Merge tag 'for-6.9/dm-vdo' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

Pull device mapper VDO target from Mike Snitzer:
 "Introduce the DM vdo target which provides block-level deduplication,
  compression, and thin provisioning. Please see:

      Documentation/admin-guide/device-mapper/vdo.rst
      Documentation/admin-guide/device-mapper/vdo-design.rst

  The DM vdo target handles its concurrency by pinning an IO, and
  subsequent stages of handling that IO, to a particular VDO thread.
  This aspect of VDO is "unique" but its overall implementation is very
  tightly coupled to its mostly lockless threading model. As such, VDO
  is not easily changed to use more traditional finer-grained locking
  and Linux workqueues. Please see the "Zones and Threading" section of
  vdo-design.rst

  The DM vdo target has been used in production for many years but has
  seen significant changes over the past ~6 years to prepare it for
  upstream inclusion. The codebase is still large but it is isolated to
  drivers/md/dm-vdo/ and has been made considerably more approachable
  and maintainable.

  Matt Sakai has been added to the MAINTAINERS file to reflect that he
  will send VDO changes upstream through the DM subsystem maintainers"

* tag 'for-6.9/dm-vdo' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm: (142 commits)
  dm vdo: document minimum metadata size requirements
  dm vdo: remove meaningless version number constant
  dm vdo: remove vdo_perform_once
  dm vdo block-map: Remove stray semicolon
  dm vdo string-utils: change from uds_ to vdo_ namespace
  dm vdo logger: change from uds_ to vdo_ namespace
  dm vdo funnel-queue: change from uds_ to vdo_ namespace
  dm vdo indexer: fix use after free
  dm vdo logger: remove log level to string conversion code
  dm vdo: document log_level parameter
  dm vdo: add 'log_level' module parameter
  dm vdo: remove all sysfs interfaces
  dm vdo target: eliminate inappropriate uses of UDS_SUCCESS
  dm vdo indexer: update ASSERT and ASSERT_LOG_ONLY usage
  dm vdo encodings: update some stale comments
  dm vdo permassert: audit all of ASSERT to test for VDO_SUCCESS
  dm-vdo funnel-workqueue: return VDO_SUCCESS from make_simple_work_queue
  dm vdo thread-utils: return VDO_SUCCESS on vdo_create_thread success
  dm vdo int-map: return VDO_SUCCESS on success
  dm vdo: check for VDO_SUCCESS return value from memory-alloc functions
  ...

1 files changed, 432 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/message-stats.c b/drivers/md/dm-vdo/message-stats.c
new file mode 100644
index 000000000000..2802cf92922b
--- /dev/null
+++ b/drivers/md/dm-vdo/message-stats.c
@@ -0,0 +1,432 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#include "dedupe.h"
+#include "logger.h"
+#include "memory-alloc.h"
+#include "message-stats.h"
+#include "statistics.h"
+#include "thread-device.h"
+#include "vdo.h"
+
+static void write_u64(char *prefix, u64 value, char *suffix, char **buf,
+		      unsigned int *maxlen)
+{
+	int count;
+
+	count = scnprintf(*buf, *maxlen, "%s%llu%s", prefix == NULL ? "" : prefix,
+			  value, suffix == NULL ? "" : suffix);
+	*buf += count;
+	*maxlen -= count;
+}
+
+static void write_u32(char *prefix, u32 value, char *suffix, char **buf,
+		      unsigned int *maxlen)
+{
+	int count;
+
+	count = scnprintf(*buf, *maxlen, "%s%u%s", prefix == NULL ? "" : prefix,
+			  value, suffix == NULL ? "" : suffix);
+	*buf += count;
+	*maxlen -= count;
+}
+
+static void write_block_count_t(char *prefix, block_count_t value, char *suffix,
+				char **buf, unsigned int *maxlen)
+{
+	int count;
+
+	count = scnprintf(*buf, *maxlen, "%s%llu%s", prefix == NULL ? "" : prefix,
+			  value, suffix == NULL ? "" : suffix);
+	*buf += count;
+	*maxlen -= count;
+}
+
+static void write_string(char *prefix, char *value, char *suffix, char **buf,
+			 unsigned int *maxlen)
+{
+	int count;
+
+	count = scnprintf(*buf, *maxlen, "%s%s%s", prefix == NULL ? "" : prefix,
+			  value, suffix == NULL ? "" : suffix);
+	*buf += count;
+	*maxlen -= count;
+}
+
+static void write_bool(char *prefix, bool value, char *suffix, char **buf,
+		       unsigned int *maxlen)
+{
+	int count;
+
