[PATCH 0/1] add option to output JSON for multipathd command

[PATCH 0/1] add option to output JSON for multipathd command

[Todd Gill]

Hi,

I had earlier sent an email to dm-devel proposing we add a feature
in multipathd to output multipath map topology in JSON format. This
patch contains to the code for that feature.

Having an option for the  CLI to output in JSON would allow higher
level applications to more easily monitor/manage multipath.

I thought it was best to take advantage of some of the existing
snprintf_xxx functions rather than adding a library dependency
to multipathd.

Will add code for groups next if this is accepted.

Thanks,
Todd

Todd Gill (1):
  add display of map information in JSON format

 libmultipath/print.c      | 122 ++++++++++++++++++++++++++++++++++++++++++++++
 libmultipath/print.h      |  50 +++++++++++++++++++
 multipathd/cli.c          |   3 ++
 multipathd/cli.h          |   2 +
 multipathd/cli_handlers.c |  93 +++++++++++++++++++++++++++++++++++
 multipathd/cli_handlers.h |   2 +
 multipathd/main.c         |   2 +
 7 files changed, 274 insertions(+)

-- 
2.5.5

[PATCH 1/1] add display of map information in JSON format

[Todd Gill]

The patch adds these commands:

multipathd show maps json
multipathd show map $map json

Each command will output the requested map(s) in JSON.

For the "show maps json" command, the patch pre-allocates
INITIAL_REPLY_LEN * 5.  The JSON text is about 5x the size of
the "show maps topology" text.

Signed-off-by: Todd Gill <tgill@redhat.com>
---
 libmultipath/print.c      | 122 ++++++++++++++++++++++++++++++++++++++++++++++
 libmultipath/print.h      |  50 +++++++++++++++++++
 multipathd/cli.c          |   3 ++
 multipathd/cli.h          |   2 +
 multipathd/cli_handlers.c |  93 +++++++++++++++++++++++++++++++++++
 multipathd/cli_handlers.h |   2 +
 multipathd/main.c         |   2 +
 7 files changed, 274 insertions(+)

