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path: root/drivers/md/dm-vdo/wait-queue.c
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Diffstat (limited to 'drivers/md/dm-vdo/wait-queue.c')
-rw-r--r--drivers/md/dm-vdo/wait-queue.c205
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 000000000000..6e1e739277ef
--- /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;
+}