Re: [PATCH] docs: show how to spawn qemu-storage-daemon with fd passing

[Markus Armbruster]

Daniel P. Berrangé <berrange@redhat.com> writes:

> On Mon, Mar 01, 2021 at 09:49:21AM -0600, Eric Blake wrote:
>> On 3/1/21 9:41 AM, Daniel P. Berrangé wrote:
>> > On Mon, Mar 01, 2021 at 03:31:59PM +0000, Stefan Hajnoczi wrote:
>> >> The QMP monitor, NBD server, and vhost-user-blk export all support file
>> >> descriptor passing. This is a useful technique because it allows the
>> >> parent process to spawn and wait for qemu-storage-daemon without busy
>> >> waiting, which may delay startup due to arbitrary sleep() calls.
>> >>
>> >> This Python example is inspired by the test case written for libnbd by
>> >> Richard W.M. Jones <rjones@redhat.com>:
>> >> https://gitlab.com/nbdkit/libnbd/-/commit/89113f484effb0e6c322314ba75c1cbe07a04543
>> >>
>> >> Thanks to Daniel P. Berrangé <berrange@redhat.com> for suggestions on
>> >> how to get this working. Now let's document it!
>> >>
>> 
>> >> +  sock_path = '/tmp/qmp-{}.sock'.format(os.getpid())
>> > 
>> > Example code inevitably gets cut+paste into real world apps, and this
>> > example is a tmpfile CVE flaw. At least put it in $CWD instead.
>> 
>> Except $CWD may be too long for a sock file name to be created.
>> Creating the sock in a securely-created subdirectory of /tmp is more
>> reliable.
>
> $XDG_RUNTIME_DIR then, which is /run/user/$UID, so safely per user on all
> modern OS.

Reach under your pillow and check the standard library:

    import tempfile

    with tempfile.TemporaryDirectory() as tmpdirname:
        print('created temporary directory', tmpdirname)

https://docs.python.org/3.6/library/tempfile.html#tempfile.TemporaryDirectory