move_obstructions behavior

  Hi Ron,

  It's very helpful if you provide a small standalone policy that
  demonstrates the behavior. I think this does it:

  ,----
  | bundle agent __main__
  | {
  |   files:
  |     "/tmp/move-obstructions.txt"
  |       content => "I am a plain file";
  |
  |     "/tmp/move-obstructions.txt"
  |       move_obstructions => "false",
  |       link_from => default:ln_s( "$(this.promise_filename)" );
  | }
  `----

  ,----
  |  info: Created file '/tmp/move-obstructions.txt', mode 0600
  |  info: Updated file '/tmp/move-obstructions.txt' with content 'I am a plain file'
  | error: Object '/tmp/move-obstructions.txt' is obstructing promise
  | error: Unable to create link '/tmp/move-obstructions.txt' -> '/home/nickanderson/org/roam/daily/work/cfengine3-0cVlsi', failed to move obstruction
  | error: Errors encountered when actuating files promise '/tmp/move-obstructions.txt'
  `----



  Based on your description alone, I can see the sense in *not* emitting
  an *error* when `move_obstructions' is `false'. Indeed, if you are
  explicit about not wanting to move something out of the way it seems a
  bit silly to emit an error. However it also seems like this might be
  better expressed in the policy to simply avoid making a promise in
  that case.

  This policy will create the link because there is no file there.

  ,----
  | bundle agent __main__
  | {
  |   files:
  |
  |     "/tmp/move-obstructions.txt"
  |       delete => default:tidy;
  |
  |     "/tmp/move-obstructions.txt"
  |       link_from => default:ln_s( "$(this.promise_filename)" ),
  |       if => not( fileexists( "/tmp/move-obstructions.txt" ) ),
  |       comment =>  "If there is nothing there, we want to have a symlink";
  |
  | }
  `----

  ,----
  | info: Deleted file '/tmp/move-obstructions.txt'
  | info: Linked files '/tmp/move-obstructions.txt' -> '/home/nickanderson/org/roam/daily/work/cfengine3-gp5E8s'
  `----


  But what if there is a symlink, but it's pointing elsewhere? With
  `move_obstructions => "false"' (the default) the symlink target won't
  be fixed:

  ,----
  | bundle agent __main__
  | {
  |   files:
  |
  |       "/tmp/move-obstructions.txt"
  |         delete => default:tidy;
  |
  |       "/tmp/move-obstructions.txt"
  |         link_from => default:ln_s( "/etc/hosts" ),
  |         if => not( fileexists( "/tmp/move-obstructions.txt" ) ),
  |         comment =>  "If there is nothing there, we link the file to /etc/hosts";
  |
  |       "/tmp/move-obstructions.txt"
  |         link_from => default:ln_s( "/etc/issue" ),
  |         if => islink( "/tmp/move-obstructions.txt" ),
  |         comment =>  "If it's a symlink, we fix the link";
  |
  |       "/tmp/move-obstructions.txt"
  |         link_from => default:ln_s( "/etc/motd" ),
  |         if => islink( "/tmp/move-obstructions.txt" ),
  |         move_obstructions => "true",
  |         comment =>  "If it's a symlink, we fix the link";
  |
  | }
  `----

  ,----
  |  info: Deleted file '/tmp/move-obstructions.txt'
  |  info: Linked files '/tmp/move-obstructions.txt' -> '/etc/hosts'
  | error: Link '/tmp/move-obstructions.txt' points to '/etc/hosts' not '/etc/issue', but not moving obstructions
  | error: Errors encountered when actuating files promise '/tmp/move-obstructions.txt'
  |  info: Overrode incorrect link '/tmp/move-obstructions.txt'
  |  info: Linked files '/tmp/move-obstructions.txt' -> '/etc/motd'
  `----


  So, what do you think? Do you still think that explicitly setting
  `move_obstructions => "false"' should suppress the error about not
  moving things out of the way?

  Actually, looking at this and reviewing the docs, I think the link
  should have been updated since that was already the same type of file.
  Still, I think it's a bit better to be more explicit about the
  conditions under which you want to actually make the promise. Based on
  your description not wanting to replace a file or directory with a
  link, but presumably wanting to fix a link that is pointing to the
  wrong place I would probably write it like this:

  ,----
  | bundle agent __main__
  | {
  |   files:
  |     "/tmp/move-obstructions.txt"
  |       content => "I am a plain file";
  |
  |     "/tmp/move-obstructions.txt"
  |       move_obstructions => "true",
  |       link_from => default:ln_s( "/etc/motd" ),
  |       if => islink( "$(this.promiser)" ),
  |       comment => concat( "If the file is a symlink, be sure to make sure it",
  |                          " points to the correct place, if the file is a plain",
  |                          " file or directory or socket etc ... then just leave it alone." );
  | }
  `----

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