* [PATCH v2] list: Add a macro to test if entry is pointing to the head
@ 2020-09-29 13:43 Andy Shevchenko
2020-09-29 14:40 ` Rojewski, Cezary
0 siblings, 1 reply; 2+ messages in thread
From: Andy Shevchenko @ 2020-09-29 13:43 UTC (permalink / raw)
To: Cezary Rojewski, linux-kernel, Andrew Morton; +Cc: Andy Shevchenko
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>
---
v2: converted users inside list.h, dropped ambiguous description
include/linux/list.h | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)
diff --git a/include/linux/list.h b/include/linux/list.h
index 796975c3c35c..89bdc92e75c3 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -609,6 +609,15 @@ 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.
@@ -617,7 +626,7 @@ 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))
/**
@@ -628,7 +637,7 @@ 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))
/**
@@ -653,7 +662,7 @@ 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))
/**
@@ -667,7 +676,7 @@ 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))
/**
@@ -679,7 +688,7 @@ 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))
/**
@@ -692,7 +701,7 @@ 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))
/**
@@ -705,7 +714,7 @@ 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))
/**
@@ -721,7 +730,7 @@ 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))
/**
@@ -736,7 +745,7 @@ 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))
/**
@@ -752,7 +761,7 @@ 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))
/**
--
2.28.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] list: Add a macro to test if entry is pointing to the head
2020-09-29 13:43 [PATCH v2] list: Add a macro to test if entry is pointing to the head Andy Shevchenko
@ 2020-09-29 14:40 ` Rojewski, Cezary
0 siblings, 0 replies; 2+ messages in thread
From: Rojewski, Cezary @ 2020-09-29 14:40 UTC (permalink / raw)
To: Andy Shevchenko; +Cc: linux-kernel@vger.kernel.org, Andrew Morton
On 2020-09-29 3:43 PM, Andy Shevchenko wrote:
> 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>
> ---
> v2: converted users inside list.h, dropped ambiguous description
Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
This is a good addition to the list of helper macros found in list.h.
When looking at below:
> /**
> * list_for_each_entry - iterate over list of given type
> * @pos: the type * to use as a loop cursor.
> @@ -617,7 +626,7 @@ 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))
>
it seems such helper should have been here a long time ago (notice the
usage of helpers for initial assignment and cursor update while the
loop-exit check was devoid of such).
Czarek
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