c/snap-bootstrap/initramfs_systemd_mount: Add support for overlayfs options and allow empty what argument for tmpfs

[sespiros]

That is for https://warthogs.atlassian.net/browse/FR-8352

[zyga]

Hey @sespiros can you please link this to a Jira card if one exists.

[valentindavid]

@zyga It works for me:

$ sudo systemd-mount '/tmp/lower '  --type overlay '--options=lowerdir=/tmp/lower\ ,upperdir=/tmp/upper\ ,workdir=/tmp/work\ ' /mnt/
Started unit mnt.mount for mount point: /mnt

Do we write the options in a unit somehow, I did not see?

[zyga]

@zyga It works for me:

$ sudo systemd-mount '/tmp/lower '  --type overlay '--options=lowerdir=/tmp/lower\ ,upperdir=/tmp/upper\ ,workdir=/tmp/work\ ' /mnt/
Started unit mnt.mount for mount point: /mnt

Do we write the options in a unit somehow, I did not see?

If those are written to mount units then the trailing space escape doesn't work. I didn't check if all code paths write it to a file first.