MFC r287103 (by avg): 5692 expose the number of hole blocks in a file

FreeBSD porting notes:
- only kernel-side changes are merged
- the new ioctl is not actually implemented yet
- thus, the goal is to synchronize DMU code

illumos/illumos-gate@2bcf0248e992f292c7b814458bcdce2f004925d6

https://www.illumos.org/issues/5692
we would like to expose the number of hole (sparse) blocks in a file.
this can be useful to for example if you want to fill in the holes with
some data; knowing the number of holes in advances allows you to report
progress on hole filling. We could use SEEK_HOLE to do that but it would
be O(n) where n is the number of holes present in the file.

Author: Max Grossman <max.grossman@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Boris Protopopov <bprotopopov@hotmail.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

1 files changed, 38 insertions, 13 deletions

diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c
index 840bd7c..2b61311 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c
@@ -1902,25 +1902,20 @@ int
 dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
 {
 	dnode_t *dn;
-	int i, err;
+	int err;
 
-	err = dnode_hold(os, object, FTAG, &dn);
-	if (err)
-		return (err);
 	/*
 	 * Sync any current changes before
 	 * we go trundling through the block pointers.
 	 */
-	for (i = 0; i < TXG_SIZE; i++) {
-		if (list_link_active(&dn->dn_dirty_link[i]))
-			break;
+	err = dmu_object_wait_synced(os, object);
+	if (err) {
+		return (err);
 	}
-	if (i != TXG_SIZE) {
-		dnode_rele(dn, FTAG);
-		txg_wait_synced(dmu_objset_pool(os), 0);
-		err = dnode_hold(os, object, FTAG, &dn);
-		if (err)
-			return (err);
+
+	err = dnode_hold(os, object, FTAG, &dn);
+	if (err) {
+		return (err);
 	}
 
 	err = dnode_next_offset(dn, (hole ? DNODE_FIND_HOLE : 0), off, 1, 1, 0);
@@ -1929,6 +1924,36 @@ dmu_offset_next(objset_t *os, uint64_t object, boolean_t hole, uint64_t *off)
 	return (err);
 }
 
+/*
+ * Given the ZFS object, if it contains any dirty nodes
+ * this function flushes all dirty blocks to disk. This
+ * ensures the DMU object info is updated. A more efficient
+ * future version might just find the TXG with the maximum
+ * ID and wait for that to be synced.
+ */
+int
+dmu_object_wait_synced(objset_t *os, uint64_t object) {
+	dnode_t *dn;
+	int error, i;
+
+	error = dnode_hold(os, object, FTAG, &dn);
+	if (error) {
+		return (error);
+	}
+
+	for (i = 0; i < TXG_SIZE; i++) {
+		if (list_link_active(&dn->dn_dirty_link[i])) {
+			break;
+		}
+	}
+	dnode_rele(dn, FTAG);
+	if (i != TXG_SIZE) {
+		txg_wait_synced(dmu_objset_pool(os), 0);
+	}
+
+	return (0);
+}
+
 void
 dmu_object_info_from_dnode(dnode_t *dn, dmu_object_info_t *doi)
 {