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252 lines
9.1 KiB
252 lines
9.1 KiB
/* SPDX-License-Identifier: GPL-2.0-only */ |
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#ifndef LLIST_H |
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#define LLIST_H |
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/* |
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* Lock-less NULL terminated single linked list |
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* |
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* Cases where locking is not needed: |
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* If there are multiple producers and multiple consumers, llist_add can be |
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* used in producers and llist_del_all can be used in consumers simultaneously |
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* without locking. Also a single consumer can use llist_del_first while |
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* multiple producers simultaneously use llist_add, without any locking. |
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* |
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* Cases where locking is needed: |
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* If we have multiple consumers with llist_del_first used in one consumer, and |
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* llist_del_first or llist_del_all used in other consumers, then a lock is |
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* needed. This is because llist_del_first depends on list->first->next not |
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* changing, but without lock protection, there's no way to be sure about that |
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* if a preemption happens in the middle of the delete operation and on being |
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* preempted back, the list->first is the same as before causing the cmpxchg in |
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* llist_del_first to succeed. For example, while a llist_del_first operation |
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* is in progress in one consumer, then a llist_del_first, llist_add, |
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* llist_add (or llist_del_all, llist_add, llist_add) sequence in another |
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* consumer may cause violations. |
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* |
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* This can be summarized as follows: |
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* |
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* | add | del_first | del_all |
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* add | - | - | - |
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* del_first | | L | L |
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* del_all | | | - |
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* |
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* Where, a particular row's operation can happen concurrently with a column's |
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* operation, with "-" being no lock needed, while "L" being lock is needed. |
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* |
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* The list entries deleted via llist_del_all can be traversed with |
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* traversing function such as llist_for_each etc. But the list |
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* entries can not be traversed safely before deleted from the list. |
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* The order of deleted entries is from the newest to the oldest added |
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* one. If you want to traverse from the oldest to the newest, you |
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* must reverse the order by yourself before traversing. |
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* |
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* The basic atomic operation of this list is cmpxchg on long. On |
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* architectures that don't have NMI-safe cmpxchg implementation, the |
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* list can NOT be used in NMI handlers. So code that uses the list in |
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* an NMI handler should depend on CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG. |
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* |
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* Copyright 2010,2011 Intel Corp. |
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* Author: Huang Ying <[email protected]> |
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*/ |
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#include <linux/atomic.h> |
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#include <linux/kernel.h> |
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struct llist_head { |
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struct llist_node *first; |
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}; |
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struct llist_node { |
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struct llist_node *next; |
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}; |
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#define LLIST_HEAD_INIT(name) { NULL } |
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#define LLIST_HEAD(name) struct llist_head name = LLIST_HEAD_INIT(name) |
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/** |
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* init_llist_head - initialize lock-less list head |
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* @head: the head for your lock-less list |
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*/ |
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static inline void init_llist_head(struct llist_head *list) |
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{ |
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list->first = NULL; |
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} |
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/** |
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* llist_entry - get the struct of this entry |
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* @ptr: the &struct llist_node pointer. |
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* @type: the type of the struct this is embedded in. |
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* @member: the name of the llist_node within the struct. |
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*/ |
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#define llist_entry(ptr, type, member) \ |
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container_of(ptr, type, member) |
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/** |
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* member_address_is_nonnull - check whether the member address is not NULL |
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* @ptr: the object pointer (struct type * that contains the llist_node) |
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* @member: the name of the llist_node within the struct. |
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* |
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* This macro is conceptually the same as |
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* &ptr->member != NULL |
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* but it works around the fact that compilers can decide that taking a member |
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* address is never a NULL pointer. |
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* |
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* Real objects that start at a high address and have a member at NULL are |
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* unlikely to exist, but such pointers may be returned e.g. by the |
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* container_of() macro. |
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*/ |
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#define member_address_is_nonnull(ptr, member) \ |
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((uintptr_t)(ptr) + offsetof(typeof(*(ptr)), member) != 0) |
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/** |
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* llist_for_each - iterate over some deleted entries of a lock-less list |
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* @pos: the &struct llist_node to use as a loop cursor |
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* @node: the first entry of deleted list entries |
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* |
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* In general, some entries of the lock-less list can be traversed |
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* safely only after being deleted from list, so start with an entry |
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* instead of list head. |
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* |
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* If being used on entries deleted from lock-less list directly, the |
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* traverse order is from the newest to the oldest added entry. If |
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* you want to traverse from the oldest to the newest, you must |
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* reverse the order by yourself before traversing. |
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*/ |
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#define llist_for_each(pos, node) \ |
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for ((pos) = (node); pos; (pos) = (pos)->next) |
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/** |
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* llist_for_each_safe - iterate over some deleted entries of a lock-less list |
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* safe against removal of list entry |
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* @pos: the &struct llist_node to use as a loop cursor |
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* @n: another &struct llist_node to use as temporary storage |
