Re: [Qemu-devel] [PATCH][RESEND] qemu/kvm_stat: Fix I/O error from kvm_stat

[Wei Huang]

On 08/30/2015 10:42 PM, Hemant Kumar wrote:
> Running kvm_stat on a powerpc macine where the kernel is compiled with
> KVM_BOOK3S_HV_EXIT_TIMING config option, generates the following error :
> 
>  # kvm_stat
> 
> Traceback (most recent call last):
>   File "/usr/bin/kvm_stat", line 644, in <module>
>     curses.wrapper(tui, stats)
>   File "/usr/lib64/python2.7/curses/wrapper.py", line 43, in wrapper
>     return func(stdscr, *args, **kwds)
>   File "/usr/bin/kvm_stat", line 550, in tui
>     refresh(sleeptime)
>   File "/usr/bin/kvm_stat", line 526, in refresh
>     s = stats.get()
>   File "/usr/bin/kvm_stat", line 486, in get
>     new = d.read()
>   File "/usr/bin/kvm_stat", line 29, in read
>     return dict([(key, val(key)) for key in self._fields])
>   File "/usr/bin/kvm_stat", line 28, in val
>     return int(file(self.base + '/' + key).read())
> IOError: [Errno 21] Is a directory: '/sys/kernel/debug/kvm/vm12840'
> 
> The error says that its trying to read the contents of a directory as if
> it were a file. The kernel here creates directories inside
> "/sys/kernel/debug/kvm/" for the individual VMs running on the
> machine. These directories contain timing information (for rm_entry,
> rm_intr, rm_exit, guest, cede) related to each vcpu of each VM. All of
> this is enabled with KVM_BOOK3S_HV_EXIT_TIMING config option for the
> kernel.

A suggestion: would it be useful to display these statistics in
perf_stat? I understand that these counters are per-vm-based; but they
might provide useful insights to end-users.

> 
> kvm_stat script isn't supposed to parse/read these directories and isn't
> even expecting any directories inside "/sys/kernel/debug/kvm/". This
> patch fixes the problem by avoiding lookup for these directories.
> 
> Reported-by: Krishnaja Balachandran <address@hidden>
> Signed-off-by: Hemant Kumar <address@hidden>
> ---
>  scripts/kvm/kvm_stat | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/kvm/kvm_stat b/scripts/kvm/kvm_stat
> index 7e5d256..1da7a53 100755
> --- a/scripts/kvm/kvm_stat
> +++ b/scripts/kvm/kvm_stat
> @@ -18,7 +18,11 @@ from ctypes import *
>  class DebugfsProvider(object):
>      def __init__(self):
>          self.base = '/sys/kernel/debug/kvm'
> -        self._fields = os.listdir(self.base)
> +        files = os.listdir(self.base)
> +        self._fields = []
> +        for f in files:
> +            if os.path.isfile(self.base + '/' + f):
> +                self._fields.append(f)
>      def fields(self):
>          return self._fields
>      def select(self, fields):
> 

I tested this patch on x86 box and didn't see any problem. So:

Reviewed-by: Wei Huang <address@hidden>

-Wei