lib/plist: add helper functions

Add PLIST_HEAD() to plist.h, equivalent to LIST_HEAD() from list.h, to
define and initialize a struct plist_head.

Add plist_for_each_continue() and plist_for_each_entry_continue(),
equivalent to list_for_each_continue() and list_for_each_entry_continue(),
to iterate over a plist continuing after the current position.

Add plist_prev() and plist_next(), equivalent to (struct list_head*)->prev
and ->next, implemented by list_prev_entry() and list_next_entry(), to
access the prev/next struct plist_node entry. These are needed because
unlike struct list_head, direct access of the prev/next struct plist_node
isn't possible; the list must be navigated via the contained struct
list_head. e.g. instead of accessing the prev by list_prev_entry(node,
node_list) it can be accessed by plist_prev(node).

Signed-off-by: Dan Streetman <[e-mail]>
Acked-by: Mel Gorman <[e-mail]>
Cc: Paul Gortmaker <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Shaohua Li <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Dan Streetman <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Christian Ehrhardt <[e-mail]>
Cc: Weijie Yang <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Bob Liu <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/plist.h

···
 }
 
 /**
+ * PLIST_HEAD - declare and init plist_head
+ * @head:	name for struct plist_head variable
+ */
+#define PLIST_HEAD(head) \
+	struct plist_head head = PLIST_HEAD_INIT(head)
+
+/**
  * PLIST_NODE_INIT - static struct plist_node initializer
  * @node:	struct plist_node variable name
  * @__prio:	initial node priority
···
 	 list_for_each_entry(pos, &(head)->node_list, node_list)
 
 /**
+ * plist_for_each_continue - continue iteration over the plist
+ * @pos:	the type * to use as a loop cursor
+ * @head:	the head for your list
+ *
+ * Continue to iterate over plist, continuing after the current position.
+ */
+#define plist_for_each_continue(pos, head)	\
+	 list_for_each_entry_continue(pos, &(head)->node_list, node_list)
+
+/**
  * plist_for_each_safe - iterate safely over a plist of given type
  * @pos:	the type * to use as a loop counter
  * @n:	another type * to use as temporary storage
···
  */
 #define plist_for_each_entry(pos, head, mem)	\
 	 list_for_each_entry(pos, &(head)->node_list, mem.node_list)
+
+/**
+ * plist_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
+ * @m:		the name of the list_struct within the struct
+ *
+ * Continue to iterate over list of given type, continuing after
+ * the current position.
+ */
+#define plist_for_each_entry_continue(pos, head, m)	\
+	list_for_each_entry_continue(pos, &(head)->node_list, m.node_list)
 
 /**
  * plist_for_each_entry_safe - iterate safely over list of given type
···
 # define plist_last_entry(head, type, member)	\
 	container_of(plist_last(head), type, member)
 #endif
+
+/**
+ * plist_next - get the next entry in list
+ * @pos:	the type * to cursor
+ */
+#define plist_next(pos) \
+	list_next_entry(pos, node_list)
+
+/**
+ * plist_prev - get the prev entry in list
+ * @pos:	the type * to cursor
+ */
+#define plist_prev(pos) \
+	list_prev_entry(pos, node_list)
 
 /**
  * plist_first - return the first node (and thus, highest priority)