Added Model Specific Register (MSR) module

Added Model Specific Register (MSR) module to allow access to MSRs. This module
provides the interfaces to read and write msr through msr_safe kernel module.

See Issue #11

nrm/coolr/msr.py

+""" Msr Module:
+    This module provides the interfaces to read and write msr through msr_safe
+    kernel module.
+
+    Note: msr_safe kernel module needs to be installed on your machine for this
+    module to work. To run with root privileges change 'msr_safe' in
+    get_file_name() function to 'msr'.
+"""
+
+import os
+import sys
+import errno
+import struct
+
+
+class Msr:
+    # get msr file name for the cpu
+    def get_file_name(self, cpu):
+        return '/dev/cpu/%d/msr_safe' % cpu
+
+    # open msr file with correct privileges
+    def file_open(self, filename, privilege):
+        try:
+            if privilege == 'r':
+                fd = os.open(filename, os.O_RDONLY)
+            elif privilege == 'w':
+                fd = os.open(filename, os.O_WRONLY)
+
+        except OSError as e:
+            if e.errno == errno.ENXIO:
+                sys.exit('file_open: No such device or address ' + filename)
+            elif e.errno == errno.EIO:
+                sys.exit('file_open: I/O error ' + filename)
+            elif e.errno == errno.EACCES:
+                sys.exit('file_open: Permission denied ' + filename)
+            else:
+                sys.exit('file_open: Error ' + filename)
+
+        return fd
+
+    # read a msr
+    def read(self, cpu, register):
+        msrfile = self.get_file_name(cpu)
+        fd = self.file_open(msrfile, 'r')
+        try:
+            os.lseek(fd, int(register), os.SEEK_SET)
+            """ read and handle binary data from msr file """
+            value = struct.unpack('Q', os.read(fd, 8))[0]
+            os.close(fd)
+
+        except OSError as e:
+            os.close(fd)
+            if e.errno == errno.EIO:
+                sys.exit('read: I/O error ' + msrfile)
+            elif e.errno == errno.EACCES:
+                sys.exit('read: Permission denied ' + msrfile)
+            else:
+                sys.exit('read: Error ' + msrfile)
+
+        return value
+
+    # write a msr
+    def write(self, cpu, register, value):
+        msrfile = self.get_file_name(cpu)
+        fd = self.file_open(msrfile, 'w')
+        try:
+            os.lseek(fd, int(register), os.SEEK_SET)
+            """ write binary data to msr file """
+            os.write(fd, struct.pack('Q', value))
+            os.close(fd)
+
+        except OSError as e:
+            os.close(fd)
+            if e.errno == errno.EIO:
+                sys.exit('write: I/O error ' + msrfile)
+            elif e.errno == errno.EACCES:
+                sys.exit('write: Permission denied ' + msrfile)
+            else:
+                sys.exit('write: Error ' + msrfile)
+
+        return value