Schroder <perseant@hitl.washington.edu>, unlock the mounted on
vnode before we call VFS_ROOT so that we cover the case where the new
root vnode shares a lock with the mounted-on vnode. Note that we have
asserted vfs_busy on the new fs before unlocking, so no other process can
steal the mount out from under us.
The problem is that if "sl" is a symbolic link, a lookup on "sl/"
will be flagged as the last component. Thus VOP_LOOKUP will lock
the parent directory if LOCKPARENT is set. In order for the symbolic
link to be resolved, this lock needs to be released. namei() would
test for this by checking if ni_pathlen == 1, which it wouldn't as
"/" is left in the name, and namei() would not unlock the parent.
The next call to lookup() to resolve the symbolic link would fail
as the parent was still locked.
1) Eliminate all of the null component name special cases; handle runs of
slashes and leading and trailing slashes completely differently.
2) Return ENOENT when doing a lookup through an empty symlink.
3) Enforce that we're doing a lookup through a directory in in chdir() and
lookup() rather than in foo_lookup().
Not yet finished.
(1) "" no longer refers to the current working directory;
looking this up will now result in ENOENT.
(2) by stripping off trailing slashes and setting a `forcedir'
flag, make code such as { mkdir("dir", m); rmdir("dir/"); }
actually work.
struct member cn_nameptr 'const', since they should never be used to
modify the path name. (Only the pathname buffer, cn_pnbuf, should be
modified.) Propagate the const poisoning to code that uses the namei
and componentname structs.