+	count = scnprintf(*buf, *maxlen, "%s%d%s", prefix == NULL ? "" : prefix,
+			  value, suffix == NULL ? "" : suffix);
+	*buf += count;
+	*maxlen -= count;
+}
+
+static void write_u8(char *prefix, u8 value, char *suffix, char **buf,
+		     unsigned int *maxlen)
+{
+	int count;
+
+	count = scnprintf(*buf, *maxlen, "%s%u%s", prefix == NULL ? "" : prefix,
+			  value, suffix == NULL ? "" : suffix);
+	*buf += count;
+	*maxlen -= count;
+}
+
+static void write_block_allocator_statistics(char *prefix,
+					     struct block_allocator_statistics *stats,
+					     char *suffix, char **buf,
+					     unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* The total number of slabs from which blocks may be allocated */
+	write_u64("slabCount : ", stats->slab_count, ", ", buf, maxlen);
+	/* The total number of slabs from which blocks have ever been allocated */
+	write_u64("slabsOpened : ", stats->slabs_opened, ", ", buf, maxlen);
+	/* The number of times since loading that a slab has been re-opened */
+	write_u64("slabsReopened : ", stats->slabs_reopened, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_commit_statistics(char *prefix, struct commit_statistics *stats,
+				    char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* The total number of items on which processing has started */
+	write_u64("started : ", stats->started, ", ", buf, maxlen);
+	/* The total number of items for which a write operation has been issued */
+	write_u64("written : ", stats->written, ", ", buf, maxlen);
+	/* The total number of items for which a write operation has completed */
+	write_u64("committed : ", stats->committed, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_recovery_journal_statistics(char *prefix,
+					      struct recovery_journal_statistics *stats,
+					      char *suffix, char **buf,
+					      unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Number of times the on-disk journal was full */
+	write_u64("diskFull : ", stats->disk_full, ", ", buf, maxlen);
+	/* Number of times the recovery journal requested slab journal commits. */
+	write_u64("slabJournalCommitsRequested : ",
+		  stats->slab_journal_commits_requested, ", ", buf, maxlen);
+	/* Write/Commit totals for individual journal entries */
+	write_commit_statistics("entries : ", &stats->entries, ", ", buf, maxlen);
+	/* Write/Commit totals for journal blocks */
+	write_commit_statistics("blocks : ", &stats->blocks, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_packer_statistics(char *prefix, struct packer_statistics *stats,
+				    char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Number of compressed data items written since startup */
+	write_u64("compressedFragmentsWritten : ",
+		  stats->compressed_fragments_written, ", ", buf, maxlen);
+	/* Number of blocks containing compressed items written since startup */
+	write_u64("compressedBlocksWritten : ",
+		  stats->compressed_blocks_written, ", ", buf, maxlen);
+	/* Number of VIOs that are pending in the packer */
+	write_u64("compressedFragmentsInPacker : ",
+		  stats->compressed_fragments_in_packer, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_slab_journal_statistics(char *prefix,
+					  struct slab_journal_statistics *stats,
+					  char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Number of times the on-disk journal was full */
+	write_u64("diskFullCount : ", stats->disk_full_count, ", ", buf, maxlen);
+	/* Number of times an entry was added over the flush threshold */
+	write_u64("flushCount : ", stats->flush_count, ", ", buf, maxlen);
+	/* Number of times an entry was added over the block threshold */
+	write_u64("blockedCount : ", stats->blocked_count, ", ", buf, maxlen);
+	/* Number of times a tail block was written */
+	write_u64("blocksWritten : ", stats->blocks_written, ", ", buf, maxlen);
+	/* Number of times we had to wait for the tail to write */
+	write_u64("tailBusyCount : ", stats->tail_busy_count, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_slab_summary_statistics(char *prefix,
+					  struct slab_summary_statistics *stats,
+					  char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Number of blocks written */
