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

[ebiederm@xmission.com (Eric W. Biederman)]

Jamie Lokier <jamie@shareable.org> writes:

> 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?

The only way I can see to confuse unshare is to add a clone
flag and not implement it in unshare.    If there is enough
in common between the implementations I don't see that being
a problem.

Eric