Fix crash if exception thrown during daemon startup

[gerboland]

The "system" loggers have different lifecycle to the client loggers.
Client loggers register/unregister themselves with the
MultiplexingLogger on creation/destruction. However "system" loggers did
not, and would leave a dangling pointer in the MultiplexingLogger if
they were destroyed before it was.

Fix is to treat system logger ownership differently from client, i.e.
have MultiplexingLogger own the system logger.

Crash without this patch can be easily reproduced by adding a throw in
the QemuVirtualMachineFactory constructor.

[gerboland]

Pet peeve: if you run multipassd via command line, no errors are printed to stdout. Can we do something about that?

[gerboland]

OSX CI failed, think infrastructure problem

[Saviq]

Pet peeve: if you run multipassd via command line, no errors are printed to stdout. Can we do something about that?

$ multipassd --help
Usage: ./build/bin/multipassd [options]
multipass service daemon

Options:
  -h, --help                                  Displays this help.
  -v, --version                               Displays version information.
  --logger <platform|stderr>                  specifies which logger to use
  -V, --verbosity <error|warning|info|debug>  specifies the logging verbosity
                                              level
  --address <server_name:port>                specifies which address to use
                                              for the multipassd service; a
                                              socket can be specified using
                                              unix:<socket_file>

[codecov]

Codecov Report

Merging #487 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #487      +/-   ##
=========================================
- Coverage   66.51%   66.5%   -0.01%     
=========================================
  Files         147     147              
  Lines        5626    5628       +2     
=========================================
+ Hits         3742    3743       +1     
- Misses       1884    1885       +1

Impacted Files	Coverage Δ
include/multipass/logging/multiplexing_logger.h	100% <ø> (ø)	⬆️
src/logging/multiplexing_logger.cpp	92.3% <100%> (-7.7%)	⬇️
src/daemon/daemon_config.cpp	50% <100%> (-0.95%)	⬇️

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[townsend2010]

Just a little inline thought I had, but not going to block on it.

But I'll wait on your feedback before having telling the bot I approve.

[gerboland]

@Saviq that's not an error. (With this patch) If an exception is thrown, the exception text is only sent to the journal, not stdout/stderr.

[townsend2010]

Hmm, I see the exception text on stderr when starting multipassd like multipassd --logger stderr...

[townsend2010]

bors r+

[albaguirre]

Ohhh I see why. I failed to account for something in mp::DaemonConfigBuilder::build() throwing before DaemonConfig is actually constructed.

[albaguirre]

@Saviq that's not an error. (With this patch) If an exception is thrown, the exception text is only sent to the journal, not stdout/stderr.

You want to look at daemon_main. I changed the exception handler to use multipass::log, you could double down and also use fmt::print(stderr, "....").

The init sequence is a little trick - that's why the logger is initialized as soon as possible, so it goes to the correct places - if multipass::log is called before a logger is in place, by default will send it to stderr.

[bors]

Build succeeded

• continuous-integration/travis-ci/push