[PATCH 38/50] mars: add new file drivers/block/mars/xio_bricks/xio_trans_logger.c

[Thomas Schoebel-Theuer]

Signed-off-by: Thomas Schoebel-Theuer <tst@xxxxxxxxxxxxxxxxxx>
---
 drivers/block/mars/xio_bricks/xio_trans_logger.c | 3295 ++++++++++++++++++++++
 1 file changed, 3295 insertions(+)
 create mode 100644 drivers/block/mars/xio_bricks/xio_trans_logger.c

diff --git a/drivers/block/mars/xio_bricks/xio_trans_logger.c b/drivers/block/mars/xio_bricks/xio_trans_logger.c
new file mode 100644
index 0000000..489299b
--- /dev/null
+++ b/drivers/block/mars/xio_bricks/xio_trans_logger.c
@@ -0,0 +1,3295 @@
+/*  (c) 2010 Thomas Schoebel-Theuer / 1&1 Internet AG */
+
+/*  Trans_Logger brick */
+
+#define XIO_DEBUGGING
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/string.h>
+#include <linux/bio.h>
+
+#include <linux/xio.h>
+#include <linux/brick/lib_rank.h>
+#include <linux/brick/lib_limiter.h>
+
+#include <linux/xio/xio_trans_logger.h>
+
+/*  variants */
+#define KEEP_UNIQUE
+#define DELAY_CALLERS			/*  this is _needed_ for production systems */
+/* When possible, queue 1 executes phase3_startio() directly without
+ * intermediate queueing into queue 3 => may be irritating, but has better
+ * performance. NOTICE: when some day the IO scheduling should be
+ * different between queue 1 and 3, you MUST disable this in order
+ * to distinguish between them!
+ */
+#define SHORTCUT_1_to_3
+
+/*  commenting this out is dangerous for data integrity! use only for testing! */
+#define USE_MEMCPY
+#define DO_WRITEBACK			/*  otherwise FAKE IO */
+#define REPLAY_DATA
+
+/*  tuning */
+#ifdef BRICK_DEBUG_MEM
+#define CONF_TRANS_CHUNKSIZE		(128 * 1024 - PAGE_SIZE * 2)
+#else
+#define CONF_TRANS_CHUNKSIZE		(128 * 1024)
+#endif
+#define CONF_TRANS_MAX_AIO_SIZE		PAGE_SIZE
+#define CONF_TRANS_ALIGN		0
+
+#define XIO_RPL(_args...) /*empty*/
+
+struct trans_logger_hash_anchor {
+	struct rw_semaphore hash_mutex;
+	struct list_head hash_anchor;
+};
+
+#define NR_HASH_PAGES			64
+
+#define MAX_HASH_PAGES			(PAGE_SIZE / sizeof(struct trans_logger_hash_anchor *))
+#define HASH_PER_PAGE			(PAGE_SIZE / sizeof(struct trans_logger_hash_anchor))
+#define HASH_TOTAL			(NR_HASH_PAGES * HASH_PER_PAGE)
+
+/************************ global tuning ***********************/
+
+int trans_logger_completion_semantics = 1;
+EXPORT_SYMBOL_GPL(trans_logger_completion_semantics);
+
+int trans_logger_do_crc =
+#ifdef CONFIG_MARS_DEBUG
+	true;
+#else
+	false;
+#endif
+EXPORT_SYMBOL_GPL(trans_logger_do_crc);
+
+int trans_logger_mem_usage; /*	in KB */
+EXPORT_SYMBOL_GPL(trans_logger_mem_usage);
+
+int trans_logger_max_interleave = -1;
+EXPORT_SYMBOL_GPL(trans_logger_max_interleave);
+
+int trans_logger_resume = 1;
+EXPORT_SYMBOL_GPL(trans_logger_resume);
+
+int trans_logger_replay_timeout = 1; /*  in s */
+EXPORT_SYMBOL_GPL(trans_logger_replay_timeout);
+
+struct writeback_group global_writeback = {
+	.lock = __RW_LOCK_UNLOCKED(global_writeback.lock),
+	.group_anchor = LIST_HEAD_INIT(global_writeback.group_anchor),
+	.until_percent = 30,
+};
+EXPORT_SYMBOL_GPL(global_writeback);
+
+static
+void add_to_group(struct writeback_group *gr, struct trans_logger_brick *brick)
+{
+	write_lock(&gr->lock);
+	list_add_tail(&brick->group_head, &gr->group_anchor);
+	write_unlock(&gr->lock);
+}
+
+static
+void remove_from_group(struct writeback_group *gr, struct trans_logger_brick *brick)
+{
+	write_lock(&gr->lock);
+	list_del_init(&brick->group_head);
+	gr->leader = NULL;
+	write_unlock(&gr->lock);
+}
+
+static
+struct trans_logger_brick *elect_leader(struct writeback_group *gr)
+{
+	struct trans_logger_brick *res = gr->leader;
+	struct list_head *tmp;
+
+	if (res && gr->until_percent >= 0) {
+		loff_t used = atomic64_read(&res->shadow_mem_used);
+
+		if (used > gr->biggest * gr->until_percent / 100)
+			goto done;
+	}
+
+	read_lock(&gr->lock);
+	for (tmp = gr->group_anchor.next; tmp != &gr->group_anchor; tmp = tmp->next) {
+		struct trans_logger_brick *test = container_of(tmp, struct trans_logger_brick, group_head);
+		loff_t new_used = atomic64_read(&test->shadow_mem_used);
+
+		if (!res || new_used > atomic64_read(&res->shadow_mem_used)) {
+			res = test;
+			gr->biggest = new_used;
+		}
+	}
+	read_unlock(&gr->lock);
+
+	gr->leader = res;
+
+done:
+	return res;
+}
+
+/************************ own type definitions ***********************/
+
+static inline
+int lh_cmp(loff_t *a, loff_t *b)
+{
+	if (*a < *b)
+		return -1;
+	if (*a > *b)
+		return 1;
+	return 0;
+}
+
+static inline
+int tr_cmp(struct pairing_heap_logger *_a, struct pairing_heap_logger *_b)
+{
+	struct logger_head *a = container_of(_a, struct logger_head, ph);
+	struct logger_head *b = container_of(_b, struct logger_head, ph);
+
+	return lh_cmp(a->lh_pos, b->lh_pos);
+}
+
+_PAIRING_HEAP_FUNCTIONS(static, logger, tr_cmp);
+
+static inline
+loff_t *lh_get(struct logger_head *th)
+{
+	return th->lh_pos;
+}
+
+QUEUE_FUNCTIONS(logger, struct logger_head, lh_head, lh_get, lh_cmp, logger);
+
+/************************* logger queue handling ***********************/
+
+static inline
+void qq_init(struct logger_queue *q, struct trans_logger_brick *brick)
+{
+	q_logger_init(q);
+	q->q_event = &brick->worker_event;
+	q->q_brick = brick;
+}
+
+static inline
+void qq_inc_flying(struct logger_queue *q)
+{
+	q_logger_inc_flying(q);
+}
+
+static inline
+void qq_dec_flying(struct logger_queue *q)
+{
+	q_logger_dec_flying(q);
+}
+
+static inline
+void qq_aio_insert(struct logger_queue *q, struct trans_logger_aio_aspect *aio_a)
+{
+	struct aio_object *aio = aio_a->object;
+
+	obj_get(aio); /*  must be paired with __trans_logger_io_put() */
+	atomic_inc(&q->q_brick->inner_balance_count);
+
+	q_logger_insert(q, &aio_a->lh);
+}
+
+static inline
+void qq_wb_insert(struct logger_queue *q, struct writeback_info *wb)
+{
+	q_logger_insert(q, &wb->w_lh);
+}
+
+static inline
+void qq_aio_pushback(struct logger_queue *q, struct trans_logger_aio_aspect *aio_a)
+{
+	obj_check(aio_a->object);
+
+	q->pushback_count++;
+
+	q_logger_pushback(q, &aio_a->lh);
+}
+
+static inline
+void qq_wb_pushback(struct logger_queue *q, struct writeback_info *wb)
+{
+	q->pushback_count++;
+	q_logger_pushback(q, &wb->w_lh);
+}
+
+static inline
+struct trans_logger_aio_aspect *qq_aio_fetch(struct logger_queue *q)
+{
+	struct logger_head *test;
+	struct trans_logger_aio_aspect *aio_a = NULL;
+
+	test = q_logger_fetch(q);
+
+	if (test) {
+		aio_a = container_of(test, struct trans_logger_aio_aspect, lh);
+		obj_check(aio_a->object);
+	}
+	return aio_a;
+}
+
+static inline
+struct writeback_info *qq_wb_fetch(struct logger_queue *q)
+{
+	struct logger_head *test;
+	struct writeback_info *res = NULL;
+
+	test = q_logger_fetch(q);
+
+	if (test)
+		res = container_of(test, struct writeback_info, w_lh);
+	return res;
+}
+
+/************************ own helper functions ***********************/
+
+static inline
+int hash_fn(loff_t pos)
+{
+	/*  simple and stupid */
+	long base_index = pos >> REGION_SIZE_BITS;
+
+	base_index += base_index / HASH_TOTAL / 7;
+	return base_index % HASH_TOTAL;
+}
+
+static inline
+struct trans_logger_aio_aspect *_hash_find(struct list_head *start,
+	loff_t pos,
+	int *max_len,
+	bool use_collect_head,
+	bool find_unstable)
+{
+	struct list_head *tmp;
+	struct trans_logger_aio_aspect *res = NULL;
+	int len = *max_len;
+
+	/* The lists are always sorted according to age (newest first).
+	 * Caution: there may be duplicates in the list, some of them
+	 * overlapping with the search area in many different ways.
+	 */
+	for (tmp = start->next; tmp != start; tmp = tmp->next) {
+		struct trans_logger_aio_aspect *test_a;
+		struct aio_object *test;
+		int diff;
+
+		if (use_collect_head)
+			test_a = container_of(tmp, struct trans_logger_aio_aspect, collect_head);
+		else
+			test_a = container_of(tmp, struct trans_logger_aio_aspect, hash_head);
+		test = test_a->object;
+
+		obj_check(test);
+
+		/*  are the regions overlapping? */
+		if (pos >= test->io_pos + test->io_len || pos + len <= test->io_pos)
+			continue; /*  not relevant */
+
+		/*  searching for unstable elements (only in special cases) */
+		if (find_unstable && test_a->is_stable)
+			break;
+
+		diff = test->io_pos - pos;
+		if (diff <= 0) {
+			int restlen = test->io_len + diff;
+
+			res = test_a;
+			if (restlen < len)
+				len = restlen;
+			break;
+		}
+		if (diff < len)
+			len = diff;
+	}
+
+	*max_len = len;
+	return res;
+}
+
+static
+struct trans_logger_aio_aspect *hash_find(struct trans_logger_brick *brick,
+	loff_t pos,
+	int *max_len,
+	bool find_unstable)
+{
+
+	int hash = hash_fn(pos);
+	struct trans_logger_hash_anchor *sub_table = brick->hash_table[hash / HASH_PER_PAGE];
+	struct trans_logger_hash_anchor *start = &sub_table[hash % HASH_PER_PAGE];
+	struct trans_logger_aio_aspect *res;
+
+	atomic_inc(&brick->total_hash_find_count);
+
+	down_read(&start->hash_mutex);
+
+	res = _hash_find(&start->hash_anchor, pos, max_len, false, find_unstable);
+
+	/* Ensure the found aio can't go away...
+	 */
+	if (res && res->object)
+		obj_get(res->object);
+
+	up_read(&start->hash_mutex);
+
+	return res;
+}
+
+static
+void hash_insert(struct trans_logger_brick *brick, struct trans_logger_aio_aspect *elem_a)
+{
+	int hash = hash_fn(elem_a->object->io_pos);
+	struct trans_logger_hash_anchor *sub_table = brick->hash_table[hash / HASH_PER_PAGE];
+	struct trans_logger_hash_anchor *start = &sub_table[hash % HASH_PER_PAGE];
+
+	CHECK_HEAD_EMPTY(&elem_a->hash_head);
+	obj_check(elem_a->object);
+
+	/*  only for statistics: */
+	atomic_inc(&brick->hash_count);
+	atomic_inc(&brick->total_hash_insert_count);
+
+	down_write(&start->hash_mutex);
+
+	list_add(&elem_a->hash_head, &start->hash_anchor);
+	elem_a->is_hashed = true;
+
+	up_write(&start->hash_mutex);
+}
+
+/* Find the transitive closure of overlapping requests
+ * and collect them into a list.
+ */
+static
+void hash_extend(struct trans_logger_brick *brick, loff_t *_pos, int *_len, struct list_head *collect_list)
+{
+	loff_t pos = *_pos;
+	int len = *_len;
+	int hash = hash_fn(pos);
+	struct trans_logger_hash_anchor *sub_table = brick->hash_table[hash / HASH_PER_PAGE];
+	struct trans_logger_hash_anchor *start = &sub_table[hash % HASH_PER_PAGE];
+	struct list_head *tmp;
+	bool extended;
+
+	if (collect_list)
+		CHECK_HEAD_EMPTY(collect_list);
+
+	atomic_inc(&brick->total_hash_extend_count);
+
+	down_read(&start->hash_mutex);
+
+	do {
+		extended = false;
+
+		for (tmp = start->hash_anchor.next; tmp != &start->hash_anchor; tmp = tmp->next) {
+			struct trans_logger_aio_aspect *test_a;
+			struct aio_object *test;
+			loff_t diff;
+
+			test_a = container_of(tmp, struct trans_logger_aio_aspect, hash_head);
+			test = test_a->object;
+
+			obj_check(test);
+
+			/*  are the regions overlapping? */
+			if (pos >= test->io_pos + test->io_len || pos + len <= test->io_pos)
+				continue; /*  not relevant */
+
+			/*  collision detection */
+			if (test_a->is_collected)
+				goto collision;
+
+			/*  no writeback of non-persistent data */
+			if (!(test_a->is_persistent & test_a->is_completed))
+				goto collision;
+
+			/*  extend the search region when necessary */
+			diff = pos - test->io_pos;
+			if (diff > 0) {
+				len += diff;
+				pos = test->io_pos;
+				extended = true;
+			}
+			diff = (test->io_pos + test->io_len)	- (pos + len);
+			if (diff > 0) {
+				len += diff;
+				extended = true;
+			}
+		}
+	} while (extended); /*	start over for transitive closure */
+
+	*_pos = pos;
+	*_len = len;
+
+	for (tmp = start->hash_anchor.next; tmp != &start->hash_anchor; tmp = tmp->next) {
+		struct trans_logger_aio_aspect *test_a;
+		struct aio_object *test;
+
+		test_a = container_of(tmp, struct trans_logger_aio_aspect, hash_head);
+		test = test_a->object;
+
+		/*  are the regions overlapping? */
+		if (pos >= test->io_pos + test->io_len || pos + len <= test->io_pos)
+			continue; /*  not relevant */
+
+		/*  collect */
+		CHECK_HEAD_EMPTY(&test_a->collect_head);
+		if (unlikely(test_a->is_collected))
+			XIO_ERR("collision detection did not work\n");
+		test_a->is_collected = true;
+		obj_check(test);
+		list_add_tail(&test_a->collect_head, collect_list);
+	}
+
+collision:
+	up_read(&start->hash_mutex);
+}
+
+/* Atomically put all elements from the list.
