I'm having some trouble with NFS.  I'm playing with some filesystem
stuff, which for ease of implementation I'm doing as an NFS server on
an unusual port number.  I've implemented only three calls, but those
are the only calls that are being made (the rest are stubs that among
other things print out the fact that they got called); they're statfs,
getattr, and lookup.

The problems come when I try to unmount the filesystem.  If I use
/sbin/umount, it fails.  The mount point is /tfs/test/1/mount, and when
I run "umount -f /tfs/test/1/mount" it says "/tfs/test/1: No such file
or directory", which if taken literally is simply incorrect.  Using
ktrace on umount reveals that it's doing a chdir() to /tfs/test/1/mount
and then appears to be walking up the filesystem tree a la /bin/pwd,
but getting confused (kdump output appended).  When this happens, the
only NFS requests made are a getattr on the filesystem's root (which
happens only sometimes) and a lookup of "." in that root.  umount
doesn't normally hiccup like this; what am I doing wrong?

The program includes a call to unmount(2) to unmount the filesystem

 if (unmount(mount_point,MNT_FORCE) < 0)
  { fprintf(stderr,"%s: unmount: %s\n",argvec[0],strerror(errno));
    exit(1);
  }

which normally works.  But in one case another process had its cwd on
the filesystem, and unmount() returned EBUSY, without unmounting
anything.  Is this a bug in MNT_FORCE, or am I misunderstanding
something?

I've even dumped out packet contents and they are what they should be.

That kdump output from umount(8) is appended after my signature.

					der Mouse

			    mouse@collatz.mcrcim.mcgill.edu

   263 ktrace   NAMI  "/sbin/umount"
   263 umount   RET   execve 0
   263 umount   CALL  sync
   263 umount   RET   sync 0
   263 umount   CALL  open(0x2e40,0,0xd624)
   263 umount   NAMI  "."
   263 umount   RET   open 3
   263 umount   CALL  chdir(0xf7fff168)
   263 umount   NAMI  "/tfs/test/1"
   263 umount   RET   chdir 0
   263 umount   CALL  lstat(0xf7fff174,0xf7fff078)
   263 umount   NAMI  "mount"
   263 umount   RET   lstat 0
   263 umount   CALL  chdir(0xf7fff174)
   263 umount   NAMI  "mount"
   263 umount   RET   chdir 0
   263 umount   CALL  __sysctl(0xf7ffeac0,0x2,0x1ed88,0xf7ffeabc,0,0)
   263 umount   RET   __sysctl 4
   263 umount   CALL  break(0x1ee48)
   263 umount   RET   break 0
   263 umount   CALL  break(0x1effc)
   263 umount   RET   break 0
   263 umount   CALL  break(0x1fffc)
   263 umount   RET   break 0
   263 umount   CALL  stat(0x8f50,0xf7ffebb0)
   263 umount   NAMI  "/"
   263 umount   RET   stat 0
   263 umount   CALL  lstat(0x1f000,0xf7ffebb0)
   263 umount   NAMI  "."
   263 umount   RET   lstat 0
   263 umount   CALL  open(0x1f000,0x4,0xf85cd900)
   263 umount   NAMI  ".."
   263 umount   RET   open 4
   263 umount   CALL  fstat(0x4,0xf7ffea68)
   263 umount   RET   fstat 0
   263 umount   CALL  fcntl(0x4,0x2,0x1)
   263 umount   RET   fcntl 0
   263 umount   CALL  break(0x20ffc)
   263 umount   RET   break 0
   263 umount   CALL  fstatfs(0x4,0xf7ffe968)
   263 umount   RET   fstatfs 0
   263 umount   CALL  break(0x22ffc)
   263 umount   RET   break 0
   263 umount   CALL  break(0x23ffc)
   263 umount   RET   break 0
   263 umount   CALL  fstat(0x4,0xf7ffebb0)
   263 umount   RET   fstat 0
   263 umount   CALL  getdirentries(0x4,0x21000,0x1000,0x20014)
   263 umount   RET   getdirentries 512/0x200
   263 umount   CALL  lstat(0x1f000,0xf7ffebb0)
   263 umount   NAMI  "../lower"
   263 umount   RET   lstat 0
   263 umount   CALL  lstat(0x1f000,0xf7ffebb0)
   263 umount   NAMI  "../upper"
   263 umount   RET   lstat 0
   263 umount   CALL  lstat(0x1f000,0xf7ffebb0)
   263 umount   NAMI  "../mount"
   263 umount   RET   lstat 0
   263 umount   CALL  getdirentries(0x4,0x21000,0x1000,0x20014)
   263 umount   RET   getdirentries 0
   263 umount   CALL  fchdir(0x3)
   263 umount   RET   fchdir 0
   263 umount   CALL  close(0x3)
   263 umount   RET   close 0
   263 umount   CALL  write(0x2,0xf7ffe808,0x8)
   263 umount   GIO   fd 2 wrote 8 bytes
       "umount: "
   263 umount   RET   write 8
   263 umount   CALL  write(0x2,0xf7ffe870,0xb)
   263 umount   GIO   fd 2 wrote 11 bytes
       "/tfs/test/1"
   263 umount   RET   write 11/0xb
   263 umount   CALL  write(0x2,0xf7ffe808,0x2)
   263 umount   GIO   fd 2 wrote 2 bytes
       ": "
   263 umount   RET   write 2
   263 umount   CALL  stat(0xf7ffeb38,0xf7ffead8)
   263 umount   NAMI  "/usr/share/nls/C/libc.cat"
   263 umount   RET   stat 0
   263 umount   CALL  open(0xf7ffeb38,0,0x13458)
   263 umount   NAMI  "/usr/share/nls/C/libc.cat"
   263 umount   RET   open 3
[...a whole bunch of stuff reading fd 3 deleted...]
   263 umount   CALL  close(0x3)
   263 umount   RET   close 0
   263 umount   CALL  write(0x2,0xf7ffe808,0x1a)
   263 umount   GIO   fd 2 wrote 26 bytes
       "No such file or directory
       "
   263 umount   RET   write 26/0x1a
   263 umount   CALL  exit(0x1)