Like the find method of standard containers, this returns an iterator
to the requested key.

I'm sure it fails for some other naming format..

An xns must fit in a page, but that doesn't allow enough buckets
to avoid physical sharing in dirbench.  This is basically a
work-around for the one page limit.

I'll be changing the dirns implementation soon.

..next step is a namex that takes no refs.

The only unexpected sharing is on the VMA refcount, which is
exactly what we expected.

This eliminates a bunch of confusing scopes that come from thread creation

With the mtrace QEMU, which now switches VCPUs when there's a PAUSE,
this speeds up my lame test (usertests vmoverlap) by a factor of 7 and
certainly makes xv6 feel much faster.

So we can hush up spurious errors.

The user errors stream is disabled by default.

These have the type-safety and extensibility of ostreams, but the
simplicity and almost the terseness of printf.

Split the inode space into per-cpu spaces of size IPB that start at
the begining of a block.  Block awareness is important to avoid
contention on blocks themselves when allocating or freeing an inode
and updating on-disk structures.  That is, I don't want to make bio
scalable.

This might be a mistake because we can't control the order of global
construction, but we already have several global constructors that
were simply not being called before.  As long as we keep all global
constructors simple, this should be okay.

Here we already treat the radix tree as the source of truth, so we
don't actually care if the VMA has been deleted or not.