Add function cpu_msr_driver_open_core()

This function is similar to cpu_msr_driver_open(), but with core number as parameter
For Linux, core number was always 0. To be able to get all core temp/voltage, we need to set the core number.

libcpuid/exports.def

@@ -28,3 +28,4 @@ cpu_msrinfo @24
 cpu_msr_driver_close @25
 cpu_clock_by_ic @26
 cpuid_get_total_cpus @27
+cpu_msr_driver_open_core @28

libcpuid/libcpuid.h

@@ -390,6 +390,7 @@ typedef enum {
 	ERR_EXTRACT  = -11,	/*!< "Cannot extract RDMSR driver (read only media?)" */
 	ERR_HANDLE   = -12,	/*!< "Bad handle" */
 	ERR_INVMSR   = -13,     /*!< "Invalid MSR" */
+	ERR_INVCNB   = -14,     /*!< "Invalid core number" */
 } cpu_error_t;
 
 /**
@@ -804,6 +805,21 @@ void cpuid_free_cpu_list(struct cpu_list_t* list);
 struct msr_driver_t;
 struct msr_driver_t* cpu_msr_driver_open(void);
 
+/**
+ * @brief Similar to \ref cpu_msr_driver_open, but accept one parameter
+ *
+ * This function works on Linux only
+ *
+ * @param core_num specify the core number for MSR.
+ *          The first core number is 0.
+ *          The last core number is \ref cpuid_get_total_cpus - 1.
+ *
+ * @returns a handle to the driver on success, and NULL on error.
+ *          The error message can be obtained by calling \ref cpuid_error.
+ *          @see cpu_error_t
+ */
+struct msr_driver_t* cpu_msr_driver_open_core(int core_num);
+
 /**
  * @brief Reads a Model-Specific Register (MSR)
  *

libcpuid/libcpuid.sym

@@ -25,3 +25,4 @@ cpu_msrinfo
 cpu_msr_driver_close
 cpu_clock_by_ic
 cpuid_get_total_cpus
+cpu_msr_driver_open_core

libcpuid/rdmsr.c

@@ -69,12 +69,24 @@ struct msr_driver_t { int fd; };
 static int rdmsr_supported(void);
 struct msr_driver_t* cpu_msr_driver_open(void)
 {
+	return cpu_msr_driver_open_core(0);
+}
+
+struct msr_driver_t* cpu_msr_driver_open_core(int core_num)
+{
+	char msr[32];
 	struct msr_driver_t* handle;
+	if(core_num < 0 && cpuid_get_total_cpus() <= core_num)
+	{
+		set_error(ERR_INVCNB);
+		return NULL;
+	}
 	if (!rdmsr_supported()) {
 		set_error(ERR_NO_RDMSR);
 		return NULL;
 	}
-		int fd = open("/dev/cpu/0/msr", O_RDONLY);
+	sprintf(msr, "/dev/cpu/%i/msr", core_num);
+	int fd = open(msr, O_RDONLY);
 	if (fd < 0) {
 		if (errno == EIO) {
 			set_error(ERR_NO_RDMSR);