[PATCH v2] btrfs-progs: device stats: add json output format

[Sidong Yang <realwakka@gmail.com>]

Add supports for json formatting, this patch changes hard coded printing
code to formatted print with output formatter. Json output would be
useful for other programs that parse output of the command. but it
changes the text format.

Example text format:

device:                 /dev/vdb
write_io_errs:          0
read_io_errs:           0
flush_io_errs:          0
corruption_errs:        0
generation_errs:        0

Example json format:

{
  "__header": {
    "version": "1"
  },
  "device-stats": {
    "/dev/vdb": {
      "device": "/dev/vdb",
      "write_io_errs": "0",
      "read_io_errs": "0",
      "flush_io_errs": "0",
      "corruption_errs": "0",
      "generation_errs": "0"
    }
  },
}

Cc: David Sterba <dsterba@suse.cz>

Signed-off-by: Sidong Yang <realwakka@gmail.com>
---
v2:
 - use output formatter
---
 cmds/device.c | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/cmds/device.c b/cmds/device.c
index d72881f8..91b45d9f 100644
--- a/cmds/device.c
+++ b/cmds/device.c
@@ -36,6 +36,7 @@
 #include "common/path-utils.h"
 #include "common/device-utils.h"
 #include "common/device-scan.h"
+#include "common/format-output.h"
 #include "mkfs/common.h"
 
 static const char * const device_cmd_group_usage[] = {
@@ -459,6 +460,16 @@ out:
 }
 static DEFINE_SIMPLE_COMMAND(device_ready, "ready");
 
+static const struct rowspec device_stats_rowspec[] = {
+	{ .key = "device", .fmt = "%s", .out_text = "device", .out_json = "device" },
+	{ .key = "write_io_errs", .fmt = "%llu", .out_text = "write_io_errs", .out_json = "write_io_errs" },
+	{ .key = "read_io_errs", .fmt = "%llu", .out_text = "read_io_errs", .out_json = "read_io_errs" },
+	{ .key = "flush_io_errs", .fmt = "%llu", .out_text = "flush_io_errs", .out_json = "flush_io_errs" },
+	{ .key = "corruption_errs", .fmt = "%llu", .out_text = "corruption_errs", .out_json = "corruption_errs" },
+	{ .key = "generation_errs", .fmt = "%llu", .out_text = "generation_errs", .out_json = "generation_errs" },
+	ROWSPEC_END
+};
+
 static const char * const cmd_device_stats_usage[] = {
 	"btrfs device stats [options] <path>|<device>",
 	"Show device IO error statistics",
@@ -482,6 +493,7 @@ static int cmd_device_stats(const struct cmd_struct *cmd, int argc, char **argv)
 	int check = 0;
 	__u64 flags = 0;
 	DIR *dirstream = NULL;
+	struct format_ctx fctx;
 
 	optind = 0;
 	while (1) {
@@ -530,6 +542,8 @@ static int cmd_device_stats(const struct cmd_struct *cmd, int argc, char **argv)
 		goto out;
 	}
 
+	fmt_start(&fctx, device_stats_rowspec, 24, 0);
+	fmt_print_start_group(&fctx, "device-stats", JSON_TYPE_MAP);
 	for (i = 0; i < fi_args.num_devices; i++) {
 		struct btrfs_ioctl_get_dev_stats args = {0};
 		char path[BTRFS_DEVICE_PATH_NAME_MAX + 1];
@@ -574,31 +588,34 @@ static int cmd_device_stats(const struct cmd_struct *cmd, int argc, char **argv)
 				snprintf(canonical_path, 32,
 					 "devid:%llu", args.devid);
 			}
+			fmt_print_start_group(&fctx, canonical_path, JSON_TYPE_MAP);
+			fmt_print(&fctx, "device", canonical_path);
 
 			for (j = 0; j < ARRAY_SIZE(dev_stats); j++) {
 				/* We got fewer items than we know */
 				if (args.nr_items < dev_stats[j].num + 1)
 					continue;
-				printf("[%s].%-16s %llu\n", canonical_path,
-					dev_stats[j].name,
-					(unsigned long long)
-					 args.values[dev_stats[j].num]);
+
+				fmt_print(&fctx, dev_stats[j].name, args.values[dev_stats[j].num]);
 				if ((check == 1)
 				    && (args.values[dev_stats[j].num] > 0))
 					err |= 64;
 			}
-
+			fmt_print_end_group(&fctx, "device");
 			free(canonical_path);
 		}
 	}
 
+	fmt_print_end_group(&fctx, "device-stats");
+	fmt_end(&fctx);
+
 out:
 	free(di_args);
 	close_file_or_dir(fdmnt, dirstream);
 
 	return err;
 }
-static DEFINE_SIMPLE_COMMAND(device_stats, "stats");
+static DEFINE_COMMAND_WITH_FLAGS(device_stats, "stats", CMD_FORMAT_JSON);
 
 static const char * const cmd_device_usage_usage[] = {
 	"btrfs device usage [options] <path> [<path>..]",
-- 
2.25.1