honor zfs_send_set_freerecords_bit

instead of only not setting the DRR_FLAG_FREERECORDS flag, also don't
create any FREE or FREEOBJECTS records when creating a full stream with
zfs_send_set_freerecords_bit disabled.

this allows to re-use this parameter to workaround hanging zfs recv on
0.6.5.x systems.

Original Author: Paul Dagnelie <[email protected]>
Ported-By: Fabian Grünbichler <[email protected]>
Signed-Off-By: Fabian Grünbichler <[email protected]>

module/zfs/dmu_send.c

@@ -199,6 +199,9 @@ dump_record(dmu_sendarg_t *dsp, void *payload, int payload_len)
  * Note that we send free records even for a full send, because we want to be
  * able to receive a full send as a clone, which requires a list of all the free
  * and freeobject records that were generated on the source.
+ *
+ * Disable this behaviour by setting zfs_send_set_freerecords_bit to false to
+ * workaround receiving implementations that cannot handle such streams.
  */
 static int
 dump_free(dmu_sendarg_t *dsp, uint64_t object, uint64_t offset,
@@ -223,6 +226,16 @@ dump_free(dmu_sendarg_t *dsp, uint64_t object, uint64_t offset,
 	    (object == dsp->dsa_last_data_object &&
 	    offset > dsp->dsa_last_data_offset));
 
+	/*
+	 * If we are doing a non-incremental send, then there can't
+	 * be any data in the dataset we're receiving into.  Unless we're receiving
+	 * a full send as a clone, a free record would simply be a no-op.
+	 * If we disable the tunable for this, save space by not sending it to
+	 * begin with.
+	 */
+	if (!zfs_send_set_freerecords_bit && !dsp->dsa_drr->drr_u.drr_begin.drr_fromguid)
+		return (0);
+
 	if (length != -1ULL && offset + length < offset)
 		length = -1ULL;
 
@@ -455,6 +468,10 @@ dump_freeobjects(dmu_sendarg_t *dsp, uint64_t firstobj, uint64_t numobjs)
 {
 	struct drr_freeobjects *drrfo = &(dsp->dsa_drr->drr_u.drr_freeobjects);
 
+	/* See comment in dump_free(). */
+	if (!zfs_send_set_freerecords_bit && !dsp->dsa_drr->drr_u.drr_begin.drr_fromguid)
+		return (0);
+
 	/*
 	 * If there is a pending op, but it's not PENDING_FREEOBJECTS,
 	 * push it out, since free block aggregation can only be done for