+ * All elements must reside in the same collision list.
+ */
+static inline
+void hash_put_all(struct trans_logger_brick *brick, struct list_head *list)
+{
+	struct list_head *tmp;
+	struct trans_logger_hash_anchor *start = NULL;
+	int first_hash = -1;
+
+	for (tmp = list->next; tmp != list; tmp = tmp->next) {
+		struct trans_logger_aio_aspect *elem_a;
+		struct aio_object *elem;
+		int hash;
+
+		elem_a = container_of(tmp, struct trans_logger_aio_aspect, collect_head);
+		elem = elem_a->object;
+		CHECK_PTR(elem, err);
+		obj_check(elem);
+
+		hash = hash_fn(elem->io_pos);
+		if (!start) {
+			struct trans_logger_hash_anchor *sub_table = brick->hash_table[hash / HASH_PER_PAGE];
+
+			start = &sub_table[hash % HASH_PER_PAGE];
+			first_hash = hash;
+			down_write(&start->hash_mutex);
+		} else if (unlikely(hash != first_hash)) {
+			XIO_ERR("oops, different hashes: %d != %d\n", hash, first_hash);
+		}
+
+		if (!elem_a->is_hashed)
+			continue;
+
+		list_del_init(&elem_a->hash_head);
+		elem_a->is_hashed = false;
+		atomic_dec(&brick->hash_count);
+	}
+
+err:
+	if (start)
+		up_write(&start->hash_mutex);
+}
+
+static inline
+void hash_ensure_stableness(struct trans_logger_brick *brick, struct trans_logger_aio_aspect *aio_a)
+{
+	if (!aio_a->is_stable) {
+		struct aio_object *aio = aio_a->object;
+		int hash = hash_fn(aio->io_pos);
+		struct trans_logger_hash_anchor *sub_table = brick->hash_table[hash / HASH_PER_PAGE];
+		struct trans_logger_hash_anchor *start = &sub_table[hash % HASH_PER_PAGE];
+
+		down_write(&start->hash_mutex);
+
+		aio_a->is_stable = true;
+
+		up_write(&start->hash_mutex);
+	}
+}
+
+static
+void _inf_callback(struct trans_logger_input *input, bool force)
+{
+	if (!force &&
+	    input->inf_last_jiffies &&
+	    input->inf_last_jiffies + 4 * HZ > (long long)jiffies)
+		goto out_return;
+	if (input->inf.inf_callback && input->is_operating) {
+		input->inf_last_jiffies = jiffies;
+
+		input->inf.inf_callback(&input->inf);
+
+		input->inf_last_jiffies = jiffies;
+	} else {
+		XIO_DBG("%p skipped callback, callback = %p is_operating = %d\n",
+			input,
+			input->inf.inf_callback,
+			input->is_operating);
+	}
+out_return:;
+}
+
+static inline
+int _congested(struct trans_logger_brick *brick)
+{
+	return atomic_read(&brick->q_phase[0].q_queued)
+		|| atomic_read(&brick->q_phase[0].q_flying)
+		|| atomic_read(&brick->q_phase[1].q_queued)
+		|| atomic_read(&brick->q_phase[1].q_flying)
+		|| atomic_read(&brick->q_phase[2].q_queued)
+		|| atomic_read(&brick->q_phase[2].q_flying)
+		|| atomic_read(&brick->q_phase[3].q_queued)
+		|| atomic_read(&brick->q_phase[3].q_flying);
+}
+
+/***************** own brick * input * output operations *****************/
+
+atomic_t   global_mshadow_count = ATOMIC_INIT(0);
+EXPORT_SYMBOL_GPL(global_mshadow_count);
+atomic64_t global_mshadow_used = ATOMIC64_INIT(0);
+EXPORT_SYMBOL_GPL(global_mshadow_used);
+
+static
+int trans_logger_get_info(struct trans_logger_output *output, struct xio_info *info)
+{
+	struct trans_logger_input *input = output->brick->inputs[TL_INPUT_READ];
+
+	return GENERIC_INPUT_CALL(input, xio_get_info, info);
+}
+
+static
+int _make_sshadow(struct trans_logger_output *output,
+	struct trans_logger_aio_aspect *aio_a,
+	struct trans_logger_aio_aspect *mshadow_a)
+{
+	struct trans_logger_brick *brick = output->brick;
+	struct aio_object *aio = aio_a->object;
+	struct aio_object *mshadow;
+	int diff;
+
+	mshadow = mshadow_a->object;
+	if (unlikely(aio->io_len > mshadow->io_len)) {
+		XIO_ERR("oops %d -> %d\n", aio->io_len, mshadow->io_len);
+		aio->io_len = mshadow->io_len;
+	}
+	if (unlikely(mshadow_a == aio_a)) {
+		XIO_ERR("oops %p == %p\n", mshadow_a, aio_a);
+		return -EINVAL;
+	}
+
+	diff = aio->io_pos - mshadow->io_pos;
+	if (unlikely(diff < 0)) {
+		XIO_ERR("oops diff = %d\n", diff);
+		return -EINVAL;
+	}
+
+	/* Attach aio to the existing shadow ("slave shadow").
+	 */
+	aio_a->shadow_data = mshadow_a->shadow_data + diff;
+	aio_a->do_dealloc = false;
+	if (!aio->io_data) { /*  buffered IO */
+		aio->io_data = aio_a->shadow_data;
+		aio_a->do_buffered = true;
+		atomic_inc(&brick->total_sshadow_buffered_count);
+	}
+	aio->io_flags = mshadow->io_flags;
+	aio_a->shadow_aio = mshadow_a;
+	aio_a->my_brick = brick;
+
+	/* Get an ordinary internal reference
+	 */
+	obj_get_first(aio); /*	must be paired with __trans_logger_io_put() */
+	atomic_inc(&brick->inner_balance_count);
+
+	/* The internal reference from slave to master is already
+	 * present due to hash_find(),
+	 * such that the master cannot go away before the slave.
+	 * It is compensated by master transition in __trans_logger_io_put()
+	 */
+	atomic_inc(&brick->inner_balance_count);
+
+	atomic_inc(&brick->sshadow_count);
+	atomic_inc(&brick->total_sshadow_count);
+
+	if (unlikely(aio->io_len <= 0)) {
+		XIO_ERR("oops, len = %d\n", aio->io_len);
+		return -EINVAL;
+	}
+
+	return aio->io_len;
+}
+
+static
+int _read_io_get(struct trans_logger_output *output, struct trans_logger_aio_aspect *aio_a)
+{
+	struct trans_logger_brick *brick = output->brick;
+	struct aio_object *aio = aio_a->object;
+	struct trans_logger_input *input = brick->inputs[TL_INPUT_READ];
+	struct trans_logger_aio_aspect *mshadow_a;
+
+	/* Look if there is a newer version on the fly, shadowing
+	 * the old one.
+	 * When a shadow is found, use it as buffer for the aio.
+	 */
+	mshadow_a = hash_find(brick, aio->io_pos, &aio->io_len, false);
+	if (!mshadow_a)
+		return GENERIC_INPUT_CALL(input, aio_get, aio);
+
+	return _make_sshadow(output, aio_a, mshadow_a);
+}
+
+static
+int _write_io_get(struct trans_logger_output *output, struct trans_logger_aio_aspect *aio_a)
+{
+	struct trans_logger_brick *brick = output->brick;
+	struct aio_object *aio = aio_a->object;
+	void *data;
+
+#ifdef KEEP_UNIQUE
+	struct trans_logger_aio_aspect *mshadow_a;
+
+#endif
+
+#ifdef CONFIG_MARS_DEBUG
+	if (unlikely(aio->io_len <= 0)) {
+		XIO_ERR("oops, io_len = %d\n", aio->io_len);
+		return -EINVAL;
+	}
+#endif
+
+#ifdef KEEP_UNIQUE
+	mshadow_a = hash_find(brick, aio->io_pos, &aio->io_len, true);
+	if (mshadow_a)
+		return _make_sshadow(output, aio_a, mshadow_a);
+#endif
+
+#ifdef DELAY_CALLERS
+	/*  delay in case of too many master shadows / memory shortage */
+	wait_event_interruptible_timeout(brick->caller_event,
+					 !brick->delay_callers &&
+					 (brick_global_memlimit < 1024 || atomic64_read(&global_mshadow_used) / 1024 < brick_global_memlimit),
+					 HZ / 2);
+#endif
+
+	/*  create a new master shadow */
+	data = brick_block_alloc(aio->io_pos, (aio_a->alloc_len = aio->io_len));
+	atomic64_add(aio->io_len, &brick->shadow_mem_used);
+#ifdef CONFIG_MARS_DEBUG
+	memset(data, 0x11, aio->io_len);
+#endif
+	aio_a->shadow_data = data;
+	aio_a->do_dealloc = true;
+	if (!aio->io_data) { /*  buffered IO */
+		aio->io_data = data;
+		aio_a->do_buffered = true;
+		atomic_inc(&brick->total_mshadow_buffered_count);
+	}
+	aio_a->my_brick = brick;
+	aio->io_flags = 0;
+	aio_a->shadow_aio = aio_a; /*  cyclic self-reference => indicates master shadow */
+
+	atomic_inc(&brick->mshadow_count);
+	atomic_inc(&brick->total_mshadow_count);
+	atomic_inc(&global_mshadow_count);
+	atomic64_add(aio->io_len, &global_mshadow_used);
+
+	atomic_inc(&brick->inner_balance_count);
+	obj_get_first(aio); /*	must be paired with __trans_logger_io_put() */
+
+	return aio->io_len;
+}
+
+static
+int trans_logger_io_get(struct trans_logger_output *output, struct aio_object *aio)
+{
+	struct trans_logger_brick *brick;
+	struct trans_logger_aio_aspect *aio_a;
+	loff_t base_offset;
+
+	CHECK_PTR(output, err);
+	brick = output->brick;
+	CHECK_PTR(brick, err);
+	CHECK_PTR(aio, err);
+
+	aio_a = trans_logger_aio_get_aspect(brick, aio);
+	CHECK_PTR(aio_a, err);
+	CHECK_ASPECT(aio_a, aio, err);
+
+	atomic_inc(&brick->outer_balance_count);
+
+	if (aio->obj_initialized) { /*	setup already performed */
+		obj_check(aio);
+		obj_get(aio); /*  must be paired with __trans_logger_io_put() */
+		return aio->io_len;
+	}
+
+	get_lamport(&aio_a->stamp);
+
+	if (aio->io_len > CONF_TRANS_MAX_AIO_SIZE && CONF_TRANS_MAX_AIO_SIZE > 0)
+		aio->io_len = CONF_TRANS_MAX_AIO_SIZE;
+
+	/*  ensure that REGION_SIZE boundaries are obeyed by hashing */
+	base_offset = aio->io_pos & (loff_t)(REGION_SIZE - 1);
+	if (aio->io_len > REGION_SIZE - base_offset)
+		aio->io_len = REGION_SIZE - base_offset;
+
+	if (aio->io_may_write == READ)
+		return _read_io_get(output, aio_a);
+
+	if (unlikely(brick->stopped_logging)) { /*  only in EMERGENCY mode */
+		aio_a->is_emergency = true;
+		/* Wait until writeback has finished.
+		 * We have to this because writeback is out-of-order.
+		 * Otherwise consistency could be violated for some time.
