[Qemu-devel] [PATCH v2] scripts/kvm/kvm_stat: Fix tracefs access checking

[Janosch Frank]

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 and warn the user. If they were not selected explicitly, we
wait five seconds to let the user read the warning and then set the
debugfs statistics to True and the tracefs ones to False. Otherwise we
exit.

Fixes: 7aa4ee5 ('scripts/kvm/kvm_stat: Improve debugfs access checking')
Signed-off-by: Janosch Frank <address@hidden>
---
 v1 to v2:
    Exit if -t is set explicitly

 scripts/kvm/kvm_stat | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/scripts/kvm/kvm_stat b/scripts/kvm/kvm_stat
index d43e8f3..4756eee 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 +791,26 @@ 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"
                          .format(PATH_DEBUGFS_TRACING))
-        sys.exit(1)
+
+        if options.tracepoints:
+            sys.exit(1)
+
+        sys.stderr.write("Falling back to debugfs statistics!\n")
+        options.debugfs = True
+        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