bedrock linux flopsie experimental shared subtree for /mnt and /media instructions

gistfile1.txt

Purpose:
In Bedrock Linux, as of flopsie, mounts in one client do not appear in others.
This is particularly annoying for things like usb drives which are mounted by a
mount command in one client, but then cannot have their contents used by
programs from other clients.

Solution:
Linux supports the ability to automatically propogate mount points in mount
trees when set up properly. Utilize that.

Hacky solution for flopsie:

1. Note: This requires testing/experimentation.  Could go horribly wrong.

2. Ensure /mnt and /media exist as directories in the core.

    mkdir -p /bedrock/clients/bedrock/mnt
    mkdir -p /bedrock/clients/bedrock/media

3. Open up /bedrock/clients/bedrock/etc/fstab and add the following:

    /mnt /mnt bind defaults,bind 0 0
    /media /media bind defaults,bind 0 0

4. Open up /bedrock/clients/bedrock/etc/init.d/rcS and just *before* the line
which announces "Setting up client shared items" (around line 230) add:

    announce "Sharing subtrees"
    mount --make-shared /mnt
    mount --make-shared /media
    result

5. Add the following to /bedrock/etc/frameworks.d/default (or some other framework/client.conf)

    bind = /mnt, /media

Thoughts/notes on solution for Hawkey:
- Have brs recognize a new key ("shared") which will check if the core has the
  given directory as a shared mount point and, if not, mount that, then
  continue as though it was a bind setting.  Will have to be careful to ensure
  we do not "leak" mount points in the core when doing this; will have to remove
  those as well when taking down a client.
- Do not create a new setting, but rather have all bind items act as described
  above.  This is conceptually simpler, but but will result in more mount
  points / overhead.
- Might be able to just make the root of the filesystem ("/") shared - then
  everything will propogate.  Experimentation seems to indicate this will not
  cause an infinite loop.  Haven't thought through possible downsides.
- When taking down a client, be sure to --make-private every mount point being
  unmounted to make sure the umount event does not propogate to other clients.
- When (re)mounting a "shared" item, will need to use --rbind to ensure the
  all of the sub-mount points propogate.