[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v5 4/6] qemu.py: cleanup launch()
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCH v5 4/6] qemu.py: cleanup launch() |
Date: |
Tue, 25 Jul 2017 17:42:33 -0300 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Tue, Jul 25, 2017 at 07:10:12PM +0200, Amador Pahim wrote:
> launch() is currently taking care of a number of flows, each one if its
> own exception treatment, depending on the VM state and the files
> creation state.
>
> This patch makes launch() more resilient, off-loading the core calls to
> the new _launch() and calling shutdown() if any exception is raised by
> _launch(), making sure VM will be terminated and cleaned up.
>
> Signed-off-by: Amador Pahim <address@hidden>
> ---
> scripts/qemu.py | 42 +++++++++++++++++++++++++-----------------
> 1 file changed, 25 insertions(+), 17 deletions(-)
>
> diff --git a/scripts/qemu.py b/scripts/qemu.py
> index 56142ed59b..45a63e8e9d 100644
> --- a/scripts/qemu.py
> +++ b/scripts/qemu.py
> @@ -99,8 +99,11 @@ class QEMUMachine(object):
> return self._popen.pid
>
> def _load_io_log(self):
> - with open(self._qemu_log_path, "r") as fh:
> - self._iolog = fh.read()
> + try:
> + with open(self._qemu_log_path, "r") as fh:
> + self._iolog = fh.read()
> + except IOError:
> + pass
I don't like the idea of ignoring errors unconditionally. It's
OK to ignore the file if we are recovering from a crash and
didn't even create it, but it's not OK if we ran QEMU
successfully and we really want to load the log file.
Maybe an optional ignore_errors argument to shutdown() and its
helpers, to tell the shutdown functions that it is really OK to
ignore errors?
>
> def _base_args(self):
> if isinstance(self._monitor_address, tuple):
> @@ -126,23 +129,28 @@ class QEMUMachine(object):
> self._remove_if_exists(self._qemu_log_path)
>
> def launch(self):
> - '''Launch the VM and establish a QMP connection'''
> - devnull = open('/dev/null', 'rb')
> - qemulog = open(self._qemu_log_path, 'wb')
This was moved inside the try block.
This means we may try to read the log file even if we failed to
create it. This will have funny side-effects if the log file
already existed and we didn't have permissions to write to it.
For example:
("/var/tmp/myvm.log" was created by another user)
>>> m = qemu.QEMUMachine(binary='/usr/bin/qemu-system-x86_64', name='myvm')
>>> m.launch()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "qemu.py", line 151, in launch
self.shutdown()
File "qemu.py", line 182, in shutdown
self._post_shutdown()
File "qemu.py", line 130, in _post_shutdown
self._remove_if_exists(self._qemu_log_path)
File "qemu.py", line 83, in _remove_if_exists
os.remove(path)
OSError: [Errno 1] Operation not permitted: '/var/tmp/myvm.log'
>>> m.get_log()
'old log file\n'
>>>
> + '''
> + Try to launch the VM and make sure we cleanup on exception.
> + '''
> + if self.is_running():
> + return
Why exactly is this necessary?
Calling launch() twice is likely to be a mistake (e.g. what if
self.args was changed?). I would raise an Exception instead.
> +
> try:
> - self._pre_launch()
> - args = self._wrapper + [self._binary] + self._base_args() +
> self.args
> - self._popen = subprocess.Popen(args, stdin=devnull,
> stdout=qemulog,
> - stderr=subprocess.STDOUT,
> shell=False)
> - self._post_launch()
> + self._launch()
> except:
> - if self.is_running():
> - self._popen.kill()
> - self._popen.wait()
> - self._load_io_log()
> - self._post_shutdown()
> + self.shutdown()
> raise
>
> + def _launch(self):
> + '''Launch the VM and establish a QMP connection.'''
> + devnull = open('/dev/null', 'rb')
> + qemulog = open(self._qemu_log_path, 'wb')
> + self._pre_launch()
> + args = self._wrapper + [self._binary] + self._base_args() +
> self._args
This looks broken:
>>> m.launch()
Error launching VM.
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "qemu.py", line 147, in launch
args = self._wrapper + [self._binary] + self._base_args() + self._args
AttributeError: 'QEMUMachine' object has no attribute '_args'
> + self._popen = subprocess.Popen(args, stdin=devnull, stdout=qemulog,
> + stderr=subprocess.STDOUT, shell=False)
> + self._post_launch()
> +
> def shutdown(self):
> '''Terminate the VM and clean up'''
> if self.is_running():
> @@ -156,8 +164,8 @@ class QEMUMachine(object):
> if exitcode < 0:
> sys.stderr.write('qemu received signal %i\n' % -exitcode)
>
> - self._load_io_log()
> - self._post_shutdown()
It looks like the existing code isn't safe, and can call
_post_shutdown() before _post_launch() was called.
What if QEMUQtestMachine._pre_launch() failed because the qtest
socket is already in use by another process? We shouldn't delete
a socket that doesn't even belong to us.
I suggest setting self._qemu_log_path, self._monitor_address,
self._qtest_path only after the files were really created, and
make _post_shutdown() delete the files only if those attributes
are not None (meaning we will only delete files that we created).
> + self._load_io_log()
> + self._post_shutdown()
>
> underscore_to_dash = string.maketrans('_', '-')
> def qmp(self, cmd, conv_keys=True, **args):
> --
> 2.13.3
>
--
Eduardo
- [Qemu-devel] [PATCH v5 6/6] qemu.py: include qemu command line and output on launch error, (continued)
- [Qemu-devel] [PATCH v5 6/6] qemu.py: include qemu command line and output on launch error, Amador Pahim, 2017/07/25
- [Qemu-devel] [PATCH v5 2/6] qemu.py: use poll() instead of 'returncode', Amador Pahim, 2017/07/25
- [Qemu-devel] [PATCH v5 3/6] qemu.py: cleanup message on negative exit code, Amador Pahim, 2017/07/25
- [Qemu-devel] [PATCH v5 4/6] qemu.py: cleanup launch(), Amador Pahim, 2017/07/25
- Re: [Qemu-devel] [PATCH v5 0/6] scripts/qemu.py fixes and cleanups, no-reply, 2017/07/27