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kvm_stat: Print errno when syscall to perf_event_open() fails
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>
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@ -13,6 +13,7 @@
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import curses
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import sys, os, time, optparse, ctypes
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from ctypes import *
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class DebugfsProvider(object):
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def __init__(self):
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@ -247,6 +248,9 @@ import struct, array
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libc = ctypes.CDLL('libc.so.6')
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syscall = libc.syscall
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get_errno = libc.__errno_location
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get_errno.restype = POINTER(c_int)
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class perf_event_attr(ctypes.Structure):
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_fields_ = [('type', ctypes.c_uint32),
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('size', ctypes.c_uint32),
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@ -330,7 +334,8 @@ class Event(object):
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group_leader = group.events[0].fd
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fd = _perf_event_open(attr, -1, group.cpu, group_leader, 0)
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if fd == -1:
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raise Exception('perf_event_open failed')
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err = get_errno()[0]
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raise Exception('perf_event_open failed, errno = ' + err.__str__())
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if filter:
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import fcntl
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fcntl.ioctl(fd, ioctl_numbers['SET_FILTER'], filter)
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