+	write_u64("blocksWritten : ", stats->blocks_written, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_ref_counts_statistics(char *prefix, struct ref_counts_statistics *stats,
+					char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Number of reference blocks written */
+	write_u64("blocksWritten : ", stats->blocks_written, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_block_map_statistics(char *prefix, struct block_map_statistics *stats,
+				       char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* number of dirty (resident) pages */
+	write_u32("dirtyPages : ", stats->dirty_pages, ", ", buf, maxlen);
+	/* number of clean (resident) pages */
+	write_u32("cleanPages : ", stats->clean_pages, ", ", buf, maxlen);
+	/* number of free pages */
+	write_u32("freePages : ", stats->free_pages, ", ", buf, maxlen);
+	/* number of pages in failed state */
+	write_u32("failedPages : ", stats->failed_pages, ", ", buf, maxlen);
+	/* number of pages incoming */
+	write_u32("incomingPages : ", stats->incoming_pages, ", ", buf, maxlen);
+	/* number of pages outgoing */
+	write_u32("outgoingPages : ", stats->outgoing_pages, ", ", buf, maxlen);
+	/* how many times free page not avail */
+	write_u32("cachePressure : ", stats->cache_pressure, ", ", buf, maxlen);
+	/* number of get_vdo_page() calls for read */
+	write_u64("readCount : ", stats->read_count, ", ", buf, maxlen);
+	/* number of get_vdo_page() calls for write */
+	write_u64("writeCount : ", stats->write_count, ", ", buf, maxlen);
+	/* number of times pages failed to read */
+	write_u64("failedReads : ", stats->failed_reads, ", ", buf, maxlen);
+	/* number of times pages failed to write */
+	write_u64("failedWrites : ", stats->failed_writes, ", ", buf, maxlen);
+	/* number of gets that are reclaimed */
+	write_u64("reclaimed : ", stats->reclaimed, ", ", buf, maxlen);
+	/* number of gets for outgoing pages */
+	write_u64("readOutgoing : ", stats->read_outgoing, ", ", buf, maxlen);
+	/* number of gets that were already there */
+	write_u64("foundInCache : ", stats->found_in_cache, ", ", buf, maxlen);
+	/* number of gets requiring discard */
+	write_u64("discardRequired : ", stats->discard_required, ", ", buf, maxlen);
+	/* number of gets enqueued for their page */
+	write_u64("waitForPage : ", stats->wait_for_page, ", ", buf, maxlen);
+	/* number of gets that have to fetch */
+	write_u64("fetchRequired : ", stats->fetch_required, ", ", buf, maxlen);
+	/* number of page fetches */
+	write_u64("pagesLoaded : ", stats->pages_loaded, ", ", buf, maxlen);
+	/* number of page saves */
+	write_u64("pagesSaved : ", stats->pages_saved, ", ", buf, maxlen);
+	/* the number of flushes issued */
+	write_u64("flushCount : ", stats->flush_count, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_hash_lock_statistics(char *prefix, struct hash_lock_statistics *stats,
+				       char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Number of times the UDS advice proved correct */
+	write_u64("dedupeAdviceValid : ", stats->dedupe_advice_valid, ", ", buf, maxlen);
+	/* Number of times the UDS advice proved incorrect */
+	write_u64("dedupeAdviceStale : ", stats->dedupe_advice_stale, ", ", buf, maxlen);
+	/* Number of writes with the same data as another in-flight write */
+	write_u64("concurrentDataMatches : ", stats->concurrent_data_matches,
+		  ", ", buf, maxlen);
+	/* Number of writes whose hash collided with an in-flight write */
+	write_u64("concurrentHashCollisions : ",
+		  stats->concurrent_hash_collisions, ", ", buf, maxlen);
+	/* Current number of dedupe queries that are in flight */
+	write_u32("currDedupeQueries : ", stats->curr_dedupe_queries, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_error_statistics(char *prefix, struct error_statistics *stats,
+				   char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* number of times VDO got an invalid dedupe advice PBN from UDS */
+	write_u64("invalidAdvicePBNCount : ", stats->invalid_advice_pbn_count,
+		  ", ", buf, maxlen);
+	/* number of times a VIO completed with a VDO_NO_SPACE error */
+	write_u64("noSpaceErrorCount : ", stats->no_space_error_count, ", ",
+		  buf, maxlen);
+	/* number of times a VIO completed with a VDO_READ_ONLY error */
