Develop tests for issues #5866 and #8858

Provide zfstest coverage for these two issues which
were a panic accessing extended attributes and
a problem comparing 64 bit and 32 bit generation
numbers.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Zuchowski <pzuchowski@datto.com>
Issue #5866
Issue #8858 
Closes #8978

tests/zfs-tests/cmd/Makefile.am

@@ -19,6 +19,7 @@ SUBDIRS = \
 	mmap_libaio \
 	mmapwrite \
 	nvlist_to_lua \
+	online_recv \
 	randfree_file \
 	randwritecomp \
 	readmmap \

tests/zfs-tests/cmd/online_recv/.gitignore

@@ -0,0 +1 @@
+/online_recv

tests/zfs-tests/cmd/online_recv/Makefile.am

@@ -0,0 +1,15 @@
+include $(top_srcdir)/config/Rules.am
+
+pkgexecdir = $(datadir)/@PACKAGE@/zfs-tests/bin
+
+DEFAULT_INCLUDES += \
+	-I$(top_srcdir)/include \
+	-I$(top_srcdir)/lib/libspl/include
+
+pkgexec_PROGRAMS = online_recv
+
+online_recv_SOURCES = online_recv.c
+online_recv_LDADD = \
+	$(top_builddir)/lib/libspl/libspl.la \
+	$(top_builddir)/lib/libnvpair/libnvpair.la \
+	$(top_builddir)/lib/libzfs_core/libzfs_core.la

tests/zfs-tests/cmd/online_recv/online_recv.c

@@ -0,0 +1,52 @@
+/*
+ * CDDL HEADER START
+ *
+ * This file and its contents are supplied under the terms of the
+ * Common Development and Distribution License ("CDDL"), version 1.0.
+ * You may only use this file in accordance with the terms of version
+ * 1.0 of the CDDL.
+ *
+ * A full copy of the text of the CDDL should have accompanied this
+ * source.  A copy of the CDDL is also available via the Internet at
+ * http://www.illumos.org/license/CDDL.
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2019 by Datto, Inc. All rights reserved.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <libzfs_core.h>
+
+int zfs_fd;
+
+/*
+ * Use libzfs_core to do a "zfs receive".  This allows us to
+ * bypass certain checks in the zfs command utility and
+ * perform an online receive into an existing filesystem for
+ * testing purposes.
+ */
+int
+main(int argc, const char *argv[])
+{
+	int err = 0;
+
+	if (argc < 2) {
+		fprintf(stderr, "usage: online_recv <destination>\n");
+		exit(2);
+	}
+
+	(void) libzfs_core_init();
+
+	err = lzc_receive(argv[1], NULL, NULL, B_TRUE, B_FALSE, 0);
+
+	libzfs_core_fini();
+
+	return (err);
+}