NOTES.txt

			DIRFS IMPLEMENTATION DRAFT

IN-MEMORY NODES (DIRFS NODES)

 struct dirfs node have a pointer to their parent, this way there is no need for
 them to be kept in any data structure (RB-trees, LIST, TAILQ).
 Every dirfs node keeps a refcnt which indicates how many nodes it is parenting
 and the node cannot be destroyed as long as it contains references. One of the
 advantages of having a pointer to the parent is that you can recurse backwards
 and find out the whole path of a node. For dirfs this is extremely useful as
 many syscalls rely on them.

 dirfs nodes are allocated via VOP_NRESOLVE() and free'ed (if possible) via
 VOP_RECLAIM().

 A dirfs node which has an active file descriptor but no opencount references
 on the vnode it points to will be stored in a TAILQ of "passive fds" so that
 nresolve can still reactivate it instead of creating a new one.

 Active dirfs nodes have fds with opencount on the vnode that represents them.

 dirfs nodes use the inode number of the host file/directory they refer to. A
 RB-tree keyed by inode number will be available to perform lookups.

 HARD LINKS
 Passive cached directory nodes disconnected from their vnode via VOP_RECLAIM
 would be re-resolved at any time. VOP_NRESOLVE would have to find the node
 instead of creating a new one.

---------------------------------
Scratch pad

- RB tree only for active dirfs nodes. file descriptor resolver would trundle up
  until a fd is found.
- dirfs nodes would have a pointer to their parent node. parents should be
  ref'ed so that they are not ripped off from the dirfs node.
- RB tree probably not needed. Only parent pointer per dirfs node and a refcount
  to the parent.
- Parent pointes would be setup in the resolver and torn-down in the reclaim
  code. Reclaim is more complex then because you can't reclaim a node which
  still has refcount to the parent.
- dirfs nodes should have an inode number which would be the real inode from the
  real file in the host.
- It would be a good idea to lstat(2) on VOP_NRESOLVE() but do not open(2).
- Passive fd cache would need to be kept in a TAILQ. Those that have
  no vp->v_opencount would be placed in this TAILQ.
- Active fds would be the ones via VOP_OPEN().
- RB tree for inode_number -> dirfs node lookup.