+		 */
+		while (_congested(brick)) {
+			/*  in case of emergency, busy-wait should be acceptable */
+			brick_msleep(HZ / 10);
+		}
+		return _read_io_get(output, aio_a);
+	}
+
+	/* FIXME: THIS IS PROVISIONARY (use event instead)
+	 */
+	while (unlikely(!brick->power.on_led))
+		brick_msleep(HZ / 10);
+
+	return _write_io_get(output, aio_a);
+
+err:
+	return -EINVAL;
+}
+
+static void pos_complete(struct trans_logger_aio_aspect *orig_aio_a);
+
+static
+void __trans_logger_io_put(struct trans_logger_brick *brick, struct trans_logger_aio_aspect *aio_a)
+{
+	struct aio_object *aio;
+	struct trans_logger_aio_aspect *shadow_a;
+	struct trans_logger_input *input;
+
+restart:
+	CHECK_PTR(aio_a, err);
+	aio = aio_a->object;
+	CHECK_PTR(aio, err);
+
+	obj_check(aio);
+
+	/*  are we a shadow (whether master or slave)? */
+	shadow_a = aio_a->shadow_aio;
+	if (shadow_a) {
+		bool finished;
+
+		CHECK_PTR(shadow_a, err);
+		CHECK_PTR(shadow_a->object, err);
+		obj_check(shadow_a->object);
+
+		finished = obj_put(aio);
+		atomic_dec(&brick->inner_balance_count);
+		if (unlikely(finished && aio_a->is_hashed)) {
+			XIO_ERR("trying to put a hashed aio, pos = %lld len = %d\n", aio->io_pos, aio->io_len);
+			finished = false; /*  leaves a memleak */
+		}
+
+		if (!finished)
+			goto out_return;
+
+		CHECK_HEAD_EMPTY(&aio_a->lh.lh_head);
+		CHECK_HEAD_EMPTY(&aio_a->hash_head);
+		CHECK_HEAD_EMPTY(&aio_a->replay_head);
+		CHECK_HEAD_EMPTY(&aio_a->collect_head);
+		CHECK_HEAD_EMPTY(&aio_a->sub_list);
+		CHECK_HEAD_EMPTY(&aio_a->sub_head);
+
+		if (aio_a->is_collected && likely(aio_a->wb_error >= 0))
+			pos_complete(aio_a);
+
+		CHECK_HEAD_EMPTY(&aio_a->pos_head);
+
+		if (shadow_a != aio_a) { /*  we are a slave shadow */
+			/* XIO_DBG("slave\n"); */
+			atomic_dec(&brick->sshadow_count);
+			CHECK_HEAD_EMPTY(&aio_a->hash_head);
+			obj_free(aio);
+			/*  now put the master shadow */
+			aio_a = shadow_a;
+			goto restart;
+		}
+		/*  we are a master shadow */
+		CHECK_PTR(aio_a->shadow_data, err);
+		if (aio_a->do_dealloc) {
+			brick_block_free(aio_a->shadow_data, aio_a->alloc_len);
+			atomic64_sub(aio->io_len, &brick->shadow_mem_used);
+			aio_a->shadow_data = NULL;
+			aio_a->do_dealloc = false;
+		}
+		if (aio_a->do_buffered)
+			aio->io_data = NULL;
+		atomic_dec(&brick->mshadow_count);
+		atomic_dec(&global_mshadow_count);
+		atomic64_sub(aio->io_len, &global_mshadow_used);
+		obj_free(aio);
+		goto out_return;
+	}
+
+	/*  only READ is allowed on non-shadow buffers */
+	if (unlikely(aio->io_rw != READ && !aio_a->is_emergency))
+		XIO_FAT("bad operation %d on non-shadow\n", aio->io_rw);
+
+	/*  no shadow => call through */
+	input = brick->inputs[TL_INPUT_READ];
+	CHECK_PTR(input, err);
+
+	GENERIC_INPUT_CALL(input, aio_put, aio);
+
+err:;
+out_return:;
+}
+
+static
+void _trans_logger_io_put(struct trans_logger_output *output, struct aio_object *aio)
+{
+	struct trans_logger_aio_aspect *aio_a;
+
+	aio_a = trans_logger_aio_get_aspect(output->brick, aio);
+	CHECK_PTR(aio_a, err);
+	CHECK_ASPECT(aio_a, aio, err);
+
+	__trans_logger_io_put(output->brick, aio_a);
+	goto out_return;
+err:
+	XIO_FAT("giving up...\n");
+out_return:;
+}
+
+static
+void trans_logger_io_put(struct trans_logger_output *output, struct aio_object *aio)
+{
+	struct trans_logger_brick *brick = output->brick;
+
+	atomic_dec(&brick->outer_balance_count);
+	_trans_logger_io_put(output, aio);
+}
+
+static
+void _trans_logger_endio(struct generic_callback *cb)
+{
+	struct trans_logger_aio_aspect *aio_a;
+	struct trans_logger_brick *brick;
+
+	aio_a = cb->cb_private;
+	CHECK_PTR(aio_a, err);
+	if (unlikely(&aio_a->cb != cb)) {
+		XIO_FAT("bad callback -- hanging up\n");
+		goto err;
+	}
+	brick = aio_a->my_brick;
+	CHECK_PTR(brick, err);
+
+	NEXT_CHECKED_CALLBACK(cb, err);
+
+	atomic_dec(&brick->any_fly_count);
+	atomic_inc(&brick->total_cb_count);
+	wake_up_interruptible_all(&brick->worker_event);
+	goto out_return;
+err:
+	XIO_FAT("cannot handle callback\n");
+out_return:;
+}
+
+static
+void trans_logger_io_io(struct trans_logger_output *output, struct aio_object *aio)
+{
+	struct trans_logger_brick *brick = output->brick;
+	struct trans_logger_aio_aspect *aio_a;
+	struct trans_logger_aio_aspect *shadow_a;
+	struct trans_logger_input *input;
+
+	obj_check(aio);
+
+	aio_a = trans_logger_aio_get_aspect(brick, aio);
+	CHECK_PTR(aio_a, err);
+	CHECK_ASPECT(aio_a, aio, err);
+
+	/*  statistics */
+	if (aio->io_rw)
+		atomic_inc(&brick->total_write_count);
+	else
+		atomic_inc(&brick->total_read_count);
+	/*  is this a shadow buffer? */
+	shadow_a = aio_a->shadow_aio;
+	if (shadow_a) {
+		CHECK_HEAD_EMPTY(&aio_a->lh.lh_head);
+		CHECK_HEAD_EMPTY(&aio_a->hash_head);
+		CHECK_HEAD_EMPTY(&aio_a->pos_head);
+
+		obj_get(aio); /*  must be paired with __trans_logger_io_put() */
+		atomic_inc(&brick->inner_balance_count);
+
+		qq_aio_insert(&brick->q_phase[0], aio_a);
+		wake_up_interruptible_all(&brick->worker_event);
+		goto out_return;
+	}
+
+	/*  only READ is allowed on non-shadow buffers */
+	if (unlikely(aio->io_rw != READ && !aio_a->is_emergency))
+		XIO_FAT("bad operation %d on non-shadow\n", aio->io_rw);
+
+	atomic_inc(&brick->any_fly_count);
+
+	aio_a->my_brick = brick;
+
+	INSERT_CALLBACK(aio, &aio_a->cb, _trans_logger_endio, aio_a);
+
+	input = output->brick->inputs[TL_INPUT_READ];
+
+	GENERIC_INPUT_CALL(input, aio_io, aio);
+	goto out_return;
+err:
+	XIO_FAT("cannot handle IO\n");
+out_return:;
+}
+
+/***************************** writeback info *****************************/
+
+/* save final completion status when necessary
+ */
+static
+void pos_complete(struct trans_logger_aio_aspect *orig_aio_a)
+{
+	struct trans_logger_brick *brick = orig_aio_a->my_brick;
+	struct trans_logger_input *log_input = orig_aio_a->log_input;
+	loff_t finished;
+	struct list_head *tmp;
+
+	CHECK_PTR(brick, err);
+	CHECK_PTR(log_input, err);
+
+	atomic_inc(&brick->total_writeback_count);
+
+	tmp = &orig_aio_a->pos_head;
+
+	down(&log_input->inf_mutex);
+
+	finished = orig_aio_a->log_pos;
+	/*  am I the first member? (means "youngest" list entry) */
+	if (tmp == log_input->pos_list.next) {
+		if (unlikely(finished <= log_input->inf.inf_min_pos))
+			XIO_ERR("backskip in log writeback: %lld -> %lld\n", log_input->inf.inf_min_pos, finished);
+		if (unlikely(finished > log_input->inf.inf_max_pos))
+			XIO_ERR("min_pos > max_pos: %lld > %lld\n", finished, log_input->inf.inf_max_pos);
+		log_input->inf.inf_min_pos = finished;
+		get_lamport(&log_input->inf.inf_min_pos_stamp);
+		_inf_callback(log_input, false);
+	} else {
+		struct trans_logger_aio_aspect *prev_aio_a;
+
+		prev_aio_a = container_of(tmp->prev, struct trans_logger_aio_aspect, pos_head);
+		if (unlikely(finished <= prev_aio_a->log_pos)) {
+			XIO_ERR("backskip: %lld -> %lld\n", finished, prev_aio_a->log_pos);
+		} else {
+			/* Transitively transfer log_pos to the predecessor
+			 * to correctly reflect the committed region.
+			 */
+			prev_aio_a->log_pos = finished;
+		}
+	}
+
+	list_del_init(tmp);
+	atomic_dec(&log_input->pos_count);
+
+	up(&log_input->inf_mutex);
+err:;
+}
+
+static
+void free_writeback(struct writeback_info *wb)
+{
+	struct list_head *tmp;
+
+	if (unlikely(wb->w_error < 0)) {
+		XIO_ERR("writeback error = %d at pos = %lld len = %d, writeback is incomplete\n",
+			wb->w_error,
+			wb->w_pos,
+			wb->w_len);
+	}
+
+	/* Now complete the original requests.
+	 */
+	while ((tmp = wb->w_collect_list.next) != &wb->w_collect_list) {
+		struct trans_logger_aio_aspect *orig_aio_a;
+		struct aio_object *orig_aio;
+
+		list_del_init(tmp);
+
+		orig_aio_a = container_of(tmp, struct trans_logger_aio_aspect, collect_head);
+		orig_aio = orig_aio_a->object;
+
+		obj_check(orig_aio);
+		if (unlikely(!orig_aio_a->is_collected)) {
+			XIO_ERR("request %lld (len = %d) was not collected\n",
+				orig_aio->io_pos,
+				orig_aio->io_len);
+		}
+		if (unlikely(wb->w_error < 0))
+			orig_aio_a->wb_error = wb->w_error;
+
+		__trans_logger_io_put(orig_aio_a->my_brick, orig_aio_a);
+	}
+
+	brick_mem_free(wb);
+}
+
+/* Generic endio() for writeback_info
+ */
+static
+void wb_endio(struct generic_callback *cb)
+{
+	struct trans_logger_aio_aspect *sub_aio_a;
+	struct aio_object *sub_aio;
+	struct trans_logger_brick *brick;
+	struct writeback_info *wb;
+	atomic_t *dec;
+	int rw;
+
+	/* make checkpatch.pl happy with a blank line - is this a false positive? */
+
+	void (**_endio)(struct generic_callback *cb);
+	void (*endio)(struct generic_callback *cb);
+
+	LAST_CALLBACK(cb);
+	sub_aio_a = cb->cb_private;
+	CHECK_PTR(sub_aio_a, err);
+	sub_aio = sub_aio_a->object;
+	CHECK_PTR(sub_aio, err);
+	wb = sub_aio_a->wb;
+	CHECK_PTR(wb, err);
+	brick = wb->w_brick;
+	CHECK_PTR(brick, err);
+
+	if (cb->cb_error < 0)
+		wb->w_error = cb->cb_error;
+
+	atomic_dec(&brick->wb_balance_count);
+
+	rw = sub_aio_a->orig_rw;
+	dec = rw ? &wb->w_sub_write_count : &wb->w_sub_read_count;
+	CHECK_ATOMIC(dec, 1);
+	if (!atomic_dec_and_test(dec))
+		goto done;
+
+	_endio = rw ? &wb->write_endio : &wb->read_endio;
+	endio = *_endio;
+	*_endio = NULL;
+	if (likely(endio))
+		endio(cb);
+	else
+		XIO_ERR("internal: no endio defined\n");
+done:
+	wake_up_interruptible_all(&brick->worker_event);
+	goto out_return;
+err:
+	XIO_FAT("hanging up....\n");
+out_return:;
+}
+
+/* Atomically create writeback info, based on "snapshot" of current hash
+ * state.
+ * Notice that the hash can change during writeback IO, thus we need
+ * struct writeback_info to precisely catch that information at a single
+ * point in time.
+ */
+static
+struct writeback_info *make_writeback(struct trans_logger_brick *brick, loff_t pos, int len)
+{
+	struct writeback_info *wb;
+	struct trans_logger_input *read_input;
+	struct trans_logger_input *write_input;
+	int write_input_nr;
+
+	/* Allocate structure representing a bunch of adjacent writebacks
+	 */
+	wb = brick_zmem_alloc(sizeof(struct writeback_info));
+	if (unlikely(len < 0))
+		XIO_ERR("len = %d\n", len);
+
+	wb->w_brick = brick;
+	wb->w_pos = pos;
+	wb->w_len = len;
+	wb->w_lh.lh_pos = &wb->w_pos;
+	INIT_LIST_HEAD(&wb->w_lh.lh_head);
+	INIT_LIST_HEAD(&wb->w_collect_list);
+	INIT_LIST_HEAD(&wb->w_sub_read_list);
+	INIT_LIST_HEAD(&wb->w_sub_write_list);
+
+	/* Atomically fetch transitive closure on all requests
+	 * overlapping with the current search region.
+	 */
+	hash_extend(brick, &wb->w_pos, &wb->w_len, &wb->w_collect_list);
+
+	if (list_empty(&wb->w_collect_list))
+		goto collision;
+
+	pos = wb->w_pos;
+	len = wb->w_len;
+
+	if (unlikely(len < 0))
+		XIO_ERR("len = %d\n", len);
+
+	/* Determine the "channels" we want to operate on
+	 */
+	read_input = brick->inputs[TL_INPUT_READ];
+	write_input_nr = TL_INPUT_WRITEBACK;
+	write_input = brick->inputs[write_input_nr];
+	if (!write_input->connect) {
+		write_input_nr = TL_INPUT_READ;
+		write_input = read_input;
+	}
+
+	/* Create sub_aios for read of old disk version (phase1)
+	 */
+	if (brick->log_reads) {
+		while (len > 0) {
+			struct trans_logger_aio_aspect *sub_aio_a;
+			struct aio_object *sub_aio;
+			struct trans_logger_input *log_input;
+			int this_len;
+			int status;
+
+			sub_aio = trans_logger_alloc_aio(brick);
+
+			sub_aio->io_pos = pos;
+			sub_aio->io_len = len;
+			sub_aio->io_may_write = READ;
+			sub_aio->io_rw = READ;
+			sub_aio->io_data = NULL;
+
+			sub_aio_a = trans_logger_aio_get_aspect(brick, sub_aio);
+			CHECK_PTR(sub_aio_a, err);
+			CHECK_ASPECT(sub_aio_a, sub_aio, err);
+
+			sub_aio_a->my_input = read_input;
+			log_input = brick->inputs[brick->log_input_nr];
+			sub_aio_a->log_input = log_input;
+			atomic_inc(&log_input->log_obj_count);
+			sub_aio_a->my_brick = brick;
+			sub_aio_a->orig_rw = READ;
+			sub_aio_a->wb = wb;
+
+			status = GENERIC_INPUT_CALL(read_input, aio_get, sub_aio);
+			if (unlikely(status < 0)) {
+				XIO_FAT("cannot get sub_aio, status = %d\n", status);
+				goto err;
+			}
+
+			list_add_tail(&sub_aio_a->sub_head, &wb->w_sub_read_list);
+			atomic_inc(&wb->w_sub_read_count);
+			atomic_inc(&brick->wb_balance_count);
+
+			this_len = sub_aio->io_len;
+			pos += this_len;
+			len -= this_len;
+		}
+		/* Re-init for startover
+		 */
+		pos = wb->w_pos;
+		len = wb->w_len;
+	}
+
+	/* Always create sub_aios for writeback (phase3)
+	 */
+	while (len > 0) {
+		struct trans_logger_aio_aspect *sub_aio_a;
+		struct aio_object *sub_aio;
+		struct trans_logger_aio_aspect *orig_aio_a;
+		struct aio_object *orig_aio;
+		struct trans_logger_input *log_input;
+		void *data;
+		int this_len = len;
+		int diff;
+		int status;
+
+		atomic_inc(&brick->total_hash_find_count);
+
+		orig_aio_a = _hash_find(&wb->w_collect_list, pos, &this_len, true, false);
+		if (unlikely(!orig_aio_a)) {
+			XIO_FAT("could not find data\n");
+			goto err;
+		}
+
+		orig_aio = orig_aio_a->object;
+		diff = pos - orig_aio->io_pos;
+		if (unlikely(diff < 0)) {
+			XIO_FAT("bad diff %d\n", diff);
+			goto err;
+		}
+		data = orig_aio_a->shadow_data + diff;
+
+		sub_aio = trans_logger_alloc_aio(brick);
+
+		sub_aio->io_pos = pos;
+		sub_aio->io_len = this_len;
+		sub_aio->io_may_write = WRITE;
+		sub_aio->io_rw = WRITE;
+		sub_aio->io_data = data;
+
+		sub_aio_a = trans_logger_aio_get_aspect(brick, sub_aio);
+		CHECK_PTR(sub_aio_a, err);
+		CHECK_ASPECT(sub_aio_a, sub_aio, err);
+
+		sub_aio_a->orig_aio_a = orig_aio_a;
+		sub_aio_a->my_input = write_input;
+		log_input = orig_aio_a->log_input;
+		sub_aio_a->log_input = log_input;
+		atomic_inc(&log_input->log_obj_count);
+		sub_aio_a->my_brick = brick;
+		sub_aio_a->orig_rw = WRITE;
+		sub_aio_a->wb = wb;
+
+		status = GENERIC_INPUT_CALL(write_input, aio_get, sub_aio);
+		if (unlikely(status < 0)) {
+			XIO_FAT("cannot get sub_aio, status = %d\n", status);
+			wb->w_error = status;
+			goto err;
+		}
+
+		list_add_tail(&sub_aio_a->sub_head, &wb->w_sub_write_list);
+		atomic_inc(&wb->w_sub_write_count);
+		atomic_inc(&brick->wb_balance_count);
+
+		this_len = sub_aio->io_len;
+		pos += this_len;
+		len -= this_len;
+	}
+
+	return wb;
+
+err:
+	XIO_ERR("cleaning up...\n");
+collision:
+	if (wb)
+		free_writeback(wb);
+	return NULL;
+}
+
+static inline
+void _fire_one(struct list_head *tmp, bool do_update)
+{
+	struct trans_logger_aio_aspect *sub_aio_a;
+	struct aio_object *sub_aio;
+	struct trans_logger_input *sub_input;
+
+	sub_aio_a = container_of(tmp, struct trans_logger_aio_aspect, sub_head);
+	sub_aio = sub_aio_a->object;
+
+	if (unlikely(sub_aio_a->is_fired)) {
+		XIO_ERR("trying to fire twice\n");
+		goto out_return;
+	}
+	sub_aio_a->is_fired = true;
+
+	SETUP_CALLBACK(sub_aio, wb_endio, sub_aio_a);
+
+	sub_input = sub_aio_a->my_input;
+
+#ifdef DO_WRITEBACK
+	GENERIC_INPUT_CALL(sub_input, aio_io, sub_aio);
+#else
+	SIMPLE_CALLBACK(sub_aio, 0);
+#endif
+	if (do_update) { /*  CHECK: shouldnt we do this always? */
+		GENERIC_INPUT_CALL(sub_input, aio_put, sub_aio);
+	}
+out_return:;
+}
+
+static inline
+void fire_writeback(struct list_head *start, bool do_update)
+{
+	struct list_head *tmp;
+
+	/* Caution! The wb structure may get deallocated
+	 * during _fire_one() in some cases (e.g. when the
+	 * callback is directly called by the aio_io operation).
