In order to allow FD Stores of user units to survive a user
session restart, propagate FDs received via the protocol up one
level from user to system manager via sd_notify.
And the other way around, propagate them down via LISTEN_FDS
tagging them with the unit name so that the child manager can
inject them in the appropriate unit.
Ensure units that are dead or not loaded can get FDs added to
their stores, and that they are correctly propagated once the
unit is started or loaded. When the unit is not loaded we don't
know what the FD max limit is, so simply increase it for each FD
injected, and then when the unit is realised prune it down to
match the unit's now available config in case the limit is lower
than the number of FDs in the store.
Each FD sent up or down is assigned a monotonic index, and the manager
also sends a JSON map that associates the index with the original
unit and FDNAME:
{
"unit-name.service": [
{ "name": "fdname1", "index": 1 },
{ "name": "fdname2", "index": 2 }
],
...
}
This allows the manager to assign back the FDs to the appropriate
unit using the appropriate name, given the FDNAMEs are not unique.
This partially reverts 36c557f7d4, which
introduced notify_remove_fd() that logs in LOG_DEBUG. However,
notify_remove_fd_warn() is still called other library functions, e.g.
notify_push_fd(), and produces warning message about the failure in
removing fd from fdstore on shutdown.
During shutdown process, we get the following logs:
```
systemd-udevd[370]: Failed to send notify message to '/run/systemd/notify': Connection refused
systemd-udevd[370]: Failed to remove file descriptor "config-serialization" from the store, ignoring: Connection refused
systemd-udevd[370]: Failed to send notify message to '/run/systemd/notify': Connection refused
systemd-udevd[370]: Failed to push serialization fd to service manager: Connection refused
```
Here, the 1st, 3rd, and 4th messages are in LOG_DEBUG, but the 2nd one
was in LOG_WARNING before this commit, and this makes it also in LOG_DEBUG.
Follow-up for 472404aca5.
Let's not leak details from src/shared and src/libsystemd into
src/basic, even though you can't actually do anything useful with
just forward declarations from src/shared.
The sd-forward.h header is put in src/libsystemd/sd-common as we
don't have a directory for shared internal headers for libsystemd
yet.
Let's also rename forward.h to basic-forward.h to keep things
self-explanatory.
Currently, NOTIFY_READY from daemon-util.h conflicts with NOTIFY_READY
from NotifyState from service.h so let's rename the constants to avoid
the conflict.
p itself is never null. Because of this, we would always
call sd_notify() in cleanup, even though the intention was to only
call it if notify_start() was executed.
Luca Boccassi
Yu Watanabe
Daan De Meyer
Mike Yuan
Zbigniew Jędrzejewski-Szmek