From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Date: Fri, 16 Oct 2020 03:11:31 +0000 (-0700)
Subject: include/linux/list.h: add a macro to test if entry is pointing to the head
X-Git-Tag: v4.19.207~170
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=386a913d4960a83cc4657ebe0c9bc462d8f5e2a1;p=users%2Fdwmw2%2Flinux.git

include/linux/list.h: add a macro to test if entry is pointing to the head

commit e130816164e244b692921de49771eeb28205152d upstream.

Add a macro to test if entry is pointing to the head of the list which is
useful in cases like:

  list_for_each_entry(pos, &head, member) {
    if (cond)
      break;
  }
  if (list_entry_is_head(pos, &head, member))
    return -ERRNO;

that allows to avoid additional variable to be added to track if loop has
not been stopped in the middle.

While here, convert list_for_each_entry*() family of macros to use a new one.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lkml.kernel.org/r/20200929134342.51489-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/include/linux/list.h b/include/linux/list.h
index de04cc5ed5367..d2c12ef7a4e32 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -484,6 +484,15 @@ static inline void list_splice_tail_init(struct list_head *list,
 	     pos != (head); \
 	     pos = n, n = pos->prev)
 
+/**
+ * list_entry_is_head - test if the entry points to the head of the list
+ * @pos:	the type * to cursor
+ * @head:	the head for your list.
+ * @member:	the name of the list_head within the struct.
+ */
+#define list_entry_is_head(pos, head, member)				\
+	(&pos->member == (head))
+
 /**
  * list_for_each_entry	-	iterate over list of given type
  * @pos:	the type * to use as a loop cursor.
@@ -492,7 +501,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  */
 #define list_for_each_entry(pos, head, member)				\
 	for (pos = list_first_entry(head, typeof(*pos), member);	\
-	     &pos->member != (head);					\
+	     !list_entry_is_head(pos, head, member);			\
 	     pos = list_next_entry(pos, member))
 
 /**
@@ -503,7 +512,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  */
 #define list_for_each_entry_reverse(pos, head, member)			\
 	for (pos = list_last_entry(head, typeof(*pos), member);		\
-	     &pos->member != (head); 					\
+	     !list_entry_is_head(pos, head, member); 			\
 	     pos = list_prev_entry(pos, member))
 
 /**
@@ -528,7 +537,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  */
 #define list_for_each_entry_continue(pos, head, member) 		\
 	for (pos = list_next_entry(pos, member);			\
-	     &pos->member != (head);					\
+	     !list_entry_is_head(pos, head, member);			\
 	     pos = list_next_entry(pos, member))
 
 /**
@@ -542,7 +551,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  */
 #define list_for_each_entry_continue_reverse(pos, head, member)		\
 	for (pos = list_prev_entry(pos, member);			\
-	     &pos->member != (head);					\
+	     !list_entry_is_head(pos, head, member);			\
 	     pos = list_prev_entry(pos, member))
 
 /**
@@ -554,7 +563,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  * Iterate over list of given type, continuing from current position.
  */
 #define list_for_each_entry_from(pos, head, member) 			\
-	for (; &pos->member != (head);					\
+	for (; !list_entry_is_head(pos, head, member);			\
 	     pos = list_next_entry(pos, member))
 
 /**
@@ -567,7 +576,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  * Iterate backwards over list of given type, continuing from current position.
  */
 #define list_for_each_entry_from_reverse(pos, head, member)		\
-	for (; &pos->member != (head);					\
+	for (; !list_entry_is_head(pos, head, member);			\
 	     pos = list_prev_entry(pos, member))
 
 /**
@@ -580,7 +589,7 @@ static inline void list_splice_tail_init(struct list_head *list,
 #define list_for_each_entry_safe(pos, n, head, member)			\
 	for (pos = list_first_entry(head, typeof(*pos), member),	\
 		n = list_next_entry(pos, member);			\
-	     &pos->member != (head); 					\
+	     !list_entry_is_head(pos, head, member); 			\
 	     pos = n, n = list_next_entry(n, member))
 
 /**
@@ -596,7 +605,7 @@ static inline void list_splice_tail_init(struct list_head *list,
 #define list_for_each_entry_safe_continue(pos, n, head, member) 		\
 	for (pos = list_next_entry(pos, member), 				\
 		n = list_next_entry(pos, member);				\
-	     &pos->member != (head);						\
+	     !list_entry_is_head(pos, head, member);				\
 	     pos = n, n = list_next_entry(n, member))
 
 /**
@@ -611,7 +620,7 @@ static inline void list_splice_tail_init(struct list_head *list,
  */
 #define list_for_each_entry_safe_from(pos, n, head, member) 			\
 	for (n = list_next_entry(pos, member);					\
-	     &pos->member != (head);						\
+	     !list_entry_is_head(pos, head, member);				\
 	     pos = n, n = list_next_entry(n, member))
 
 /**
@@ -627,7 +636,7 @@ static inline void list_splice_tail_init(struct list_head *list,
 #define list_for_each_entry_safe_reverse(pos, n, head, member)		\
 	for (pos = list_last_entry(head, typeof(*pos), member),		\
 		n = list_prev_entry(pos, member);			\
-	     &pos->member != (head); 					\
+	     !list_entry_is_head(pos, head, member); 			\
 	     pos = n, n = list_prev_entry(n, member))
 
 /**