From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Subject: include/linux/list.h: add a macro to test if entry is pointing to the head
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.
Link: https://lkml.kernel.org/r/20200929134342.51489-1-andriy.shevchenko@xxxxxxxxxxxxxxx
Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Reviewed-by: Cezary Rojewski <cezary.rojewski@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/list.h | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)
--- a/include/linux/list.h~list-add-a-macro-to-test-if-entry-is-pointing-to-the-head
+++ a/include/linux/list.h
@@ -610,6 +610,15 @@ static inline void list_splice_tail_init
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.
* @head: the head for your list.
@@ -617,7 +626,7 @@ static inline void list_splice_tail_init
*/
#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))
/**
@@ -628,7 +637,7 @@ static inline void list_splice_tail_init
*/
#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))
/**
@@ -653,7 +662,7 @@ static inline void list_splice_tail_init
*/
#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))
/**
@@ -667,7 +676,7 @@ static inline void list_splice_tail_init
*/
#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))
/**
@@ -679,7 +688,7 @@ static inline void list_splice_tail_init
* 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))
/**
@@ -692,7 +701,7 @@ static inline void list_splice_tail_init
* 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))
/**
@@ -705,7 +714,7 @@ static inline void list_splice_tail_init
#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))
/**
@@ -721,7 +730,7 @@ static inline void list_splice_tail_init
#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))
/**
@@ -736,7 +745,7 @@ static inline void list_splice_tail_init
*/
#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))
/**
@@ -752,7 +761,7 @@ static inline void list_splice_tail_init
#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))
/**
_
