scripts/kvm/kvm_stat: Improve debugfs access checking

Access checking with F_OK was replaced with the better readable
os.path.exists().

On Linux exists() returns False when the user doesn't have sufficient
permissions for statting the directory. Therefore the error message
now states that sufficient rights are needed when the check fails.

Also added check for /sys/kernel/debug/tracing/.

Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Message-Id: <1452525484-32309-9-git-send-email-frankja@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/scripts/kvm/kvm_stat b/scripts/kvm/kvm_stat
index 5ca09f46d8174ea3344b10a17c21b5bc29647c40..6f0692d60a520c4d61f9e1858076e26bcbf76087 100755 (executable)
--- a/scripts/kvm/kvm_stat
+++ b/scripts/kvm/kvm_stat
@@ -473,12 +473,18 @@ class Stats:
                 self.values[key] = (newval, newdelta)
         return self.values
 
-if not os.access('/sys/kernel/debug', os.F_OK):
-    print 'Please enable CONFIG_DEBUG_FS in your kernel'
+if not os.path.exists('/sys/kernel/debug'):
+    sys.stderr.write('Please enable CONFIG_DEBUG_FS in your kernel.')
     sys.exit(1)
-if not os.access(PATH_DEBUGFS_KVM, os.F_OK):
-    print "Please mount debugfs ('mount -t debugfs debugfs /sys/kernel/debug')"
-    print "and ensure the kvm modules are loaded"
+if not os.path.exists(PATH_DEBUGFS_KVM):
+    sys.stderr.write("Please make sure, that debugfs is mounted and "
+                     "readable by the current user:\n"
+                     "('mount -t debugfs debugfs /sys/kernel/debug')\n"
+                     "Also ensure, that the kvm modules are loaded.\n")
+    sys.exit(1)
+if not os.path.exists(PATH_DEBUGFS_TRACING):
+    sys.stderr.write("Please make {0} readable by the current user.\n"
+                     .format(PATH_DEBUGFS_TRACING))
     sys.exit(1)
 
 LABEL_WIDTH = 40