+	 * Ensure that no ptr dereferencing can take
+	 * place after working on the last list member.
+	 */
+	tmp = start->next;
+	while (tmp != start) {
+		struct list_head *next = tmp->next;
+
+		list_del_init(tmp);
+		_fire_one(tmp, do_update);
+		tmp = next;
+	}
+}
+
+static inline
+void update_max_pos(struct trans_logger_aio_aspect *orig_aio_a)
+{
+	loff_t max_pos = orig_aio_a->log_pos;
+	struct trans_logger_input *log_input = orig_aio_a->log_input;
+
+	CHECK_PTR(log_input, done);
+
+	down(&log_input->inf_mutex);
+
+	if (unlikely(max_pos < log_input->inf.inf_min_pos))
+		XIO_ERR("new max_pos < min_pos: %lld < %lld\n", max_pos, log_input->inf.inf_min_pos);
+	if (log_input->inf.inf_max_pos < max_pos) {
+		log_input->inf.inf_max_pos = max_pos;
+		get_lamport(&log_input->inf.inf_max_pos_stamp);
+		_inf_callback(log_input, false);
+	}
+
+	up(&log_input->inf_mutex);
+done:;
+}
+
+static inline
+void update_writeback_info(struct writeback_info *wb)
+{
+	struct list_head *start = &wb->w_collect_list;
+	struct list_head *tmp;
+
+	/* Notice: in case of log rotation, each list member
+	 * may belong to a different log_input.
+	 */
+	for (tmp = start->next; tmp != start; tmp = tmp->next) {
+		struct trans_logger_aio_aspect *orig_aio_a;
+
+		orig_aio_a = container_of(tmp, struct trans_logger_aio_aspect, collect_head);
+		update_max_pos(orig_aio_a);
+	}
+}
+
+/***************************** worker thread *****************************/
+
+/*********************************************************************
+ * Phase 0: write transaction log entry for the original write request.
+ */
+
+static
+void _complete(struct trans_logger_brick *brick, struct trans_logger_aio_aspect *orig_aio_a, int error, bool pre_io)
+{
+	struct aio_object *orig_aio;
+
+	orig_aio = orig_aio_a->object;
+	CHECK_PTR(orig_aio, err);
+
+	if (orig_aio_a->is_completed ||
+	    (pre_io &&
+	     (trans_logger_completion_semantics >= 2 ||
+	      (trans_logger_completion_semantics >= 1 && !orig_aio->io_skip_sync)))) {
+		goto done;
+	}
+
+	if (cmpxchg(&orig_aio_a->is_completed, false, true))
+		goto done;
+
+	atomic_dec(&brick->log_fly_count);
+
+	if (likely(error >= 0)) {
+		aio_checksum(orig_aio);
+		orig_aio->io_flags &= ~AIO_WRITING;
+		orig_aio->io_flags |= AIO_UPTODATE;
+	}
+	CHECKED_CALLBACK(orig_aio, error, err);
+
+done:
+	goto out_return;
+err:
+	XIO_ERR("giving up...\n");
+out_return:;
+}
+
+static
+void phase0_preio(void *private)
+{
+	struct trans_logger_aio_aspect *orig_aio_a;
+	struct trans_logger_brick *brick;
+
+	orig_aio_a = private;
+	CHECK_PTR(orig_aio_a, err);
+	CHECK_PTR(orig_aio_a->object, err);
+	brick = orig_aio_a->my_brick;
+	CHECK_PTR(brick, err);
+
+	/*  signal completion to the upper layer */
+/**/
+
+	obj_check(orig_aio_a->object);
+	_complete(brick, orig_aio_a, 0, true);
+	obj_check(orig_aio_a->object);
+	goto out_return;
+err:
+	XIO_ERR("giving up...\n");
+out_return:;
+}
+
+static
+void phase0_endio(void *private, int error)
+{
+	struct aio_object *orig_aio;
+	struct trans_logger_aio_aspect *orig_aio_a;
+	struct trans_logger_brick *brick;
+
+	orig_aio_a = private;
+	CHECK_PTR(orig_aio_a, err);
+	brick = orig_aio_a->my_brick;
+	CHECK_PTR(brick, err);
+	orig_aio = orig_aio_a->object;
+	CHECK_PTR(orig_aio, err);
+
+	orig_aio_a->is_persistent = true;
+	qq_dec_flying(&brick->q_phase[0]);
+
+	/* Pin aio->obj_count so it can't go away
+	 * after _complete().
+	 */
+	_CHECK(orig_aio_a->shadow_aio, err);
+	obj_get(orig_aio); /*  must be paired with __trans_logger_io_put() */
+	atomic_inc(&brick->inner_balance_count);
+
+	/*  signal completion to the upper layer */
+	_complete(brick, orig_aio_a, error, false);
+
+	/* Queue up for the next phase.
+	 */
+	qq_aio_insert(&brick->q_phase[1], orig_aio_a);
+
+	/* Undo the above pinning
+	 */
+	__trans_logger_io_put(brick, orig_aio_a);
+
+	banning_reset(&brick->q_phase[0].q_banning);
+
+	wake_up_interruptible_all(&brick->worker_event);
+	goto out_return;
+err:
+	XIO_ERR("giving up...\n");
+out_return:;
+}
+
+static
+bool phase0_startio(struct trans_logger_aio_aspect *orig_aio_a)
+{
+	struct aio_object *orig_aio;
+	struct trans_logger_brick *brick;
+	struct trans_logger_input *input;
+	struct log_status *logst;
+	loff_t log_pos;
+	void *data;
+	bool ok;
+
+	CHECK_PTR(orig_aio_a, err);
+	orig_aio = orig_aio_a->object;
+	CHECK_PTR(orig_aio, err);
+	brick = orig_aio_a->my_brick;
+	CHECK_PTR(brick, err);
+	input = orig_aio_a->log_input;
+	CHECK_PTR(input, err);
+	logst = &input->logst;
+	logst->do_crc = trans_logger_do_crc;
+
+	{
+		struct log_header l = {
+			.l_stamp = orig_aio_a->stamp,
+			.l_pos = orig_aio->io_pos,
+			.l_len = orig_aio->io_len,
+			.l_code = CODE_WRITE_NEW,
+		};
+		data = log_reserve(logst, &l);
+	}
+	if (unlikely(!data))
+		goto err;
+
+	hash_ensure_stableness(brick, orig_aio_a);
+
+	memcpy(data, orig_aio_a->shadow_data, orig_aio->io_len);
+
+	atomic_inc(&brick->log_fly_count);
+
+	ok = log_finalize(logst, orig_aio->io_len, phase0_endio, orig_aio_a);
+	if (unlikely(!ok)) {
+		atomic_dec(&brick->log_fly_count);
+		goto err;
+	}
+	log_pos = logst->log_pos + logst->offset;
+	orig_aio_a->log_pos = log_pos;
+
+	/*  update new log_pos in the symlinks */
+	down(&input->inf_mutex);
+	input->inf.inf_log_pos = log_pos;
+	memcpy(&input->inf.inf_log_pos_stamp, &logst->log_pos_stamp, sizeof(input->inf.inf_log_pos_stamp));
+	_inf_callback(input, false);
+
+#ifdef CONFIG_MARS_DEBUG
+	if (!list_empty(&input->pos_list)) {
+		struct trans_logger_aio_aspect *last_aio_a;
+
+		last_aio_a = container_of(input->pos_list.prev, struct trans_logger_aio_aspect, pos_head);
+		if (last_aio_a->log_pos >= orig_aio_a->log_pos)
+			XIO_ERR("backskip in pos_list, %lld >= %lld\n", last_aio_a->log_pos, orig_aio_a->log_pos);
+	}
+#endif
+	list_add_tail(&orig_aio_a->pos_head, &input->pos_list);
+	atomic_inc(&input->pos_count);
+	up(&input->inf_mutex);
+
+	qq_inc_flying(&brick->q_phase[0]);
+
+	phase0_preio(orig_aio_a);
+
+	return true;
+
+err:
+	return false;
+}
+
+static
+bool prep_phase_startio(struct trans_logger_aio_aspect *aio_a)
+{
+	struct aio_object *aio = aio_a->object;
+	struct trans_logger_aio_aspect *shadow_a;
+	struct trans_logger_brick *brick;
+
+	CHECK_PTR(aio, err);
+	shadow_a = aio_a->shadow_aio;
+	CHECK_PTR(shadow_a, err);
+	brick = aio_a->my_brick;
+	CHECK_PTR(brick, err);
+
+	if (aio->io_rw == READ) {
+		/*  nothing to do: directly signal success. */
+		struct aio_object *shadow = shadow_a->object;
+
+		if (unlikely(shadow == aio))
+			XIO_ERR("oops, we should be a slave shadow, but are a master one\n");
+#ifdef USE_MEMCPY
+		if (aio_a->shadow_data != aio->io_data) {
+			if (unlikely(aio->io_len <= 0 || aio->io_len > PAGE_SIZE))
+				XIO_ERR("implausible io_len = %d\n", aio->io_len);
+			memcpy(aio->io_data, aio_a->shadow_data, aio->io_len);
+		}
+#endif
+		aio->io_flags |= AIO_UPTODATE;
+
+		CHECKED_CALLBACK(aio, 0, err);
+
+		__trans_logger_io_put(brick, aio_a);
+
+		return true;
+	}
+	/*  else WRITE */
+	CHECK_HEAD_EMPTY(&aio_a->lh.lh_head);
+	CHECK_HEAD_EMPTY(&aio_a->hash_head);
+	if (unlikely(aio->io_flags & (AIO_READING | AIO_WRITING)))
+		XIO_ERR("bad flags %d\n", aio->io_flags);
+	/* In case of non-buffered IO, the buffer is
+	 * under control of the user. In particular, he
+	 * may change it without telling us.
+	 * Therefore we make a copy (or "snapshot") here.
+	 */
+	aio->io_flags |= AIO_WRITING;
+#ifdef USE_MEMCPY
+	if (aio_a->shadow_data != aio->io_data) {
+		if (unlikely(aio->io_len <= 0 || aio->io_len > PAGE_SIZE))
+			XIO_ERR("implausible io_len = %d\n", aio->io_len);
+		memcpy(aio_a->shadow_data, aio->io_data, aio->io_len);
+	}
+#endif
+	aio_a->is_dirty = true;
+	aio_a->shadow_aio->is_dirty = true;
+#ifndef KEEP_UNIQUE
+	if (unlikely(aio_a->shadow_aio != aio_a))
+		XIO_ERR("something is wrong: %p != %p\n", aio_a->shadow_aio, aio_a);
+#endif
+	if (likely(!aio_a->is_hashed)) {
+		struct trans_logger_input *log_input;
+
+		log_input = brick->inputs[brick->log_input_nr];
+		aio_a->log_input = log_input;
+		atomic_inc(&log_input->log_obj_count);
+		hash_insert(brick, aio_a);
+	} else {
+		XIO_ERR("tried to hash twice\n");
+	}
+	return phase0_startio(aio_a);
+
+err:
+	XIO_ERR("cannot work\n");
+	brick_msleep(1000);
+	return false;
+}
+
+/*********************************************************************
+ * Phase 1: read original version of data.
+ * This happens _after_ phase 0, deliberately.
+ * We are explicitly dealing with old and new versions.
+ * The new version is hashed in memory all the time (such that parallel
+ * READs will see them), so we have plenty of time for getting the
+ * old version from disk somewhen later, e.g. when IO contention is low.
