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

[Eduardo Habkost <ehabkost@redhat.com>]

On Thu, Sep 14, 2017 at 09:38:13PM +0200, Amador Pahim wrote:
> On Tue, Sep 5, 2017 at 5:18 AM, Fam Zheng <famz@redhat.com> 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 <apahim@redhat.com>
> >> ---
> >>  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.

Isn't this exactly what Python does when an exception is raised
with no "try" 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.

I'm not sure this extra complexity is really necessary.  We could
fix all that by using mkdtemp() and deleting the temporary
directory on shutdown.

> 
> >
> >> +        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

-- 
Eduardo