On Wednesday, April 18, 2012 11:00:18 am Andriy Gapon wrote: > on 18/04/2012 17:40 Ian Lepore said the following: > > On Wed, 2012-04-18 at 17:36 +0300, Andriy Gapon wrote: > >> on 18/04/2012 17:22 Ian Lepore said the following: > >>> YES! A size field (preferably as the first field in the struct) along > >>> with a flag to indicate that it's a new-style boot info struct that > >>> starts with a size field, will allow future changes without a lot of > >>> drama. It can allow code that has to deal with the struct without > >>> interpretting it (such as trampoline code that has to copy it to a new > >>> stack or memory area as part of loading the kernel) to be immune to > >>> future changes. > >> > >> Yeah, placing the new field at front would immediately break compatibility > >> and > >> even access to the flags field :-) > >> > > > > Code would only assume the new field was at the front of the struct if > > the new flag is set, otherwise it would use the historical struct > > layout. > > Right, but where the flag would reside? > And how the older code that is not aware of the new flag would cope with the > new > layout?
I think the size should be appended to the end of the current structure. However, it will buy us more flexibility in the future. -- John Baldwin _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
