Augment systemd-stdio-bridge a bit to make it a 1:1 bridge from legacy
DBus clients to kdbus. In particular,
* allow setting the bus path of the upstream bus as command line
argument
* use sd_listen_fds() for systemd's socket activation
* omit calling sd_bus_negotiate_fds() when upstream bus is kdbus
* reply to bus send errors with proper dbus error messages
* treat -ECONNRESET as expected end-of-connection condition
Among other things this also adds a few things necessary for the change:
- Considerably more powerful error returning APIs in libsystemd-bus
- Adapter for connecting an sd_bus to an sd_event
- As I reworked the PolicyKit logic to the new library I also made it
asynchronous, so that PolicyKit requests of one user cannot block out
another user anymore.
- We always use the macro names for common bus error. That way it is
harder to mistype them since the compiler will notice
Before, we would initialize many fields twice: first
by filling the structure with zeros, and then a second
time with the real values. We can let the compiler do
the job for us, avoiding one copy.
A downside of this patch is that text gets slightly
bigger. This is because all zero() calls are effectively
inlined:
$ size build/.libs/systemd
text data bss dec hex filename
before 897737 107300 2560 1007597 f5fed build/.libs/systemd
after 897873 107300 2560 1007733 f6075 build/.libs/systemd
… actually less than 1‰.
A few asserts that the parameter is not null had to be removed. I
don't think this changes much, because first, it is quite unlikely
for the assert to fail, and second, an immediate SEGV is almost as
good as an assert.
