osfs should implement billy.Changer

[rydrman]

I have been loving this abstraction that you guys have created so kudos to that! Trying to change the permissions on a file using the osfs but it seems that it doesn't implement the billy.Changer interface. I was looking into making some changes for this but the relationship between the osfs.OS type and the chroot seems to mess it up a little since I guess we don't want the ChrootHelper to assume the given underlying fs is a changer... Any insight into how I might go about this would be greatly appreciated.

[smola]

@rydrman It can always implement the function and return ErrNotSupported if the underlying filesystem does not support it.

@mcuadros what do you think?

[mcuadros]

If we add Change interface to Filesystem will force 3rd party implementation change

[ajnavarro]

Not add Change into Filesystem interface, but implement Changer interface on osfs implementation will not break backward compatibility.