diff --git a/libmultipath/print.c b/libmultipath/print.c
index 7fec6e9..818c634 100644
--- a/libmultipath/print.c
+++ b/libmultipath/print.c
@@ -998,6 +998,128 @@ snprint_multipath_topology (char * buff, int len, struct multipath * mpp,
 	}
 	return fwd;
 }
+int
+snprint_json (char * line, int len, int indent, char *json_str)
+{
+	int fwd = 0, i;
+
+	for (i = 0; i < indent; i++) {
+		fwd += snprintf(line + fwd, len - fwd, "\t");
+	}
+
+	fwd += snprintf(line + fwd, len - fwd, "%s", json_str);
+
+	return fwd;
+}
+
+int
+snprint_json_elem_footer (char * line, int len, int indent, int last)
+{
+	int fwd = 0, i;
+
+	for (i = 0; i < indent; i++) {
+		fwd += snprintf(line + fwd, len - fwd, "\t");
+	}
+
+	if (last == 1)
+		fwd += snprintf(line + fwd, len - fwd, "%s",
+				PRINT_JSON_END_LAST);
+	else
+		fwd += snprintf(line + fwd, len - fwd, "%s",
+				PRINT_JSON_END_ELEM);
+
+	return fwd;
+}
+
+int
+snprint_multipath_json (char * buff, int len, struct multipath * mpp, int last)
+{
+	int i, fwd = 0;
+	struct path *pp;
+
+	fwd +=  snprint_json(buff + fwd,
+			len - fwd, 1, PRINT_JSON_START_ELEM);
+	if (fwd > len)
+		return len;
+
+	fwd += snprint_multipath(buff + fwd, len - fwd,
+			PRINT_JSON_MAP, mpp, 0);
+	if (fwd > len)
+		return len;
+
+	fwd +=  snprint_json(buff + fwd,
+		len - fwd, 1, PRINT_JSON_START_PATHS);
+	if (fwd > len)
+		return len;
+
+	fwd +=  snprint_json(buff + fwd,
+			len - fwd, 0, PRINT_JSON_START_ARRAY);
+	if (fwd > len)
+		return len;
+
+	vector_foreach_slot (mpp->paths, pp, i) {
+		fwd +=  snprint_json(buff + fwd,
+			len - fwd, 2, PRINT_JSON_START_ELEM);
+		if (fwd > len)
+			return len;
+
+		fwd += snprint_path(buff + fwd,
+			len - fwd, PRINT_JSON_PATH, pp, 0);
+		if (fwd > len)
+			return len;
+
+		fwd +=  snprint_json_elem_footer(buff + fwd,
+			len - fwd, 2, i + 1 == VECTOR_SIZE(mpp->paths));
+		if (fwd > len)
+			return len;
+	}
+	fwd +=  snprint_json(buff + fwd,
+		len - fwd, 1, PRINT_JSON_END_ARRAY);
+	if (fwd > len)
+		return len;
+
+	fwd +=  snprint_json_elem_footer(buff + fwd, len - fwd, 1, last);
+	if (fwd > len)
+		return len;
+
+	return fwd;
+}
+
+int
+snprint_multipath_topology_json (char * buff, int len, struct vectors * vecs)
+{
+	int i, fwd = 0;
+	struct multipath * mpp;
+
+	memset(buff, 0, len);
+	fwd +=  snprint_json(buff, len, 0,
+			PRINT_JSON_START_ELEM PRINT_JSON_START_MAPS);
+	if (fwd > len)
+		return len;
+
+	fwd +=  snprint_json(buff + fwd,
+			len - fwd, 0, PRINT_JSON_START_ARRAY);
+	if (fwd > len)
+		return len;
+
+	vector_foreach_slot(vecs->mpvec, mpp, i) {
+		fwd += snprint_multipath_json(buff + fwd, len - fwd,
+				mpp, i + 1 == VECTOR_SIZE(vecs->mpvec));
+		if (fwd > len)
+			return len;
+	}
+
+	fwd +=  snprint_json(buff + fwd,
+		len - fwd, 0, PRINT_JSON_END_ARRAY);
+	if (fwd > len)
+		return len;
+
+	fwd +=  snprint_json(buff + fwd, len - fwd, 0, PRINT_JSON_END_MAPS);
+	if (fwd > len)
+		return len;
+
+	return fwd;
+}
 
 static int
 snprint_hwentry (char * buff, int len, struct hwentry * hwe)
diff --git a/libmultipath/print.h b/libmultipath/print.h
index 8bd0bbc..4d6b3ef 100644
--- a/libmultipath/print.h
+++ b/libmultipath/print.h
@@ -7,6 +7,52 @@
 #define PRINT_MAP_PROPS      "size=%S features='%f' hwhandler='%h' wp=%r"
 #define PRINT_PG_INDENT      "policy='%s' prio=%p status=%t"
 
