On Fri, 23 Jun 2000, Tim Waugh wrote:
> On Fri, Jun 23, 2000 at 05:18:03PM +0100, Tigran Aivazian wrote:
>
> > How?
>
> ptrace
>
in the world where one can single-step a process and replace any
instruction with any other one could say "everything is possible in
userspace". So I still see no valid way to do it other than the same thing
that causes some people to say that it is possible to replace system calls
in userspace (there is even a very interesting program with a very long
name that does it - forgot the name, that fiddles with ptrace "beyond
the normal human's anticipation of what ptrace(2) is for"). Existence of
programs that do the impossible is not a proof that that "impossible" is
now possible :)
So, I still think that at the moment there is NO (neither kernel nor
userspace) way to close a given process' file descriptor. To do that one
needs to (at least, there are lots of other issues!) enhance the lock
subsystem to get rid of all references to 'current' context (used for
deadlock avoidance detection, presumably). The only thing that *can* be
done now is to switch a reference to a file to another file from a
specially written filesystem for this very purpose. This will leak a
little memory until the POSIX locks are fixed but is the best one can do
for now.
Regards,
Tigran
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