Re: [Qemu-devel] [PATCH v8 06/13] qemu.py: make sure we only remove files we create

[Amador Pahim]

On Tue, Sep 5, 2017 at 5:18 AM, Fam Zheng <address@hidden> wrote:
> On Fri, 09/01 13:28, Amador Pahim wrote:
>> To launch a VM, we need to create basically two files: the monitor
>> socket (if it's a UNIX socket) and the qemu log file.
>>
>> For the qemu log file, we currently just open the path, which will
>> create the file if it does not exist or overwrite the file if it does
>> exist.
>>
>> For the monitor socket, if it already exists, we are currently removing
>> it, even if it's not created by us.
>>
>> This patch moves to pre_launch() the responsibility to make sure we only
>> create files that are not pre-existent and to populate a list of
>> controlled files. This list will then be used as the reference of
>> files to remove during the cleanup (post_shutdown()).
>>
>> Signed-off-by: Amador Pahim <address@hidden>
>> ---
>>  scripts/qemu.py | 30 +++++++++++++++++++++++-------
>>  1 file changed, 23 insertions(+), 7 deletions(-)
>>
>> diff --git a/scripts/qemu.py b/scripts/qemu.py
>> index 3ebe5ee0a4..c26e1412f9 100644
>> --- a/scripts/qemu.py
>> +++ b/scripts/qemu.py
>> @@ -41,6 +41,7 @@ class QEMUMachine(object):
>>              monitor_address = os.path.join(test_dir, name + "-monitor.sock")
>>          self._monitor_address = monitor_address
>>          self._qemu_log_path = os.path.join(test_dir, name + ".log")
>> +        self._qemu_log_fd = None
>>          self._popen = None
>>          self._binary = binary
>>          self._args = list(args) # Force copy args in case we modify them
>> @@ -50,6 +51,7 @@ class QEMUMachine(object):
>>          self._socket_scm_helper = socket_scm_helper
>>          self._debug = debug
>>          self._qemu_full_args = None
>> +        self._created_files = []
>>
>>      # This can be used to add an unused monitor instance.
>>      def add_monitor_telnet(self, ip, port):
>> @@ -128,30 +130,44 @@ class QEMUMachine(object):
>>                  '-display', 'none', '-vga', 'none']
>>
>>      def _pre_launch(self):
>> -        self._qmp = qmp.qmp.QEMUMonitorProtocol(self._monitor_address, 
>> server=True,
>> -                                                debug=self._debug)
>> +        try:
>> +            self._qmp = qmp.qmp.QEMUMonitorProtocol(self._monitor_address,
>> +                                                    server=True,
>> +                                                    debug=self._debug)
>> +        except:
>> +            raise
>
> What's the point of "except: raise"? It seems useless.

The point is to execute the block in the else only when no exception
happens. When some exception happens, I want to raise it without
executing the else block.

>
>> +        else:
>> +            if not isinstance(self._monitor_address, tuple):
>> +                self._created_files.append(self._monitor_address)
>> +
>> +        try:
>> +            flags = os.O_CREAT | os.O_EXCL | os.O_WRONLY
>> +            os.open(self._qemu_log_path, flags)
>
> Why change to os.open() instead of open()?

I want to create the file only if it does not exist. The open() flag
'x' is available only in python 3.3. For python <3.3, we need the
os.open() to have that feature.

>
>> +        except:
>> +            raise
>> +        else:
>> +            self._created_files.append(self._qemu_log_path)
>> +            self._qemu_log_fd = open(self._qemu_log_path, 'wb')
>>
>>      def _post_launch(self):
>>          self._qmp.accept()
>>
>>      def _post_shutdown(self):
>> -        if not isinstance(self._monitor_address, tuple):
>> -            self._remove_if_exists(self._monitor_address)
>> -        self._remove_if_exists(self._qemu_log_path)
>> +        while self._created_files:
>> +            self._remove_if_exists(self._created_files.pop())
>>
>>      def launch(self):
>>          '''Launch the VM and establish a QMP connection'''
>>          self._iolog = None
>>          self._qemu_full_args = None
>>          devnull = open(os.path.devnull, 'rb')
>> -        qemulog = open(self._qemu_log_path, 'wb')
>>          try:
>>              self._pre_launch()
>>              self._qemu_full_args = (self._wrapper + [self._binary] +
>>                                      self._base_args() + self._args)
>>              self._popen = subprocess.Popen(self._qemu_full_args,
>>                                             stdin=devnull,
>> -                                           stdout=qemulog,
>> +                                           stdout=self._qemu_log_fd,
>>                                             stderr=subprocess.STDOUT,
>>                                             shell=False)
>>              self._post_launch()
>> --
>> 2.13.5
>>
>
> Fam