+#define PRINT_JSON_START_ARRAY    "[\n"
+#define PRINT_JSON_START_ELEM     "{\n"
+#define PRINT_JSON_START_MAPS     "\"maps\":"
+#define PRINT_JSON_END_MAPS       "}  \n"
+#define PRINT_JSON_START_PATHS    "\"paths\":"
+#define PRINT_JSON_END_ELEM       "},\n"
+#define PRINT_JSON_END_LAST       "}\n"
+#define PRINT_JSON_END_ARRAY      "]\n"
+#define PRINT_JSON_MAP       "\t\"name\" : \"%n\",\n" \
+                             "\t\"uuid\" : \"%w\",\n" \
+                             "\t\"sysfs\" : \"%d\",\n" \
+                             "\t\"failback\" : \"%F\",\n" \
+                             "\t\"queueing\" : \"%Q\",\n" \
+                             "\t\"paths\" : \"%N\",\n" \
+                             "\t\"write_prot\" : \"%r\",\n" \
+                             "\t\"dm-st\" : \"%t\",\n" \
+                             "\t\"size\" : \"%S\",\n" \
+                             "\t\"features\" : \"%f\",\n" \
+                             "\t\"hwhandler\" : \"%h\",\n" \
+                             "\t\"action\" : \"%A\",\n" \
+                             "\t\"path_faults\" : \"%0\",\n" \
+                             "\t\"vend/prod/rev\" : \"%s\",\n" \
+                             "\t\"switch_grp\" : \"%1\",\n" \
+                             "\t\"map_loads\" : \"%2\",\n" \
+                             "\t\"total_q_time\" : \"%3\",\n" \
+                             "\t\"q_timeouts\" : \"%4\","
+
+#define PRINT_JSON_PATH      "\t\t\"uuid\" : \"%w\",\n" \
+                             "\t\t\"hcil\" : \"%i\",\n" \
+                             "\t\t\"dev\" : \"%d\",\n"\
+                             "\t\t\"dev_t\" : \"%D\",\n" \
+                             "\t\t\"dm_st\" : \"%t\",\n" \
+                             "\t\t\"dev_st\" : \"%o\",\n" \
+                             "\t\t\"chk_st\" : \"%T\",\n" \
+                             "\t\t\"vend/prod/rev\" : \"%s\",\n" \
+                             "\t\t\"checker\" : \"%c\",\n" \
+                             "\t\t\"next_check\" : \"%C\",\n" \
+                             "\t\t\"pri\" : \"%p\",\n" \
+                             "\t\t\"size\" : \"%S\",\n" \
+                             "\t\t\"serial\" : \"%z\",\n" \
+                             "\t\t\"multipath\" : \"%m\",\n" \
+                             "\t\t\"host WWNN\" : \"%N\",\n" \
+                             "\t\t\"target WWNN\" : \"%n\",\n" \
+                             "\t\t\"host WWPN\" : \"%R\",\n" \
+                             "\t\t\"target WWPN\" : \"%r\",\n" \
+                             "\t\t\"host adapter\" : \"%a\""
 #define MAX_LINE_LEN  80
 #define MAX_LINES     64
 #define MAX_FIELD_LEN 64
@@ -41,6 +87,10 @@ int snprint_path (char *, int, char *, struct path *, int);
 int snprint_multipath (char *, int, char *, struct multipath *, int);
 int snprint_multipath_topology (char *, int, struct multipath * mpp,
 				int verbosity);
+int snprint_multipath_topology_json (char * buff, int len,
+				struct vectors * vecs);
+int snprint_multipath_json (char * buff, int len,
+				struct multipath * mpp, int last);
 int snprint_defaults (char *, int);
 int snprint_blacklist (char *, int);
 int snprint_blacklist_except (char *, int);
diff --git a/multipathd/cli.c b/multipathd/cli.c
index d991cd0..20ee3db 100644
--- a/multipathd/cli.c
+++ b/multipathd/cli.c
@@ -207,6 +207,7 @@ load_keys (void)
 	r += add_key(keys, "setprstatus", SETPRSTATUS, 0);
 	r += add_key(keys, "unsetprstatus", UNSETPRSTATUS, 0);
 	r += add_key(keys, "format", FMT, 1);
+	r += add_key(keys, "json", JSON, 0);
 
 	if (r) {
 		free_keys(keys);
@@ -537,8 +538,10 @@ cli_init (void) {
 	add_handler(LIST+MAPS+FMT, NULL);
 	add_handler(LIST+MAPS+RAW+FMT, NULL);
 	add_handler(LIST+MAPS+TOPOLOGY, NULL);
+	add_handler(LIST+MAPS+JSON, NULL);
 	add_handler(LIST+TOPOLOGY, NULL);
 	add_handler(LIST+MAP+TOPOLOGY, NULL);
+	add_handler(LIST+MAP+JSON, NULL);
 	add_handler(LIST+MAP+FMT, NULL);
 	add_handler(LIST+MAP+RAW+FMT, NULL);
 	add_handler(LIST+CONFIG, NULL);
diff --git a/multipathd/cli.h b/multipathd/cli.h
index 84ca40f..92cb41b 100644
--- a/multipathd/cli.h
+++ b/multipathd/cli.h
@@ -36,6 +36,7 @@ enum {
 	__SETPRSTATUS,
 	__UNSETPRSTATUS,
 	__FMT,
+	__JSON,
 };
 
 #define LIST		(1 << __LIST)
@@ -74,6 +75,7 @@ enum {
 #define SETPRSTATUS	(1ULL << __SETPRSTATUS)
 #define UNSETPRSTATUS	(1ULL << __UNSETPRSTATUS)
 #define FMT		(1ULL << __FMT)
+#define JSON		(1ULL << __JSON)
 