+ */
+
+static
+void phase1_endio(struct generic_callback *cb)
+{
+	struct trans_logger_aio_aspect *sub_aio_a;
+	struct writeback_info *wb;
+	struct trans_logger_brick *brick;
+
+	CHECK_PTR(cb, err);
+	sub_aio_a = cb->cb_private;
+	CHECK_PTR(sub_aio_a, err);
+	wb = sub_aio_a->wb;
+	CHECK_PTR(wb, err);
+	brick = wb->w_brick;
+	CHECK_PTR(brick, err);
+
+	if (unlikely(cb->cb_error < 0)) {
+		XIO_FAT("IO error %d\n", cb->cb_error);
+		goto err;
+	}
+
+	qq_dec_flying(&brick->q_phase[1]);
+
+	banning_reset(&brick->q_phase[1].q_banning);
+
+	/*  queue up for the next phase */
+	qq_wb_insert(&brick->q_phase[2], wb);
+	wake_up_interruptible_all(&brick->worker_event);
+	goto out_return;
+err:
+	XIO_FAT("hanging up....\n");
+out_return:;
+}
+
+static void phase3_endio(struct generic_callback *cb);
+
+static bool phase3_startio(struct writeback_info *wb);
+
+static
+bool phase1_startio(struct trans_logger_aio_aspect *orig_aio_a)
+{
+	struct aio_object *orig_aio;
+	struct trans_logger_brick *brick;
+	struct writeback_info *wb = NULL;
+
+	CHECK_PTR(orig_aio_a, err);
+	orig_aio = orig_aio_a->object;
+	CHECK_PTR(orig_aio, err);
+	brick = orig_aio_a->my_brick;
+	CHECK_PTR(brick, err);
+
+	if (orig_aio_a->is_collected)
+		goto done;
+	if (!orig_aio_a->is_hashed)
+		goto done;
+
+	wb = make_writeback(brick, orig_aio->io_pos, orig_aio->io_len);
+	if (unlikely(!wb))
+		goto collision;
+
+	if (unlikely(list_empty(&wb->w_sub_write_list))) {
+		XIO_ERR("sub_write_list is empty, orig pos = %lld len = %d (collected=%d), extended pos = %lld len = %d\n",
+			orig_aio->io_pos,
+			orig_aio->io_len,
+			(int)orig_aio_a->is_collected,
+			wb->w_pos,
+			wb->w_len);
+		goto err;
+	}
+
+	wb->read_endio = phase1_endio;
+	wb->write_endio = phase3_endio;
+	atomic_set(&wb->w_sub_log_count, atomic_read(&wb->w_sub_read_count));
+
+	if (brick->log_reads) {
+		qq_inc_flying(&brick->q_phase[1]);
+		fire_writeback(&wb->w_sub_read_list, false);
+	} else { /*  shortcut */
+#ifndef SHORTCUT_1_to_3
+		qq_wb_insert(&brick->q_phase[3], wb);
+		wake_up_interruptible_all(&brick->worker_event);
+#else
+		return phase3_startio(wb);
+#endif
+	}
+
+done:
+	return true;
+
+err:
+	if (wb)
+		free_writeback(wb);
+collision:
+	return false;
+}
+
+/*********************************************************************
+ * Phase 2: log the old disk version.
+ */
+
+static inline
+void _phase2_endio(struct writeback_info *wb)
+{
+	struct trans_logger_brick *brick = wb->w_brick;
+
+	/*  queue up for the next phase */
+	qq_wb_insert(&brick->q_phase[3], wb);
+	wake_up_interruptible_all(&brick->worker_event);
+	goto out_return;
+out_return:;
+}
+
+static
+void phase2_endio(void *private, int error)
+{
+	struct trans_logger_aio_aspect *sub_aio_a;
+	struct trans_logger_brick *brick;
+	struct writeback_info *wb;
+
+	sub_aio_a = private;
+	CHECK_PTR(sub_aio_a, err);
+	wb = sub_aio_a->wb;
+	CHECK_PTR(wb, err);
+	brick = wb->w_brick;
+	CHECK_PTR(brick, err);
+
+	qq_dec_flying(&brick->q_phase[2]);
+
+	if (unlikely(error < 0)) {
+		XIO_FAT("IO error %d\n", error);
+		goto err; /*  FIXME: this leads to hanging requests. do better. */
+	}
+
+	CHECK_ATOMIC(&wb->w_sub_log_count, 1);
+	if (atomic_dec_and_test(&wb->w_sub_log_count)) {
+		banning_reset(&brick->q_phase[2].q_banning);
+		_phase2_endio(wb);
+	}
+	goto out_return;
+err:
+	XIO_FAT("hanging up....\n");
+out_return:;
+}
+
+static
+bool _phase2_startio(struct trans_logger_aio_aspect *sub_aio_a)
+{
+	struct aio_object *sub_aio = NULL;
+	struct writeback_info *wb;
+	struct trans_logger_input *input;
+	struct trans_logger_brick *brick;
+	struct log_status *logst;
+	void *data;
+	bool ok;
+
+	CHECK_PTR(sub_aio_a, err);
+	sub_aio = sub_aio_a->object;
+	CHECK_PTR(sub_aio, err);
+	wb = sub_aio_a->wb;
+	CHECK_PTR(wb, err);
+	brick = wb->w_brick;
+	CHECK_PTR(brick, err);
+	input = sub_aio_a->log_input;
+	CHECK_PTR(input, err);
+	logst = &input->logst;
+	logst->do_crc = trans_logger_do_crc;
+
+	{
+		struct log_header l = {
+			.l_stamp = sub_aio_a->stamp,
+			.l_pos = sub_aio->io_pos,
+			.l_len = sub_aio->io_len,
+			.l_code = CODE_WRITE_OLD,
+		};
+		data = log_reserve(logst, &l);
+	}
+
+	if (unlikely(!data))
+		goto err;
+
+	memcpy(data, sub_aio->io_data, sub_aio->io_len);
+
+	ok = log_finalize(logst, sub_aio->io_len, phase2_endio, sub_aio_a);
+	if (unlikely(!ok))
+		goto err;
+
+	qq_inc_flying(&brick->q_phase[2]);
+
+	return true;
+
+err:
+	XIO_FAT("cannot log old data, pos = %lld len = %d\n",
+		sub_aio ? sub_aio->io_pos : 0,
+		sub_aio ? sub_aio->io_len : 0);
+	return false;
+}
+
+static
+bool phase2_startio(struct writeback_info *wb)
+{
+	struct trans_logger_brick *brick;
+	bool ok = true;
+
+	CHECK_PTR(wb, err);
+	brick = wb->w_brick;
+	CHECK_PTR(brick, err);
+
+	if (brick->log_reads && atomic_read(&wb->w_sub_log_count) > 0) {
+		struct list_head *start;
+		struct list_head *tmp;
+
+		start = &wb->w_sub_read_list;
+		for (tmp = start->next; tmp != start; tmp = tmp->next) {
+			struct trans_logger_aio_aspect *sub_aio_a;
+			struct aio_object *sub_aio;
+
+			sub_aio_a = container_of(tmp, struct trans_logger_aio_aspect, sub_head);
+			sub_aio = sub_aio_a->object;
+
+			if (!_phase2_startio(sub_aio_a))
+				ok = false;
+		}
+		wake_up_interruptible_all(&brick->worker_event);
+	} else {
+		_phase2_endio(wb);
+	}
+	return ok;
+err:
+	return false;
+}
+
+/*********************************************************************
+ * Phase 3: overwrite old disk version with new version.
+ */
+
+static
+void phase3_endio(struct generic_callback *cb)
+{
+	struct trans_logger_aio_aspect *sub_aio_a;
+	struct writeback_info *wb;
+	struct trans_logger_brick *brick;
+
+	CHECK_PTR(cb, err);
+	sub_aio_a = cb->cb_private;
+	CHECK_PTR(sub_aio_a, err);
+	wb = sub_aio_a->wb;
+	CHECK_PTR(wb, err);
+	brick = wb->w_brick;
+	CHECK_PTR(brick, err);
+
+	if (unlikely(cb->cb_error < 0)) {
+		XIO_FAT("IO error %d\n", cb->cb_error);
+		goto err;
+	}
+
+	hash_put_all(brick, &wb->w_collect_list);
+
+	qq_dec_flying(&brick->q_phase[3]);
+	atomic_inc(&brick->total_writeback_cluster_count);
+
+	free_writeback(wb);
+
+	banning_reset(&brick->q_phase[3].q_banning);
+
+	wake_up_interruptible_all(&brick->worker_event);
+
+	goto out_return;
+err:
+	XIO_FAT("hanging up....\n");
+out_return:;
+}
+
+static
+bool phase3_startio(struct writeback_info *wb)
+{
+	struct list_head *start = &wb->w_sub_read_list;
+	struct list_head *tmp;
+
+	/* Cleanup read requests (if they exist from previous phases)
+	 */
+	while ((tmp = start->next) != start) {
+		struct trans_logger_aio_aspect *sub_aio_a;
+		struct aio_object *sub_aio;
+		struct trans_logger_input *sub_input;
+
+		list_del_init(tmp);
+
+		sub_aio_a = container_of(tmp, struct trans_logger_aio_aspect, sub_head);
+		sub_aio = sub_aio_a->object;
+		sub_input = sub_aio_a->my_input;
+
+		GENERIC_INPUT_CALL(sub_input, aio_put, sub_aio);
+	}
+
+	update_writeback_info(wb);
+
+	/* Start writeback IO
+	 */
+	qq_inc_flying(&wb->w_brick->q_phase[3]);
+	fire_writeback(&wb->w_sub_write_list, true);
+	return true;
+}
+
+/*********************************************************************
+ * The logger thread.
+ * There is only a single instance, dealing with all requests in parallel.
+ */
+
+static
+int run_aio_queue(struct logger_queue *q,
+	bool (*startio)(struct trans_logger_aio_aspect *sub_aio_a),
+	int max,
+	bool do_limit)
+{
+	struct trans_logger_brick *brick = q->q_brick;
+	int total_len = 0;
+	bool found = false;
+	bool ok;
+	int res = 0;
+
+	do {
+		struct trans_logger_aio_aspect *aio_a;
+
+		aio_a = qq_aio_fetch(q);
+		if (!aio_a)
+			goto done;
+
+		if (do_limit && likely(aio_a->object))
+			total_len += aio_a->object->io_len;
+
+		ok = startio(aio_a);
+		if (unlikely(!ok)) {
+			qq_aio_pushback(q, aio_a);
+			goto done;
+		}
+		res++;
+		found = true;
+		__trans_logger_io_put(aio_a->my_brick, aio_a);
+	} while (--max > 0);
+
+done:
+	if (found) {
+		xio_limit(&global_writeback.limiter, (total_len - 1) / 1024 + 1);
+		wake_up_interruptible_all(&brick->worker_event);
+	}
+	return res;
+}
+
+static
+int run_wb_queue(struct logger_queue *q, bool (*startio)(struct writeback_info *wb), int max)
+{
+	struct trans_logger_brick *brick = q->q_brick;
+	int total_len = 0;
+	bool found = false;
+	bool ok;
+	int res = 0;
+
+	do {
+		struct writeback_info *wb;
+
+		wb = qq_wb_fetch(q);
+		if (!wb)
+			goto done;
+
+		total_len += wb->w_len;
+
+		ok = startio(wb);
+		if (unlikely(!ok)) {
+			qq_wb_pushback(q, wb);
+			goto done;
+		}
+		res++;
+		found = true;
+	} while (--max > 0);
+
+done:
+	if (found) {
+		xio_limit(&global_writeback.limiter, (total_len - 1) / 1024 + 1);
+		wake_up_interruptible_all(&brick->worker_event);
+	}
+	return res;
+}
+
+/* Ranking tables.
+ */
+static
+struct rank_info float_queue_rank_log[] = {
+	{     0,    0 },
+	{     1,  100 },
+	{ RKI_DUMMY }
+};
+
+static
+struct rank_info float_queue_rank_io[] = {
+	{     0,    0 },
+	{     1,    1 },
+	{ RKI_DUMMY }
+};
+
+static
+struct rank_info float_fly_rank_log[] = {
+	{     0,    0 },
+	{     1,    1 },
+	{    32,   10 },
+	{ RKI_DUMMY }
+};
+
+static
+struct rank_info float_fly_rank_io[] = {
+	{     0,    0 },
+	{     1,   10 },
+	{     2,  -10 },
+	{ 10000, -200 },
+	{ RKI_DUMMY }
+};
+
+static
+struct rank_info nofloat_queue_rank_log[] = {
+	{     0,    0 },
+	{     1,   10 },
+	{ RKI_DUMMY }
+};
+
+static
+struct rank_info nofloat_queue_rank_io[] = {
+	{     0,    0 },
+	{     1,   10 },
+	{   100,  100 },
+	{ RKI_DUMMY }
+};
+
+#define nofloat_fly_rank_log float_fly_rank_log
+
+static
+struct rank_info nofloat_fly_rank_io[] = {
+	{     0,    0 },
+	{     1,   10 },
+	{   128,    8 },
+	{   129, -200 },
+	{ RKI_DUMMY }
+};
+
+static
+struct rank_info *queue_ranks[2][LOGGER_QUEUES] = {
+	[0] = {
+		[0] = float_queue_rank_log,
+		[1] = float_queue_rank_io,
+		[2] = float_queue_rank_io,
+		[3] = float_queue_rank_io,
+	},
+	[1] = {
+		[0] = nofloat_queue_rank_log,
+		[1] = nofloat_queue_rank_io,
+		[2] = nofloat_queue_rank_io,
+		[3] = nofloat_queue_rank_io,
+	},
+};
+static
+struct rank_info *fly_ranks[2][LOGGER_QUEUES] = {
+	[0] = {
+		[0] = float_fly_rank_log,
+		[1] = float_fly_rank_io,
+		[2] = float_fly_rank_io,
+		[3] = float_fly_rank_io,
+	},
+	[1] = {
+		[0] = nofloat_fly_rank_log,
+		[1] = nofloat_fly_rank_io,
+		[2] = nofloat_fly_rank_io,
+		[3] = nofloat_fly_rank_io,
+	},
+};
+
+static
+struct rank_info extra_rank_aio_flying[] = {
+	{     0,    0 },
+	{     1,   10 },
+	{    16,   30 },
+	{    31,    0 },
+	{    32, -200 },
+	{ RKI_DUMMY }
+};
+
+static
+struct rank_info global_rank_aio_flying[] = {
+	{     0,    0 },
+	{    63,    0 },
+	{    64, -200 },
+	{ RKI_DUMMY }
+};
+
+static
+int _do_ranking(struct trans_logger_brick *brick, struct rank_data rkd[])
+{
+	int res;
+	int i;
+	int floating_mode;
+	int aio_flying;
+	bool delay_callers;
+
+	ranking_start(rkd, LOGGER_QUEUES);
+
+	/*  check the memory situation... */
+	delay_callers = false;
+	floating_mode = 1;
+	if (brick_global_memlimit >= 1024) {
+		int global_mem_used = atomic64_read(&global_mshadow_used) / 1024;
+
+		trans_logger_mem_usage = global_mem_used;
+
+		floating_mode = (global_mem_used < brick_global_memlimit / 2) ? 0 : 1;
+
+		if (global_mem_used >= brick_global_memlimit)
+			delay_callers = true;
+
+	} else if (brick->shadow_mem_limit >= 8) {
+		int local_mem_used = atomic64_read(&brick->shadow_mem_used) / 1024;
+
+		floating_mode = (local_mem_used < brick->shadow_mem_limit / 2) ? 0 : 1;
+
+		if (local_mem_used >= brick->shadow_mem_limit)
+			delay_callers = true;
+	}
+	if (delay_callers) {
+		if (!brick->delay_callers) {
+			brick->delay_callers = true;
+			atomic_inc(&brick->total_delay_count);
+		}
+	} else if (brick->delay_callers) {
+		brick->delay_callers = false;
+		wake_up_interruptible(&brick->caller_event);
+	}
+
+	/*  global limit for flying aios */
+	ranking_compute(&rkd[0], global_rank_aio_flying, atomic_read(&global_aio_flying));
+
+	/*  local limit for flying aios */
+	aio_flying = 0;
+	for (i = TL_INPUT_LOG1; i <= TL_INPUT_LOG2; i++) {
+		struct trans_logger_input *input = brick->inputs[i];
+
+		aio_flying += atomic_read(&input->logst.aio_flying);
+	}
+
+	/*  obey the basic rules... */
+	for (i = 0; i < LOGGER_QUEUES; i++) {
+		int queued = atomic_read(&brick->q_phase[i].q_queued);
+		int flying;
+
+		/* This must come first.
