diff options
Diffstat (limited to 'drivers/md/dm-vdo/wait-queue.c')
| -rw-r--r-- | drivers/md/dm-vdo/wait-queue.c | 205 |
1 files changed, 205 insertions, 0 deletions
diff --git a/drivers/md/dm-vdo/wait-queue.c b/drivers/md/dm-vdo/wait-queue.c new file mode 100644 index 0000000000..6e1e739277 --- /dev/null +++ b/drivers/md/dm-vdo/wait-queue.c @@ -0,0 +1,205 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright 2023 Red Hat + */ + +#include "wait-queue.h" + +#include <linux/device-mapper.h> + +#include "permassert.h" + +#include "status-codes.h" + +/** + * vdo_waitq_enqueue_waiter() - Add a waiter to the tail end of a waitq. + * @waitq: The vdo_wait_queue to which to add the waiter. + * @waiter: The waiter to add to the waitq. + * + * The waiter must not already be waiting in a waitq. + */ +void vdo_waitq_enqueue_waiter(struct vdo_wait_queue *waitq, struct vdo_waiter *waiter) +{ + BUG_ON(waiter->next_waiter != NULL); + + if (waitq->last_waiter == NULL) { + /* + * The waitq is empty, so form the initial circular list by self-linking the + * initial waiter. + */ + waiter->next_waiter = waiter; + } else { + /* Splice the new waiter in at the end of the waitq. */ + waiter->next_waiter = waitq->last_waiter->next_waiter; + waitq->last_waiter->next_waiter = waiter; + } + + /* In both cases, the waiter we added to the ring becomes the last waiter. */ + waitq->last_waiter = waiter; + waitq->length += 1; +} + +/** + * vdo_waitq_transfer_all_waiters() - Transfer all waiters from one waitq to + * a second waitq, emptying the first waitq. + * @from_waitq: The waitq containing the waiters to move. + * @to_waitq: The waitq that will receive the waiters from the first waitq. + */ +void vdo_waitq_transfer_all_waiters(struct vdo_wait_queue *from_waitq, + struct vdo_wait_queue *to_waitq) +{ + /* If the source waitq is empty, there's nothing to do. */ + if (!vdo_waitq_has_waiters(from_waitq)) + return; + + if (vdo_waitq_has_waiters(to_waitq)) { + /* + * Both are non-empty. Splice the two circular lists together + * by swapping the next (head) pointers in the list tails. + */ + struct vdo_waiter *from_head = from_waitq->last_waiter->next_waiter; + struct vdo_waiter *to_head = to_waitq->last_waiter->next_waiter; + + to_waitq->last_waiter->next_waiter = from_head; + from_waitq->last_waiter->next_waiter = to_head; + } + + to_waitq->last_waiter = from_waitq->last_waiter; + to_waitq->length += from_waitq->length; + vdo_waitq_init(from_waitq); +} + +/** + * vdo_waitq_notify_all_waiters() - Notify all the entries waiting in a waitq. + * @waitq: The vdo_wait_queue containing the waiters to notify. + * @callback: The function to call to notify each waiter, or NULL to invoke the callback field + * registered in each waiter. + * @context: The context to pass to the callback function. + * + * Notifies all the entries waiting in a waitq to continue execution by invoking a callback + * function on each of them in turn. The waitq is copied and emptied before invoking any callbacks, + * and only the waiters that were in the waitq at the start of the call will be notified. + */ +void vdo_waitq_notify_all_waiters(struct vdo_wait_queue *waitq, + vdo_waiter_callback_fn callback, void *context) +{ + /* + * Copy and empty the waitq first, avoiding the possibility of an infinite + * loop if entries are returned to the waitq by the callback function. + */ + struct vdo_wait_queue waiters; + + vdo_waitq_init(&waiters); + vdo_waitq_transfer_all_waiters(waitq, &waiters); + + /* Drain the copied waitq, invoking the callback on every entry. */ + while (vdo_waitq_has_waiters(&waiters)) + vdo_waitq_notify_next_waiter(&waiters, callback, context); +} + +/** + * vdo_waitq_get_first_waiter() - Return the waiter that is at the head end of a waitq. + * @waitq: The vdo_wait_queue from which to get the first waiter. + * + * Return: The first (oldest) waiter in the waitq, or NULL if the waitq is empty. + */ +struct vdo_waiter *vdo_waitq_get_first_waiter(const struct vdo_wait_queue *waitq) +{ + struct vdo_waiter *last_waiter = waitq->last_waiter; + + if (last_waiter == NULL) { + /* There are no waiters, so we're done. */ + return NULL; + } + + /* The waitq is circular, so the last entry links to the head of the waitq. */ + return last_waiter->next_waiter; +} + +/** + * vdo_waitq_dequeue_matching_waiters() - Remove all waiters that match based on the specified + * matching method and append them to a vdo_wait_queue. + * @waitq: The vdo_wait_queue to process. + * @waiter_match: The method to determine matching. + * @match_context: Contextual info for the match method. + * @matched_waitq: A wait_waitq to store matches. + */ +void vdo_waitq_dequeue_matching_waiters(struct vdo_wait_queue *waitq, + vdo_waiter_match_fn waiter_match, + void *match_context, + struct vdo_wait_queue *matched_waitq) +{ + struct vdo_wait_queue iteration_waitq; + + vdo_waitq_init(&iteration_waitq); + vdo_waitq_transfer_all_waiters(waitq, &iteration_waitq); + + while (vdo_waitq_has_waiters(&iteration_waitq)) { + struct vdo_waiter *waiter = vdo_waitq_dequeue_waiter(&iteration_waitq); + + vdo_waitq_enqueue_waiter((waiter_match(waiter, match_context) ? + matched_waitq : waitq), waiter); + } +} + +/** + * vdo_waitq_dequeue_waiter() - Remove the first (oldest) waiter from a waitq. + * @waitq: The vdo_wait_queue from which to remove the first entry. + * + * The caller will be responsible for waking the waiter by continuing its + * execution appropriately. + * + * Return: The first (oldest) waiter in the waitq, or NULL if the waitq is empty. + */ +struct vdo_waiter *vdo_waitq_dequeue_waiter(struct vdo_wait_queue *waitq) +{ + struct vdo_waiter *first_waiter = vdo_waitq_get_first_waiter(waitq); + struct vdo_waiter *last_waiter = waitq->last_waiter; + + if (first_waiter == NULL) + return NULL; + + if (first_waiter == last_waiter) { + /* The waitq has a single entry, so empty it by nulling the tail. */ + waitq->last_waiter = NULL; + } else { + /* + * The waitq has multiple waiters, so splice the first waiter out + * of the circular waitq. + */ + last_waiter->next_waiter = first_waiter->next_waiter; + } + + /* The waiter is no longer in a waitq. */ + first_waiter->next_waiter = NULL; + waitq->length -= 1; + + return first_waiter; +} + +/** + * vdo_waitq_notify_next_waiter() - Notify the next entry waiting in a waitq. + * @waitq: The vdo_wait_queue containing the waiter to notify. + * @callback: The function to call to notify the waiter, or NULL to invoke the callback field + * registered in the waiter. + * @context: The context to pass to the callback function. + * + * Notifies the next entry waiting in a waitq to continue execution by invoking a callback function + * on it after removing it from the waitq. + * + * Return: true if there was a waiter in the waitq. + */ +bool vdo_waitq_notify_next_waiter(struct vdo_wait_queue *waitq, + vdo_waiter_callback_fn callback, void *context) +{ + struct vdo_waiter *waiter = vdo_waitq_dequeue_waiter(waitq); + + if (waiter == NULL) + return false; + + if (callback == NULL) + callback = waiter->callback; + callback(waiter, context); + + return true; +} |