 #define INITIAL_REPLY_LEN	1200
 
diff --git a/multipathd/cli_handlers.c b/multipathd/cli_handlers.c
index 0397353..a1ce916 100644
--- a/multipathd/cli_handlers.c
+++ b/multipathd/cli_handlers.c
@@ -156,6 +156,70 @@ show_maps_topology (char ** r, int * len, struct vectors * vecs)
 }
 
 int
+show_maps_json (char ** r, int * len, struct vectors * vecs)
+{
+	int i;
+	struct multipath * mpp;
+	char * c;
+	char * reply;
+	unsigned int maxlen = INITIAL_REPLY_LEN * 5;
+	int again = 1;
+
+	vector_foreach_slot(vecs->mpvec, mpp, i) {
+		if (update_multipath(vecs, mpp->alias, 0)) {
+			return 1;
+		}
+	}
+
+	reply = MALLOC(maxlen);
+
+	while (again) {
+		if (!reply)
+			return 1;
+
+		c = reply;
+
+		c += snprint_multipath_topology_json(c, reply + maxlen - c,
+				vecs);
+		again = ((c - reply) == maxlen);
+
+		REALLOC_REPLY(reply, again, maxlen);
+	}
+	*r = reply;
+	*len = (int)(c - reply + 1);
+	return 0;
+}
+
+int
+show_map_json (char ** r, int * len, struct multipath * mpp,
+		   struct vectors * vecs)
+{
+	char * c;
+	char * reply;
+	unsigned int maxlen = INITIAL_REPLY_LEN;
+	int again = 1;
+
+	if (update_multipath(vecs, mpp->alias, 0))
+		return 1;
+	reply = MALLOC(maxlen);
+
+	while (again) {
+		if (!reply)
+			return 1;
+
+		c = reply;
+
+		c += snprint_multipath_json(c, reply + maxlen - c, mpp, 1);
+		again = ((c - reply) == maxlen);
+
+		REALLOC_REPLY(reply, again, maxlen);
+	}
+	*r = reply;
+	*len = (int)(c - reply + 1);
+	return 0;
+}
+
+int
 show_config (char ** r, int * len)
 {
 	char * c;
@@ -291,6 +355,35 @@ cli_list_maps_topology (void * v, char ** reply, int * len, void * data)
 }
 
 int
+cli_list_map_json (void * v, char ** reply, int * len, void * data)
+{
+	struct multipath * mpp;
+	struct vectors * vecs = (struct vectors *)data;
+	char * param = get_keyparam(v, MAP);
+
+	param = convert_dev(param, 0);
+	get_path_layout(vecs->pathvec, 0);
+	mpp = find_mp_by_str(vecs->mpvec, param);
+
+	if (!mpp)
+		return 1;
+
+	condlog(3, "list multipath json %s (operator)", param);
+
+	return show_map_json(reply, len, mpp, vecs);
+}
+
+int
+cli_list_maps_json (void * v, char ** reply, int * len, void * data)
+{
+	struct vectors * vecs = (struct vectors *)data;
+
+	condlog(3, "list multipaths json (operator)");
+
+	return show_maps_json(reply, len, vecs);
+}
+
+int
 cli_list_wildcards (void * v, char ** reply, int * len, void * data)
 {
 	char * c;
diff --git a/multipathd/cli_handlers.h b/multipathd/cli_handlers.h
index 5d51018..e838f19 100644
--- a/multipathd/cli_handlers.h
+++ b/multipathd/cli_handlers.h
@@ -13,6 +13,8 @@ int cli_list_maps_status (void * v, char ** reply, int * len, void * data);
 int cli_list_maps_stats (void * v, char ** reply, int * len, void * data);
 int cli_list_map_topology (void * v, char ** reply, int * len, void * data);
 int cli_list_maps_topology (void * v, char ** reply, int * len, void * data);
+int cli_list_map_json (void * v, char ** reply, int * len, void * data);
+int cli_list_maps_json (void * v, char ** reply, int * len, void * data);
 int cli_list_config (void * v, char ** reply, int * len, void * data);
 int cli_list_blacklist (void * v, char ** reply, int * len, void * data);
 int cli_list_devices (void * v, char ** reply, int * len, void * data);
diff --git a/multipathd/main.c b/multipathd/main.c
index 58e8854..33f38cd 100644
--- a/multipathd/main.c
+++ b/multipathd/main.c
@@ -1120,9 +1120,11 @@ uxlsnrloop (void * ap)
 	set_handler_callback(LIST+MAPS+RAW+FMT, cli_list_maps_raw);
 	set_handler_callback(LIST+MAPS+TOPOLOGY, cli_list_maps_topology);
 	set_handler_callback(LIST+TOPOLOGY, cli_list_maps_topology);
+	set_handler_callback(LIST+MAPS+JSON, cli_list_maps_json);
 	set_handler_callback(LIST+MAP+TOPOLOGY, cli_list_map_topology);
 	set_handler_callback(LIST+MAP+FMT, cli_list_map_fmt);
 	set_handler_callback(LIST+MAP+RAW+FMT, cli_list_map_fmt);
+	set_handler_callback(LIST+MAP+JSON, cli_list_map_json);
 	set_unlocked_handler_callback(LIST+CONFIG, cli_list_config);
 	set_unlocked_handler_callback(LIST+BLACKLIST, cli_list_blacklist);
 	set_handler_callback(LIST+DEVICES, cli_list_devices);
-- 
2.5.5

