i dont see where this breaks...  if a server doesnt support/implement
it, we get just back a Rerror from the server.  and mv will do the
same thing it did before...  copying the file... mv is probably the
only program that will make use of the new syscall...

there are cases where Tmove can not work like when the source and
target are on different file systems... the kernel can figure this out and
just let the move syscall fail in that case...

maybe Tmove is a bad name... it is really means inter directory rename...

we are not really short of p9 opcodes... and the implementation will 
be in the expected places... 9p is not smb where all kinds of extensions
are crammed into complicated sub protocol transactions...

--
cinap