Dear Max,
thanks for taking the time to fix the race condition!
Max Reitz <mre...@redhat.com> writes:
> Using the --fork option, one can make qemu-nbd fork the worker process.
> The original process will exit on error of the worker or once the worker
> enters the main loop.
> @@ -773,7 +780,7 @@ int main(int argc, char **argv)
> return 0;
> }
>
> - if (device && !verbose) {
> + if ((device && !verbose) || fork_process) {
> int stderr_fd[2];
> pid_t pid;
> int ret;
Looking at the surrounding (unchanged) code I see that qemu-nbd already
implemented a daemon mode. It's just that it's completely undocumented
and hinges on both the --device and the --verbose option. Yuck.
It seems there are two things --verbose does (from a user point of
view):
1. Print "NBD device %s is now connected to %s" and keep stderr open.
Debug messages are always printed to stderr, but in non-verbose
daemon mode they end up at /dev/null.
This is more or less what one usually expects from an option named
--verbose. Except that it only affects daemon mode and messages are
always printed (but end up at /dev/null).
2. Disable daemon mode.
I might expect this for an option named --debug, but certainly not
for --verbose...
A clean way forward would be something like this:
1. Introduce --foreground / --daemon, --quiet
Default to daemon mode with silent output if --connect is given,
foreground mode with visible output otherwise. Set non-daemon mode
with visible output if --verbose is given. Let --foreground /
--daemon / --quiet any default or implicit value. Document that
--verbose implicitly enables daemon mode for compatibility with
previous versions and that future versions may stop doing so
(i.e. users should use either --verbose --foreground or --verbose
--daemon).
3. At some point in the future (qemu 3.0?) we can stop having --verbose
imply --foreground.
I can give it a try if it's out of scope for your current task.
Sascha
--
Softwareentwicklung Sascha Silbe, Niederhofenstraße 5/1, 71229 Leonberg
https://se-silbe.de/
USt-IdNr. DE281696641
