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kvm_stat: Print errno when syscall to perf_event_open() fails

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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 such 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 <wei@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Wei Huang 2015-01-21 16:15:31 -05:00 committed by Paolo Bonzini
parent 2c9d535a2e
commit 874b1cfad5
1 changed files with 6 additions and 1 deletions
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7
scripts/kvm/kvm_stat
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@ -13,6 +13,7 @@
import curses
import sys, os, time, optparse, ctypes
from ctypes import *
class DebugfsProvider(object):
def __init__(self):
@ -247,6 +248,9 @@ 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),
@ -330,7 +334,8 @@ 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)