+	write_u64("readOnlyErrorCount : ", stats->read_only_error_count, ", ",
+		  buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_bio_stats(char *prefix, struct bio_stats *stats, char *suffix,
+			    char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Number of REQ_OP_READ bios */
+	write_u64("read : ", stats->read, ", ", buf, maxlen);
+	/* Number of REQ_OP_WRITE bios with data */
+	write_u64("write : ", stats->write, ", ", buf, maxlen);
+	/* Number of bios tagged with REQ_PREFLUSH and containing no data */
+	write_u64("emptyFlush : ", stats->empty_flush, ", ", buf, maxlen);
+	/* Number of REQ_OP_DISCARD bios */
+	write_u64("discard : ", stats->discard, ", ", buf, maxlen);
+	/* Number of bios tagged with REQ_PREFLUSH */
+	write_u64("flush : ", stats->flush, ", ", buf, maxlen);
+	/* Number of bios tagged with REQ_FUA */
+	write_u64("fua : ", stats->fua, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_memory_usage(char *prefix, struct memory_usage *stats, char *suffix,
+			       char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Tracked bytes currently allocated. */
+	write_u64("bytesUsed : ", stats->bytes_used, ", ", buf, maxlen);
+	/* Maximum tracked bytes allocated. */
+	write_u64("peakBytesUsed : ", stats->peak_bytes_used, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_index_statistics(char *prefix, struct index_statistics *stats,
+				   char *suffix, char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	/* Number of records stored in the index */
+	write_u64("entriesIndexed : ", stats->entries_indexed, ", ", buf, maxlen);
+	/* Number of post calls that found an existing entry */
+	write_u64("postsFound : ", stats->posts_found, ", ", buf, maxlen);
+	/* Number of post calls that added a new entry */
+	write_u64("postsNotFound : ", stats->posts_not_found, ", ", buf, maxlen);
+	/* Number of query calls that found an existing entry */
+	write_u64("queriesFound : ", stats->queries_found, ", ", buf, maxlen);
+	/* Number of query calls that added a new entry */
+	write_u64("queriesNotFound : ", stats->queries_not_found, ", ", buf, maxlen);
+	/* Number of update calls that found an existing entry */
+	write_u64("updatesFound : ", stats->updates_found, ", ", buf, maxlen);
+	/* Number of update calls that added a new entry */
+	write_u64("updatesNotFound : ", stats->updates_not_found, ", ", buf, maxlen);
+	/* Number of entries discarded */
+	write_u64("entriesDiscarded : ", stats->entries_discarded, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+static void write_vdo_statistics(char *prefix, struct vdo_statistics *stats, char *suffix,
+				 char **buf, unsigned int *maxlen)
+{
+	write_string(prefix, "{ ", NULL, buf, maxlen);
+	write_u32("version : ", stats->version, ", ", buf, maxlen);
+	/* Number of blocks used for data */
+	write_u64("dataBlocksUsed : ", stats->data_blocks_used, ", ", buf, maxlen);
+	/* Number of blocks used for VDO metadata */
+	write_u64("overheadBlocksUsed : ", stats->overhead_blocks_used, ", ",
+		  buf, maxlen);
+	/* Number of logical blocks that are currently mapped to physical blocks */
+	write_u64("logicalBlocksUsed : ", stats->logical_blocks_used, ", ", buf, maxlen);
+	/* number of physical blocks */
+	write_block_count_t("physicalBlocks : ", stats->physical_blocks, ", ",
+			    buf, maxlen);
+	/* number of logical blocks */
+	write_block_count_t("logicalBlocks : ", stats->logical_blocks, ", ",
+			    buf, maxlen);
+	/* Size of the block map page cache, in bytes */
+	write_u64("blockMapCacheSize : ", stats->block_map_cache_size, ", ",
+		  buf, maxlen);
+	/* The physical block size */
+	write_u64("blockSize : ", stats->block_size, ", ", buf, maxlen);
+	/* Number of times the VDO has successfully recovered */
+	write_u64("completeRecoveries : ", stats->complete_recoveries, ", ",
+		  buf, maxlen);
+	/* Number of times the VDO has recovered from read-only mode */
+	write_u64("readOnlyRecoveries : ", stats->read_only_recoveries, ", ",
+		  buf, maxlen);
+	/* String describing the operating mode of the VDO */
+	write_string("mode : ", stats->mode, ", ", buf, maxlen);
+	/* Whether the VDO is in recovery mode */
