[gentoo-dev] rfc: improve file system mounting and unmounting in OpenRC

[William Hubbs]

All,

I have been looking over this bug for some time attempting to find a
good solution [1].

The original proposal is to add a "want" dependency which would work
like "need" but would not fail if the services wanted did not start [2].

I agree that the "want" dependency is a valid feature request. However, I
believe there is a better way to handle the issue in the original bug.
Basically, I want to follow the suggestion in this bug instead [3].

My concern about the original proposal is that it will make netmount try
to start all daemons that handle file systems, whether or not they are
actually necessary.

The proposal in [3], on the other hand, is to create a mount script that
works like netifrc. It would mount a single file system, which would be
determined by the link it was called from, much like how netifrc
determines which interface to work on.

Some of the advantages of this approach are listed in the bug. Here are
a few more I can think of.

- it will eliminate some of our incompatibilities with busybox [4] [5].

- It will give us honest reports of success or failure with regard to
  mounting file systems (netmount and localmount can't do that).

- Currently, we have to skip over certain file systems that we can't
  unmount during shutdown. With the new approach, if the mount script
  mounts a file system during boot, it will be able to unmount the same
  filesystem during shutdown, so that will eliminate more complexity in
  our mount/unmount handling.

The one down side of the new approach is the migration away from
netmount and localmount. I I will need to keep them as wrappers
for a release or two so we can fix all of our other services that
have dependencies on them.

I'll also work on making the transition as smooth as possible for our
users. I believe I'll be able to set up the initial symlinks for the
multiplexed mount script based on fstab contents automatically, but I'm
not sure about how much more automation I'll be able to do. I will
automate more as I come across ways to do so, and I am open to
suggestions for how to do so.

Let me know what you think.

William

[1] https://bugs.gentoo.org/show_bug.cgi?id=537996
[2] https://bugs.gentoo.org/show_bug.cgi?id=406021
[3] https://bugs.gentoo.org/show_bug.cgi?id=426944
[4] https://bugs.gentoo.org/show_bug.cgi?id=468600
[5] https://bugs.gentoo.org/show_bug.cgi?id=468604