the head for your list.
- * @member:	the name of the hlist_node within the struct.
- */
-#define hlist_for_each_entry(tpos, pos, head, member)			 \
-	for (pos = (head)->first;					 \
-	     pos && ({ prefetch(pos->next); 1;}) &&			 \
-		({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
-	     pos = pos->next)
-
-/**
- * hlist_for_each_entry_continue - iterate over a hlist continuing after existing point
- * @tpos:	the type * to use as a loop counter.
- * @pos:	the &struct hlist_node to use as a loop counter.
- * @member:	the name of the hlist_node within the struct.
- */
-#define hlist_for_each_entry_continue(tpos, pos, member)		 \
-	for (pos = (pos)->next;						 \
-	     pos && ({ prefetch(pos->next); 1;}) &&			 \
-		({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
-	     pos = pos->next)
-
-/**
- * hlist_for_each_entry_from - iterate over a hlist continuing from existing point
- * @tpos:	the type * to use as a loop counter.
- * @pos:	the &struct hlist_node to use as a loop counter.
- * @member:	the name of the hlist_node within the struct.
- */
-#define hlist_for_each_entry_from(tpos, pos, member)			 \
-	for (; pos && ({ prefetch(pos->next); 1;}) &&			 \
-		({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
-	     pos = pos->next)
-
-/**
- * hlist_for_each_entry_safe - iterate over list of given type safe against removal of list entry
- * @tpos:	the type * to use as a loop counter.
- * @pos:	the &struct hlist_node to use as a loop counter.
- * @n:		another &struct hlist_node to use as temporary storage
- * @head:	the head for your list.
- * @member:	the name of the hlist_node within the struct.
- */
-#define hlist_for_each_entry_safe(tpos, pos, n, head, member) 		 \
-	for (pos = (head)->first;					 \
-	     pos && ({ n = pos->next; 1; }) && 				 \
-		({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
-	     pos = n)
-
-/**
- * hlist_for_each_entry_rcu - iterate over rcu list of given type
- * @pos:	the type * to use as a loop counter.
- * @pos:	the &struct hlist_node to use as a loop counter.
- * @head:	the head for your list.
- * @member:	the name of the hlist_node within the struct.
- *
- * This list-traversal primitive may safely run concurrently with
- * the _rcu list-mutation primitives such as hlist_add_rcu()
- * as long as the traversal is guarded by rcu_read_lock().
- */
-#define hlist_for_each_entry_rcu(tpos, pos, head, member)		 \
-	for (pos = (head)->first;					 \
-	     pos && ({ prefetch(pos->next); 1;}) &&			 \
-		({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
-	     pos = pos->next, ({ smp_read_barrier_depends(); 0; }) )
-
-#endif