On Wed, Apr 01, 2015 at 09:24:20AM +0200, Jonathan Corbet wrote: > On Tue, 31 Mar 2015 15:02:24 -0700 > josh@xxxxxxxxxxxxxxxx wrote: > > > > This would appear to assume that a clonefd_info structure is the only > > > thing that will ever be read from this descriptor. It seems to me that > > > there is the potential for, someday, wanting to be able to read and write > > > other things as well. Should this structure be marked with type and > > > length fields so that other structures could be added in the future? > > > > I don't think it makes sense for a caller to get an arbitrary structure > > on read(), and have to figure out what they got and ignore something > > they don't understand. Instead, I think it makes more sense for the > > caller to say "Hey, here's a flag saying I understand the new thing, go > > ahead and give me the new thing". So, for instance, if you want to > > receive SIGSTOP/SIGCONT messages for child processes through this > > descriptor, we could add a flag for that. > > The flag is fine, but, once we have set that flag saying we want those > messages, how do we know which type of structure we've gotten? That's > the piece of the puzzle I'm missing, sorry if I'm being overly slow. If you pass a flag saying you can handle a new set of potential structures, those structures can then include any necessary disambiguating flags/IDs/etc. No need for them to match the current clonefd_info structure if userspace has opted into a new version. - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
