specific nodes when the process exits)
Move the vnode-cache-walking loop which was duplicated in pfs_exit() and
pfs_disable() into its own function, pfs_purge(), which looks for vnodes
marked as dead and / or belonging to the specified pfs_node and reclaims
them. Note that this loop is still extremely inefficient.
Add a comment in pfs_vncache_alloc() explaining why we have to purge the
vnode from the vnode cache before returning, in case anyone should be
tempted to remove the call to cache_purge().
Move the special handling for pfstype_root nodes into pfs_fileno_alloc()
and pfs_fileno_free() (the root node's fileno must always be 2). This
also fixes a bug where pfs_fileno_free() would reclaim the root node's
fileno, triggering a panic in the unr code, as that fileno was never
allocated from unr to begin with.
When destroying a pfs_node, release its fileno and purge it from the
vnode cache. I wish we could put off the call to pfs_purge() until
after the entire tree had been destroyed, but then we'd have vnodes
referencing freed pfs nodes. This probably doesn't matter while we're
still under Giant, but might become an issue later.
When destroying a pseudofs instance, destroy the tree before tearing
down the fileno allocator.
In pfs_mount(), acquire the mountpoint interlock when required.
MFC after: 3 weeks
517c13e66c