Re: [PATCH -mm 1/9] unshare system call: system call handler function

[Jamie Lokier]

Eric W. Biederman wrote:
> > Like clone(), unshare() will have to change from year to year, as new
> > flags are added.  It would be good if the default behaviour of 0 bits
> > to unshare() also did the right thing, so that programs compiled in
> > 2006 still function as expected in 2010.  Hmm, this
> > forward-compatibility does not look pretty.
> 
> Why all it requires is that whenever someone updates clone they update
> unshare.  Given the tiniest bit of refactoring we should be
> able to share all of the interesting code paths.

That only works if unshare() should always mean "unshare everything
except specified things", including things that we currently don't
unshare.

I guess that is probably fine.  Anything that would break
unshare()-using programs in future if it unshared by default, would be
likely to break clone()-using programs too.  Is that right?  Any
counterexamples?

-- Jamie
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