dmfilemapd: do not wait if file has been truncated

The file block count stored in the filemap_monitor was lazily
initialised at the time of the first check. This causes problems
in the case that the file has been truncated between this time and
the time the daemon started: the initial block count and current
block count match and the daemon fails to detect a change.

Separate the setting of the block count from the check and make a
call to update the value at the start of _dmfilemapd().

WHATS_NEW_DM

@@ -1,5 +1,6 @@
 Version 1.02.141 - 
 ===============================
+  Accept truncated files in calls to dm_stats_update_regions_from_fd().
   Restore Warning by 5% increment when thin-pool is over 80% (1.02.138).
 
 Version 1.02.140 - 3rd May 2017

daemons/dmfilemapd/dmfilemapd.c

@@ -357,30 +357,33 @@ static int _parse_args(int argc, char **argv, struct filemap_monitor *fm)
 	return 1;
 }
 
-static int _filemap_fd_check_changed(struct filemap_monitor *fm)
+static int _filemap_fd_update_blocks(struct filemap_monitor *fm)
 {
-	int64_t blocks, old_blocks;
 	struct stat buf;
 
 	if (fm->fd < 0) {
 		log_error("Filemap fd is not open.");
-		return -1;
+		return 0;
 	}
 
 	if (fstat(fm->fd, &buf)) {
 		log_error("Failed to fstat filemap file descriptor.");
-		return -1;
+		return 0;
 	}
 
-	blocks = buf.st_blocks;
+	fm->blocks = buf.st_blocks;
 
-	/* first check? */
+	return 1;
-	if (fm->blocks < 0)
+}
-		old_blocks = buf.st_blocks;
-	else
-		old_blocks = fm->blocks;
 
-	fm->blocks = blocks;
+static int _filemap_fd_check_changed(struct filemap_monitor *fm)
+{
+	int64_t old_blocks;
+
+	old_blocks = fm->blocks;
+
+	if (!_filemap_fd_update_blocks(fm))
+		return -1;
 
 	return (fm->blocks != old_blocks);
 }
@@ -683,7 +686,10 @@ static int _update_regions(struct dm_stats *dms, struct filemap_monitor *fm)
 	for (region = regions; *region != DM_STATS_REGIONS_ALL; region++)
 		nr_regions++;
 
-	if (regions[0] != fm->group_id) {
+	if (!nr_regions)
+		log_warn("File contains no extents: exiting.");
+
+	if (nr_regions && (regions[0] != fm->group_id)) {
 		log_warn("group_id changed from " FMTu64 " to " FMTu64,
 			 fm->group_id, regions[0]);
 		fm->group_id = regions[0];
@@ -714,6 +720,9 @@ static int _dmfilemapd(struct filemap_monitor *fm)
 	if (!_filemap_monitor_set_notify(fm))
 		goto bad;
 
+	if (!_filemap_fd_update_blocks(fm))
+		goto bad;
+
 	if (!dm_stats_list(dms, DM_STATS_ALL_PROGRAMS)) {
 		log_error("Failed to list stats handle.");
 		goto bad;
@@ -747,17 +756,16 @@ static int _dmfilemapd(struct filemap_monitor *fm)
 		if ((check = _filemap_fd_check_changed(fm)) < 0)
 			goto bad;
 
-		if (!check)
+		if (check && !_update_regions(dms, fm))
-			goto wait;
-
-		if (!_update_regions(dms, fm))
 			goto bad;
 
+		running = !!fm->nr_regions;
+		if (!running)
+			continue;
+
 wait:
 		_filemap_monitor_wait(FILEMAPD_WAIT_USECS);
 
-		running = !!fm->nr_regions;
-
 		/* mode=inode termination condions */
 		if (fm->mode == DM_FILEMAPD_FOLLOW_INODE) {
 			if (!_filemap_monitor_check_file_unlinked(fm))

libdm/libdm-stats.c

@@ -4466,6 +4466,7 @@ static struct _extent *_stats_get_extents_for_file(struct dm_pool *mem, int fd,
 	return extents;
 
 bad:
+	*count = 0;
 	dm_pool_abandon_object(mem);
 	dm_free(buf);
 	return NULL;
@@ -4536,7 +4537,7 @@ static int _stats_unmap_regions(struct dm_stats *dms, uint64_t group_id,
 		region = &dms->regions[i];
 		nr_old++;
 
-		if (_find_extent(*count, extents,
+		if (extents && _find_extent(*count, extents,
 				  region->start, region->len)) {
 			ext.start = region->start;
 			ext.len = region->len;
@@ -4653,11 +4654,12 @@ static uint64_t *_stats_map_file_regions(struct dm_stats *dms, int fd,
          * causing complications in the error path.
          */
 	if (!(extent_mem = dm_pool_create("extents", sizeof(*extents))))
-		return_0;
+		return_NULL;
 
 	if (!(extents = _stats_get_extents_for_file(extent_mem, fd, count))) {
-		dm_pool_destroy(extent_mem);
+		log_very_verbose("No extents found in fd %d", fd);
-		return_0;
+		if (!update)
+			goto out;
 	}
 
 	if (update) {
@@ -4734,7 +4736,10 @@ static uint64_t *_stats_map_file_regions(struct dm_stats *dms, int fd,
 	if (bounds)
 		dm_free(hist_arg);
 
-	dm_pool_free(extent_mem, extents);
+	/* the extent table will be empty if the file has been truncated. */
+	if (extents)
+		dm_pool_free(extent_mem, extents);
+
 	dm_pool_destroy(extent_mem);
 
 	return regions;
@@ -4755,12 +4760,6 @@ out_remove:
 	*count = 0;
 
 out:
-	/*
-	 * The table of file extents in 'extents' is always built, so free
-	 * it explicitly: this will also free any 'old_extents' table that
-	 * was later allocated from the 'extent_mem' pool by this function.
-	 */
-	dm_pool_free(extent_mem, extents);
 	dm_pool_destroy(extent_mem);
 	dm_free(hist_arg);
 	dm_free(regions);
@@ -4872,7 +4871,8 @@ uint64_t *dm_stats_update_regions_from_fd(struct dm_stats *dms, int fd,
 	if (!dm_stats_list(dms, NULL))
 		goto bad;
 
-	if (regroup)
+	/* regroup if there are regions to group */
+	if (regroup && (*regions != DM_STATS_REGION_NOT_PRESENT))
 		if (!_stats_group_file_regions(dms, regions, count, alias))
 			goto bad;