pping: Add option to write to file

Add an option -w/--write <filename> which writes the output to the
provided file instead of to stdout. Fail if file the provided file
already exists to avoid data loss (if truncating file) or corrupting
data (if appending file, JSON is not concatable).

Signed-off-by: Simon Sundberg <simon.sundberg@kau.se>

Author: simosund

pping/pping.c

@@ -26,6 +26,7 @@ static const char *__doc__ =
 #include <sys/epoll.h>
 #include <linux/unistd.h>
 #include <linux/membarrier.h>
+#include <limits.h>
 
 #include "json_writer.h"
 #include "pping.h" //common structs for user-space and BPF parts
@@ -37,8 +38,6 @@ static const char *__doc__ =
 
 #define PERF_BUFFER_PAGES 64 // Related to the perf-buffer size?
 
-#define MAX_PATH_LEN 1024
-
 #define MON_TO_REAL_UPDATE_FREQ                                                \
 	(1 * NS_PER_SECOND) // Update offset between CLOCK_MONOTONIC and CLOCK_REALTIME once per second
 
@@ -129,10 +128,10 @@ struct pping_config {
 	struct bpf_config bpf_config;
 	struct bpf_tc_opts tc_ingress_opts;
 	struct bpf_tc_opts tc_egress_opts;
-	struct output_context out_ctx;
 	struct map_cleanup_args clean_args;
 	struct aggregation_config agg_conf;
 	struct aggregation_maps agg_maps;
+	struct output_context *out_ctx;
 	char *object_path;
 	char *ingress_prog;
 	char *egress_prog;
@@ -146,7 +145,10 @@ struct pping_config {
 	int ingress_prog_id;
 	int egress_prog_id;
 	char ifname[IF_NAMESIZE];
+	char filename[PATH_MAX];
+	enum pping_output_format format;
 	enum xdp_attach_mode xdp_mode;
+	bool write_to_file;
 	bool force;
 	bool created_tc_hook;
 };
@@ -171,6 +173,7 @@ static const struct option long_options[] = {
 	{ "aggregate-subnets-v6", required_argument, NULL, '6' }, // Set the subnet size for IPv6 when aggregating (default 48)
 	{ "aggregate-reverse",    no_argument,       NULL, ARG_AGG_REVERSE }, // Aggregate RTTs by dst IP of reply packet (instead of src like default)
 	{ "aggregate-timeout",    required_argument, NULL, AGG_ARG_TIMEOUT }, // Interval for timing out subnet entries in seconds (default 30s)
+	{ "write",                required_argument, NULL, 'w' }, // Write output to file (instead of stdout)
 	{ 0, 0, NULL, 0 }
 };
 
@@ -265,7 +268,7 @@ static int parse_bounded_long(long long *res, const char *str, long long low,
 
 static int parse_arguments(int argc, char *argv[], struct pping_config *config)
 {
-	int err, opt;
+	int err, opt, len;
 	double user_float;
 	long long user_int;
 
@@ -280,15 +283,17 @@ static int parse_arguments(int argc, char *argv[], struct pping_config *config)
 	config->bpf_config.agg_rtts = false;
 	config->bpf_config.agg_by_dst = false;
 
-	while ((opt = getopt_long(argc, argv, "hflTCsi:r:R:t:c:F:I:x:a:4:6:",
+	while ((opt = getopt_long(argc, argv, "hflTCsi:r:R:t:c:F:I:x:a:4:6:w:",
 				  long_options, NULL)) != -1) {
 		switch (opt) {
 		case 'i':
-			if (strlen(optarg) > IF_NAMESIZE) {
+			len = strlen(optarg);
+			if (len >= IF_NAMESIZE) {
 				fprintf(stderr, "interface name too long\n");
 				return -EINVAL;
 			}
-			strncpy(config->ifname, optarg, IF_NAMESIZE);
+			memcpy(config->ifname, optarg, len);
+			config->ifname[len] = '\0';
 
 			config->ifindex = if_nametoindex(config->ifname);
 			if (config->ifindex == 0) {
@@ -340,11 +345,11 @@ static int parse_arguments(int argc, char *argv[], struct pping_config *config)
 			break;
 		case 'F':
 			if (strcmp(optarg, "standard") == 0) {
-				config->out_ctx.format = PPING_OUTPUT_STANDARD;
+				config->format = PPING_OUTPUT_STANDARD;
 			} else if (strcmp(optarg, "json") == 0) {
-				config->out_ctx.format = PPING_OUTPUT_JSON;
+				config->format = PPING_OUTPUT_JSON;
 			} else if (strcmp(optarg, "ppviz") == 0) {
-				config->out_ctx.format = PPING_OUTPUT_PPVIZ;
+				config->format = PPING_OUTPUT_PPVIZ;
 			} else {
 				fprintf(stderr,
 					"format must be \"standard\", \"json\" or \"ppviz\"\n");
@@ -429,6 +434,17 @@ static int parse_arguments(int argc, char *argv[], struct pping_config *config)
 			config->agg_conf.timeout_interval =
 				user_int * NS_PER_SECOND;
 			break;
+		case 'w':
+			len = strlen(optarg);
+			if (len >= sizeof(config->filename)) {
+				fprintf(stderr, "File name too long\n");
+				return -ENAMETOOLONG;
+			}
+
+			memcpy(config->filename, optarg, len);
+			config->filename[len] = '\0';
+			config->write_to_file = true;
+			break;
 		case 'h':
 			printf("HELP:\n");
 			print_usage(argv);
@@ -1075,7 +1091,7 @@ static void print_map_clean_info(FILE *stream, const struct map_clean_event *e)
 
 static void handle_event(void *ctx, int cpu, void *data, __u32 data_size)
 {
-	struct output_context *out_ctx = ctx;
+	struct output_context *out_ctx = *(struct output_context **)ctx;
 	const union pping_event *e = data;
 
 	if (data_size < sizeof(e->event_type))
@@ -1640,6 +1656,60 @@ static int setup_periodical_map_cleaning(struct bpf_object *obj,
 	return err;
 }
 
