diff --git a/scrub/Makefile b/scrub/Makefile
index 4d1c908..24e0c44 100644
--- a/scrub/Makefile
+++ b/scrub/Makefile
@@ -19,6 +19,7 @@ HFILES = \
 common.h \
 disk.h \
 inodes.h \
+spacemap.h \
 xfs_scrub.h
 
 CFILES = \
@@ -26,6 +27,7 @@ common.c \
 disk.c \
 inodes.c \
 phase1.c \
+spacemap.c \
 xfs_scrub.c
 
 LLDLIBS += $(LIBHANDLE) $(LIBFROG) $(LIBPTHREAD)
diff --git a/scrub/spacemap.c b/scrub/spacemap.c
new file mode 100644
index 0000000..2dc6e2b
--- /dev/null
+++ b/scrub/spacemap.c
@@ -0,0 +1,256 @@
+/*
+ * Copyright (C) 2018 Oracle.  All Rights Reserved.
+ *
+ * Author: Darrick J. Wong <darrick.wong@oracle.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+#include <pthread.h>
+#include <sys/statvfs.h>
+#include "workqueue.h"
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "path.h"
+#include "xfs_scrub.h"
+#include "common.h"
+#include "spacemap.h"
+
+/*
+ * Filesystem space map iterators.
+ *
+ * Logically, we call GETFSMAP to fetch a set of space map records and
+ * call a function to iterate over the records.  However, that's not
+ * what actually happens -- the work is split into separate items, with
+ * each AG, the realtime device, and the log device getting their own
+ * work items.  For an XFS with a realtime device and an external log,
+ * this means that we can have up to ($agcount + 2) threads running at
+ * once.
+ *
+ * This comes into play if we want to have per-workitem memory.  Maybe.
+ * XXX: do we really need all that ?
+ */
+
+#define FSMAP_NR	65536
+
+/* Iterate all the fs block mappings between the two keys. */
+bool
+xfs_iterate_fsmap(
+	struct scrub_ctx	*ctx,
+	const char		*descr,
+	struct fsmap		*keys,
+	xfs_fsmap_iter_fn	fn,
+	void			*arg)
+{
+	struct fsmap_head	*head;
+	struct fsmap		*p;
+	bool			moveon = true;
+	int			i;
+	int			error;
+
+	head = malloc(fsmap_sizeof(FSMAP_NR));
+	if (!head) {
+		str_errno(ctx, descr);
+		return false;
+	}
+
+	memset(head, 0, sizeof(*head));
+	memcpy(head->fmh_keys, keys, sizeof(struct fsmap) * 2);
+	head->fmh_count = FSMAP_NR;
+
+	while ((error = ioctl(ctx->mnt_fd, FS_IOC_GETFSMAP, head)) == 0) {
+		for (i = 0, p = head->fmh_recs;
+		     i < head->fmh_entries;
+		     i++, p++) {
+			moveon = fn(ctx, descr, p, arg);
+			if (!moveon)
+				goto out;
+			if (xfs_scrub_excessive_errors(ctx)) {
+				moveon = false;
+				goto out;
+			}
+		}
+
+		if (head->fmh_entries == 0)
+			break;
+		p = &head->fmh_recs[head->fmh_entries - 1];
+		if (p->fmr_flags & FMR_OF_LAST)
+			break;
+		fsmap_advance(head);
+	}
+
+	if (error) {
+		str_errno(ctx, descr);
+		moveon = false;
+	}
+out:
+	free(head);
+	return moveon;
+}
+
+/* GETFSMAP wrappers routines. */
+struct xfs_scan_blocks {
+	xfs_fsmap_iter_fn	fn;
+	void			*arg;
+	bool			moveon;
+};
+
+/* Iterate all the reverse mappings of an AG. */
+static void
+xfs_scan_ag_blocks(
+	struct workqueue	*wq,
+	xfs_agnumber_t		agno,
+	void			*arg)
+{
+	struct scrub_ctx	*ctx = (struct scrub_ctx *)wq->wq_ctx;
+	struct xfs_scan_blocks	*sbx = arg;
+	char			descr[DESCR_BUFSZ];
+	struct fsmap		keys[2];
+	off64_t			bperag;
+	bool			moveon;
+
+	bperag = (off64_t)ctx->geo.agblocks *
+		 (off64_t)ctx->geo.blocksize;
+
+	snprintf(descr, DESCR_BUFSZ, _("dev %d:%d AG %u fsmap"),
+				major(ctx->fsinfo.fs_datadev),
+				minor(ctx->fsinfo.fs_datadev),
+				agno);
+
+	memset(keys, 0, sizeof(struct fsmap) * 2);
+	keys->fmr_device = ctx->fsinfo.fs_datadev;
+	keys->fmr_physical = agno * bperag;
+	(keys + 1)->fmr_device = ctx->fsinfo.fs_datadev;
+	(keys + 1)->fmr_physical = ((agno + 1) * bperag) - 1;
+	(keys + 1)->fmr_owner = ULLONG_MAX;
+	(keys + 1)->fmr_offset = ULLONG_MAX;
