On Thu, May 30, 2013 at 01:28:26PM +0930, Rusty Russell wrote: > >> Yet the structure definitions are descriptive, capturing layout, size > >> and endianness in natural a format readable by any C programmer. > > > >>From an API design point of view, here are the problems I see: > > > > 1) C makes no guarantees about structure layout beyond the first > > member. Yes, if it's naturally aligned or has a packed attribute, > > GCC does the right thing. But this isn't kernel land anymore, > > portability matters and there are more compilers than GCC. > > [ I argued in detail here, then deleted. Damn bikeshedding... ] > > I think the best thing is to add the decoded integer versions as macros, > and have a heap of BUILD_BUG_ON() in the kernel source to make sure they > match. Hmm you want to have both in the header? That would confuse users for sure :) I guess we could put in a big comment explaning why do we have both, and which version should userspace use. I tried to write it: /* * On all known C compilers, you can use the * offsetof macro to find the correct offset of each field - * if your compiler doesn't implement this correctly, use the * integer versions below, instead. * In that case please don't use the structures above, to avoid confusion. */ -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