+static struct output_context *open_output(const char *filename,
+					  enum pping_output_format format,
+					  struct aggregation_config *agg_conf)
+{
+	struct output_context *out_ctx;
+
+	out_ctx = calloc(1, sizeof(*out_ctx));
+	if (!out_ctx)
+		return NULL;
+
+	out_ctx->format = format;
+
+	if (filename) {
+		out_ctx->stream = fopen(filename, "ax");
+		if (!out_ctx->stream)
+			goto err;
+	} else {
+		out_ctx->stream = stdout;
+	}
+
+	if (out_ctx->format == PPING_OUTPUT_JSON) {
+		out_ctx->jctx = jsonw_new(out_ctx->stream);
+		if (!out_ctx->jctx)
+			goto err;
+		jsonw_start_array(out_ctx->jctx);
+	}
+
+	if (agg_conf)
+		print_aggmetadata(out_ctx, agg_conf);
+
+	return out_ctx;
+err:
+	free(out_ctx);
+	return NULL;
+}
+
+static int close_output(struct output_context *out_ctx)
+{
+	int err = 0;
+
+	if (out_ctx->jctx) {
+		jsonw_end_array(out_ctx->jctx);
+		jsonw_destroy(&out_ctx->jctx);
+	}
+
+	if (out_ctx->stream && out_ctx->stream != stdout) {
+		if (fclose(out_ctx->stream) != 0)
+			err = -errno;
+	}
+
+	free(out_ctx);
+	return err;
+}
+
 static int init_signalfd(void)
 {
 	sigset_t mask;
@@ -1976,7 +2046,7 @@ static int epoll_poll_events(int epfd, struct pping_config *config,
 		case PPING_EPEVENT_TYPE_AGGTIMER:
 			err = handle_aggregation_timer(
 				events[i].data.u64 & PPING_EPEVENT_MASK,
-				&config->out_ctx, &config->agg_maps,
+				config->out_ctx, &config->agg_maps,
 				&config->agg_conf);
 			break;
 		case PPING_EPEVENT_TYPE_SIGNAL:
@@ -2014,9 +2084,6 @@ int main(int argc, char *argv[])
 		.bpf_config = { .rate_limit = 100 * NS_PER_MS,
 				.rtt_rate = 0,
 				.use_srtt = false },
-		.out_ctx = { .format = PPING_OUTPUT_STANDARD,
-			     .stream = stdout,
-			     .jctx = NULL },
 		.clean_args = { .cleanup_interval = 1 * NS_PER_SECOND,
 				.valid_thread = false },
 		.agg_conf = { .aggregation_interval = 1 * NS_PER_SECOND,
@@ -2063,7 +2130,7 @@ int main(int argc, char *argv[])
 	if (!config.bpf_config.track_tcp && !config.bpf_config.track_icmp)
 		config.bpf_config.track_tcp = true;
 
-	if (config.out_ctx.format == PPING_OUTPUT_PPVIZ) {
+	if (config.format == PPING_OUTPUT_PPVIZ) {
 		if (config.bpf_config.agg_rtts) {
 			fprintf(stderr,
 				"The ppviz format does not support aggregated output\n");
@@ -2075,17 +2142,20 @@ int main(int argc, char *argv[])
 	}
 
 	fprintf(stderr, "Starting ePPing in %s mode tracking %s on %s\n",
-		output_format_to_str(config.out_ctx.format),
+		output_format_to_str(config.format),
 		tracked_protocols_to_str(&config), config.ifname);
 
-	if (config.out_ctx.format == PPING_OUTPUT_JSON) {
-		config.out_ctx.jctx = jsonw_new(config.out_ctx.stream);
-		jsonw_start_array(config.out_ctx.jctx);
+	config.out_ctx = open_output(
+		config.write_to_file ? config.filename : NULL, config.format,
+		config.bpf_config.agg_rtts ? &config.agg_conf : NULL);
+	if (!config.out_ctx) {
+		err = -errno;
+		fprintf(stderr, "Unable to open %s: %s\n",
+			config.write_to_file ? config.filename : "output",
+			get_libbpf_strerror(err));
+		return EXIT_FAILURE;
 	}
 
-	if (config.bpf_config.agg_rtts)
-		print_aggmetadata(&config.out_ctx, &config.agg_conf);
-
 	// Setup signalhandling (allow graceful shutdown on SIGINT/SIGTERM)
 	sigfd = init_signalfd();
 	if (sigfd < 0) {
@@ -2205,10 +2275,7 @@ int main(int argc, char *argv[])
 	close(sigfd);
 
 cleanup_output:
-	if (config.out_ctx.format == PPING_OUTPUT_JSON && config.out_ctx.jctx) {
-		jsonw_end_array(config.out_ctx.jctx);
-		jsonw_destroy(&config.out_ctx.jctx);
-	}
+	close_output(config.out_ctx);
 
 	return err != 0 || detach_err != 0;
 }