Re: [PATCH 0/1] add option to output JSON for multipathd command

[Alasdair G Kergon]

On Wed, May 04, 2016 at 04:23:47PM -0400, Todd Gill wrote:
> I had earlier sent an email to dm-devel proposing we add a feature
> in multipathd to output multipath map topology in JSON format. This
> patch contains to the code for that feature.
> Having an option for the  CLI to output in JSON would allow higher
> level applications to more easily monitor/manage multipath.
 
Got any examples to show what the output actually looks like?

Alasdair

Re: [PATCH 0/1] add option to output JSON for multipathd command

[Bart Van Assche]

On 05/04/16 13:23, Todd Gill wrote:
> I had earlier sent an email to dm-devel proposing we add a feature
> in multipathd to output multipath map topology in JSON format. This
> patch contains to the code for that feature.
>
> Having an option for the  CLI to output in JSON would allow higher
> level applications to more easily monitor/manage multipath.
>
> I thought it was best to take advantage of some of the existing
> snprintf_xxx functions rather than adding a library dependency
> to multipathd.
>
> Will add code for groups next if this is accepted.

XML is better standardized than JSON, so why to use JSON? An overview of 
the advantages of XML is available on 
http://www.yegor256.com/2015/11/16/json-vs-xml.html. A good overview of 
JSON and also of some of its disadvantages is available on 
https://en.wikipedia.org/wiki/JSON.

Sorry that I missed your previous e-mail about this topic.

Bart.

Re: [PATCH 0/1] add option to output JSON for multipathd command

[Todd Gill]

On 05/04/2016 07:22 PM, Alasdair G Kergon wrote:
> On Wed, May 04, 2016 at 04:23:47PM -0400, Todd Gill wrote:
>> I had earlier sent an email to dm-devel proposing we add a feature
>> in multipathd to output multipath map topology in JSON format. This
>> patch contains to the code for that feature.
>> Having an option for the  CLI to output in JSON would allow higher
>> level applications to more easily monitor/manage multipath.
>  
> Got any examples to show what the output actually looks like?
> 

I edited the following JSON to only include 2 of the multipath maps on
the system.

The JSON contains an array of maps.  Inside each map are elements and
the array of paths.

I was planning on adding they path groups if this gets accepted.