+	(keys + 1)->fmr_flags = UINT_MAX;
+
+	moveon = xfs_iterate_fsmap(ctx, descr, keys, sbx->fn, sbx->arg);
+	if (!moveon)
+		sbx->moveon = false;
+}
+
+/* Iterate all the reverse mappings of a standalone device. */
+static void
+xfs_scan_dev_blocks(
+	struct scrub_ctx	*ctx,
+	int			idx,
+	dev_t			dev,
+	struct xfs_scan_blocks	*sbx)
+{
+	struct fsmap		keys[2];
+	char			descr[DESCR_BUFSZ];
+	bool			moveon;
+
+	snprintf(descr, DESCR_BUFSZ, _("dev %d:%d fsmap"),
+			major(dev), minor(dev));
+
+	memset(keys, 0, sizeof(struct fsmap) * 2);
+	keys->fmr_device = dev;
+	(keys + 1)->fmr_device = dev;
+	(keys + 1)->fmr_physical = ULLONG_MAX;
+	(keys + 1)->fmr_owner = ULLONG_MAX;
+	(keys + 1)->fmr_offset = ULLONG_MAX;
+	(keys + 1)->fmr_flags = UINT_MAX;
+
+	moveon = xfs_iterate_fsmap(ctx, descr, keys, sbx->fn, sbx->arg);
+	if (!moveon)
+		sbx->moveon = false;
+}
+
+/* Iterate all the reverse mappings of the realtime device. */
+static void
+xfs_scan_rt_blocks(
+	struct workqueue	*wq,
+	xfs_agnumber_t		agno,
+	void			*arg)
+{
+	struct scrub_ctx	*ctx = (struct scrub_ctx *)wq->wq_ctx;
+
+	xfs_scan_dev_blocks(ctx, agno, ctx->fsinfo.fs_rtdev, arg);
+}
+
+/* Iterate all the reverse mappings of the log device. */
+static void
+xfs_scan_log_blocks(
+	struct workqueue	*wq,
+	xfs_agnumber_t		agno,
+	void			*arg)
+{
+	struct scrub_ctx	*ctx = (struct scrub_ctx *)wq->wq_ctx;
+
+	xfs_scan_dev_blocks(ctx, agno, ctx->fsinfo.fs_logdev, arg);
+}
+
+/* Scan all the blocks in a filesystem. */
+bool
+xfs_scan_all_spacemaps(
+	struct scrub_ctx	*ctx,
+	xfs_fsmap_iter_fn	fn,
+	void			*arg)
+{
+	struct workqueue	wq;
+	struct xfs_scan_blocks	sbx;
+	xfs_agnumber_t		agno;
+	int			ret;
+
+	sbx.moveon = true;
+	sbx.fn = fn;
+	sbx.arg = arg;
+
+	ret = workqueue_create(&wq, (struct xfs_mount *)ctx,
+			scrub_nproc_workqueue(ctx));
+	if (ret) {
+		str_error(ctx, ctx->mntpoint, _("Could not create workqueue."));
+		return false;
+	}
+	if (ctx->fsinfo.fs_rt) {
+		ret = workqueue_add(&wq, xfs_scan_rt_blocks,
+				ctx->geo.agcount + 1, &sbx);
+		if (ret) {
+			sbx.moveon = false;
+			str_error(ctx, ctx->mntpoint,
+_("Could not queue rtdev fsmap work."));
+			goto out;
+		}
+	}
+	if (ctx->fsinfo.fs_log) {
+		ret = workqueue_add(&wq, xfs_scan_log_blocks,
+				ctx->geo.agcount + 2, &sbx);
+		if (ret) {
+			sbx.moveon = false;
+			str_error(ctx, ctx->mntpoint,
+_("Could not queue logdev fsmap work."));
+			goto out;
+		}
+	}
+	for (agno = 0; agno < ctx->geo.agcount; agno++) {
+		ret = workqueue_add(&wq, xfs_scan_ag_blocks, agno, &sbx);
+		if (ret) {
+			sbx.moveon = false;
+			str_error(ctx, ctx->mntpoint,
+_("Could not queue AG %u fsmap work."), agno);
+			break;
+		}
+	}
+out:
+	workqueue_destroy(&wq);
+
+	return sbx.moveon;
+}
diff --git a/scrub/spacemap.h b/scrub/spacemap.h
new file mode 100644
index 0000000..9ee46f7
--- /dev/null
+++ b/scrub/spacemap.h
@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2018 Oracle.  All Rights Reserved.
+ *
+ * Author: Darrick J. Wong <darrick.wong@oracle.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it would be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write the Free Software Foundation,
+ * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.
+ */
+#ifndef XFS_SCRUB_SPACEMAP_H_
+#define XFS_SCRUB_SPACEMAP_H_
+
+typedef bool (*xfs_fsmap_iter_fn)(struct scrub_ctx *ctx, const char *descr,
+		struct fsmap *fsr, void *arg);
+
+bool xfs_iterate_fsmap(struct scrub_ctx *ctx, const char *descr,
+		struct fsmap *keys, xfs_fsmap_iter_fn fn, void *arg);
+bool xfs_scan_all_spacemaps(struct scrub_ctx *ctx, xfs_fsmap_iter_fn fn,
+		void *arg);
+
+#endif /* XFS_SCRUB_SPACEMAP_H_ */
