fstab-generator: add x-systemd.requires and x-systemd.requires-mounts-for
Currently we have no way how to specify dependencies between fstab
entries (or another units) in the /etc/fstab. It means that users are
forced to bypass fstab and write .mount units manually.
The patch introduces new systemd fstab options:
x-systemd.requires=<PATH>
- to specify dependence an another mount (PATH is translated to unit name)
x-systemd.requires=<UNIT>
- to specify dependence on arbitrary UNIT
x-systemd.requires-mounts-for=<PATH ...>
- to specify dependence on another paths, implemented by
RequiresMountsFor=. The option may be specified more than once.
For example two bind mounts where B depends on A:
/mnt/test/A /mnt/test/A none bind,defaults
/mnt/test/A /mnt/test/B none bind,x-systemd.requires=/mnt/test/A
More complex example with overlay FS where one mount point depends on
"low" and "upper" directories:
/dev/sdc1 /mnt/low ext4 defaults
/dev/sdc2 /mnt/high ext4 defaults
overlay /mnt/merged overlay lowerdir=/mnt/low,upperdir=/mnt/high/data,workdir=/mnt/high/work,x-systemd.requires-mounts-for=/mnt/low,x-systemd.requires-mounts-for=mnt/high
https://bugzilla.redhat.com/show_bug.cgi?id=812826
https://bugzilla.redhat.com/show_bug.cgi?id=1164334