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

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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>
This commit is contained in:
Andy Shevchenko 2020-10-15 20:11:31 -07:00 committed by Linus Torvalds
parent 1d339638a9
commit e130816164
1 changed files with 19 additions and 10 deletions
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29
include/linux/list.h
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@ -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))
/**