+		 * When a queue is empty, you must not credit any positive points.
+		 * Otherwise, (almost) infinite selection of untreatable
+		 * queues may occur.
+		 */
+		if (queued <= 0)
+			continue;
+
+		if (banning_is_hit(&brick->q_phase[i].q_banning))
+			break;
+
+		if (i == 0) {
+			/*  limit aio IO parallelism on transaction log */
+			ranking_compute(&rkd[0], extra_rank_aio_flying, aio_flying);
+		} else if (i == 1 && !floating_mode) {
+			struct trans_logger_brick *leader;
+			int lim;
+
+			if (!aio_flying && atomic_read(&brick->q_phase[0].q_queued) > 0)
+				break;
+
+			leader = elect_leader(&global_writeback);
+			if (leader != brick)
+				break;
+
+			if (banning_is_hit(&xio_global_ban))
+				break;
+
+			lim = xio_limit(&global_writeback.limiter, 0);
+			if (lim > 0)
+				break;
+		}
+
+		ranking_compute(&rkd[i], queue_ranks[floating_mode][i], queued);
+
+		flying = atomic_read(&brick->q_phase[i].q_flying);
+
+		ranking_compute(&rkd[i], fly_ranks[floating_mode][i], flying);
+	}
+
+	/*  finalize it */
+	ranking_stop(rkd, LOGGER_QUEUES);
+
+	res = ranking_select(rkd, LOGGER_QUEUES);
+
+	return res;
+}
+
+static
+void _init_input(struct trans_logger_input *input, loff_t start_pos, loff_t end_pos)
+{
+	struct trans_logger_brick *brick = input->brick;
+	struct log_status *logst = &input->logst;
+
+	init_logst(logst, (void *)input, start_pos, end_pos);
+	logst->signal_event = &brick->worker_event;
+	logst->align_size = CONF_TRANS_ALIGN;
+	logst->chunk_size = CONF_TRANS_CHUNKSIZE;
+	logst->max_size = CONF_TRANS_MAX_AIO_SIZE;
+
+	input->inf.inf_min_pos = start_pos;
+	input->inf.inf_max_pos = end_pos;
+	get_lamport(&input->inf.inf_max_pos_stamp);
+	memcpy(&input->inf.inf_min_pos_stamp, &input->inf.inf_max_pos_stamp, sizeof(input->inf.inf_min_pos_stamp));
+
+	logst->log_pos = start_pos;
+	input->inf.inf_log_pos = start_pos;
+	input->inf_last_jiffies = jiffies;
+	input->inf.inf_is_replaying = false;
+	input->inf.inf_is_logging = false;
+
+	input->is_operating = true;
+}
+
+static
+void _init_inputs(struct trans_logger_brick *brick, bool is_first)
+{
+	struct trans_logger_input *input;
+	int old_nr = brick->old_input_nr;
+	int log_nr = brick->log_input_nr;
+	int new_nr = brick->new_input_nr;
+
+	if (!is_first &&
+	    (new_nr == log_nr ||
+	     log_nr != old_nr)) {
+		goto done;
+	}
+	if (unlikely(new_nr < TL_INPUT_LOG1 || new_nr > TL_INPUT_LOG2)) {
+		XIO_ERR("bad new_input_nr = %d\n", new_nr);
+		goto done;
+	}
+
+	input = brick->inputs[new_nr];
+	CHECK_PTR(input, done);
+
+	if (input->is_operating || !input->connect)
+		goto done;
+
+	down(&input->inf_mutex);
+
+	_init_input(input, 0, 0);
+	input->inf.inf_is_logging = is_first;
+
+	/*  from now on, new requests should go to the new input */
+	brick->log_input_nr = new_nr;
+	XIO_INF("switched over to new logfile %d (old = %d)\n", new_nr, old_nr);
+
+	/* Flush the old log buffer and update its symlinks.
+	 * Notice: for some short time, _both_ logfiles may grow
+	 * due to (harmless) races with log_flush().
+	 */
+	if (likely(!is_first)) {
+		struct trans_logger_input *other_input = brick->inputs[old_nr];
+
+		down(&other_input->inf_mutex);
+		log_flush(&other_input->logst);
+		_inf_callback(other_input, true);
+		up(&other_input->inf_mutex);
+	}
+
+	_inf_callback(input, true);
+
+	up(&input->inf_mutex);
+done:;
+}
+
+static
+int _nr_flying_inputs(struct trans_logger_brick *brick)
+{
+	int count = 0;
+	int i;
+
+	for (i = TL_INPUT_LOG1; i <= TL_INPUT_LOG2; i++) {
+		struct trans_logger_input *input = brick->inputs[i];
+		struct log_status *logst = &input->logst;
+
+		if (input->is_operating)
+			count += logst->count;
+	}
+	return count;
+}
+
+static
+void _flush_inputs(struct trans_logger_brick *brick)
+{
+	int i;
+
+	for (i = TL_INPUT_LOG1; i <= TL_INPUT_LOG2; i++) {
+		struct trans_logger_input *input = brick->inputs[i];
+		struct log_status *logst = &input->logst;
+
+		if (input->is_operating && logst->count > 0) {
+			atomic_inc(&brick->total_flush_count);
+			log_flush(logst);
+		}
+	}
+}
+
+static
+void _exit_inputs(struct trans_logger_brick *brick, bool force)
+{
+	int i;
+
+	for (i = TL_INPUT_LOG1; i <= TL_INPUT_LOG2; i++) {
+		struct trans_logger_input *input = brick->inputs[i];
+		struct log_status *logst = &input->logst;
+
+		if (input->is_operating &&
+		    (force || !input->connect)) {
+			bool old_replaying = input->inf.inf_is_replaying;
+			bool old_logging = input->inf.inf_is_logging;
+
+			XIO_DBG("cleaning up input %d (log = %d old = %d), old_replaying = %d old_logging = %d\n",
+				i,
+				brick->log_input_nr,
+				brick->old_input_nr,
+				old_replaying,
+				old_logging);
+			exit_logst(logst);
+			/*  no locking here: we should be the only thread doing this. */
+			_inf_callback(input, true);
+			input->inf_last_jiffies = 0;
+			input->inf.inf_is_replaying = false;
+			input->inf.inf_is_logging = false;
+			input->is_operating = false;
+			if (i == brick->old_input_nr && i != brick->log_input_nr) {
+				struct trans_logger_input *other_input = brick->inputs[brick->log_input_nr];
+
+				down(&other_input->inf_mutex);
+				brick->old_input_nr = brick->log_input_nr;
+				other_input->inf.inf_is_replaying = old_replaying;
+				other_input->inf.inf_is_logging = old_logging;
+				_inf_callback(other_input, true);
+				up(&other_input->inf_mutex);
+			}
+		}
+	}
+}
+
+/* Performance-critical:
+ * Calling log_flush() too often may result in
+ * increased overhead (and thus in lower throughput).
+ * Call it only when the IO scheduler need not do anything else.
+ * OTOH, calling it too seldom may hold back
+ * IO completion for the end user for too long time.
+ *
+ * Be careful to flush any leftovers in the log buffer, at least after
+ * some short delay.
+ *
+ * Description of flush_mode:
+ *  0 = flush unconditionally
+ *  1 = flush only when nothing can be appended to the transaction log
+ *  2 = see 1 && flush only when the user is waiting for an answer
+ *  3 = see 1 && not 2 && flush only when there is no other activity (background mode)
+ * Notice: 3 makes only sense for leftovers where the user is _not_ waiting for
+ */
+static inline
+void flush_inputs(struct trans_logger_brick *brick, int flush_mode)
+{
+	if (flush_mode < 1 ||
+	    /*	there is nothing to append any more */
+	    (atomic_read(&brick->q_phase[0].q_queued) <= 0 &&
+	     /*  and the user is waiting for an answer */
+	     (flush_mode < 2 ||
+	      atomic_read(&brick->log_fly_count) > 0 ||
+	     /*  else flush any leftovers in background, when there is no writeback activity */
+	      (flush_mode == 3 &&
+	       atomic_read(&brick->q_phase[1].q_flying) + atomic_read(&brick->q_phase[3].q_flying) <= 0))))
+		_flush_inputs(brick);
+}
+
+static
+void trans_logger_log(struct trans_logger_brick *brick)
+{
+	struct rank_data rkd[LOGGER_QUEUES] = {};
+	long long old_jiffies = jiffies;
+	long long work_jiffies = jiffies;
+	int interleave = 0;
+	int nr_flying;
+
+	brick->replay_code = 0; /*  indicates "running" */
+	brick->disk_io_error = 0;
+
+	_init_inputs(brick, true);
+
+	xio_set_power_on_led((void *)brick, true);
+
+	while (!brick_thread_should_stop() || _congested(brick)) {
+		int winner;
+		int nr;
+
+		wait_event_interruptible_timeout(
+			brick->worker_event,
+			({
+				winner = _do_ranking(brick, rkd);
+				if (winner < 0) { /*  no more work to do */
+					int flush_mode = 2 - ((int)(jiffies - work_jiffies)) / (HZ * 2);
+
+					flush_inputs(brick, flush_mode);
+					interleave = 0;
+				} else { /*  reset the timer whenever something is to do */
+					work_jiffies = jiffies;
+				}
+				winner >= 0;
+			}),
+			HZ / 10);
+
+		atomic_inc(&brick->total_round_count);
+
+		if (brick->cease_logging)
+			brick->stopped_logging = true;
+		else if (brick->stopped_logging && !_congested(brick))
+			brick->stopped_logging = false;
+
+		_init_inputs(brick, false);
+
+		switch (winner) {
+		case 0:
+			interleave = 0;
+			nr = run_aio_queue(&brick->q_phase[0],
+				prep_phase_startio,
+				brick->q_phase[0].q_batchlen,
+				true);
+			goto done;
+		case 1:
+			if (interleave >= trans_logger_max_interleave && trans_logger_max_interleave >= 0) {
+				interleave = 0;
+				flush_inputs(brick, 3);
+			}
+			nr = run_aio_queue(&brick->q_phase[1], phase1_startio, brick->q_phase[1].q_batchlen, true);
+			interleave += nr;
+			goto done;
+		case 2:
+			interleave = 0;
+			nr = run_wb_queue(&brick->q_phase[2], phase2_startio, brick->q_phase[2].q_batchlen);
+			goto done;
+		case 3:
+			if (interleave >= trans_logger_max_interleave && trans_logger_max_interleave >= 0) {
+				interleave = 0;
+				flush_inputs(brick, 3);
+			}
+			nr = run_wb_queue(&brick->q_phase[3], phase3_startio, brick->q_phase[3].q_batchlen);
+			interleave += nr;
+done:
+			if (unlikely(nr <= 0)) {
+				/* This should not happen!
+				 * However, in error situations, the ranking
+				 * algorithm cannot foresee anything.
+				 */
+				brick->q_phase[winner].no_progress_count++;
+				banning_hit(&brick->q_phase[winner].q_banning, 10000);
+				flush_inputs(brick, 0);
+			}
+			ranking_select_done(rkd, winner, nr);
+			break;
+
+		default:
+			break;
+		}
+
+		/* Update symlinks even during pauses.
+		 */
+		if (winner < 0 && ((long long)jiffies) - old_jiffies >= HZ) {
+			int i;
+
+			old_jiffies = jiffies;
+			for (i = TL_INPUT_LOG1; i <= TL_INPUT_LOG2; i++) {
+				struct trans_logger_input *input = brick->inputs[i];
+
+				down(&input->inf_mutex);
+				_inf_callback(input, false);
+				up(&input->inf_mutex);
+			}
+		}
+
+		_exit_inputs(brick, false);
+	}
+
+	for (;;) {
+		_exit_inputs(brick, true);
+		nr_flying = _nr_flying_inputs(brick);
+		if (nr_flying <= 0)
+			break;
+		XIO_INF("%d inputs are operating\n", nr_flying);
+		brick_msleep(1000);
+	}
+}
+
+/***************************** log replay *****************************/
+
+static
+void replay_endio(struct generic_callback *cb)
+{
+	struct trans_logger_aio_aspect *aio_a = cb->cb_private;
+	struct trans_logger_brick *brick;
+	bool ok;
+
+	LAST_CALLBACK(cb);
+	CHECK_PTR(aio_a, err);
+	brick = aio_a->my_brick;
+	CHECK_PTR(brick, err);
+
+	if (unlikely(cb->cb_error < 0)) {
+		brick->disk_io_error = cb->cb_error;
+		XIO_ERR("IO error = %d\n", cb->cb_error);
+	}
+
+	spin_lock(&brick->replay_lock);
+	ok = !list_empty(&aio_a->replay_head);
+	list_del_init(&aio_a->replay_head);
+	spin_unlock(&brick->replay_lock);
+
+	if (likely(ok))
+		atomic_dec(&brick->replay_count);
+	else
+		XIO_ERR("callback with empty replay_head (replay_count=%d)\n", atomic_read(&brick->replay_count));
+	wake_up_interruptible_all(&brick->worker_event);
+	goto out_return;
+err:
+	XIO_FAT("cannot handle replay IO\n");
+out_return:;
+}
+
+static
+bool _has_conflict(struct trans_logger_brick *brick, struct trans_logger_aio_aspect *aio_a)
+{
+	struct aio_object *aio = aio_a->object;
+	struct list_head *tmp;
+	bool res = false;
+
+/**/
+
+	spin_lock(&brick->replay_lock);
+
+	for (tmp = brick->replay_list.next; tmp != &brick->replay_list; tmp = tmp->next) {
+		struct trans_logger_aio_aspect *tmp_a;
+		struct aio_object *tmp_aio;
+
+		tmp_a = container_of(tmp, struct trans_logger_aio_aspect, replay_head);
+		tmp_aio = tmp_a->object;
+		if (tmp_aio->io_pos + tmp_aio->io_len > aio->io_pos && tmp_aio->io_pos < aio->io_pos + aio->io_len) {
+			res = true;
+			break;
+		}
+	}
+
+	spin_unlock(&brick->replay_lock);
+	return res;
+}
+
+static
+void wait_replay(struct trans_logger_brick *brick, struct trans_logger_aio_aspect *aio_a)
+{
+	const int max = 512; /*  limit parallelism somewhat */
+	int conflicts = 0;
+	bool ok = false;
+	bool was_empty;
+
+	wait_event_interruptible_timeout(brick->worker_event,
+					 atomic_read(&brick->replay_count) < max
+					 && (_has_conflict(brick, aio_a) ? conflicts++ : (ok = true), ok),
+					 60 * HZ);
+
+	atomic_inc(&brick->total_replay_count);
+	if (conflicts)
+		atomic_inc(&brick->total_replay_conflict_count);
+
+	spin_lock(&brick->replay_lock);
+	was_empty = !!list_empty(&aio_a->replay_head);
+	if (likely(was_empty))
+		atomic_inc(&brick->replay_count);
+	else
+		list_del(&aio_a->replay_head);
+	list_add(&aio_a->replay_head, &brick->replay_list);
+	spin_unlock(&brick->replay_lock);
+
+	if (unlikely(!was_empty)) {
+		XIO_ERR("replay_head was already used (ok=%d, conflicts=%d, replay_count=%d)\n",
+			ok,
+			conflicts,
+			atomic_read(&brick->replay_count));
+	}
+}
+
+static
+int replay_data(struct trans_logger_brick *brick, loff_t pos, void *buf, int len)
+{
+	struct trans_logger_input *input = brick->inputs[TL_INPUT_WRITEBACK];
+	int status;
+
+	if (!input->connect)
+		input = brick->inputs[TL_INPUT_READ];
+
+	/* TODO for better efficiency:
+	 * Instead of starting IO here, just put the data into the hashes
+	 * and queues such that ordinary IO will be corrected.
