Fix systemd_ RPM macros usage on Debian-based distributions

[loli10K]

Description

Debian-based distributions do not seem to provide RPM macros for dealing with systemd pre- and post- (un)install actions: this results in errors when installing or upgrading .deb packages because the
resulting control scripts contain the following unresolved macros:

• %systemd_post
• %systemd_preun
• %systemd_postun

Fix this by providing default values for postinstall, preuninstall and postuninstall scripts when these macros are not defined.

I think this was accidentally introduced by fixing systemd packaging (ee410ee).

Motivation and Context

Fix #7074

How Has This Been Tested?

Tested on Debian8 (both with --enable-systemd and --disable-systemd):

without systemd:

root@linux:/usr/src/zfs# strace -tf -e trace=execve dpkg -i zfs_0.7.0-266_amd64.deb |& grep chkconfig
[pid 19453] 23:45:15 execve("/sbin/chkconfig", ["/sbin/chkconfig", "--add", "zfs-import"], [/* 19 vars */]) = 0
[pid 19455] 23:45:15 execve("/sbin/chkconfig", ["/sbin/chkconfig", "--add", "zfs-mount"], [/* 19 vars */]) = 0
[pid 19457] 23:45:15 execve("/sbin/chkconfig", ["/sbin/chkconfig", "--add", "zfs-share"], [/* 19 vars */]) = 0
[pid 19459] 23:45:15 execve("/sbin/chkconfig", ["/sbin/chkconfig", "--add", "zfs-zed"], [/* 19 vars */]) = 0
root@linux:/usr/src/zfs# strace -tf -e trace=execve dpkg -r zfs |& grep chkconfig
[pid 19916] 23:45:21 execve("/sbin/chkconfig", ["/sbin/chkconfig", "--del", "zfs-import"], [/* 19 vars */]) = 0
[pid 19918] 23:45:22 execve("/sbin/chkconfig", ["/sbin/chkconfig", "--del", "zfs-mount"], [/* 19 vars */]) = 0
[pid 19920] 23:45:22 execve("/sbin/chkconfig", ["/sbin/chkconfig", "--del", "zfs-share"], [/* 19 vars */]) = 0
[pid 19922] 23:45:22 execve("/sbin/chkconfig", ["/sbin/chkconfig", "--del", "zfs-zed"], [/* 19 vars */]) = 0

with systemd:

root@linux:/usr/src/zfs# strace -tf -e trace=execve dpkg -i zfs_0.7.0-266_amd64.deb |& grep systemctl
[pid 21845] 00:11:54 execve("/bin/systemctl", ["systemctl", "--system", "daemon-reload"], [/* 21 vars */]) = 0
root@linux:/usr/src/zfs# strace -tf -e trace=execve dpkg -r zfs |& grep systemctl
[pid 22413] 00:12:04 execve("/bin/systemctl", ["systemctl", "--no-reload", "disable", "zfs-import-cache.service", "zfs-import-scan.service", "zfs-mount.service", "zfs-share.service", "zfs-zed.service", "zfs.target", "zfs-import.target"], [/* 21 vars */]) = 0
[pid 22414] 00:12:04 execve("/bin/systemctl", ["systemctl", "stop", "zfs-import-cache.service", "zfs-import-scan.service", "zfs-mount.service", "zfs-share.service", "zfs-zed.service", "zfs.target", "zfs-import.target"], [/* 21 vars */]) = 0
[pid 22417] 00:12:04 execve("/bin/systemctl", ["systemctl", "--system", "daemon-reload"], [/* 21 vars */]) = 0

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.
• Change has been approved by a ZFS on Linux member.

[dinatale2]

@loli10K There appears to be a package called dh-systemd which provides helpers. I'm not sure if it can be leveraged for this. I'm attempting to find a good example.

[codecov]

Codecov Report

Merging #7100 into master will decrease coverage by 0.18%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7100      +/-   ##
==========================================
- Coverage   75.53%   75.35%   -0.19%     
==========================================
  Files         296      296              
  Lines       95713    95713              
==========================================
- Hits        72298    72124     -174     
- Misses      23415    23589     +174

Flag	Coverage Δ
#kernel	74.87% <ø> (-0.15%)	⬇️
#user	67.43% <ø> (-0.32%)	⬇️

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[behlendorf]

This LGTM. @dinatale2 in this case I think it's best not to pull in an additional dependency when providing the needed macros ourselves is straight forward.

[loli10K]

@dinatale2 i opted to hardcode the systemctl binary because dh-systemd seems to only be used to transition from X to systemd: in newer versions (https://packages.debian.org/sid/dh-systemd) the package description reads:

This package is for transitional purposes and can be removed safely.

Another issue with using Debian-specific helpers (deb-systemd-invoke from the init-system-helpers package) is that rpms produced on Debian cannot be installed on RPM-based systems[1]

[1] there are other issues with this, for instance:

[root@centos ~]# rpm -ivh *.rpm
error: Failed dependencies:
	libcrypto.so.1.0.0()(64bit) is needed by libzfs2-0.7.0-266_g405ec51.x86_64
	libcrypto.so.1.0.0(OPENSSL_1.0.0)(64bit) is needed by libzfs2-0.7.0-266_g405ec51.x86_64
	libssl.so.1.0.0()(64bit) is needed by libzfs2-0.7.0-266_g405ec51.x86_64