+	write_bool("inRecoveryMode : ", stats->in_recovery_mode, ", ", buf, maxlen);
+	/* What percentage of recovery mode work has been completed */
+	write_u8("recoveryPercentage : ", stats->recovery_percentage, ", ", buf, maxlen);
+	/* The statistics for the compressed block packer */
+	write_packer_statistics("packer : ", &stats->packer, ", ", buf, maxlen);
+	/* Counters for events in the block allocator */
+	write_block_allocator_statistics("allocator : ", &stats->allocator,
+					 ", ", buf, maxlen);
+	/* Counters for events in the recovery journal */
+	write_recovery_journal_statistics("journal : ", &stats->journal, ", ",
+					  buf, maxlen);
+	/* The statistics for the slab journals */
+	write_slab_journal_statistics("slabJournal : ", &stats->slab_journal,
+				      ", ", buf, maxlen);
+	/* The statistics for the slab summary */
+	write_slab_summary_statistics("slabSummary : ", &stats->slab_summary,
+				      ", ", buf, maxlen);
+	/* The statistics for the reference counts */
+	write_ref_counts_statistics("refCounts : ", &stats->ref_counts, ", ",
+				    buf, maxlen);
+	/* The statistics for the block map */
+	write_block_map_statistics("blockMap : ", &stats->block_map, ", ", buf, maxlen);
+	/* The dedupe statistics from hash locks */
+	write_hash_lock_statistics("hashLock : ", &stats->hash_lock, ", ", buf, maxlen);
+	/* Counts of error conditions */
+	write_error_statistics("errors : ", &stats->errors, ", ", buf, maxlen);
+	/* The VDO instance */
+	write_u32("instance : ", stats->instance, ", ", buf, maxlen);
+	/* Current number of active VIOs */
+	write_u32("currentVIOsInProgress : ", stats->current_vios_in_progress,
+		  ", ", buf, maxlen);
+	/* Maximum number of active VIOs */
+	write_u32("maxVIOs : ", stats->max_vios, ", ", buf, maxlen);
+	/* Number of times the UDS index was too slow in responding */
+	write_u64("dedupeAdviceTimeouts : ", stats->dedupe_advice_timeouts,
+		  ", ", buf, maxlen);
+	/* Number of flush requests submitted to the storage device */
+	write_u64("flushOut : ", stats->flush_out, ", ", buf, maxlen);
+	/* Logical block size */
+	write_u64("logicalBlockSize : ", stats->logical_block_size, ", ", buf, maxlen);
+	/* Bios submitted into VDO from above */
+	write_bio_stats("biosIn : ", &stats->bios_in, ", ", buf, maxlen);
+	write_bio_stats("biosInPartial : ", &stats->bios_in_partial, ", ", buf, maxlen);
+	/* Bios submitted onward for user data */
+	write_bio_stats("biosOut : ", &stats->bios_out, ", ", buf, maxlen);
+	/* Bios submitted onward for metadata */
+	write_bio_stats("biosMeta : ", &stats->bios_meta, ", ", buf, maxlen);
+	write_bio_stats("biosJournal : ", &stats->bios_journal, ", ", buf, maxlen);
+	write_bio_stats("biosPageCache : ", &stats->bios_page_cache, ", ", buf, maxlen);
+	write_bio_stats("biosOutCompleted : ", &stats->bios_out_completed, ", ",
+			buf, maxlen);
+	write_bio_stats("biosMetaCompleted : ", &stats->bios_meta_completed,
+			", ", buf, maxlen);
+	write_bio_stats("biosJournalCompleted : ",
+			&stats->bios_journal_completed, ", ", buf, maxlen);
+	write_bio_stats("biosPageCacheCompleted : ",
+			&stats->bios_page_cache_completed, ", ", buf, maxlen);
+	write_bio_stats("biosAcknowledged : ", &stats->bios_acknowledged, ", ",
+			buf, maxlen);
+	write_bio_stats("biosAcknowledgedPartial : ",
+			&stats->bios_acknowledged_partial, ", ", buf, maxlen);
+	/* Current number of bios in progress */
+	write_bio_stats("biosInProgress : ", &stats->bios_in_progress, ", ",
+			buf, maxlen);
+	/* Memory usage stats. */
+	write_memory_usage("memoryUsage : ", &stats->memory_usage, ", ", buf, maxlen);
+	/* The statistics for the UDS index */
+	write_index_statistics("index : ", &stats->index, ", ", buf, maxlen);
+	write_string(NULL, "}", suffix, buf, maxlen);
+}
+
+int vdo_write_stats(struct vdo *vdo, char *buf, unsigned int maxlen)
+{
+	struct vdo_statistics *stats;
+	int result;
+
+	result = vdo_allocate(1, struct vdo_statistics, __func__, &stats);
+	if (result != VDO_SUCCESS) {
+		vdo_log_error("Cannot allocate memory to write VDO statistics");
+		return result;
+	}
+
+	vdo_fetch_statistics(vdo, stats);
+	write_vdo_statistics(NULL, stats, NULL, &buf, &maxlen);
+	vdo_free(stats);
+	return VDO_SUCCESS;
+}