+	 * Writeback will be lazy then.
+	 * The switch infrastructure must be changed before this
+	 * becomes possible.
+	 */
+#ifdef REPLAY_DATA
+	while (len > 0) {
+		struct aio_object *aio;
+		struct trans_logger_aio_aspect *aio_a;
+
+		status = -ENOMEM;
+		aio = trans_logger_alloc_aio(brick);
+		aio_a = trans_logger_aio_get_aspect(brick, aio);
+		CHECK_PTR(aio_a, done);
+		CHECK_ASPECT(aio_a, aio, done);
+
+		aio->io_pos = pos;
+		aio->io_data = NULL;
+		aio->io_len = len;
+		aio->io_may_write = WRITE;
+		aio->io_rw = WRITE;
+
+		status = GENERIC_INPUT_CALL(input, aio_get, aio);
+		if (unlikely(status < 0)) {
+			XIO_ERR("cannot get aio, status = %d\n", status);
+			goto done;
+		}
+		if (unlikely(!aio->io_data)) {
+			status = -ENOMEM;
+			XIO_ERR("cannot get aio, status = %d\n", status);
+			goto done;
+		}
+		if (unlikely(aio->io_len <= 0 || aio->io_len > len)) {
+			status = -EINVAL;
+			XIO_ERR("bad aio len = %d (requested = %d)\n", aio->io_len, len);
+			goto done;
+		}
+
+		wait_replay(brick, aio_a);
+
+		memcpy(aio->io_data, buf, aio->io_len);
+
+		SETUP_CALLBACK(aio, replay_endio, aio_a);
+		aio_a->my_brick = brick;
+
+		GENERIC_INPUT_CALL(input, aio_io, aio);
+
+		if (unlikely(aio->io_len <= 0)) {
+			status = -EINVAL;
+			XIO_ERR("bad aio len = %d (requested = %d)\n", aio->io_len, len);
+			goto done;
+		}
+
+		pos += aio->io_len;
+		buf += aio->io_len;
+		len -= aio->io_len;
+
+		GENERIC_INPUT_CALL(input, aio_put, aio);
+	}
+#endif
+	status = 0;
+done:
+	return status;
+}
+
+static
+void trans_logger_replay(struct trans_logger_brick *brick)
+{
+	struct trans_logger_input *input = brick->inputs[brick->log_input_nr];
+	struct log_header lh = {};
+	loff_t start_pos;
+	loff_t end_pos;
+	loff_t finished_pos = -1;
+	loff_t new_finished_pos = -1;
+	long long old_jiffies = jiffies;
+	int nr_flying;
+	int backoff = 0;
+	int status = 0;
+
+	brick->replay_code = 0; /*  indicates "running" */
+	brick->disk_io_error = 0;
+
+	start_pos = brick->replay_start_pos;
+	end_pos = brick->replay_end_pos;
+	brick->replay_current_pos = start_pos;
+
+	_init_input(input, start_pos, end_pos);
+
+	input->inf.inf_min_pos = start_pos;
+	input->inf.inf_max_pos = end_pos;
+	input->inf.inf_log_pos = end_pos;
+	input->inf.inf_is_replaying = true;
+	input->inf.inf_is_logging = false;
+
+	XIO_INF("starting replay from %lld to %lld\n", start_pos, end_pos);
+
+	xio_set_power_on_led((void *)brick, true);
+
+	for (;;) {
+		void *buf = NULL;
+		int len = 0;
+
+		if (brick_thread_should_stop() ||
+		   (!brick->continuous_replay_mode && finished_pos >= brick->replay_end_pos)) {
+			status = 0; /*	treat as EOF */
+			break;
+		}
+
+		status = log_read(&input->logst, false, &lh, &buf, &len);
+
+		new_finished_pos = input->logst.log_pos + input->logst.offset;
+		XIO_RPL("read	%lld %lld\n", finished_pos, new_finished_pos);
+
+		if (status == -EAGAIN) {
+			loff_t remaining = brick->replay_end_pos - new_finished_pos;
+
+			XIO_DBG("got -EAGAIN, remaining = %lld\n", remaining);
+			if (brick->replay_tolerance > 0 && remaining < brick->replay_tolerance) {
+				XIO_WRN("logfile is truncated at position %lld (end_pos = %lld, remaining = %lld, tolerance = %d)\n",
+					 new_finished_pos,
+					 brick->replay_end_pos,
+					 remaining,
+					 brick->replay_tolerance);
+				finished_pos = new_finished_pos;
+				brick->replay_code = status;
+				break;
+			}
+			brick_msleep(backoff);
+			if (backoff < trans_logger_replay_timeout * 1000) {
+				backoff += 100;
+			} else {
+				XIO_WRN("logfile replay not possible at position %lld (end_pos = %lld, remaining = %lld), please check/repair your logfile in userspace by some tool!\n",
+					 new_finished_pos,
+					 brick->replay_end_pos,
+					 remaining);
+				brick->replay_code = status;
+				break;
+			}
+			continue;
+		}
+		if (unlikely(status < 0)) {
+			brick->replay_code = status;
+			XIO_WRN("cannot read logfile data, status = %d\n", status);
+			break;
+		}
+
+		if ((!status && len <= 0) ||
+		   new_finished_pos > brick->replay_end_pos) { /*  EOF -> wait until brick_thread_should_stop() */
+			XIO_DBG("EOF at %lld (old = %lld, end_pos = %lld)\n",
+				new_finished_pos,
+				finished_pos,
+				brick->replay_end_pos);
+			if (!brick->continuous_replay_mode) {
+				/*  notice: finished_pos remains at old value here! */
+				break;
+			}
+			brick_msleep(1000);
+			continue;
+		}
+
+		if (lh.l_code != CODE_WRITE_NEW) {
+			/* ignore other records silently */;
+		} else if (unlikely(brick->disk_io_error)) {
+			status = brick->disk_io_error;
+			brick->replay_code = status;
+			XIO_ERR("IO error %d\n", status);
+			break;
+		} else if (likely(buf && len)) {
+			if (brick->replay_limiter)
+				xio_limit_sleep(brick->replay_limiter, (len - 1) / 1024 + 1);
+			status = replay_data(brick, lh.l_pos, buf, len);
+			XIO_RPL("replay %lld %lld (pos=%lld status=%d)\n",
+				finished_pos,
+				new_finished_pos,
+				lh.l_pos,
+				status);
+			if (unlikely(status < 0)) {
+				brick->replay_code = status;
+				XIO_ERR("cannot replay data at pos = %lld len = %d, status = %d\n",
+					lh.l_pos,
+					len,
+					status);
+				break;
+			} else {
+				finished_pos = new_finished_pos;
+			}
+		}
+
+		/*  do this _after_ any opportunities for errors... */
+		if ((atomic_read(&brick->replay_count) <= 0 ||
+		     ((long long)jiffies) - old_jiffies >= HZ * 3) &&
+		    finished_pos >= 0) {
+			/*  for safety, wait until the IO queue has drained. */
+			wait_event_interruptible_timeout(brick->worker_event,
+				atomic_read(&brick->replay_count) <= 0,
+				30 * HZ);
+
+			if (unlikely(brick->disk_io_error)) {
+				status = brick->disk_io_error;
+				brick->replay_code = status;
+				XIO_ERR("IO error %d\n", status);
+				break;
+			}
+
+			down(&input->inf_mutex);
+			input->inf.inf_min_pos = finished_pos;
+			get_lamport(&input->inf.inf_min_pos_stamp);
+			old_jiffies = jiffies;
+			_inf_callback(input, false);
+			up(&input->inf_mutex);
+		}
+		_exit_inputs(brick, false);
+	}
+
+	XIO_INF("waiting for finish...\n");
+
+	wait_event_interruptible_timeout(brick->worker_event, atomic_read(&brick->replay_count) <= 0, 60 * HZ);
+
+	if (unlikely(finished_pos > brick->replay_end_pos)) {
+		XIO_ERR("finished_pos too large: %lld + %d = %lld > %lld\n",
+			input->logst.log_pos,
+			input->logst.offset,
+			finished_pos,
+			brick->replay_end_pos);
+	}
+
+	if (finished_pos >= 0 && !brick->disk_io_error) {
+		input->inf.inf_min_pos = finished_pos;
+		brick->replay_current_pos = finished_pos;
+	}
+
+	get_lamport(&input->inf.inf_min_pos_stamp);
+
+	if (status >= 0 && finished_pos == brick->replay_end_pos) {
+		XIO_INF("replay finished at %lld\n", finished_pos);
+		brick->replay_code = 1;
+	} else if (status == -EAGAIN && finished_pos + brick->replay_tolerance > brick->replay_end_pos) {
+		XIO_INF("TOLERANCE: logfile is incomplete at %lld (of %lld)\n", finished_pos, brick->replay_end_pos);
+		brick->replay_code = 2;
+	} else if (status < 0) {
+		if (finished_pos < 0)
+			finished_pos = new_finished_pos;
+		if (finished_pos + brick->replay_tolerance > brick->replay_end_pos) {
+			XIO_INF("TOLERANCE: logfile is incomplete at %lld (of %lld), status = %d\n",
+				finished_pos,
+				brick->replay_end_pos,
+				status);
+		} else {
+			XIO_ERR("replay error %d at %lld (of %lld)\n", status, finished_pos, brick->replay_end_pos);
+		}
+		brick->replay_code = status;
+	} else {
+		XIO_INF("replay stopped prematurely at %lld (of %lld)\n", finished_pos, brick->replay_end_pos);
+		brick->replay_code = 2;
+	}
+
+	for (;;) {
+		_exit_inputs(brick, true);
+		nr_flying = _nr_flying_inputs(brick);
+		if (nr_flying <= 0)
+			break;
+		XIO_INF("%d inputs are operating\n", nr_flying);
+		brick_msleep(1000);
+	}
+
+	local_trigger();
+
+	while (!brick_thread_should_stop())
+		brick_msleep(500);
+}
+
+/************************ logger thread * switching ************************/
+
+static
+int trans_logger_thread(void *data)
+{
+	struct trans_logger_output *output = data;
+	struct trans_logger_brick *brick = output->brick;
+
+	XIO_INF("........... logger has started.\n");
+
+	if (brick->replay_mode)
+		trans_logger_replay(brick);
+	else
+		trans_logger_log(brick);
+	XIO_INF("........... logger has stopped.\n");
+	xio_set_power_on_led((void *)brick, false);
+	xio_set_power_off_led((void *)brick, true);
+	return 0;
+}
+
+static
+int trans_logger_switch(struct trans_logger_brick *brick)
+{
+	static int index;
+	struct trans_logger_output *output = brick->outputs[0];
+
+	if (brick->power.button) {
+		if (!brick->thread && brick->power.off_led) {
+			xio_set_power_off_led((void *)brick, false);
+
+			brick->thread = brick_thread_create(trans_logger_thread, output, "xio_logger%d", index++);
+			if (unlikely(!brick->thread)) {
+				XIO_ERR("cannot create logger thread\n");
+				return -ENOENT;
+			}
+		}
+	} else {
+		xio_set_power_on_led((void *)brick, false);
+		if (brick->thread) {
+			XIO_INF("stopping thread...\n");
+			brick_thread_stop(brick->thread);
+			brick->thread = NULL;
+		}
+	}
+	return 0;
+}
+
+/*************** informational * statistics **************/
+
+static
+char *trans_logger_statistics(struct trans_logger_brick *brick, int verbose)
+{
+	char *res = brick_string_alloc(1024);
+
+	snprintf(res, 1023,
+		 "mode replay=%d continuous=%d replay_code=%d disk_io_error=%d log_reads=%d | cease_logging=%d stopped_logging=%d congested=%d | replay_start_pos = %lld replay_end_pos = %lld | new_input_nr = %d log_input_nr = %d (old = %d) inf_min_pos1 = %lld inf_max_pos1 = %lld inf_min_pos2 = %lld inf_max_pos2 = %lld | total hash_insert=%d hash_find=%d hash_extend=%d replay=%d replay_conflict=%d  (%d%%) callbacks=%d reads=%d writes=%d flushes=%d (%d%%) wb_clusters=%d writebacks=%d (%d%%) shortcut=%d (%d%%) mshadow=%d sshadow=%d mshadow_buffered=%d sshadow_buffered=%d rounds=%d restarts=%d delays=%d phase0=%d phase1=%d phase2=%d phase3=%d | current #aios = %d shadow_mem_used=%ld/%lld replay_count=%d mshadow=%d/%d sshadow=%d hash_count=%d balance=%d/%d/%d/%d pos_count1=%d pos_count2=%d log_aios1=%d log_aios2=%d any_fly=%d log_fly=%d aio_flying1=%d aio_flying2=%d phase0=%d+%d <%d/%d> phase1=%d+%d <%d/%d> phase2=%d+%d <%d/%d> phase3=%d+%d <%d/%d>\n",
+		 brick->replay_mode,
+		 brick->continuous_replay_mode,
+		 brick->replay_code,
+		 brick->disk_io_error,
+		 brick->log_reads,
+		 brick->cease_logging,
+		 brick->stopped_logging,
+		 _congested(brick),
+		 brick->replay_start_pos,
+		 brick->replay_end_pos,
+		 brick->new_input_nr,
+		 brick->log_input_nr,
+		 brick->old_input_nr,
+		 brick->inputs[TL_INPUT_LOG1]->inf.inf_min_pos,
+		 brick->inputs[TL_INPUT_LOG1]->inf.inf_max_pos,
+		 brick->inputs[TL_INPUT_LOG2]->inf.inf_min_pos,
+		 brick->inputs[TL_INPUT_LOG2]->inf.inf_max_pos,
+		 atomic_read(&brick->total_hash_insert_count),