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* @node: the first entry of deleted list entries |
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* |
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* In general, some entries of the lock-less list can be traversed |
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* safely only after being deleted from list, so start with an entry |
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* instead of list head. |
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* |
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* If being used on entries deleted from lock-less list directly, the |
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* traverse order is from the newest to the oldest added entry. If |
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* you want to traverse from the oldest to the newest, you must |
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* reverse the order by yourself before traversing. |
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*/ |
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#define llist_for_each_safe(pos, n, node) \ |
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for ((pos) = (node); (pos) && ((n) = (pos)->next, true); (pos) = (n)) |
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/** |
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* llist_for_each_entry - iterate over some deleted entries of lock-less list of given type |
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* @pos: the type * to use as a loop cursor. |
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* @node: the fist entry of deleted list entries. |
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* @member: the name of the llist_node with the struct. |
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* |
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* In general, some entries of the lock-less list can be traversed |
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* safely only after being removed from list, so start with an entry |
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* instead of list head. |
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* |
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* If being used on entries deleted from lock-less list directly, the |
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* traverse order is from the newest to the oldest added entry. If |
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* you want to traverse from the oldest to the newest, you must |
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* reverse the order by yourself before traversing. |
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*/ |
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#define llist_for_each_entry(pos, node, member) \ |
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for ((pos) = llist_entry((node), typeof(*(pos)), member); \ |
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member_address_is_nonnull(pos, member); \ |
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(pos) = llist_entry((pos)->member.next, typeof(*(pos)), member)) |
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/** |
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* llist_for_each_entry_safe - iterate over some deleted entries of lock-less list of given type |
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* safe against removal of list entry |
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* @pos: the type * to use as a loop cursor. |
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* @n: another type * to use as temporary storage |
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* @node: the first entry of deleted list entries. |
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* @member: the name of the llist_node with the struct. |
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* |
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* In general, some entries of the lock-less list can be traversed |
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* safely only after being removed from list, so start with an entry |
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* instead of list head. |
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* |
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* If being used on entries deleted from lock-less list directly, the |
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* traverse order is from the newest to the oldest added entry. If |
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* you want to traverse from the oldest to the newest, you must |
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* reverse the order by yourself before traversing. |
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*/ |
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#define llist_for_each_entry_safe(pos, n, node, member) \ |
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for (pos = llist_entry((node), typeof(*pos), member); \ |
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member_address_is_nonnull(pos, member) && \ |
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(n = llist_entry(pos->member.next, typeof(*n), member), true); \ |
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pos = n) |
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/** |
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* llist_empty - tests whether a lock-less list is empty |
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* @head: the list to test |
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* |
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* Not guaranteed to be accurate or up to date. Just a quick way to |
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* test whether the list is empty without deleting something from the |
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* list. |
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*/ |
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static inline bool llist_empty(const struct llist_head *head) |
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{ |
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return READ_ONCE(head->first) == NULL; |
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} |
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static inline struct llist_node *llist_next(struct llist_node *node) |
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{ |
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return node->next; |
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} |
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extern bool llist_add_batch(struct llist_node *new_first, |
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struct llist_node *new_last, |
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struct llist_head *head); |
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static inline bool __llist_add_batch(struct llist_node *new_first, |
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struct llist_node *new_last, |
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struct llist_head *head) |
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{ |
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new_last->next = head->first; |
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head->first = new_first; |
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return new_last->next == NULL; |
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} |
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/** |
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* llist_add - add a new entry |
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* @new: new entry to be added |
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* @head: the head for your lock-less list |
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* |
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* Returns true if the list was empty prior to adding this entry. |
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*/ |
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static inline bool llist_add(struct llist_node *new, struct llist_head *head) |
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{ |
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return llist_add_batch(new, new, head); |
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} |
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static inline bool __llist_add(struct llist_node *new, struct llist_head *head) |
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{ |
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return __llist_add_batch(new, new, head); |
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} |
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/** |
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* llist_del_all - delete all entries from lock-less list |
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* @head: the head of lock-less list to delete all entries |
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* |
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* If list is empty, return NULL, otherwise, delete all entries and |
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* return the pointer to the first entry. The order of entries |
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* deleted is from the newest to the oldest added one. |
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*/ |
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static inline struct llist_node *llist_del_all(struct llist_head *head) |
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{ |
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return xchg(&head->first, NULL); |
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} |
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static inline struct llist_node *__llist_del_all(struct llist_head *head) |
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{ |
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struct llist_node *first = head->first; |
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head->first = NULL; |
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return first; |
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} |
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extern struct llist_node *llist_del_first(struct llist_head *head); |
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struct llist_node *llist_reverse_order(struct llist_node *head); |
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#endif /* LLIST_H */
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