dbus: Introduce GetAllProperties() for fetching all systemd unit properties

[martynasb]

Hi,

I would like to fetch a bunch of systemd service unit properties (e.g. NRestarts, ActiveState, SubState, etc.) in a single call, similar to what I get by running systemctl show <service>.

Currently, dbus/methods.go exposes two methods for retrieving unit properties:

GetUnitTypeProperties(unit string, unitType string)
|-> return c.getProperties(path, "org.freedesktop.systemd1."+unitType) // unitType = Service

GetUnitProperties(unit string)
|-> return c.getProperties(path, "org.freedesktop.systemd1.Unit")

Both of these methods call the getProperties() helper method:

getProperties(path dbus.ObjectPath, dbusInterface string)
|   ...
|-> err = obj.Call("org.freedesktop.DBus.Properties.GetAll", 0, dbusInterface).Store(&props)

getProperties() will return a different set of properties depending on the dbusInterface parameter value (i.e. org.freedesktop.systemd1.Unit vs org.freedesktop.systemd1.Service). See the dbus-send examples below that illustrate this:

$ dbus-send --system --dest=org.freedesktop.systemd1 --type=method_call /org/freedesktop/systemd1/unit/<MYSERVICE>_2eservice --print-reply org.freedesktop.DBus.Properties.GetAll string:"org.freedesktop.systemd1.Service" | grep -A 1 -e NRestarts -e ActiveState -e SubState
         string "NRestarts"
         variant             uint32 0

$ dbus-send --system --dest=org.freedesktop.systemd1 --type=method_call /org/freedesktop/systemd1/unit/<MYSERVICE>_2eservice --print-reply org.freedesktop.DBus.Properties.GetAll string:"org.freedesktop.systemd1.Unit" | grep -A 1 -e NRestarts -e ActiveState -e SubState
         string "ActiveState"
         variant             string "active"
--
         string "SubState"
         variant             string "running"

However, if we set the interface argument to an empty string, we get all of these properties in a single call:

$ dbus-send --system --dest=org.freedesktop.systemd1 --type=method_call /org/freedesktop/systemd1/unit/<MYSERVICE>_2eservice --print-reply org.freedesktop.DBus.Properties.GetAll string:"" | grep -A 1 -e NRestarts -e ActiveState -e SubState
         string "NRestarts"
         variant             uint32 0
--
         string "ActiveState"
         variant             string "inactive"
--
         string "SubState"
         variant             string "dead"

I would like to be able to do the same using this lib by invoking something along the lines of dbus.GetProperties("<MYSERVICE>.service", "")

[lucab]

Thanks for the PR! I'm currently away from my usual workstation; I'll give a look at this once I'm back
(with the rest of the backlog), likely in a few days.

[martynasb]

ping

[lucab]

Sorry for the long delay. I'm fine with adding this feature to the library.

The only comment I have is that if the actual goal of the PR is to expose all-interfaces properties, I'd directly call this GetAllProperties and get rid of the last string parameter. @martynasb do you have a usecase where you need to pass a non-empty arbitrary string, which is not already covered by the other methods?

[martynasb]

The only comment I have is that if the actual goal of the PR is to expose all-interfaces properties, I'd directly call this GetAllProperties and get rid of the last string parameter.

I've updated my PR accordingly. I hope I'm not missing anything obvious ;)

@martynasb do you have a usecase where you need to pass a non-empty arbitrary string, which is not already covered by the other methods?

Nope. GetAllProperties() should cover all of our use cases.

[lucab]

Great, thanks! Please just squash the commits, and I'll approve and merge.

[lucab]

LGTM, thanks!

[martynasb]

Thanks. Can you cut a new release?

[lucab]

Yep, but I'd like to get #310 in first. It shouldn't take too long, I'll ping back here once done.

[lucab]

https://github.com/coreos/go-systemd/releases/tag/v20

[martynasb]

Thanks!