The code has an explicit fallback using runtime_scope_to_string(), which
is also documented in the man page. So -ENXIO should only be returned when
the fallback doesn't work, i.e. bus->runtime_scope == -EINVAL.
Fixup for f4b2933ee7.
This should fix the following errors during boot:
May 18 16:05:37 fedora systemd-update-utmp[263]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:38 fedora systemctl[360]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:38 fedora systemctl[363]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:38 fedora systemd-update-utmp[372]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:38 fedora @ystemctl[387]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:40 fedora systemd-update-utmp[477]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:41 fedora systemd-homed[509]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:41 fedora systemd-logind[510]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:41 fedora systemd-update-utmp[529]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:42 fedora systemd-user-runtime-dir[531]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:42 fedora systemctl[542]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
May 18 16:05:42 fedora systemd-hostnamed[556]: Assertion 'bus->description' failed at src/libsystemd/sd-bus/sd-bus.c:4201, function sd_bus_get_description(). Ignoring.
systemd-nspawn doesn't like invalid machine IDs and refuses to boot with one:
TEST-74-AUX-UTILS RUN: Tests for auxiliary utilities
...
Spawning container TEST-74-AUX-UTILS--3 on /var/tmp/systemd-test-TEST-74-AUX-UTILS_3/root.
Press Ctrl-] three times within 1s to kill container.
Failed to read machine ID from container image: Structure needs cleaning
E: nspawn failed with exit code 1
Follow-up to b4d42a82eb.
Fixes#26413: the docs said that the filter prevents writes, but it just a
filter at the system call level, and some of those calls are used for writing
and reading. This is confusing esp. when a higher level library call like
ntp_gettime() is denied.
I don't think it's realistic that we'll make the filter smarter in the near
future, so let's change the docs to describe the implementation.
Also, split out the advice part into a separate paragraph.
Unlike most other bus connections in our codebase this one is created
manually and every setting set invididually. It hence does not have a
description by default (as all automatic connections have). Set one
explicitly.
Now that clients might convey comm/description strings via the sockaddr,
let's actually use them on the other side, read the data via
getpeername() parse it, and include it in the "owner" creds (which is
how we call the peer's creds).
