04.10.2019 21:05, Eric Blake wrote: > On 9/24/19 3:31 AM, Vladimir Sementsov-Ogievskiy wrote: > >>>> +def qemu_nbd_popen(*args): >>>> + '''Run qemu-nbd in daemon mode and return the parent's exit code''' >>>> + return subprocess.Popen(qemu_nbd_args + ['--persistent'] + list(args)) >>>> + >>> >>> Should you also use a pid file here, and wait for the existence of the >>> pid file before returning (rather than hard-coding sleep(1))? >> >> What do you mean / how to do it? >> >> We want to wait until listening socket is prepared.. > > In shell: > > qemu-nbd --pid-file=/path/to/file ... > while [ ! -e /path/to/file ]; do > sleep ... # fractional second, or exponential, or whatever... > done > # Now the listening socket is indeed prepared > > You'd have to translate that idiom to python.
Don't see, how it is better than what I've done in 04.. But I can resend with this. At least, the fact that socket is initialized before creating pid file is undocumented.. > > Or: > > pre-open Unix socket at /path/to/socket > LISTEN_PID=... LISTEN_FDS=1 qemu-nbd ... 3<>/path/to/socket > > Now the socket is pre-created and passed into qemu-nbd via systemd socket > activation, so you know the listening socket is ready without having to do > any loop at all. Here's a patch in libnbd where we just switched from > waiting for the port to appear (because the test predated qemu-nbd pidfile > support) to instead using socket activation, for reference: > https://github.com/libguestfs/libnbd/commit/352331d177 > Hmm, I'm afraid I need more help in it, I don't know socket activation and googling for some time didn't help. How to pre-open the socket? How to set LISTEN_PID? Looking at the code I see that activation path failed if LISTEN_PID != getpid().. So I need to know qemu-nbd pid before starting it? o_O -- Best regards, Vladimir
