to recycle inodes after a destroy_dev() but not until all mounts
have picked up the change.
Add support for an overflow table for DEVFS inodes. The static
table defaults to 1024 inodes, if that fills, an overflow table
of 32k inodes is allocated. Both numbers can be changed at
compile time, the size of the overflow table also with the
sysctl vfs.devfs.noverflow.
Use atomic instructions to barrier between make_dev()/destroy_dev()
and the mounts.
Add lockmgr() locking of directories for operations accessing or
modifying the directory TAILQs.
Various nitpicking here and there.
de95b6cc45