daemon: listeners: make systemd listener optional

[metux]

On non systemd systems, the systemd-based activation is not needed at all,
thus make it build-time optional. It won't be built in if the 'nosystemd'
tag is set.

Signed-off-by: Enrico Weigelt, metux IT consult info@metux.net

- What I did

- How I did it

- How to verify it

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[thaJeztah]

Could you describe the problem you're trying to resolve, other than "I don't want to use systemd", as (if I'm not mistaken) this code will only be called when running as a systemd service, using the fd:// for the socket;

moby/daemon/listeners/listeners_linux.go

Lines 22 to 27 in 41be729

	case "fd":
	fds, err := listenFD(addr, tlsConfig)
	if err != nil {
	return nil, err
	}
	ls = append(ls, fds...)

[metux]

Could you describe the problem you're trying to resolve, other than "I don't want to use systemd", as (if I'm not mistaken) this code will only be called when running as a systemd service, using the fd:// for the socket;

moby/daemon/listeners/listeners_linux.go

Lines 22 to 27 in 41be729

	case "fd":
	fds, err := listenFD(addr, tlsConfig)
	if err != nil {
	return nil, err
	}
	ls = append(ls, fds...)

reduce unnecessary code, eg. for small systems, easier audits, ...

[AkihiroSuda]

reduce unnecessary code, eg. for small systems, easier audits, ...

How many bytes are reduced?

[thaJeztah]

How many bytes are reduced?

Was curious as well; did a quick try with this PR:

hack/make.sh binary

ls -l --block-size=1 ./bundles/binary-daemon/
total 204955648
-rwxr-xr-x 1 root root 37224448 Aug 24 12:13 containerd
-rwxr-xr-x 1 root root 11862016 Aug 24 12:13 containerd-shim-runc-v2
-rwxr-xr-x 1 root root 18219008 Aug 24 12:13 ctr
-rwxr-xr-x 1 root root   535800 Aug 24 12:13 docker-init
-rwxr-xr-x 1 root root  2046594 Aug 24 12:13 docker-proxy
-rwxr-xr-x 1 root root 63013608 Aug 24 12:13 dockerd
-rwxr-xr-x 1 root root    14185 Aug 24 12:13 dockerd-rootless-setuptool.sh
-rwxr-xr-x 1 root root     5190 Aug 24 12:13 dockerd-rootless.sh
-rwxr-xr-x 1 root root 11002021 Aug 24 12:13 rootlesskit
-rwxr-xr-x 1 root root  7055888 Aug 24 12:13 rootlesskit-docker-proxy
-rwxr-xr-x 1 root root 14348976 Aug 24 12:13 runc
-rwxr-xr-x 1 root root 39607984 Aug 24 12:13 vpnkit


hack/make.sh dynbinary
ls -l --block-size=1 ./bundles/dynbinary-daemon/
total 71487488
-rwxr-xr-x 1 root root  2246690 Aug 24 12:12 docker-proxy
-rwxr-xr-x 1 root root 69234944 Aug 24 12:12 dockerd

DOCKER_BUILDTAGS=no_systemd hack/make.sh binary

ls -l --block-size=1 ./bundles/binary-daemon/
total 204935168
-rwxr-xr-x 1 root root 37224448 Aug 24 12:14 containerd
-rwxr-xr-x 1 root root 11862016 Aug 24 12:14 containerd-shim-runc-v2
-rwxr-xr-x 1 root root 18219008 Aug 24 12:14 ctr
-rwxr-xr-x 1 root root   535800 Aug 24 12:14 docker-init
-rwxr-xr-x 1 root root  2046594 Aug 24 12:14 docker-proxy
-rwxr-xr-x 1 root root 62995856 Aug 24 12:14 dockerd
-rwxr-xr-x 1 root root    14185 Aug 24 12:14 dockerd-rootless-setuptool.sh
-rwxr-xr-x 1 root root     5190 Aug 24 12:14 dockerd-rootless.sh
-rwxr-xr-x 1 root root 11002021 Aug 24 12:14 rootlesskit
-rwxr-xr-x 1 root root  7055888 Aug 24 12:14 rootlesskit-docker-proxy
-rwxr-xr-x 1 root root 14348976 Aug 24 12:14 runc
-rwxr-xr-x 1 root root 39607984 Aug 24 12:14 vpnkit



DOCKER_BUILDTAGS=no_systemd hack/make.sh dynbinary
ls -l --block-size=1 ./bundles/dynbinary-daemon/
total 71471104
-rwxr-xr-x 1 root root  2246690 Aug 24 12:08 docker-proxy
-rwxr-xr-x 1 root root 69221448 Aug 24 12:08 dockerd

Looks like it's saving 20k max (on a ~60Mib binary);

• binary (static): 204955648-204935168=20480 (20kib)
• dynbinary: 71471104-71487488=16384 (16kib)