1 files changed, 140 insertions, 0 deletions
diff --git a/drivers/md/dm-vdo/completion.c b/drivers/md/dm-vdo/completion.c
new file mode 100644
index 0000000000..5ad8533463
--- /dev/null
+++ b/drivers/md/dm-vdo/completion.c
@@ -0,0 +1,140 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#include "completion.h"
+
+#include <linux/kernel.h>
+
+#include "logger.h"
+#include "permassert.h"
+
+#include "status-codes.h"
+#include "types.h"
+#include "vio.h"
+#include "vdo.h"
+
+/**
+ * DOC: vdo completions.
+ *
+ * Most of vdo's data structures are lock free, each either belonging to a single "zone," or
+ * divided into a number of zones whose accesses to the structure do not overlap. During normal
+ * operation, at most one thread will be operating in any given zone. Each zone has a
+ * vdo_work_queue which holds vdo_completions that are to be run in that zone. A completion may
+ * only be enqueued on one queue or operating in a single zone at a time.
+ *
+ * At each step of a multi-threaded operation, the completion performing the operation is given a
+ * callback, error handler, and thread id for the next step. A completion is "run" when it is
+ * operating on the correct thread (as specified by its callback_thread_id). If the value of its
+ * "result" field is an error (i.e. not VDO_SUCCESS), the function in its "error_handler" will be
+ * invoked. If the error_handler is NULL, or there is no error, the function set as its "callback"
+ * will be invoked. Generally, a completion will not be run directly, but rather will be
+ * "launched." In this case, it will check whether it is operating on the correct thread. If it is,
+ * it will run immediately. Otherwise, it will be enqueue on the vdo_work_queue associated with the
+ * completion's "callback_thread_id". When it is dequeued, it will be on the correct thread, and
+ * will get run. In some cases, the completion should get queued instead of running immediately,
+ * even if it is being launched from the correct thread. This is usually in cases where there is a
+ * long chain of callbacks, all on the same thread, which could overflow the stack. In such cases,
+ * the completion's "requeue" field should be set to true. Doing so will skip the current thread
+ * check and simply enqueue the completion.
+ *
+ * A completion may be "finished," in which case its "complete" field will be set to true before it
+ * is next run. It is a bug to attempt to set the result or re-finish a finished completion.
+ * Because a completion's fields are not safe to examine from any thread other than the one on
+ * which the completion is currently operating, this field is used only to aid in detecting
+ * programming errors. It can not be used for cross-thread checking on the status of an operation.
+ * A completion must be "reset" before it can be reused after it has been finished. Resetting will
+ * also clear any error from the result field.
+ **/
+
+void vdo_initialize_completion(struct vdo_completion *completion,
+			       struct vdo *vdo,
+			       enum vdo_completion_type type)
+{
+	memset(completion, 0, sizeof(*completion));
+	completion->vdo = vdo;
+	completion->type = type;
+	vdo_reset_completion(completion);
+}
+
+static inline void assert_incomplete(struct vdo_completion *completion)
+{
+	VDO_ASSERT_LOG_ONLY(!completion->complete, "completion is not complete");
+}
+
+/**
+ * vdo_set_completion_result() - Set the result of a completion.
+ *
+ * Older errors will not be masked.
+ */
+void vdo_set_completion_result(struct vdo_completion *completion, int result)
+{
+	assert_incomplete(completion);
+	if (completion->result == VDO_SUCCESS)
+		completion->result = result;
+}
+
+/**
+ * vdo_launch_completion_with_priority() - Run or enqueue a completion.
+ * @priority: The priority at which to enqueue the completion.
+ *
+ * If called on the correct thread (i.e. the one specified in the completion's callback_thread_id
+ * field) and not marked for requeue, the completion will be run immediately. Otherwise, the
+ * completion will be enqueued on the specified thread.
+ */
+void vdo_launch_completion_with_priority(struct vdo_completion *completion,
+					 enum vdo_completion_priority priority)
+{
+	thread_id_t callback_thread = completion->callback_thread_id;
+
+	if (completion->requeue || (callback_thread != vdo_get_callback_thread_id())) {
+		vdo_enqueue_completion(completion, priority);
+		return;
+	}
+
+	vdo_run_completion(completion);
+}
+
+/** vdo_finish_completion() - Mark a completion as complete and then launch it. */
+void vdo_finish_completion(struct vdo_completion *completion)
+{
+	assert_incomplete(completion);
+	completion->complete = true;
+	if (completion->callback != NULL)
+		vdo_launch_completion(completion);
+}
+
+void vdo_enqueue_completion(struct vdo_completion *completion,
+			    enum vdo_completion_priority priority)
+{
+	struct vdo *vdo = completion->vdo;
+	thread_id_t thread_id = completion->callback_thread_id;
+
+	if (VDO_ASSERT(thread_id < vdo->thread_config.thread_count,
+		       "thread_id %u (completion type %d) is less than thread count %u",
+		       thread_id, completion->type,
+		       vdo->thread_config.thread_count) != VDO_SUCCESS)
+		BUG();
+
+	completion->requeue = false;
+	completion->priority = priority;
+	completion->my_queue = NULL;
+	vdo_enqueue_work_queue(vdo->threads[thread_id].queue, completion);
+}
+
+/**
+ * vdo_requeue_completion_if_needed() - Requeue a completion if not called on the specified thread.
+ *
+ * Return: True if the completion was requeued; callers may not access the completion in this case.
+ */
+bool vdo_requeue_completion_if_needed(struct vdo_completion *completion,
+				      thread_id_t callback_thread_id)
+{
+	if (vdo_get_callback_thread_id() == callback_thread_id)
+		return false;
+
+	completion->callback_thread_id = callback_thread_id;
+	vdo_enqueue_completion(completion, VDO_WORK_Q_DEFAULT_PRIORITY);
+	return true;
+}