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[Qemu-devel] [PATCH] scripts/kvm/kvm_stat: Fix tracefs access checking


From: Janosch Frank
Subject: [Qemu-devel] [PATCH] scripts/kvm/kvm_stat: Fix tracefs access checking
Date: Wed, 3 Feb 2016 08:41:31 +0100

On kernels build without CONFIG_TRACING kvm_stat will bail out even
when traces are not used. This is not very helpful, especially if the
user can't install a new kernel. Instead, we should warn the user and
fall back to debugfs statistics.

These changes check if trace statistics were selected without kernel
support, warn with a small timeout, set the debugfs statistics option
to True and the tracefs one to False.

Fixes: 7aa4ee5 ('scripts/kvm/kvm_stat: Improve debugfs access checking')
Signed-off-by: Janosch Frank <address@hidden>
---
 scripts/kvm/kvm_stat | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/scripts/kvm/kvm_stat b/scripts/kvm/kvm_stat
index d43e8f3..bab34bb 100755
--- a/scripts/kvm/kvm_stat
+++ b/scripts/kvm/kvm_stat
@@ -22,6 +22,7 @@ import resource
 import struct
 import re
 from collections import defaultdict
+from time import sleep
 
 VMX_EXIT_REASONS = {
     'EXCEPTION_NMI':        0,
@@ -778,7 +779,7 @@ def get_providers(options):
 
     return providers
 
-def check_access():
+def check_access(options):
     if not os.path.exists('/sys/kernel/debug'):
         sys.stderr.write('Please enable CONFIG_DEBUG_FS in your kernel.')
         sys.exit(1)
@@ -790,14 +791,23 @@ def check_access():
                          "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"
+    if not os.path.exists(PATH_DEBUGFS_TRACING) and (options.tracepoints
+                                                     or not options.debugfs):
+        sys.stderr.write("Please enable CONFIG_TRACING in your kernel "
+                         "when using the option -t (default).\n"
+                         "If it is enabled, make {0} readable by the "
+                         "current user.\n"
+                         "Falling back to debugfs statistics!\n"
                          .format(PATH_DEBUGFS_TRACING))
-        sys.exit(1)
+        options.debugfs = True
+        options.tracepoints = False
+        sleep(5)
+
+    return options
 
 def main():
-    check_access()
     options = get_options()
+    options = check_access(options)
     providers = get_providers(options)
     stats = Stats(providers, fields=options.fields)
 
-- 
2.3.0




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