# multipathd show maps json
{
"maps":[
	{
	"name" : "360a98000423664653024426830595062",
	"uuid" : "360a98000423664653024426830595062",
	"sysfs" : "dm-9",
	"failback" : "immediate",
	"queueing" : "on",
	"paths" : "2",
	"write_prot" : "rw",
	"dm-st" : "active",
	"size" : "16G",
	"features" : "4 queue_if_no_path pg_init_retries 50
retain_attached_hw_handle",
	"hwhandler" : "0",
	"action" : "",
	"path_faults" : "0",
	"vend/prod/rev" : "NETAPP,LUN",
	"switch_grp" : "0",
	"map_loads" : "1",
	"total_q_time" : "0",
	"q_timeouts" : "0",
	"paths":[
		{
		"uuid" : "360a98000423664653024426830595062",
		"hcil" : "6:0:0:0",
		"dev" : "sdc",
		"dev_t" : "8:32",
		"dm_st" : "active",
		"dev_st" : "running",
		"chk_st" : "ready",
		"vend/prod/rev" : "NETAPP,LUN",
		"checker" : "tur",
		"next_check" : "XXXXXXXX.. 16/20",
		"pri" : "50",
		"size" : "16G",
		"serial" : "B6de0$Bh0YPb",
		"multipath" : "360a98000423664653024426830595062",
		"host WWNN" : "0x50014380120d8425",
		"target WWNN" : "0x500a098080ba5a64",
		"host WWPN" : "0x50014380120d8424",
		"target WWPN" : "0x500a098180ba5a64",
		"host adapter" : "0000:00:03.0"
		},
		{
		"uuid" : "360a98000423664653024426830595062",
		"hcil" : "7:0:0:0",
		"dev" : "sdj",
		"dev_t" : "8:144",
		"dm_st" : "active",
		"dev_st" : "running",
		"chk_st" : "ready",
		"vend/prod/rev" : "NETAPP,LUN",
		"checker" : "tur",
		"next_check" : "XXXXXXXX.. 16/20",
		"pri" : "10",
		"size" : "16G",
		"serial" : "B6de0$Bh0YPb",
		"multipath" : "360a98000423664653024426830595062",
		"host WWNN" : "0x50014380120d8427",
		"target WWNN" : "0x500a098080ba5a64",
		"host WWPN" : "0x50014380120d8426",
		"target WWPN" : "0x500a098190ba5a64",
		"host adapter" : "0000:00:03.0"
		}
	]
	},
	{
	"name" : "360a98000423664653024426830595064",
	"uuid" : "360a98000423664653024426830595064",
	"sysfs" : "dm-2",
	"failback" : "immediate",
	"queueing" : "on",
	"paths" : "2",
	"write_prot" : "rw",
	"dm-st" : "active",
	"size" : "16G",
	"features" : "4 queue_if_no_path pg_init_retries 50
retain_attached_hw_handle",
	"hwhandler" : "0",
	"action" : "",
	"path_faults" : "0",
	"vend/prod/rev" : "NETAPP,LUN",
	"switch_grp" : "0",
	"map_loads" : "1",
	"total_q_time" : "0",
	"q_timeouts" : "0",
	"paths":[
		{
		"uuid" : "360a98000423664653024426830595064",
		"hcil" : "6:0:0:1",
		"dev" : "sdd",
		"dev_t" : "8:48",
		"dm_st" : "active",
		"dev_st" : "running",
		"chk_st" : "ready",
		"vend/prod/rev" : "NETAPP,LUN",
		"checker" : "tur",
		"next_check" : "XXXXXXXX.. 16/20",
		"pri" : "50",
		"size" : "16G",
		"serial" : "B6de0$Bh0YPd",
		"multipath" : "360a98000423664653024426830595064",
		"host WWNN" : "0x50014380120d8425",
		"target WWNN" : "0x500a098080ba5a64",
		"host WWPN" : "0x50014380120d8424",
		"target WWPN" : "0x500a098180ba5a64",
		"host adapter" : "0000:00:03.0"
		},
		{
		"uuid" : "360a98000423664653024426830595064",
		"hcil" : "7:0:0:1",
		"dev" : "sdk",
		"dev_t" : "8:160",
		"dm_st" : "active",
		"dev_st" : "running",
		"chk_st" : "ready",
		"vend/prod/rev" : "NETAPP,LUN",
		"checker" : "tur",
		"next_check" : "XXXXXXXX.. 16/20",
		"pri" : "10",
		"size" : "16G",
		"serial" : "B6de0$Bh0YPd",
		"multipath" : "360a98000423664653024426830595064",
		"host WWNN" : "0x50014380120d8427",
		"target WWNN" : "0x500a098080ba5a64",
		"host WWPN" : "0x50014380120d8426",
		"target WWPN" : "0x500a098190ba5a64",
		"host adapter" : "0000:00:03.0"
		}
	]
	}
]
}

