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include: list.h: allow zero-initialization of struct xorg_list 

Up until now, xorg_list's always need to be explicitly initialized by
calling xorg_list_init(), otherwise next access attempt will segfault.
This is adding extra complexity and risk of subtle bugs.

Adding some extra NULL check are trivial and their cost is so tiny
that it's even hard to practically measure.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
This commit is contained in:
Enrico Weigelt, metux IT consult 2025-05-27 17:20:52 +02:00
parent 74766ee6bd
commit 9461072ab4
1 changed files with 12 additions and 3 deletions
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15
include/list.h
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@ -130,6 +130,13 @@ xorg_list_init(struct xorg_list *list)
list->next = list->prev = list;
}
static inline void
__xorg_list_autoinit(struct xorg_list *head)
{
if ((!head->prev) && (!head->next))
xorg_list_init(head);
}
static inline void
__xorg_list_add(struct xorg_list *entry,
struct xorg_list *prev, struct xorg_list *next)
@ -158,6 +165,7 @@ __xorg_list_add(struct xorg_list *entry,
static inline void
xorg_list_add(struct xorg_list *entry, struct xorg_list *head)
{
__xorg_list_autoinit(head);
__xorg_list_add(entry, head, head->next);
}
@ -179,6 +187,7 @@ xorg_list_add(struct xorg_list *entry, struct xorg_list *head)
static inline void
xorg_list_append(struct xorg_list *entry, struct xorg_list *head)
{
__xorg_list_autoinit(head);
__xorg_list_add(entry, head->prev, head);
}
@ -222,7 +231,7 @@ xorg_list_del(struct xorg_list *entry)
static inline int
xorg_list_is_empty(struct xorg_list *head)
{
return head->next == head;
return ((head->next == NULL) || (head->next == head));
}
/**
@ -302,7 +311,7 @@ xorg_list_is_empty(struct xorg_list *head)
#define xorg_list_for_each_entry(pos, head, member) \
for (pos = NULL, \
pos = __container_of((head)->next, pos, member); \
&pos->member != (head); \
(((head)->next != NULL) && &pos->member != (head)); \
pos = __container_of(pos->member.next, pos, member))
/**
@ -316,7 +325,7 @@ xorg_list_is_empty(struct xorg_list *head)
for (pos = NULL, \
pos = __container_of((head)->next, pos, member), \
tmp = __container_of(pos->member.next, pos, member); \
&pos->member != (head); \
(((head)->next != NULL) && (&pos->member != (head))); \
pos = tmp, tmp = __container_of(pos->member.next, tmp, member))
/* NULL-Terminated List Interface