tools/power turbostat: print the kernel boot commandline

It would be handy to have cmdline in turbostat output. For example,
according to the turbostat output, there are no C-states requested.
In this case the user is very curious if something like
intel_idle.max_cstate=0 was used, or may be idle=none too. It is
also curious whether things like intel_pstate=nohwp were used.

Print the boot command line accordingly:
turbostat version 21.05.04 - Len Brown <lenb@kernel.org>
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-5.16.0+ root=UUID=
 b42359ed-1e05-42eb-8757-6bf2a1c19070 ro quiet splash vt.handoff=7
Suggested-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

tools/power/x86/turbostat/turbostat.c

@@ -6132,6 +6132,29 @@ void print_version()
 	fprintf(outf, "turbostat version 2022.04.16 - Len Brown <lenb@kernel.org>\n");
 }
 
+#define COMMAND_LINE_SIZE 2048
+
+void print_bootcmd(void)
+{
+	char bootcmd[COMMAND_LINE_SIZE];
+	FILE *fp;
+	int ret;
+
+	memset(bootcmd, 0, COMMAND_LINE_SIZE);
+	fp = fopen("/proc/cmdline", "r");
+	if (!fp)
+		return;
+
+	ret = fread(bootcmd, sizeof(char), COMMAND_LINE_SIZE - 1, fp);
+	if (ret) {
+		bootcmd[ret] = '\0';
+		/* the last character is already '\n' */
+		fprintf(outf, "Kernel command line: %s", bootcmd);
+	}
+
+	fclose(fp);
+}
+
 int add_counter(unsigned int msr_num, char *path, char *name,
 		unsigned int width, enum counter_scope scope,
 		enum counter_type type, enum counter_format format, int flags)
@@ -6603,8 +6626,10 @@ int main(int argc, char **argv)
 	outf = stderr;
 	cmdline(argc, argv);
 
-	if (!quiet)
+	if (!quiet) {
 		print_version();
+		print_bootcmd();
+	}
 
 	probe_sysfs();