Re: [PATCH 1/1] add display of map information in JSON format

[Gris Ge]

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On Wed, May 04, 2016 at 04:23:48PM -0400, Todd Gill wrote:
> The patch adds these commands:
>
> multipathd show maps json
> multipathd show map $map json
>
> Each command will output the requested map(s) in JSON.
>
> For the "show maps json" command, the patch pre-allocates
> INITIAL_REPLY_LEN * 5.  The JSON text is about 5x the size of
> the "show maps topology" text.
Hi Todd,

How about define a constant with this line as comment, instead of
using magic number directly?
>
> Signed-off-by: Todd Gill <tgill@redhat.com>
> ---
> +int
> +snprint_multipath_json (char * buff, int len, struct multipath * mpp, int last)
> +{
> +	int i, fwd = 0;
> +	struct path *pp;
> +
> +	fwd +=  snprint_json(buff + fwd,
> +			len - fwd, 1, PRINT_JSON_START_ELEM);
> +	if (fwd > len)
> +		return len;
> +
> +	fwd += snprint_multipath(buff + fwd, len - fwd,
> +			PRINT_JSON_MAP, mpp, 0);
If we are using snprint_multipath() there, basally this is just a
daemon version of 'show maps raw format <fancy_json_format>'.

So if I may sum up, we have three options to provide a user-friendly
library.

 A) Expand 'show maps raw format' to include all formation where
    user/client could selectively print needed properties out in their
    favored format. And create a wrapper library(check my previous
    post on libdmmp).

        Pros:
            * Minimum changes to daemon.
            * Client only have to parse properties they are
              interested which saves the CPU time and IPC
              communication.

        Cons:
            * We have to document every formatters,
              example: the meanings and possible values of "%N".

 B) Provide 'show maps json' and do the string
    formatting(JSON/XML/etc) at the daemon side.

        Pros:
            * Easy for client to parse IPC output.

        Cons:
            * More IPC communication, like Todd said, about 5 times.
              And client will waste their CPU and memory on parsing
              un-needed properties if only interested on few.
              For example, you have 1000 maps, and just want to know
              which maps has failed path, then you have to parse
              about 108,000 lines of json string.

            * People (we already have) might suggest XML or whatever
              format is better than JSON, why not use that.

 C) Provide both expanded 'show maps raw format' and 'show maps json'
        Pros:
            * All pros above.

        Cons:
            * Do we have to maintain these two ways?

My negligible vote to option B), ideally the wrapper library should be
user's first choice instead messing with 'raw format'.

Thanks for the patch.
Best regards.

-- 
Gris Ge

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Re: [PATCH 0/1] add option to output JSON for multipathd command

[Todd Gill]

On 05/04/2016 09:17 PM, Bart Van Assche wrote:
> On 05/04/16 13:23, Todd Gill wrote:
>> I had earlier sent an email to dm-devel proposing we add a feature
>> in multipathd to output multipath map topology in JSON format. This
>> patch contains to the code for that feature.
>>
>> Having an option for the  CLI to output in JSON would allow higher
>> level applications to more easily monitor/manage multipath.
>>
>> I thought it was best to take advantage of some of the existing
>> snprintf_xxx functions rather than adding a library dependency
>> to multipathd.
>>
>> Will add code for groups next if this is accepted.
> 
> XML is better standardized than JSON, so why to use JSON? An overview of
> the advantages of XML is available on
> http://www.yegor256.com/2015/11/16/json-vs-xml.html. A good overview of
> JSON and also of some of its disadvantages is available on
> https://en.wikipedia.org/wiki/JSON.
> 

I was on the fence between XML and JSON.  I think JSON is more simple.

I'm not sure we'd need the features listed as advantages in the first
link you sent.

> Sorry that I missed your previous e-mail about this topic.
> 

No problem.  Thanks for the feedback.  I'm interested in making the data
easily available to higher level applications.  So, any common/easily
consumed data format would be fine.

Todd