Re: [Libguestfs] [PATCH v2 00/11] rvh-upload: Various fixes and cleanups

On Tue, Nov 19, 2019 at 02:36:36PM +0100, Martin Kletzander wrote: This is very likely. Shutdown on error is complicated. Virt-v2v starts one or more nbdkit processes in the background and then simply runs “qemu-img convert”. If nbdkit notices an error then it returns an error over NBD to qemu-img. If qemu-img exits with an error then virt-v2v exits. Before virt-v2v exits, it runs any exit handlers. In particular if you're using OCaml's at_exit, C's atexit(3) or wrappers like Tools_utils.unlink_on_exit or Tools_utils.rmdir_on_exit, then those have already run before nbdkit starts to shut down. Nbdkit should receive a signal from the kernel when its parent process (virt-v2v) goes away, because we're using prctl + PR_SET_PDEATHSIG + SIGTERM (via ‘nbdkit --exit-with-parent’). Note this happens *after* virt-v2v has fully exited. Hence what I say about the above being likely, since rmdir_on_exit "/var/tmp/rhvupload.XXXXXX" is being called from virt-v2v on exit: https://github.com/libguestfs/virt-v2v/blob/b8b9dcc90dbd91aec4b6bb82dd511... To further complicate things, in nbdkit < 1.16 the shutdown path from a signal was pretty racy. nbdkit 1.16 attempts to fix the shutdown path so that we now properly wait for all threads to exit before exiting nbdkit. The upstream commit is: https://github.com/libguestfs/nbdkit/commit/07806d6d5511bb5da2dfae2bf0009... nbdkit 1.16 is available in Fedora 31+ and RHEL 8.2 AV (out of brew at the moment), and while it probably won't make any difference here, if possible you should upgrade to it. It's fully backwards compatible. Oh and finally if we're running in a systemd unit, then systemd might try to kill everything when virt-v2v exits (but before nbdkit exits) and it's anyone's guess what happens then. Good luck! Probably best to try to make the code as bulletproof as possible so it doesn't depend on clean ups always running correctly. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com Fedora Windows cross-compiler. Compile Windows programs, test, and build Windows installers. Over 100 libraries supported. http://fedoraproject.org/wiki/MinGW