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[Qemu-devel] [PATCH V3 2/4] kvm_stat: Print errno when syscall to perf_e
From: |
Wei Huang |
Subject: |
[Qemu-devel] [PATCH V3 2/4] kvm_stat: Print errno when syscall to perf_event_open() fails |
Date: |
Fri, 23 Jan 2015 15:56:02 -0500 |
kvm_stat uses syscall() to call perf_event_open(). If this function
call fails, the returned value is -1, which doesn't tell the details
of the failure (i.e. ENOSYS or EINVAL). This patch retrieves errno
and prints it when syscall() fails. The error message will look like
"Exception: perf_event_open failed, errno = 38".
Signed-off-by: Wei Huang <address@hidden>
---
scripts/kvm/kvm_stat | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/scripts/kvm/kvm_stat b/scripts/kvm/kvm_stat
index 7ec84c0..cb23877 100755
--- a/scripts/kvm/kvm_stat
+++ b/scripts/kvm/kvm_stat
@@ -13,6 +13,7 @@
import curses
import sys, os, time, optparse, ctypes
+from ctypes import *
class DebugfsProvider(object):
def __init__(self):
@@ -239,6 +240,9 @@ import struct, array
libc = ctypes.CDLL('libc.so.6')
syscall = libc.syscall
+get_errno = libc.__errno_location
+get_errno.restype = POINTER(c_int)
+
class perf_event_attr(ctypes.Structure):
_fields_ = [('type', ctypes.c_uint32),
('size', ctypes.c_uint32),
@@ -322,7 +326,8 @@ class Event(object):
group_leader = group.events[0].fd
fd = _perf_event_open(attr, -1, group.cpu, group_leader, 0)
if fd == -1:
- raise Exception('perf_event_open failed')
+ err = get_errno()[0]
+ raise Exception('perf_event_open failed, errno = ' + err.__str__())
if filter:
import fcntl
fcntl.ioctl(fd, ioctl_numbers['SET_FILTER'], filter)
--
1.8.3.1