In order to unmount, we need to drop all vnodes on a mount point, so we
need to find all directory entries pointing to them.

Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

Signed-off-by: Avi Kivity <avi@cloudius-systems.com>

Create a new dentry structure for pathname components, following the Linux
VFS model.  The vnodes are left-as is for now but are always fronted by
dentries for pathname lookups.  In a second step they will be moved to
use non-pathname indices.

[penberg: fix open(O_CREAT|O_EXCL) breakage ]

When a file incorrectly is used as a directory ("/bin/sh/foo"), namei()
detects this and fails, but returns 0 as the error code.  Later on open()
uses an uninitialized vnode and segaults.

Fix by returning ENOENT.

Fixes fontconfig segfault when it randomly tries to open files as Mac fonts
with resource/data forks.

I've also added an osv/ prefix to make sure we don't clash with system headers.

We probably should either adopt this globally or drop it, but I fear we'll run into
problems with the latter approach.

Various changes to fit into the OSv environment.  This also includes
a ramfs in-memory full filesystem.  Bootfs is rewritten as a simple
unpacker into ramfs, and the fs class is modified to wrap the VFS
instead of being an abstract subclass.