Add JSON output support to channel programs

The changes piggyback JSON output support on top of channel programs 
(#6558).  This way the JSON output support is targeted to scripting 
use cases and is easily maintainable since it really only touches 
one function (zfs_do_channel_program()).

This patch ports Joyent's JSON nvlist library from illumos to enable 
easy JSON printing of channel program output nvlist.  To keep the 
delta small I also took advantage of the fact that printing in
zfs_do_channel_program() was almost always done before exiting 
the program.

Reviewed by: Matt Ahrens <mahrens@delphix.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alek Pinchuk <apinchuk@datto.com>
Closes #7281

cmd/zfs/zfs_main.c

@@ -27,6 +27,7 @@
  * Copyright (c) 2013 Steven Hartland.  All rights reserved.
  * Copyright 2016 Igor Kozhukhov <ikozhukhov@gmail.com>.
  * Copyright 2016 Nexenta Systems, Inc.
+ * Copyright (c) 2018 Datto Inc.
  */
 
 #include <assert.h>
@@ -358,7 +359,7 @@ get_usage(zfs_help_t idx)
 	case HELP_BOOKMARK:
 		return (gettext("\tbookmark <snapshot> <bookmark>\n"));
 	case HELP_CHANNEL_PROGRAM:
-		return (gettext("\tprogram [-n] [-t <instruction limit>] "
+		return (gettext("\tprogram [-jn] [-t <instruction limit>] "
 		    "[-m <memory limit (b)>] <pool> <program file> "
 		    "[lua args...]\n"));
 	case HELP_LOAD_KEY:
@@ -7220,11 +7221,11 @@ zfs_do_channel_program(int argc, char **argv)
 	nvlist_t *outnvl;
 	uint64_t instrlimit = ZCP_DEFAULT_INSTRLIMIT;
 	uint64_t memlimit = ZCP_DEFAULT_MEMLIMIT;
-	boolean_t sync_flag = B_TRUE;
+	boolean_t sync_flag = B_TRUE, json_output = B_FALSE;
 	zpool_handle_t *zhp;
 
 	/* check options */
-	while ((c = getopt(argc, argv, "nt:m:")) != -1) {
+	while ((c = getopt(argc, argv, "nt:m:j")) != -1) {
 		switch (c) {
 		case 't':
 		case 'm': {
@@ -7266,6 +7267,10 @@ zfs_do_channel_program(int argc, char **argv)
 			sync_flag = B_FALSE;
 			break;
 		}
+		case 'j': {
+			json_output = B_TRUE;
+			break;
+		}
 		case '?':
 			(void) fprintf(stderr, gettext("invalid option '%c'\n"),
 			    optopt);
@@ -7391,14 +7396,18 @@ zfs_do_channel_program(int argc, char **argv)
 		    gettext("Channel program execution failed:\n%s\n"),
 		    errstring);
 		if (ret == ETIME && instructions != 0)
-			(void) fprintf(stderr, "%llu Lua instructions\n",
+			(void) fprintf(stderr,
+			    gettext("%llu Lua instructions\n"),
 			    (u_longlong_t)instructions);
 	} else {
-		(void) printf("Channel program fully executed ");
-		if (nvlist_empty(outnvl)) {
-			(void) printf("with no return value.\n");
+		if (json_output) {
+			(void) nvlist_print_json(stdout, outnvl);
+		} else if (nvlist_empty(outnvl)) {
+			(void) fprintf(stdout, gettext("Channel program fully "
+			    "executed and did not produce output.\n"));
 		} else {
-			(void) printf("with return value:\n");
+			(void) fprintf(stdout, gettext("Channel program fully "
+			    "executed and produced output:\n"));
 			dump_nvlist(outnvl, 4);
 		}
 	}

configure.ac

@@ -205,6 +205,7 @@ AC_CONFIG_FILES([
 	tests/zfs-tests/tests/functional/cli_root/zfs_load-key/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zfs/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zfs_mount/Makefile
+	tests/zfs-tests/tests/functional/cli_root/zfs_program/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zfs_promote/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zfs_property/Makefile
 	tests/zfs-tests/tests/functional/cli_root/zfs_receive/Makefile

include/libnvpair.h

@@ -20,6 +20,7 @@
  */
 /*
  * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, Joyent, Inc. All rights reserved.
  */
 
 #ifndef	_LIBNVPAIR_H
@@ -46,6 +47,7 @@ extern int nvpair_value_match_regex(nvpair_t *, int, char *, regex_t *,
     char **);
 
 extern void nvlist_print(FILE *, nvlist_t *);
+int nvlist_print_json(FILE *, nvlist_t *);
 extern void dump_nvlist(nvlist_t *, int);
 
 /*

lib/libnvpair/Makefile.am

@@ -18,6 +18,7 @@ lib_LTLIBRARIES = libnvpair.la
 
 USER_C = \
 	libnvpair.c \
+	libnvpair_json.c \
 	nvpair_alloc_system.c
 
 KERNEL_C = \