Hi Hans, On Wed, May 02, 2012 at 10:45:22PM +0200, Hans Verkuil wrote: > On Wed May 2 2012 21:13:47 Sakari Ailus wrote: > > Replace enums in IOCTL structs by __u32. The size of enums is variable and > > thus problematic. Compatibility structs having exactly the same as original > > definition are provided for compatibility with old binaries with the > > required conversion code. > > Does someone actually have hard proof that there really is a problem? You know, > demonstrate it with actual example code? > > It's pretty horrible that you have to do all those conversions and that code > will be with us for years to come. > > For most (if not all!) architectures sizeof(enum) == sizeof(u32), so there is > no need for any compat code for those. Cases I know where this can go wrong are, but there may well be others: - ppc64: int is 64 bits there, and thus also enums, - Enums are quite a different concept in C++ than in C --- the compiler may make assumpton based on the value range of the enums --- videodev2.h should be included with extern "C" in that case, though, - C does not specify which integer type enums actually use; this is what GCC manual says about it: <URL:http://www.gnu.org/software/gnu-c-manual/gnu-c-manual.html#Enumerations> So a compiler other than GCC should use 16-bit enums and conform to C while breaking V4L2. This might be a theoretical issue, though. More discussion took place in this thread: <URL:http://www.spinics.net/lists/linux-media/msg46167.html> Regards, -- Sakari Ailus e-mail: sakari.ailus@xxxxxx jabber/XMPP/Gmail: sailus@xxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