+		 atomic_read(&brick->total_hash_find_count),
+		 atomic_read(&brick->total_hash_extend_count),
+		 atomic_read(&brick->total_replay_count),
+		 atomic_read(&brick->total_replay_conflict_count),
+		 atomic_read(&brick->total_replay_count) ? atomic_read(&brick->total_replay_conflict_count) * 100 / atomic_read(&brick->total_replay_count) : 0,
+		 atomic_read(&brick->total_cb_count),
+		 atomic_read(&brick->total_read_count),
+		 atomic_read(&brick->total_write_count),
+		 atomic_read(&brick->total_flush_count),
+		 atomic_read(&brick->total_write_count) ? atomic_read(&brick->total_flush_count) * 100 / atomic_read(&brick->total_write_count) : 0,
+		 atomic_read(&brick->total_writeback_cluster_count),
+		 atomic_read(&brick->total_writeback_count),
+		 atomic_read(&brick->total_writeback_cluster_count) ? atomic_read(&brick->total_writeback_count) * 100 / atomic_read(&brick->total_writeback_cluster_count) : 0,
+		 atomic_read(&brick->total_shortcut_count),
+		 atomic_read(&brick->total_writeback_count) ? atomic_read(&brick->total_shortcut_count) * 100 / atomic_read(&brick->total_writeback_count) : 0,
+		 atomic_read(&brick->total_mshadow_count),
+		 atomic_read(&brick->total_sshadow_count),
+		 atomic_read(&brick->total_mshadow_buffered_count),
+		 atomic_read(&brick->total_sshadow_buffered_count),
+		 atomic_read(&brick->total_round_count),
+		 atomic_read(&brick->total_restart_count),
+		 atomic_read(&brick->total_delay_count),
+		 atomic_read(&brick->q_phase[0].q_total),
+		 atomic_read(&brick->q_phase[1].q_total),
+		 atomic_read(&brick->q_phase[2].q_total),
+		 atomic_read(&brick->q_phase[3].q_total),
+		 atomic_read(&brick->aio_object_layout.alloc_count),
+		 atomic64_read(&brick->shadow_mem_used) / 1024,
+		 brick_global_memlimit,
+		 atomic_read(&brick->replay_count),
+		 atomic_read(&brick->mshadow_count),
+		 brick->shadow_mem_limit,
+		 atomic_read(&brick->sshadow_count),
+		 atomic_read(&brick->hash_count),
+		 atomic_read(&brick->sub_balance_count),
+		 atomic_read(&brick->inner_balance_count),
+		 atomic_read(&brick->outer_balance_count),
+		 atomic_read(&brick->wb_balance_count),
+		 atomic_read(&brick->inputs[TL_INPUT_LOG1]->pos_count),
+		 atomic_read(&brick->inputs[TL_INPUT_LOG2]->pos_count),
+		 atomic_read(&brick->inputs[TL_INPUT_LOG1]->log_obj_count),
+		 atomic_read(&brick->inputs[TL_INPUT_LOG2]->log_obj_count),
+		 atomic_read(&brick->any_fly_count),
+		 atomic_read(&brick->log_fly_count),
+		 atomic_read(&brick->inputs[TL_INPUT_LOG1]->logst.aio_flying),
+		 atomic_read(&brick->inputs[TL_INPUT_LOG2]->logst.aio_flying),
+		 atomic_read(&brick->q_phase[0].q_queued),
+		 atomic_read(&brick->q_phase[0].q_flying),
+		 brick->q_phase[0].pushback_count,
+		 brick->q_phase[0].no_progress_count,
+		 atomic_read(&brick->q_phase[1].q_queued),
+		 atomic_read(&brick->q_phase[1].q_flying),
+		 brick->q_phase[1].pushback_count,
+		 brick->q_phase[1].no_progress_count,
+		 atomic_read(&brick->q_phase[2].q_queued),
+		 atomic_read(&brick->q_phase[2].q_flying),
+		 brick->q_phase[2].pushback_count,
+		 brick->q_phase[2].no_progress_count,
+		 atomic_read(&brick->q_phase[3].q_queued),
+		 atomic_read(&brick->q_phase[3].q_flying),
+		 brick->q_phase[3].pushback_count,
+		 brick->q_phase[3].no_progress_count);
+	return res;
+}
+
+static
+void trans_logger_reset_statistics(struct trans_logger_brick *brick)
+{
+	atomic_set(&brick->total_hash_insert_count, 0);
+	atomic_set(&brick->total_hash_find_count, 0);
+	atomic_set(&brick->total_hash_extend_count, 0);
+	atomic_set(&brick->total_replay_count, 0);
+	atomic_set(&brick->total_replay_conflict_count, 0);
+	atomic_set(&brick->total_cb_count, 0);
+	atomic_set(&brick->total_read_count, 0);
+	atomic_set(&brick->total_write_count, 0);
+	atomic_set(&brick->total_flush_count, 0);
+	atomic_set(&brick->total_writeback_count, 0);
+	atomic_set(&brick->total_writeback_cluster_count, 0);
+	atomic_set(&brick->total_shortcut_count, 0);
+	atomic_set(&brick->total_mshadow_count, 0);
+	atomic_set(&brick->total_sshadow_count, 0);
+	atomic_set(&brick->total_mshadow_buffered_count, 0);
+	atomic_set(&brick->total_sshadow_buffered_count, 0);
+	atomic_set(&brick->total_round_count, 0);
+	atomic_set(&brick->total_restart_count, 0);
+	atomic_set(&brick->total_delay_count, 0);
+}
+
+/*************** object * aspect constructors * destructors **************/
+
+static
+int trans_logger_aio_aspect_init_fn(struct generic_aspect *_ini)
+{
+	struct trans_logger_aio_aspect *ini = (void *)_ini;
+
+	ini->lh.lh_pos = &ini->object->io_pos;
+	INIT_LIST_HEAD(&ini->lh.lh_head);
+	INIT_LIST_HEAD(&ini->hash_head);
+	INIT_LIST_HEAD(&ini->pos_head);
+	INIT_LIST_HEAD(&ini->replay_head);
+	INIT_LIST_HEAD(&ini->collect_head);
+	INIT_LIST_HEAD(&ini->sub_list);
+	INIT_LIST_HEAD(&ini->sub_head);
+	return 0;
+}
+
+static
+void trans_logger_aio_aspect_exit_fn(struct generic_aspect *_ini)
+{
+	struct trans_logger_aio_aspect *ini = (void *)_ini;
+
+	CHECK_HEAD_EMPTY(&ini->lh.lh_head);
+	CHECK_HEAD_EMPTY(&ini->hash_head);
+	CHECK_HEAD_EMPTY(&ini->pos_head);
+	CHECK_HEAD_EMPTY(&ini->replay_head);
+	CHECK_HEAD_EMPTY(&ini->collect_head);
+	CHECK_HEAD_EMPTY(&ini->sub_list);
+	CHECK_HEAD_EMPTY(&ini->sub_head);
+	if (ini->log_input)
+		atomic_dec(&ini->log_input->log_obj_count);
+}
+
+XIO_MAKE_STATICS(trans_logger);
+
+/********************* brick constructors * destructors *******************/
+
+static
+void _free_pages(struct trans_logger_brick *brick)
+{
+	int i;
+
+	for (i = 0; i < NR_HASH_PAGES; i++) {
+		struct trans_logger_hash_anchor *sub_table = brick->hash_table[i];
+		int j;
+
+		if (!sub_table)
+			continue;
+		for (j = 0; j < HASH_PER_PAGE; j++) {
+			struct trans_logger_hash_anchor *start = &sub_table[j];
+
+			CHECK_HEAD_EMPTY(&start->hash_anchor);
+		}
+		brick_block_free(sub_table, PAGE_SIZE);
+	}
+	brick_block_free(brick->hash_table, PAGE_SIZE);
+}
+
+static
+int trans_logger_brick_construct(struct trans_logger_brick *brick)
+{
+	int i;
+
+	brick->hash_table = brick_block_alloc(0, PAGE_SIZE);
+	memset(brick->hash_table, 0, PAGE_SIZE);
+
+	for (i = 0; i < NR_HASH_PAGES; i++) {
+		struct trans_logger_hash_anchor *sub_table;
+		int j;
+
+		/*  this should be usually optimized away as dead code */
+		if (unlikely(i >= MAX_HASH_PAGES)) {
+			XIO_ERR("sorry, subtable index %d is too large.\n", i);
+			_free_pages(brick);
+			return -EINVAL;
+		}
+
+		sub_table = brick_block_alloc(0, PAGE_SIZE);
+		brick->hash_table[i] = sub_table;
+
+		memset(sub_table, 0, PAGE_SIZE);
+		for (j = 0; j < HASH_PER_PAGE; j++) {
+			struct trans_logger_hash_anchor *start = &sub_table[j];
+
+			init_rwsem(&start->hash_mutex);
+			INIT_LIST_HEAD(&start->hash_anchor);
+		}
+	}
+
+	atomic_set(&brick->hash_count, 0);
+	spin_lock_init(&brick->replay_lock);
+	INIT_LIST_HEAD(&brick->replay_list);
+	INIT_LIST_HEAD(&brick->group_head);
+	init_waitqueue_head(&brick->worker_event);
+	init_waitqueue_head(&brick->caller_event);
+	qq_init(&brick->q_phase[0], brick);
+	qq_init(&brick->q_phase[1], brick);
+	qq_init(&brick->q_phase[2], brick);
+	qq_init(&brick->q_phase[3], brick);
+	brick->q_phase[0].q_insert_info   = "q0_ins";
+	brick->q_phase[0].q_pushback_info = "q0_push";
+	brick->q_phase[0].q_fetch_info	  = "q0_fetch";
+	brick->q_phase[1].q_insert_info   = "q1_ins";
+	brick->q_phase[1].q_pushback_info = "q1_push";
+	brick->q_phase[1].q_fetch_info	  = "q1_fetch";
+	brick->q_phase[2].q_insert_info   = "q2_ins";
+	brick->q_phase[2].q_pushback_info = "q2_push";
+	brick->q_phase[2].q_fetch_info	  = "q2_fetch";
+	brick->q_phase[3].q_insert_info   = "q3_ins";
+	brick->q_phase[3].q_pushback_info = "q3_push";
+	brick->q_phase[3].q_fetch_info	  = "q3_fetch";
+	brick->new_input_nr = TL_INPUT_LOG1;
+	brick->log_input_nr = TL_INPUT_LOG1;
+	brick->old_input_nr = TL_INPUT_LOG1;
+	add_to_group(&global_writeback, brick);
+	return 0;
+}
+
+static
+int trans_logger_brick_destruct(struct trans_logger_brick *brick)
+{
+	_free_pages(brick);
+	CHECK_HEAD_EMPTY(&brick->replay_list);
+	remove_from_group(&global_writeback, brick);
+	return 0;
+}
+
+static
+int trans_logger_output_construct(struct trans_logger_output *output)
+{
+	return 0;
+}
+
+static
+int trans_logger_input_construct(struct trans_logger_input *input)
+{
+	INIT_LIST_HEAD(&input->pos_list);
+	sema_init(&input->inf_mutex, 1);
+	return 0;
+}
+
+static
+int trans_logger_input_destruct(struct trans_logger_input *input)
+{
+	CHECK_HEAD_EMPTY(&input->pos_list);
+	return 0;
+}
+
+/************************ static structs ***********************/
+
+static struct trans_logger_brick_ops trans_logger_brick_ops = {
+	.brick_switch = trans_logger_switch,
+	.brick_statistics = trans_logger_statistics,
+	.reset_statistics = trans_logger_reset_statistics,
+};
+
+static struct trans_logger_output_ops trans_logger_output_ops = {
+	.xio_get_info = trans_logger_get_info,
+	.aio_get = trans_logger_io_get,
+	.aio_put = trans_logger_io_put,
+	.aio_io = trans_logger_io_io,
+};
+
+const struct trans_logger_input_type trans_logger_input_type = {
+	.type_name = "trans_logger_input",
+	.input_size = sizeof(struct trans_logger_input),
+	.input_construct = &trans_logger_input_construct,
+	.input_destruct = &trans_logger_input_destruct,
+};
+
+static const struct trans_logger_input_type *trans_logger_input_types[] = {
+	&trans_logger_input_type,
+	&trans_logger_input_type,
+	&trans_logger_input_type,
+	&trans_logger_input_type,
+	&trans_logger_input_type,
+	&trans_logger_input_type,
+};
+
+const struct trans_logger_output_type trans_logger_output_type = {
+	.type_name = "trans_logger_output",
+	.output_size = sizeof(struct trans_logger_output),
+	.master_ops = &trans_logger_output_ops,
+	.output_construct = &trans_logger_output_construct,
+};
+
+static const struct trans_logger_output_type *trans_logger_output_types[] = {
+	&trans_logger_output_type,
+};
+
+const struct trans_logger_brick_type trans_logger_brick_type = {
+	.type_name = "trans_logger_brick",
+	.brick_size = sizeof(struct trans_logger_brick),
+	.max_inputs = TL_INPUT_NR,
+	.max_outputs = 1,
+	.master_ops = &trans_logger_brick_ops,
+	.aspect_types = trans_logger_aspect_types,
+	.default_input_types = trans_logger_input_types,
+	.default_output_types = trans_logger_output_types,
+	.brick_construct = &trans_logger_brick_construct,
+	.brick_destruct = &trans_logger_brick_destruct,
+};
+EXPORT_SYMBOL_GPL(trans_logger_brick_type);
+
+/***************** module init stuff ************************/
+
+int __init init_xio_trans_logger(void)
+{
+	XIO_INF("init_trans_logger()\n");
+	return trans_logger_register_brick_type();
+}
+
+void exit_xio_trans_logger(void)
+{
+	XIO_INF("exit_trans_logger()\n");
+	trans_logger_unregister_brick_type();
+}
-- 
2.0.0

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