Re: [patch 1/4] Add routine for generating an ID for kernel pointer

From: Pavel Emelyanov
Date: Wed Dec 28 2011 - 04:47:43 EST

> A thought: if all we're trying to do here is to check for the sameness
> of objects, can we push the comparison into the kernel so we don't have
> this exporting-sensitive-info problem at all? Just return a boolean to
> userspace?
> Something like
> int sys_pid_fields_equal(pid_t pid1, pid_t pid2, enum pid_field field_id);
> ?
> For /proc/pid/fdinfo/* userspace can open /proc/pid1/fdinfo/0 and
> /proc/pid2/fdinfo/0 and call sys_are_these_files_the_same(fd1, fd2, ...).
> Perhaps sys_pid_fields_equal() can use sys_are_these_files_the_same()
> as well, if we can think up a way of passing it two fds to represent
> the two pids.
> Have a think about it ;)

With this the complexity of determining sharing for N files scattered across
several tasks would be N^2, since we'll have to compare each file to each file.

On the other hand having just N IDs at hands would allow us to use more efficient
algorithms resulting in e.g. N*log(N) complexity.

That said I'd really appreciate if we work out a solution with IDs.

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