info: Add utc_offset info for external usage

In some cases, there is a requirement to get the time offset between UTC
time and our timestamp from the given clock source, CLOCK_MONOTONIC by
default.

This patch provides an additional info to provide UTC time offset in the
output of uftrace info.

This number can be used to make time adjustment easier for external
tools such as tracecompass[1].

Closes: #1916

[1] https://eclipse.dev/tracecompass
Requested-by: Matthew Khouzam <matthew.khouzam@gmail.com>
Signed-off-by: Honggyu Kim <honggyu.kp@gmail.com>

cmds/dump.c

@@ -540,7 +540,7 @@ static void dump_raw_header(struct uftrace_dump_ops *ops, struct uftrace_data *h
 	const char *info_str[] = { "EXE_NAME",	   "EXE_BUILD_ID", "EXIT_STATUS", "CMDLINE",
 				   "CPUINFO",	   "MEMINFO",	   "OSINFO",	  "TASKINFO",
 				   "USAGEINFO",	   "LOADINFO",	   "ARG_SPEC",	  "RECORD_DATE",
-				   "PATTERN_TYPE", "VERSION" };
+				   "PATTERN_TYPE", "VERSION",	   "UTC_OFFSET" };
 
 	pr_out("uftrace file header: magic         = ");
 	for (i = 0; i < UFTRACE_MAGIC_LEN; i++)

cmds/info.c

@@ -851,6 +851,41 @@ static int read_uftrace_version(void *arg)
 	return 0;
 }
 
+static int fill_utc_offset(void *arg)
+{
+	struct fill_handler_arg *fha = arg;
+	time_t current_time;
+	struct timespec ts;
+	long offset;
+
+	time(&current_time);
+	clock_gettime(clock_source, &ts);
+
+	/* calculate time offset between UTC and clock_source. */
+	offset = (long)difftime(current_time, ts.tv_sec);
+
+	dprintf(fha->fd, "utc_offset:%ld\n", offset);
+	return 0;
+}
+
+static int read_utc_offset(void *arg)
+{
+	struct read_handler_arg *rha = arg;
+	struct uftrace_data *handle = rha->handle;
+	struct uftrace_info *info = &handle->info;
+	char *buf = rha->buf;
+
+	if (fgets(buf, sizeof(rha->buf), handle->fp) == NULL)
+		return -1;
+
+	if (strncmp(buf, "utc_offset:", 11))
+		return -1;
+
+	info->utc_offset = copy_info_str(&buf[11]);
+
+	return 0;
+}
+
 struct uftrace_info_handler {
 	enum uftrace_info_bits bit;
 	int (*handler)(void *arg);
@@ -883,6 +918,7 @@ void fill_uftrace_info(uint64_t *info_mask, int fd, struct uftrace_opts *opts, i
 		{ RECORD_DATE, fill_record_date },
 		{ PATTERN_TYPE, fill_pattern_type },
 		{ VERSION, fill_uftrace_version },
+		{ UTC_OFFSET, fill_utc_offset },
 	};
 
 	for (i = 0; i < ARRAY_SIZE(fill_handlers); i++) {
@@ -926,6 +962,7 @@ int read_uftrace_info(uint64_t info_mask, struct uftrace_data *handle)
 		{ RECORD_DATE, read_record_date },
 		{ PATTERN_TYPE, read_pattern_type },
 		{ VERSION, read_uftrace_version },
+		{ UTC_OFFSET, read_utc_offset },
 	};
 
 	memset(&handle->info, 0, sizeof(handle->info));
@@ -955,6 +992,7 @@ void clear_uftrace_info(struct uftrace_info *info)
 	free(info->argspec);
 	free(info->record_date);
 	free(info->elapsed_time);
+	free(info->utc_offset);
 	free(info->uftrace_version);
 	free(info->retspec);
 	free(info->autoarg);

uftrace.h

@@ -98,6 +98,7 @@ enum uftrace_info_bits {
 	RECORD_DATE_BIT,
 	PATTERN_TYPE_BIT,
 	VERSION_BIT,
+	UTC_OFFSET_BIT,
 
 	INFO_BIT_MAX,
 
@@ -116,6 +117,7 @@ enum uftrace_info_bits {
 	RECORD_DATE = (1U << RECORD_DATE_BIT),
 	PATTERN_TYPE = (1U << PATTERN_TYPE_BIT),
 	VERSION = (1U << VERSION_BIT),
+	UTC_OFFSET = (1U << UTC_OFFSET_BIT),
 };
 
 struct uftrace_info {
@@ -142,6 +144,7 @@ struct uftrace_info {
 	double utime;
 	char *record_date;
 	char *elapsed_time;
+	char *utc_offset;
 	long vctxsw;
 	long ictxsw;
 	long maxrss;